diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
index 0be67b3..ca74a42 100644
--- a/.cargo_vcs_info.json
+++ b/.cargo_vcs_info.json
@@ -1,5 +1,6 @@
 {
   "git": {
-    "sha1": "3eabf141db9d0d69961ba8a1eaf2907c7aeb8ff9"
-  }
-}
+    "sha1": "ec31ce829473039ac598ca6fdcb245cbd6fa82ba"
+  },
+  "path_in_vcs": "protobuf"
+}
\ No newline at end of file
diff --git a/Android.bp b/Android.bp
index babd7e3..78e5734 100644
--- a/Android.bp
+++ b/Android.bp
@@ -29,6 +29,8 @@
     name: "libprotobuf",
     host_supported: true,
     crate_name: "protobuf",
+    cargo_env_compat: true,
+    cargo_pkg_version: "2.27.1",
     srcs: [
         "src/lib.rs",
         ":copy_protobuf_build_out",
@@ -40,9 +42,9 @@
     ],
     apex_available: [
         "//apex_available:platform",
+        "com.android.bluetooth",
+        "com.android.compos",
         "com.android.virt",
     ],
+    min_sdk_version: "29",
 }
-
-// dependent_library ["feature_list"]
-//   bytes-1.0.1 "default,std"
diff --git a/Cargo.toml b/Cargo.toml
index 165e125..9e4935f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,29 +3,32 @@
 # When uploading crates to the registry Cargo will automatically
 # "normalize" Cargo.toml files for maximal compatibility
 # with all versions of Cargo and also rewrite `path` dependencies
-# to registry (e.g., crates.io) dependencies
+# to registry (e.g., crates.io) dependencies.
 #
-# If you believe there's an error in this file please file an
-# issue against the rust-lang/cargo repository. If you're
-# editing this file be aware that the upstream Cargo.toml
-# will likely look very different (and much more reasonable)
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
 
 [package]
 edition = "2018"
 name = "protobuf"
-version = "2.22.1"
+version = "2.27.1"
 authors = ["Stepan Koltsov <stepan.koltsov@gmail.com>"]
-description = "Rust implementation of Google protocol buffers\n"
+description = """
+Rust implementation of Google protocol buffers
+"""
 homepage = "https://github.com/stepancheg/rust-protobuf/"
 documentation = "https://github.com/stepancheg/rust-protobuf/blob/master/README.md"
 license = "MIT"
 repository = "https://github.com/stepancheg/rust-protobuf/"
+
 [package.metadata.docs.rs]
 all-features = true
 
 [lib]
 doctest = false
 bench = false
+
 [dependencies.bytes]
 version = "1.0"
 optional = true
@@ -41,4 +44,7 @@
 
 [features]
 with-bytes = ["bytes"]
-with-serde = ["serde", "serde_derive"]
+with-serde = [
+    "serde",
+    "serde_derive",
+]
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
index ea70e2c..c1be2f7 100644
--- a/Cargo.toml.orig
+++ b/Cargo.toml.orig
@@ -1,7 +1,7 @@
 [package]
 
 name = "protobuf"
-version = "2.22.1"
+version = "2.27.1"
 authors = ["Stepan Koltsov <stepan.koltsov@gmail.com>"]
 edition = "2018"
 license = "MIT"
diff --git a/METADATA b/METADATA
index 586a998..2bcb504 100644
--- a/METADATA
+++ b/METADATA
@@ -7,13 +7,13 @@
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/protobuf/protobuf-2.22.1.crate"
+    value: "https://static.crates.io/crates/protobuf/protobuf-2.27.1.crate"
   }
-  version: "2.22.1"
+  version: "2.27.1"
   license_type: NOTICE
   last_upgrade_date {
-    year: 2021
-    month: 4
-    day: 2
+    year: 2022
+    month: 3
+    day: 1
   }
 }
diff --git a/README.md b/README.md
index c16838b..af32486 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,95 @@
-## How to develop rust-protobuf itself
+<!-- cargo-sync-readme start -->
 
-`cargo test --all` to build everything.
+# Library to read and write protocol buffers data
 
-If code generator is changed, code needs to be regenerated, see
-`regenerate.sh`.
+# Version 2 is stable
+
+Currently developed branch of rust-protobuf [is 3](https://docs.rs/protobuf/%3E=3.0.0-alpha).
+It has the same spirit as version 2, but contains numerous improvements like:
+* runtime reflection for mutability, not just for access
+* protobuf text format and JSON parsing (which rely on reflection)
+* dynamic message support: work with protobuf data without generating code from schema
+
+Stable version of rust-protobuf will be supported until version 3 released.
+
+[Tracking issue for version 3](https://github.com/stepancheg/rust-protobuf/issues/518).
+
+# How to generate rust code
+
+There are several ways to generate rust code from `.proto` files
+
+## Invoke `protoc` programmatically with protoc-rust crate (recommended)
+
+Have a look at readme in [protoc-rust crate](https://docs.rs/protoc-rust/=2).
+
+## Use pure rust protobuf parser and code generator
+
+Readme should be in
+[protobuf-codegen-pure crate](https://docs.rs/protobuf-codegen-pure/=2).
+
+## Use protoc-gen-rust plugin
+
+Readme is [here](https://docs.rs/protobuf-codegen/=2).
+
+## Generated code
+
+Have a look at generated files (for current development version),
+used internally in rust-protobuf:
+
+* [descriptor.rs](https://github.com/stepancheg/rust-protobuf/blob/master/protobuf/src/descriptor.rs)
+  for [descriptor.proto](https://github.com/stepancheg/rust-protobuf/blob/master/protoc-bin-vendored/include/google/protobuf/descriptor.proto)
+  (that is part of Google protobuf)
+
+# Copy on write
+
+Rust-protobuf can be used with [bytes crate](https://github.com/tokio-rs/bytes).
+
+To enable `Bytes` you need to:
+
+1. Enable `with-bytes` feature in rust-protobuf:
+
+```rust
+[dependencies]
+protobuf = { version = "~2.0", features = ["with-bytes"] }
+```
+
+2. Enable bytes option
+
+with `Customize` when codegen is invoked programmatically:
+
+```rust
+protoc_rust::run(protoc_rust::Args {
+    ...
+    customize: Customize {
+        carllerche_bytes_for_bytes: Some(true),
+        carllerche_bytes_for_string: Some(true),
+        ..Default::default()
+    },
+});
+```
+
+or in `.proto` file:
+
+```rust
+import "rustproto.proto";
+
+option (rustproto.carllerche_bytes_for_bytes_all) = true;
+option (rustproto.carllerche_bytes_for_string_all) = true;
+```
+
+With these options enabled, fields of type `bytes` or `string` are
+generated as `Bytes` or `Chars` respectively. When `CodedInputStream` is constructed
+from `Bytes` object, fields of these types get subslices of original `Bytes` object,
+instead of being allocated on heap.
+
+# Accompanying crates
+
+* [`protoc-rust`](https://docs.rs/protoc-rust/=2)
+  and [`protobuf-codegen-pure`](https://docs.rs/protobuf-codegen-pure/=2)
+  can be used to rust code from `.proto` crates.
+* [`protobuf-codegen`](https://docs.rs/protobuf-codegen/=2) for `protoc-gen-rust` protoc plugin.
+* [`protoc`](https://docs.rs/protoc/=2) crate can be used to invoke `protoc` programmatically.
+* [`protoc-bin-vendored`](https://docs.rs/protoc-bin-vendored/=2) contains `protoc` command
+  packed into the crate.
+
+<!-- cargo-sync-readme end -->
diff --git a/TEST_MAPPING b/TEST_MAPPING
new file mode 100644
index 0000000..8229f22
--- /dev/null
+++ b/TEST_MAPPING
@@ -0,0 +1,25 @@
+// Generated by update_crate_tests.py for tests that depend on this crate.
+{
+  "presubmit": [
+    {
+      "name": "authfs_device_test_src_lib"
+    },
+    {
+      "name": "microdroid_manager_test"
+    },
+    {
+      "name": "virtualizationservice_device_test"
+    }
+  ],
+  "presubmit-rust": [
+    {
+      "name": "authfs_device_test_src_lib"
+    },
+    {
+      "name": "microdroid_manager_test"
+    },
+    {
+      "name": "virtualizationservice_device_test"
+    }
+  ]
+}
diff --git a/benches/coded_output_stream.rs b/benches/coded_output_stream.rs
index 0f57a38..9edf95c 100644
--- a/benches/coded_output_stream.rs
+++ b/benches/coded_output_stream.rs
@@ -5,9 +5,10 @@
 extern crate protobuf;
 extern crate test;
 
-use self::test::Bencher;
 use protobuf::CodedOutputStream;
 
+use self::test::Bencher;
+
 #[inline]
 fn buffer_write_byte(os: &mut CodedOutputStream) {
     for i in 0..10 {
diff --git a/cargo2android.json b/cargo2android.json
index 85afab5..ceee8b5 100644
--- a/cargo2android.json
+++ b/cargo2android.json
@@ -1,11 +1,14 @@
 {
   "apex-available": [
     "//apex_available:platform",
+    "com.android.bluetooth",
+    "com.android.compos",
     "com.android.virt"
   ],
   "copy-out": true,
   "dependencies": true,
   "device": true,
   "features": "bytes",
+  "min-sdk-version": "29",
   "run": true
-}
\ No newline at end of file
+}
diff --git a/out/version.rs b/out/version.rs
index dcf078d..18bbac5 100644
--- a/out/version.rs
+++ b/out/version.rs
@@ -1,7 +1,7 @@
 /// protobuf crate version
-pub const VERSION: &'static str = "2.22.1";
+pub const VERSION: &'static str = "2.27.1";
 /// This symbol is used by codegen
 #[doc(hidden)]
-pub const VERSION_IDENT: &'static str = "VERSION_2_22_1";
+pub const VERSION_IDENT: &'static str = "VERSION_2_27_1";
 /// This symbol can be referenced to assert that proper version of crate is used
-pub const VERSION_2_22_1: () = ();
+pub const VERSION_2_27_1: () = ();
diff --git a/regenerate.sh b/regenerate.sh
index 672106e..0173496 100755
--- a/regenerate.sh
+++ b/regenerate.sh
@@ -1,6 +1,6 @@
 #!/bin/sh -ex
 
-cd $(dirname $0)
+cd "$(dirname "$0")"
 
 die() {
     echo "$@" >&2
@@ -9,29 +9,35 @@
 
 protoc_ver=$(protoc --version)
 case "$protoc_ver" in
-    "libprotoc 3"*) ;;
-    *)
-        die "you need to use protobuf 3 to regenerate .rs from .proto"
+"libprotoc 3"*) ;;
+*)
+    die "you need to use protobuf 3 to regenerate .rs from .proto"
     ;;
 esac
 
 cargo build --manifest-path=../protobuf-codegen/Cargo.toml
+cargo build --manifest-path=../protoc-bin-vendored/Cargo.toml --bin protoc-bin-which
 
-where_am_i=$(cd ..; pwd)
+PROTOC=$(cargo run --manifest-path=../protoc-bin-vendored/Cargo.toml --bin protoc-bin-which)
+
+where_am_i=$(
+    cd ..
+    pwd
+)
 
 rm -rf tmp-generated
 mkdir tmp-generated
 
-case `uname` in
-    Linux)
-        exe_suffix=""
+case $(uname) in
+Linux)
+    exe_suffix=""
     ;;
-    MSYS_NT*)
-        exe_suffix=".exe"
+MSYS_NT*)
+    exe_suffix=".exe"
     ;;
 esac
 
-protoc \
+"$PROTOC" \
     --plugin=protoc-gen-rust="$where_am_i/target/debug/protoc-gen-rust$exe_suffix" \
     --rust_out tmp-generated \
     --rust_opt 'serde_derive=true inside_protobuf=true' \
@@ -45,13 +51,14 @@
 mv tmp-generated/*.rs src/well_known_types/
 (
     cd src/well_known_types
-    exec > mod.rs
+    exec >mod.rs
     echo "// This file is generated. Do not edit"
     echo '//! Generated code for "well known types"'
     echo "//!"
     echo "//! [This document](https://developers.google.com/protocol-buffers/docs/reference/google.protobuf) describes these types."
 
     mod_list() {
+        # shellcheck disable=SC2010
         ls | grep -v mod.rs | sed -e 's,\.rs$,,'
     }
 
@@ -59,7 +66,7 @@
     mod_list | sed -e 's,^,mod ,; s,$,;,'
 
     echo
-    mod_list | while read mod; do
+    mod_list | while read -r mod; do
         echo "pub use self::$mod::*;"
     done
 )
diff --git a/src/buf_read_iter.rs b/src/buf_read_iter.rs
index 21f51a1..ff1fce2 100644
--- a/src/buf_read_iter.rs
+++ b/src/buf_read_iter.rs
@@ -3,6 +3,7 @@
 use std::io::BufReader;
 use std::io::Read;
 use std::mem;
+use std::mem::MaybeUninit;
 use std::u64;
 
 #[cfg(feature = "bytes")]
@@ -14,8 +15,11 @@
 #[cfg(feature = "bytes")]
 use bytes::BytesMut;
 
+use crate::buf_read_or_reader::BufReadOrReader;
 use crate::coded_input_stream::READ_RAW_BYTES_MAX_ALLOC;
 use crate::error::WireError;
+use crate::misc::maybe_uninit_write_slice;
+use crate::misc::vec_spare_capacity_mut;
 use crate::ProtobufError;
 use crate::ProtobufResult;
 
@@ -29,8 +33,7 @@
 
 /// Hold all possible combinations of input source
 enum InputSource<'a> {
-    BufRead(&'a mut dyn BufRead),
-    Read(BufReader<&'a mut dyn Read>),
+    Read(BufReadOrReader<'a>),
     Slice(&'a [u8]),
     #[cfg(feature = "bytes")]
     Bytes(&'a Bytes),
@@ -50,7 +53,7 @@
 /// It is important for `CodedInputStream` performance that small reads
 /// (e. g. 4 bytes reads) do not involve virtual calls or switches.
 /// This is achievable with `BufReadIter`.
-pub struct BufReadIter<'a> {
+pub(crate) struct BufReadIter<'a> {
     input_source: InputSource<'a>,
     buf: &'a [u8],
     pos_within_buf: usize,
@@ -62,22 +65,19 @@
 impl<'a> Drop for BufReadIter<'a> {
     fn drop(&mut self) {
         match self.input_source {
-            InputSource::BufRead(ref mut buf_read) => buf_read.consume(self.pos_within_buf),
-            InputSource::Read(_) => {
-                // Nothing to flush, because we own BufReader
-            }
+            InputSource::Read(ref mut buf_read) => buf_read.consume(self.pos_within_buf),
             _ => {}
         }
     }
 }
 
 impl<'ignore> BufReadIter<'ignore> {
-    pub fn from_read<'a>(read: &'a mut dyn Read) -> BufReadIter<'a> {
+    pub(crate) fn from_read<'a>(read: &'a mut dyn Read) -> BufReadIter<'a> {
         BufReadIter {
-            input_source: InputSource::Read(BufReader::with_capacity(
+            input_source: InputSource::Read(BufReadOrReader::BufReader(BufReader::with_capacity(
                 INPUT_STREAM_BUFFER_SIZE,
                 read,
-            )),
+            ))),
             buf: &[],
             pos_within_buf: 0,
             limit_within_buf: 0,
@@ -86,9 +86,9 @@
         }
     }
 
-    pub fn from_buf_read<'a>(buf_read: &'a mut dyn BufRead) -> BufReadIter<'a> {
+    pub(crate) fn from_buf_read<'a>(buf_read: &'a mut dyn BufRead) -> BufReadIter<'a> {
         BufReadIter {
-            input_source: InputSource::BufRead(buf_read),
+            input_source: InputSource::Read(BufReadOrReader::BufRead(buf_read)),
             buf: &[],
             pos_within_buf: 0,
             limit_within_buf: 0,
@@ -97,7 +97,7 @@
         }
     }
 
-    pub fn from_byte_slice<'a>(bytes: &'a [u8]) -> BufReadIter<'a> {
+    pub(crate) fn from_byte_slice<'a>(bytes: &'a [u8]) -> BufReadIter<'a> {
         BufReadIter {
             input_source: InputSource::Slice(bytes),
             buf: bytes,
@@ -109,7 +109,7 @@
     }
 
     #[cfg(feature = "bytes")]
-    pub fn from_bytes<'a>(bytes: &'a Bytes) -> BufReadIter<'a> {
+    pub(crate) fn from_bytes<'a>(bytes: &'a Bytes) -> BufReadIter<'a> {
         BufReadIter {
             input_source: InputSource::Bytes(bytes),
             buf: &bytes,
@@ -128,7 +128,7 @@
     }
 
     #[inline(always)]
-    pub fn pos(&self) -> u64 {
+    pub(crate) fn pos(&self) -> u64 {
         self.pos_of_buf_start + self.pos_within_buf as u64
     }
 
@@ -144,7 +144,7 @@
         self.assertions();
     }
 
-    pub fn push_limit(&mut self, limit: u64) -> ProtobufResult<u64> {
+    pub(crate) fn push_limit(&mut self, limit: u64) -> ProtobufResult<u64> {
         let new_limit = match self.pos().checked_add(limit) {
             Some(new_limit) => new_limit,
             None => return Err(ProtobufError::WireError(WireError::Other)),
@@ -162,7 +162,7 @@
     }
 
     #[inline]
-    pub fn pop_limit(&mut self, limit: u64) {
+    pub(crate) fn pop_limit(&mut self, limit: u64) {
         assert!(limit >= self.limit);
 
         self.limit = limit;
@@ -171,7 +171,7 @@
     }
 
     #[inline]
-    pub fn remaining_in_buf(&self) -> &[u8] {
+    pub(crate) fn remaining_in_buf(&self) -> &[u8] {
         if USE_UNSAFE_FOR_SPEED {
             unsafe {
                 &self
@@ -184,12 +184,12 @@
     }
 
     #[inline(always)]
-    pub fn remaining_in_buf_len(&self) -> usize {
+    pub(crate) fn remaining_in_buf_len(&self) -> usize {
         self.limit_within_buf - self.pos_within_buf
     }
 
     #[inline(always)]
-    pub fn bytes_until_limit(&self) -> u64 {
+    pub(crate) fn bytes_until_limit(&self) -> u64 {
         if self.limit == NO_LIMIT {
             NO_LIMIT
         } else {
@@ -198,7 +198,7 @@
     }
 
     #[inline(always)]
-    pub fn eof(&mut self) -> ProtobufResult<bool> {
+    pub(crate) fn eof(&mut self) -> ProtobufResult<bool> {
         if self.pos_within_buf == self.limit_within_buf {
             Ok(self.fill_buf()?.is_empty())
         } else {
@@ -207,7 +207,7 @@
     }
 
     #[inline(always)]
-    pub fn read_byte(&mut self) -> ProtobufResult<u8> {
+    pub(crate) fn read_byte(&mut self) -> ProtobufResult<u8> {
         if self.pos_within_buf == self.limit_within_buf {
             self.do_fill_buf()?;
             if self.remaining_in_buf_len() == 0 {
@@ -239,6 +239,101 @@
         Ok(len)
     }
 
+    #[cfg(feature = "bytes")]
+    pub(crate) fn read_exact_bytes(&mut self, len: usize) -> ProtobufResult<Bytes> {
+        if let InputSource::Bytes(bytes) = self.input_source {
+            let end = match self.pos_within_buf.checked_add(len) {
+                Some(end) => end,
+                None => return Err(ProtobufError::WireError(WireError::UnexpectedEof)),
+            };
+
+            if end > self.limit_within_buf {
+                return Err(ProtobufError::WireError(WireError::UnexpectedEof));
+            }
+
+            let r = bytes.slice(self.pos_within_buf..end);
+            self.pos_within_buf += len;
+            Ok(r)
+        } else {
+            if len >= READ_RAW_BYTES_MAX_ALLOC {
+                // We cannot trust `len` because protobuf message could be malformed.
+                // Reading should not result in OOM when allocating a buffer.
+                let mut v = Vec::new();
+                self.read_exact_to_vec(len, &mut v)?;
+                Ok(Bytes::from(v))
+            } else {
+                let mut r = BytesMut::with_capacity(len);
+                unsafe {
+                    let buf = Self::uninit_slice_as_mut_slice(&mut r.chunk_mut()[..len]);
+                    self.read_exact(buf)?;
+                    r.advance_mut(len);
+                }
+                Ok(r.freeze())
+            }
+        }
+    }
+
+    #[cfg(feature = "bytes")]
+    unsafe fn uninit_slice_as_mut_slice(slice: &mut UninitSlice) -> &mut [MaybeUninit<u8>] {
+        use std::slice;
+        slice::from_raw_parts_mut(slice.as_mut_ptr() as *mut MaybeUninit<u8>, slice.len())
+    }
+
+    /// Returns 0 when EOF or limit reached.
+    pub(crate) fn read(&mut self, buf: &mut [u8]) -> ProtobufResult<usize> {
+        self.fill_buf()?;
+
+        let rem = &self.buf[self.pos_within_buf..self.limit_within_buf];
+
+        let len = cmp::min(rem.len(), buf.len());
+        buf[..len].copy_from_slice(&rem[..len]);
+        self.pos_within_buf += len;
+        Ok(len)
+    }
+
+    fn read_exact_slow(&mut self, buf: &mut [MaybeUninit<u8>]) -> ProtobufResult<()> {
+        if self.bytes_until_limit() < buf.len() as u64 {
+            return Err(ProtobufError::WireError(WireError::UnexpectedEof));
+        }
+
+        let consume = self.pos_within_buf;
+        self.pos_of_buf_start += self.pos_within_buf as u64;
+        self.pos_within_buf = 0;
+        self.buf = &[];
+        self.limit_within_buf = 0;
+
+        match self.input_source {
+            InputSource::Read(ref mut buf_read) => {
+                buf_read.consume(consume);
+                buf_read.read_exact_uninit(buf)?;
+            }
+            _ => {
+                return Err(ProtobufError::WireError(WireError::UnexpectedEof));
+            }
+        }
+
+        self.pos_of_buf_start += buf.len() as u64;
+
+        self.assertions();
+
+        Ok(())
+    }
+
+    #[inline]
+    pub(crate) fn read_exact(&mut self, buf: &mut [MaybeUninit<u8>]) -> ProtobufResult<()> {
+        if self.remaining_in_buf_len() >= buf.len() {
+            let buf_len = buf.len();
+            maybe_uninit_write_slice(
+                buf,
+                &self.buf[self.pos_within_buf..self.pos_within_buf + buf_len],
+            );
+            self.pos_within_buf += buf_len;
+            return Ok(());
+        }
+
+        self.read_exact_slow(buf)
+    }
+
     /// Read exact number of bytes into `Vec`.
     ///
     /// `Vec` is cleared in the beginning.
@@ -273,7 +368,7 @@
             target.reserve_exact(count);
 
             unsafe {
-                self.read_exact(&mut target.get_unchecked_mut(..count))?;
+                self.read_exact(&mut vec_spare_capacity_mut(target)[..count])?;
                 target.set_len(count);
             }
         }
@@ -283,97 +378,6 @@
         Ok(())
     }
 
-    #[cfg(feature = "bytes")]
-    pub fn read_exact_bytes(&mut self, len: usize) -> ProtobufResult<Bytes> {
-        if let InputSource::Bytes(bytes) = self.input_source {
-            let end = match self.pos_within_buf.checked_add(len) {
-                Some(end) => end,
-                None => return Err(ProtobufError::WireError(WireError::UnexpectedEof)),
-            };
-
-            if end > self.limit_within_buf {
-                return Err(ProtobufError::WireError(WireError::UnexpectedEof));
-            }
-
-            let r = bytes.slice(self.pos_within_buf..end);
-            self.pos_within_buf += len;
-            Ok(r)
-        } else {
-            if len >= READ_RAW_BYTES_MAX_ALLOC {
-                // We cannot trust `len` because protobuf message could be malformed.
-                // Reading should not result in OOM when allocating a buffer.
-                let mut v = Vec::new();
-                self.read_exact_to_vec(len, &mut v)?;
-                Ok(Bytes::from(v))
-            } else {
-                let mut r = BytesMut::with_capacity(len);
-                unsafe {
-                    let buf = Self::uninit_slice_as_mut_slice(&mut r.chunk_mut()[..len]);
-                    self.read_exact(buf)?;
-                    r.advance_mut(len);
-                }
-                Ok(r.freeze())
-            }
-        }
-    }
-
-    #[cfg(feature = "bytes")]
-    unsafe fn uninit_slice_as_mut_slice(slice: &mut UninitSlice) -> &mut [u8] {
-        use std::slice;
-        slice::from_raw_parts_mut(slice.as_mut_ptr(), slice.len())
-    }
-
-    /// Returns 0 when EOF or limit reached.
-    pub fn read(&mut self, buf: &mut [u8]) -> ProtobufResult<usize> {
-        self.fill_buf()?;
-
-        let rem = &self.buf[self.pos_within_buf..self.limit_within_buf];
-
-        let len = cmp::min(rem.len(), buf.len());
-        &mut buf[..len].copy_from_slice(&rem[..len]);
-        self.pos_within_buf += len;
-        Ok(len)
-    }
-
-    pub fn read_exact(&mut self, buf: &mut [u8]) -> ProtobufResult<()> {
-        if self.remaining_in_buf_len() >= buf.len() {
-            let buf_len = buf.len();
-            buf.copy_from_slice(&self.buf[self.pos_within_buf..self.pos_within_buf + buf_len]);
-            self.pos_within_buf += buf_len;
-            return Ok(());
-        }
-
-        if self.bytes_until_limit() < buf.len() as u64 {
-            return Err(ProtobufError::WireError(WireError::UnexpectedEof));
-        }
-
-        let consume = self.pos_within_buf;
-        self.pos_of_buf_start += self.pos_within_buf as u64;
-        self.pos_within_buf = 0;
-        self.buf = &[];
-        self.limit_within_buf = 0;
-
-        match self.input_source {
-            InputSource::Read(ref mut buf_read) => {
-                buf_read.consume(consume);
-                buf_read.read_exact(buf)?;
-            }
-            InputSource::BufRead(ref mut buf_read) => {
-                buf_read.consume(consume);
-                buf_read.read_exact(buf)?;
-            }
-            _ => {
-                return Err(ProtobufError::WireError(WireError::UnexpectedEof));
-            }
-        }
-
-        self.pos_of_buf_start += buf.len() as u64;
-
-        self.assertions();
-
-        Ok(())
-    }
-
     fn do_fill_buf(&mut self) -> ProtobufResult<()> {
         debug_assert!(self.pos_within_buf == self.limit_within_buf);
 
@@ -394,10 +398,6 @@
                 buf_read.consume(consume);
                 self.buf = unsafe { mem::transmute(buf_read.fill_buf()?) };
             }
-            InputSource::BufRead(ref mut buf_read) => {
-                buf_read.consume(consume);
-                self.buf = unsafe { mem::transmute(buf_read.fill_buf()?) };
-            }
             _ => {
                 return Ok(());
             }
@@ -409,7 +409,7 @@
     }
 
     #[inline(always)]
-    pub fn fill_buf(&mut self) -> ProtobufResult<&[u8]> {
+    pub(crate) fn fill_buf(&mut self) -> ProtobufResult<&[u8]> {
         if self.pos_within_buf == self.limit_within_buf {
             self.do_fill_buf()?;
         }
@@ -425,7 +425,7 @@
     }
 
     #[inline(always)]
-    pub fn consume(&mut self, amt: usize) {
+    pub(crate) fn consume(&mut self, amt: usize) {
         assert!(amt <= self.limit_within_buf - self.pos_within_buf);
         self.pos_within_buf += amt;
     }
@@ -433,9 +433,10 @@
 
 #[cfg(all(test, feature = "bytes"))]
 mod test_bytes {
-    use super::*;
     use std::io::Write;
 
+    use super::*;
+
     fn make_long_string(len: usize) -> Vec<u8> {
         let mut s = Vec::new();
         while s.len() < len {
@@ -467,11 +468,12 @@
 
 #[cfg(test)]
 mod test {
-    use super::*;
     use std::io;
     use std::io::BufRead;
     use std::io::Read;
 
+    use super::*;
+
     #[test]
     fn eof_at_limit() {
         struct Read5ThenPanic {
@@ -509,7 +511,12 @@
         let _prev_limit = buf_read_iter.push_limit(5);
         buf_read_iter.read_byte().expect("read_byte");
         buf_read_iter
-            .read_exact(&mut [1, 2, 3, 4])
+            .read_exact(&mut [
+                MaybeUninit::uninit(),
+                MaybeUninit::uninit(),
+                MaybeUninit::uninit(),
+                MaybeUninit::uninit(),
+            ])
             .expect("read_exact");
         assert!(buf_read_iter.eof().expect("eof"));
     }
diff --git a/src/buf_read_or_reader.rs b/src/buf_read_or_reader.rs
new file mode 100644
index 0000000..6a47c76
--- /dev/null
+++ b/src/buf_read_or_reader.rs
@@ -0,0 +1,85 @@
+//! `BufRead` pointer or `BufReader` owned.
+
+use std::cmp;
+use std::io;
+use std::io::BufRead;
+use std::io::BufReader;
+use std::io::Read;
+use std::mem::MaybeUninit;
+
+use crate::misc::maybe_uninit_write_slice;
+
+/// Helper type to simplify `BufReadIter` implementation.
+pub(crate) enum BufReadOrReader<'a> {
+    BufReader(BufReader<&'a mut dyn Read>),
+    BufRead(&'a mut dyn BufRead),
+}
+
+impl<'a> Read for BufReadOrReader<'a> {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, io::Error> {
+        match self {
+            BufReadOrReader::BufReader(r) => r.read(buf),
+            BufReadOrReader::BufRead(r) => r.read(buf),
+        }
+    }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, io::Error> {
+        match self {
+            BufReadOrReader::BufReader(r) => r.read_to_end(buf),
+            BufReadOrReader::BufRead(r) => r.read_to_end(buf),
+        }
+    }
+
+    fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), io::Error> {
+        match self {
+            BufReadOrReader::BufReader(r) => r.read_exact(buf),
+            BufReadOrReader::BufRead(r) => r.read_exact(buf),
+        }
+    }
+}
+
+impl<'a> BufReadOrReader<'a> {
+    /// Similar to `read_exact` but reads into `MaybeUninit`.
+    pub(crate) fn read_exact_uninit(
+        &mut self,
+        buf: &mut [MaybeUninit<u8>],
+    ) -> Result<(), io::Error> {
+        let mut pos = 0;
+        while pos != buf.len() {
+            let fill_buf = match self {
+                BufReadOrReader::BufReader(r) => r.fill_buf()?,
+                BufReadOrReader::BufRead(r) => r.fill_buf()?,
+            };
+            if fill_buf.is_empty() {
+                return Err(io::Error::new(
+                    io::ErrorKind::UnexpectedEof,
+                    "Unexpected end of file",
+                ));
+            }
+            let consume = cmp::min(fill_buf.len(), buf.len() - pos);
+            maybe_uninit_write_slice(&mut buf[pos..pos + consume], &fill_buf[..consume]);
+            match self {
+                BufReadOrReader::BufReader(r) => r.consume(consume),
+                BufReadOrReader::BufRead(r) => r.consume(consume),
+            }
+            pos += consume;
+        }
+        Ok(())
+    }
+}
+
+impl<'a> BufRead for BufReadOrReader<'a> {
+    fn fill_buf(&mut self) -> Result<&[u8], io::Error> {
+        match self {
+            BufReadOrReader::BufReader(r) => r.fill_buf(),
+            BufReadOrReader::BufRead(r) => r.fill_buf(),
+        }
+    }
+
+    fn consume(&mut self, amt: usize) {
+        match self {
+            BufReadOrReader::BufReader(r) => r.consume(amt),
+            BufReadOrReader::BufRead(r) => r.consume(amt),
+        }
+    }
+}
diff --git a/src/coded_input_stream.rs b/src/coded_input_stream.rs
index 52a13a6..a49563c 100644
--- a/src/coded_input_stream.rs
+++ b/src/coded_input_stream.rs
@@ -6,19 +6,21 @@
 use std::io::BufRead;
 use std::io::Read;
 use std::mem;
+use std::mem::MaybeUninit;
 use std::slice;
 
 #[cfg(feature = "bytes")]
-use crate::chars::Chars;
-#[cfg(feature = "bytes")]
 use bytes::Bytes;
 
 use crate::buf_read_iter::BufReadIter;
+#[cfg(feature = "bytes")]
+use crate::chars::Chars;
 use crate::enums::ProtobufEnum;
 use crate::error::ProtobufError;
 use crate::error::ProtobufResult;
 use crate::error::WireError;
 use crate::message::Message;
+use crate::misc::maybe_ununit_array_assume_init;
 use crate::unknown::UnknownValue;
 use crate::wire_format;
 use crate::zigzag::decode_zig_zag_32;
@@ -105,12 +107,21 @@
     }
 
     /// Read bytes into given `buf`.
+    #[inline]
+    fn read_exact_uninit(&mut self, buf: &mut [MaybeUninit<u8>]) -> ProtobufResult<()> {
+        self.source.read_exact(buf)
+    }
+
+    /// Read bytes into given `buf`.
     ///
     /// Return `0` on EOF.
     // TODO: overload with `Read::read`
     pub fn read(&mut self, buf: &mut [u8]) -> ProtobufResult<()> {
-        self.source.read_exact(buf)?;
-        Ok(())
+        // SAFETY: same layout
+        let buf = unsafe {
+            slice::from_raw_parts_mut(buf.as_mut_ptr() as *mut MaybeUninit<u8>, buf.len())
+        };
+        self.read_exact_uninit(buf)
     }
 
     /// Read exact number of bytes as `Bytes` object.
@@ -248,24 +259,20 @@
 
     /// Read little-endian 32-bit integer
     pub fn read_raw_little_endian32(&mut self) -> ProtobufResult<u32> {
-        let mut r = 0u32;
-        let bytes: &mut [u8] = unsafe {
-            let p: *mut u8 = mem::transmute(&mut r);
-            slice::from_raw_parts_mut(p, mem::size_of::<u32>())
-        };
-        self.read(bytes)?;
-        Ok(r.to_le())
+        let mut bytes = [MaybeUninit::uninit(); 4];
+        self.read_exact_uninit(&mut bytes)?;
+        // SAFETY: `read_exact` guarantees that the buffer is filled.
+        let bytes = unsafe { maybe_ununit_array_assume_init(bytes) };
+        Ok(u32::from_le_bytes(bytes))
     }
 
     /// Read little-endian 64-bit integer
     pub fn read_raw_little_endian64(&mut self) -> ProtobufResult<u64> {
-        let mut r = 0u64;
-        let bytes: &mut [u8] = unsafe {
-            let p: *mut u8 = mem::transmute(&mut r);
-            slice::from_raw_parts_mut(p, mem::size_of::<u64>())
-        };
-        self.read(bytes)?;
-        Ok(r.to_le())
+        let mut bytes = [MaybeUninit::uninit(); 8];
+        self.read_exact_uninit(&mut bytes)?;
+        // SAFETY: `read_exact` guarantees that the buffer is filled.
+        let bytes = unsafe { maybe_ununit_array_assume_init(bytes) };
+        Ok(u64::from_le_bytes(bytes))
     }
 
     /// Read tag
@@ -596,41 +603,7 @@
     /// Read raw bytes into the supplied vector.  The vector will be resized as needed and
     /// overwritten.
     pub fn read_raw_bytes_into(&mut self, count: u32, target: &mut Vec<u8>) -> ProtobufResult<()> {
-        if false {
-            // Master uses this version, but keep existing version for a while
-            // to avoid possible breakages.
-            return self.source.read_exact_to_vec(count as usize, target);
-        }
-
-        let count = count as usize;
-
-        // TODO: also do some limits when reading from unlimited source
-        if count as u64 > self.source.bytes_until_limit() {
-            return Err(ProtobufError::WireError(WireError::TruncatedMessage));
-        }
-
-        unsafe {
-            target.set_len(0);
-        }
-
-        if count >= READ_RAW_BYTES_MAX_ALLOC {
-            // avoid calling `reserve` on buf with very large buffer: could be a malformed message
-
-            let mut take = self.by_ref().take(count as u64);
-            take.read_to_end(target)?;
-
-            if target.len() != count {
-                return Err(ProtobufError::WireError(WireError::TruncatedMessage));
-            }
-        } else {
-            target.reserve(count);
-            unsafe {
-                target.set_len(count);
-            }
-
-            self.source.read_exact(target)?;
-        }
-        Ok(())
+        self.source.read_exact_to_vec(count as usize, target)
     }
 
     /// Read exact number of bytes
@@ -795,13 +768,12 @@
     use std::io::BufRead;
     use std::io::Read;
 
+    use super::CodedInputStream;
+    use super::READ_RAW_BYTES_MAX_ALLOC;
     use crate::error::ProtobufError;
     use crate::error::ProtobufResult;
     use crate::hex::decode_hex;
 
-    use super::CodedInputStream;
-    use super::READ_RAW_BYTES_MAX_ALLOC;
-
     fn test_read_partial<F>(hex: &str, mut callback: F)
     where
         F: FnMut(&mut CodedInputStream),
diff --git a/src/coded_output_stream.rs b/src/coded_output_stream.rs
index fb7e75c..2bbe0a3 100644
--- a/src/coded_output_stream.rs
+++ b/src/coded_output_stream.rs
@@ -1,17 +1,23 @@
-use crate::misc::remaining_capacity_as_slice_mut;
-use crate::misc::remove_lifetime_mut;
+use std::io;
+use std::io::Write;
+use std::mem;
+use std::mem::MaybeUninit;
+use std::ptr;
+use std::slice;
+
+use crate::misc::maybe_uninit_write;
+use crate::misc::maybe_uninit_write_slice;
+use crate::misc::vec_spare_capacity_mut;
 use crate::varint;
 use crate::wire_format;
 use crate::zigzag::encode_zig_zag_32;
 use crate::zigzag::encode_zig_zag_64;
 use crate::Message;
 use crate::ProtobufEnum;
+use crate::ProtobufError;
 use crate::ProtobufResult;
 use crate::UnknownFields;
 use crate::UnknownValueRef;
-use std::io;
-use std::io::Write;
-use std::mem;
 
 /// Equal to the default buffer size of `BufWriter`, so when
 /// `CodedOutputStream` wraps `BufWriter`, it often skips double buffering.
@@ -58,17 +64,27 @@
     Ok(v)
 }
 
+/// Output buffer/writer for `CodedOutputStream`.
 enum OutputTarget<'a> {
     Write(&'a mut dyn Write, Vec<u8>),
     Vec(&'a mut Vec<u8>),
+    /// The buffer is passed as `&[u8]` to `CodedOutputStream` constructor
+    /// and immediately converted to `buffer` field of `CodedOutputStream`,
+    /// it is not needed to be stored here.
+    /// Lifetime parameter of `CodedOutputStream` guarantees the buffer is valid
+    /// during the lifetime of `CodedOutputStream`.
     Bytes,
 }
 
 /// Buffered write with handy utilities
 pub struct CodedOutputStream<'a> {
     target: OutputTarget<'a>,
-    // alias to buf from target
-    buffer: &'a mut [u8],
+    // Actual buffer is owned by `OutputTarget`,
+    // and here we alias the buffer so access to the buffer is branchless:
+    // access does not require switch by actual target type: `&[], `Vec`, `Write` etc.
+    // We don't access the actual buffer in `OutputTarget` except when
+    // we initialize `buffer` field here.
+    buffer: *mut [MaybeUninit<u8>],
     // within buffer
     position: usize,
 }
@@ -81,15 +97,16 @@
         let buffer_len = OUTPUT_STREAM_BUFFER_SIZE;
 
         let mut buffer_storage = Vec::with_capacity(buffer_len);
-        unsafe {
-            buffer_storage.set_len(buffer_len);
-        }
 
-        let buffer = unsafe { remove_lifetime_mut(&mut buffer_storage as &mut [u8]) };
+        // SAFETY: we are not using the `buffer_storage`
+        // except for initializing the `buffer` field.
+        // See `buffer` field documentation.
+        let buffer = vec_spare_capacity_mut(&mut buffer_storage);
+        let buffer: *mut [MaybeUninit<u8>] = buffer;
 
         CodedOutputStream {
             target: OutputTarget::Write(writer, buffer_storage),
-            buffer: buffer,
+            buffer,
             position: 0,
         }
     }
@@ -98,9 +115,12 @@
     ///
     /// Attempt to write more than bytes capacity results in error.
     pub fn bytes(bytes: &'a mut [u8]) -> CodedOutputStream<'a> {
+        // SAFETY: it is safe to cast from &mut [u8] to &mut [MaybeUninit<u8>].
+        let buffer =
+            ptr::slice_from_raw_parts_mut(bytes.as_mut_ptr() as *mut MaybeUninit<u8>, bytes.len());
         CodedOutputStream {
             target: OutputTarget::Bytes,
-            buffer: bytes,
+            buffer,
             position: 0,
         }
     }
@@ -110,9 +130,10 @@
     /// Caller should call `flush` at the end to guarantee vec contains
     /// all written data.
     pub fn vec(vec: &'a mut Vec<u8>) -> CodedOutputStream<'a> {
+        let buffer: *mut [MaybeUninit<u8>] = &mut [];
         CodedOutputStream {
             target: OutputTarget::Vec(vec),
-            buffer: &mut [],
+            buffer,
             position: 0,
         }
     }
@@ -125,7 +146,7 @@
     pub fn check_eof(&self) {
         match self.target {
             OutputTarget::Bytes => {
-                assert_eq!(self.buffer.len() as u64, self.position as u64);
+                assert_eq!(self.buffer().len() as u64, self.position as u64);
             }
             OutputTarget::Write(..) | OutputTarget::Vec(..) => {
                 panic!("must not be called with Writer or Vec");
@@ -133,10 +154,25 @@
         }
     }
 
+    #[inline(always)]
+    fn buffer(&self) -> &[MaybeUninit<u8>] {
+        // SAFETY: see the `buffer` field documentation about invariants.
+        unsafe { &*(self.buffer as *mut [MaybeUninit<u8>]) }
+    }
+
+    #[inline(always)]
+    fn filled_buffer_impl<'s>(buffer: *mut [MaybeUninit<u8>], position: usize) -> &'s [u8] {
+        // SAFETY: this function is safe assuming `buffer` and `position`
+        //   are `self.buffer` and `safe.position`:
+        //   * `CodedOutputStream` has invariant that `position <= buffer.len()`.
+        //   * `buffer` is filled up to `position`.
+        unsafe { slice::from_raw_parts_mut(buffer as *mut u8, position) }
+    }
+
     fn refresh_buffer(&mut self) -> ProtobufResult<()> {
         match self.target {
             OutputTarget::Write(ref mut write, _) => {
-                write.write_all(&self.buffer[0..self.position as usize])?;
+                write.write_all(Self::filled_buffer_impl(self.buffer, self.position))?;
                 self.position = 0;
             }
             OutputTarget::Vec(ref mut vec) => unsafe {
@@ -144,11 +180,14 @@
                 assert!(vec_len + self.position <= vec.capacity());
                 vec.set_len(vec_len + self.position);
                 vec.reserve(1);
-                self.buffer = remove_lifetime_mut(remaining_capacity_as_slice_mut(vec));
+                self.buffer = vec_spare_capacity_mut(vec);
                 self.position = 0;
             },
             OutputTarget::Bytes => {
-                panic!("refresh_buffer must not be called on CodedOutputStream create from slice");
+                return Err(ProtobufError::IoError(io::Error::new(
+                    io::ErrorKind::Other,
+                    "given slice is too small to serialize the message",
+                )));
             }
         }
         Ok(())
@@ -167,20 +206,22 @@
 
     /// Write a byte
     pub fn write_raw_byte(&mut self, byte: u8) -> ProtobufResult<()> {
-        if self.position as usize == self.buffer.len() {
+        if self.position as usize == self.buffer().len() {
             self.refresh_buffer()?;
         }
-        self.buffer[self.position as usize] = byte;
+        unsafe { maybe_uninit_write(&mut (&mut *self.buffer)[self.position as usize], byte) };
         self.position += 1;
         Ok(())
     }
 
     /// Write bytes
     pub fn write_raw_bytes(&mut self, bytes: &[u8]) -> ProtobufResult<()> {
-        if bytes.len() <= self.buffer.len() - self.position {
+        if bytes.len() <= self.buffer().len() - self.position {
             let bottom = self.position as usize;
             let top = bottom + (bytes.len() as usize);
-            self.buffer[bottom..top].copy_from_slice(bytes);
+            // SAFETY: see the `buffer` field documentation about invariants.
+            let buffer = unsafe { &mut (&mut *self.buffer)[bottom..top] };
+            maybe_uninit_write_slice(buffer, bytes);
             self.position += bytes.len();
             return Ok(());
         }
@@ -189,8 +230,11 @@
 
         assert!(self.position == 0);
 
-        if self.position + bytes.len() < self.buffer.len() {
-            &mut self.buffer[self.position..self.position + bytes.len()].copy_from_slice(bytes);
+        if self.position + bytes.len() < self.buffer().len() {
+            // SAFETY: see the `buffer` field documentation about invariants.
+            let buffer =
+                unsafe { &mut (&mut *self.buffer)[self.position..self.position + bytes.len()] };
+            maybe_uninit_write_slice(buffer, bytes);
             self.position += bytes.len();
             return Ok(());
         }
@@ -204,9 +248,7 @@
             }
             OutputTarget::Vec(ref mut vec) => {
                 vec.extend(bytes);
-                unsafe {
-                    self.buffer = remove_lifetime_mut(remaining_capacity_as_slice_mut(vec));
-                }
+                self.buffer = vec_spare_capacity_mut(vec)
             }
         }
         Ok(())
@@ -223,30 +265,38 @@
 
     /// Write varint
     pub fn write_raw_varint32(&mut self, value: u32) -> ProtobufResult<()> {
-        if self.buffer.len() - self.position >= 5 {
+        if self.buffer().len() - self.position >= 5 {
             // fast path
-            let len = varint::encode_varint32(value, &mut self.buffer[self.position..]);
+            let len = unsafe {
+                varint::encode_varint32(value, &mut (&mut *self.buffer)[self.position..])
+            };
             self.position += len;
             Ok(())
         } else {
             // slow path
             let buf = &mut [0u8; 5];
-            let len = varint::encode_varint32(value, buf);
+            let len = varint::encode_varint32(value, unsafe {
+                slice::from_raw_parts_mut(buf.as_mut_ptr() as *mut MaybeUninit<u8>, buf.len())
+            });
             self.write_raw_bytes(&buf[..len])
         }
     }
 
     /// Write varint
     pub fn write_raw_varint64(&mut self, value: u64) -> ProtobufResult<()> {
-        if self.buffer.len() - self.position >= 10 {
+        if self.buffer().len() - self.position >= 10 {
             // fast path
-            let len = varint::encode_varint64(value, &mut self.buffer[self.position..]);
+            let len = unsafe {
+                varint::encode_varint64(value, &mut (&mut *self.buffer)[self.position..])
+            };
             self.position += len;
             Ok(())
         } else {
             // slow path
             let buf = &mut [0u8; 10];
-            let len = varint::encode_varint64(value, buf);
+            let len = varint::encode_varint64(value, unsafe {
+                slice::from_raw_parts_mut(buf.as_mut_ptr() as *mut MaybeUninit<u8>, buf.len())
+            });
             self.write_raw_bytes(&buf[..len])
         }
     }
@@ -532,13 +582,14 @@
 
 #[cfg(test)]
 mod test {
+    use std::io::Write;
+    use std::iter;
+
     use crate::coded_output_stream::CodedOutputStream;
     use crate::hex::decode_hex;
     use crate::hex::encode_hex;
     use crate::wire_format;
     use crate::ProtobufResult;
-    use std::io::Write;
-    use std::iter;
 
     fn test_write<F>(expected: &str, mut gen: F)
     where
diff --git a/src/compiler_plugin.rs b/src/compiler_plugin.rs
index e056071..122eeb3 100644
--- a/src/compiler_plugin.rs
+++ b/src/compiler_plugin.rs
@@ -1,13 +1,14 @@
 // TODO: move into separate crate
 #![doc(hidden)]
 
-use crate::descriptor::FileDescriptorProto;
-use crate::plugin::*;
-use crate::Message;
 use std::io::stdin;
 use std::io::stdout;
 use std::str;
 
+use crate::descriptor::FileDescriptorProto;
+use crate::plugin::*;
+use crate::Message;
+
 pub struct GenRequest<'a> {
     pub file_descriptors: &'a [FileDescriptorProto],
     pub files_to_generate: &'a [String],
diff --git a/src/descriptor.rs b/src/descriptor.rs
index 8f3dd2f..7ca155d 100644
--- a/src/descriptor.rs
+++ b/src/descriptor.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/descriptorx.rs b/src/descriptorx.rs
index 82baab8..7b046ec 100644
--- a/src/descriptorx.rs
+++ b/src/descriptorx.rs
@@ -8,7 +8,6 @@
 /// utilities to work with descriptor
 use crate::descriptor::FileDescriptorProto;
 use crate::descriptor::OneofDescriptorProto;
-
 use crate::rust;
 use crate::strx;
 
diff --git a/src/lazy.rs b/src/lazy.rs
index 5b01502..3575dd0 100644
--- a/src/lazy.rs
+++ b/src/lazy.rs
@@ -56,13 +56,14 @@
 
 #[cfg(test)]
 mod test {
-    use super::Lazy;
     use std::sync::atomic::AtomicIsize;
     use std::sync::atomic::Ordering;
     use std::sync::Arc;
     use std::sync::Barrier;
     use std::thread;
 
+    use super::Lazy;
+
     #[test]
     fn many_threads_calling_get() {
         const N_THREADS: usize = 32;
diff --git a/src/lazy_v2.rs b/src/lazy_v2.rs
index 4ba10a5..6f9ac1e 100644
--- a/src/lazy_v2.rs
+++ b/src/lazy_v2.rs
@@ -33,13 +33,14 @@
 
 #[cfg(test)]
 mod test {
-    use super::LazyV2;
     use std::sync::atomic::AtomicIsize;
     use std::sync::atomic::Ordering;
     use std::sync::Arc;
     use std::sync::Barrier;
     use std::thread;
 
+    use super::LazyV2;
+
     #[test]
     fn many_threads_calling_get() {
         const N_THREADS: usize = 32;
diff --git a/src/lib.rs b/src/lib.rs
index 8eee9d3..d88e029 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,97 @@
-//! Library to read and write protocol buffers data.
+//! # Library to read and write protocol buffers data
+//!
+//! # Version 2 is stable
+//!
+//! Currently developed branch of rust-protobuf [is 3](https://docs.rs/protobuf/%3E=3.0.0-alpha).
+//! It has the same spirit as version 2, but contains numerous improvements like:
+//! * runtime reflection for mutability, not just for access
+//! * protobuf text format and JSON parsing (which rely on reflection)
+//! * dynamic message support: work with protobuf data without generating code from schema
+//!
+//! Stable version of rust-protobuf will be supported until version 3 released.
+//!
+//! [Tracking issue for version 3](https://github.com/stepancheg/rust-protobuf/issues/518).
+//!
+//! # How to generate rust code
+//!
+//! There are several ways to generate rust code from `.proto` files
+//!
+//! ## Invoke `protoc` programmatically with protoc-rust crate (recommended)
+//!
+//! Have a look at readme in [protoc-rust crate](https://docs.rs/protoc-rust/=2).
+//!
+//! ## Use pure rust protobuf parser and code generator
+//!
+//! Readme should be in
+//! [protobuf-codegen-pure crate](https://docs.rs/protobuf-codegen-pure/=2).
+//!
+//! ## Use protoc-gen-rust plugin
+//!
+//! Readme is [here](https://docs.rs/protobuf-codegen/=2).
+//!
+//! ## Generated code
+//!
+//! Have a look at generated files (for current development version),
+//! used internally in rust-protobuf:
+//!
+//! * [descriptor.rs](https://github.com/stepancheg/rust-protobuf/blob/master/protobuf/src/descriptor.rs)
+//!   for [descriptor.proto](https://github.com/stepancheg/rust-protobuf/blob/master/protoc-bin-vendored/include/google/protobuf/descriptor.proto)
+//!   (that is part of Google protobuf)
+//!
+//! # Copy on write
+//!
+//! Rust-protobuf can be used with [bytes crate](https://github.com/tokio-rs/bytes).
+//!
+//! To enable `Bytes` you need to:
+//!
+//! 1. Enable `with-bytes` feature in rust-protobuf:
+//!
+//! ```
+//! [dependencies]
+//! protobuf = { version = "~2.0", features = ["with-bytes"] }
+//! ```
+//!
+//! 2. Enable bytes option
+//!
+//! with `Customize` when codegen is invoked programmatically:
+//!
+//! ```ignore
+//! protoc_rust::run(protoc_rust::Args {
+//!     ...
+//!     customize: Customize {
+//!         carllerche_bytes_for_bytes: Some(true),
+//!         carllerche_bytes_for_string: Some(true),
+//!         ..Default::default()
+//!     },
+//! });
+//! ```
+//!
+//! or in `.proto` file:
+//!
+//! ```ignore
+//! import "rustproto.proto";
+//!
+//! option (rustproto.carllerche_bytes_for_bytes_all) = true;
+//! option (rustproto.carllerche_bytes_for_string_all) = true;
+//! ```
+//!
+//! With these options enabled, fields of type `bytes` or `string` are
+//! generated as `Bytes` or `Chars` respectively. When `CodedInputStream` is constructed
+//! from `Bytes` object, fields of these types get subslices of original `Bytes` object,
+//! instead of being allocated on heap.
+//!
+//! # Accompanying crates
+//!
+//! * [`protoc-rust`](https://docs.rs/protoc-rust/=2)
+//!   and [`protobuf-codegen-pure`](https://docs.rs/protobuf-codegen-pure/=2)
+//!   can be used to rust code from `.proto` crates.
+//! * [`protobuf-codegen`](https://docs.rs/protobuf-codegen/=2) for `protoc-gen-rust` protoc plugin.
+//! * [`protoc`](https://docs.rs/protoc/=2) crate can be used to invoke `protoc` programmatically.
+//! * [`protoc-bin-vendored`](https://docs.rs/protoc-bin-vendored/=2) contains `protoc` command
+//!   packed into the crate.
 
 #![deny(missing_docs)]
-#![deny(broken_intra_doc_links)]
+#![deny(rustdoc::broken_intra_doc_links)]
 
 #[cfg(feature = "bytes")]
 extern crate bytes;
@@ -90,6 +180,7 @@
 mod misc;
 
 mod buf_read_iter;
+mod buf_read_or_reader;
 
 /// This symbol is in generated `version.rs`, include here for IDE
 #[cfg(never)]
diff --git a/src/misc.rs b/src/misc.rs
index d923d58..faef34f 100644
--- a/src/misc.rs
+++ b/src/misc.rs
@@ -1,37 +1,52 @@
 use std::mem;
+use std::mem::MaybeUninit;
 use std::slice;
 
-/// Slice from `vec[vec.len()..vec.capacity()]`
-pub unsafe fn remaining_capacity_as_slice_mut<A>(vec: &mut Vec<A>) -> &mut [A] {
-    slice::from_raw_parts_mut(
-        vec.as_mut_slice().as_mut_ptr().offset(vec.len() as isize),
-        vec.capacity() - vec.len(),
-    )
-}
-
-pub unsafe fn remove_lifetime_mut<A: ?Sized>(a: &mut A) -> &'static mut A {
-    mem::transmute(a)
-}
-
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn test_remaining_capacity_as_slice_mut() {
-        let mut v = Vec::with_capacity(5);
-        v.push(10);
-        v.push(11);
-        v.push(12);
-        unsafe {
-            {
-                let s = remaining_capacity_as_slice_mut(&mut v);
-                assert_eq!(2, s.len());
-                s[0] = 13;
-                s[1] = 14;
-            }
-            v.set_len(5);
-        }
-        assert_eq!(vec![10, 11, 12, 13, 14], v);
+/// `Vec::spare_capacity_mut` is not stable until Rust 1.60.
+pub(crate) fn vec_spare_capacity_mut<A>(vec: &mut Vec<A>) -> &mut [MaybeUninit<A>] {
+    // SAFETY: copy-paste from rust stdlib.
+    unsafe {
+        slice::from_raw_parts_mut(
+            vec.as_mut_ptr().add(vec.len()) as *mut MaybeUninit<A>,
+            vec.capacity() - vec.len(),
+        )
     }
 }
+
+/// `MaybeUninit::write_slice` is not stable.
+pub(crate) fn maybe_uninit_write_slice<'a, T>(
+    this: &'a mut [MaybeUninit<T>],
+    src: &[T],
+) -> &'a mut [T]
+where
+    T: Copy,
+{
+    // SAFETY: copy-paste from rust stdlib.
+
+    let uninit_src: &[MaybeUninit<T>] = unsafe { mem::transmute(src) };
+
+    this.copy_from_slice(uninit_src);
+
+    unsafe { &mut *(this as *mut [MaybeUninit<T>] as *mut [T]) }
+}
+
+/// `MaybeUninit::array_assume_init` is not stable.
+#[inline]
+pub(crate) unsafe fn maybe_ununit_array_assume_init<T, const N: usize>(
+    array: [MaybeUninit<T>; N],
+) -> [T; N] {
+    // SAFETY:
+    // * The caller guarantees that all elements of the array are initialized
+    // * `MaybeUninit<T>` and T are guaranteed to have the same layout
+    // * `MaybeUninit` does not drop, so there are no double-frees
+    // And thus the conversion is safe
+    (&array as *const _ as *const [T; N]).read()
+}
+
+/// `MaybeUninit::write` is stable since 1.55.
+#[inline]
+pub(crate) fn maybe_uninit_write<T>(uninit: &mut MaybeUninit<T>, val: T) -> &mut T {
+    // SAFETY: copy-paste from rust stdlib.
+    *uninit = MaybeUninit::new(val);
+    unsafe { &mut *uninit.as_mut_ptr() }
+}
diff --git a/src/plugin.rs b/src/plugin.rs
index 77e1666..93f2ca8 100644
--- a/src/plugin.rs
+++ b/src/plugin.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/reflect/acc/v1.rs b/src/reflect/acc/v1.rs
index 5cf53d5..4c55f8f 100644
--- a/src/reflect/acc/v1.rs
+++ b/src/reflect/acc/v1.rs
@@ -9,21 +9,20 @@
 use crate::enums::ProtobufEnum;
 use crate::message::message_down_cast;
 use crate::message::Message;
-use crate::reflect::EnumValueDescriptor;
-use crate::reflect::ProtobufValue;
-use crate::reflect::ReflectFieldRef;
-use crate::reflect::ReflectValueRef;
-use crate::types::*;
-
 use crate::reflect::map::ReflectMap;
 use crate::reflect::optional::ReflectOptional;
 use crate::reflect::repeated::ReflectRepeated;
 use crate::reflect::repeated::ReflectRepeatedEnum;
 use crate::reflect::repeated::ReflectRepeatedMessage;
 use crate::reflect::rt::FieldAccessor;
+use crate::reflect::EnumValueDescriptor;
+use crate::reflect::ProtobufValue;
+use crate::reflect::ReflectFieldRef;
+use crate::reflect::ReflectValueRef;
 use crate::repeated::RepeatedField;
 use crate::singular::SingularField;
 use crate::singular::SingularPtrField;
+use crate::types::*;
 
 /// this trait should not be used directly, use `FieldDescriptor` instead
 pub trait FieldAccessorTrait: Sync + 'static {
@@ -249,7 +248,24 @@
                 get_set: SingularGetSet::Enum(ref get),
                 ..
             } => get.get_enum(message_down_cast(m)),
-            _ => panic!(),
+            FieldAccessorFunctions::Optional(ref t) => {
+                match t
+                    .get_field(message_down_cast(m))
+                    .to_option()
+                    .expect("field unset")
+                    .as_ref()
+                {
+                    ReflectValueRef::Enum(e) => e,
+                    _ => panic!("not an enum"),
+                }
+            }
+            FieldAccessorFunctions::Simple(ref t) => {
+                match t.get_field(message_down_cast(m)).as_ref() {
+                    ReflectValueRef::Enum(e) => e,
+                    _ => panic!("not an enum"),
+                }
+            }
+            ref fns => panic!("unknown accessor type: {:?}", fns),
         }
     }
 
diff --git a/src/reflect/enums.rs b/src/reflect/enums.rs
index f1ad901..a25be6f 100644
--- a/src/reflect/enums.rs
+++ b/src/reflect/enums.rs
@@ -1,3 +1,5 @@
+use std::collections::HashMap;
+
 use crate::descriptor::EnumDescriptorProto;
 use crate::descriptor::EnumValueDescriptorProto;
 use crate::descriptor::FileDescriptorProto;
@@ -5,7 +7,6 @@
 use crate::reflect::find_message_or_enum::find_message_or_enum;
 use crate::reflect::find_message_or_enum::MessageOrEnum;
 use crate::ProtobufEnum;
-use std::collections::HashMap;
 
 /// Description for enum variant.
 ///
diff --git a/src/reflect/message.rs b/src/reflect/message.rs
index 53ea2ce..0db9821 100644
--- a/src/reflect/message.rs
+++ b/src/reflect/message.rs
@@ -1,3 +1,6 @@
+use std::collections::HashMap;
+use std::marker;
+
 use crate::descriptor::DescriptorProto;
 use crate::descriptor::FileDescriptorProto;
 use crate::descriptorx::find_message_by_rust_name;
@@ -6,8 +9,6 @@
 use crate::reflect::find_message_or_enum::MessageOrEnum;
 use crate::reflect::FieldDescriptor;
 use crate::Message;
-use std::collections::HashMap;
-use std::marker;
 
 trait MessageFactory: Send + Sync + 'static {
     fn new_instance(&self) -> Box<dyn Message>;
diff --git a/src/reflect/mod.rs b/src/reflect/mod.rs
index 392f629..e120e16 100644
--- a/src/reflect/mod.rs
+++ b/src/reflect/mod.rs
@@ -23,8 +23,6 @@
 
 pub use self::enums::EnumDescriptor;
 pub use self::enums::EnumValueDescriptor;
-
-pub use self::message::MessageDescriptor;
-
 pub use self::field::FieldDescriptor;
 pub use self::field::ReflectFieldRef;
+pub use self::message::MessageDescriptor;
diff --git a/src/reflect/optional.rs b/src/reflect/optional.rs
index f81f973..f719a2c 100644
--- a/src/reflect/optional.rs
+++ b/src/reflect/optional.rs
@@ -1,7 +1,6 @@
 use std::mem;
 
 use super::value::ProtobufValue;
-
 use crate::singular::*;
 
 pub trait ReflectOptional: 'static {
diff --git a/src/reflect/repeated.rs b/src/reflect/repeated.rs
index be232f4..710de3e 100644
--- a/src/reflect/repeated.rs
+++ b/src/reflect/repeated.rs
@@ -2,7 +2,6 @@
 
 use super::value::ProtobufValue;
 use super::value::ReflectValueRef;
-
 use crate::repeated::RepeatedField;
 
 pub trait ReflectRepeated: 'static {
diff --git a/src/reflect/value.rs b/src/reflect/value.rs
index 16d5266..9598b9f 100644
--- a/src/reflect/value.rs
+++ b/src/reflect/value.rs
@@ -1,11 +1,11 @@
 use std::any::Any;
 
 #[cfg(feature = "bytes")]
-use crate::chars::Chars;
-#[cfg(feature = "bytes")]
 use bytes::Bytes;
 
 use super::*;
+#[cfg(feature = "bytes")]
+use crate::chars::Chars;
 
 /// Type implemented by all protobuf elementary types
 /// (ints, floats, bool, string, bytes, enums, messages).
diff --git a/src/repeated.rs b/src/repeated.rs
index 8068d0c..0b749d9 100644
--- a/src/repeated.rs
+++ b/src/repeated.rs
@@ -1,6 +1,3 @@
-#[cfg(feature = "with-serde")]
-use serde;
-
 use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::default::Default;
@@ -16,6 +13,9 @@
 use std::slice;
 use std::vec;
 
+#[cfg(feature = "with-serde")]
+use serde;
+
 use crate::clear::Clear;
 
 /// Wrapper around vector to avoid deallocations on clear.
@@ -396,6 +396,18 @@
 
 impl<T: Eq> Eq for RepeatedField<T> {}
 
+impl<T: PartialEq> PartialEq<[T]> for RepeatedField<T> {
+    fn eq(&self, other: &[T]) -> bool {
+        self.as_slice() == other
+    }
+}
+
+impl<T: PartialEq> PartialEq<RepeatedField<T>> for [T] {
+    fn eq(&self, other: &RepeatedField<T>) -> bool {
+        self == other.as_slice()
+    }
+}
+
 impl<T: PartialEq> RepeatedField<T> {
     /// True iff this container contains given element.
     #[inline]
@@ -455,6 +467,22 @@
     }
 }
 
+impl<T> Extend<T> for RepeatedField<T> {
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        self.vec.truncate(self.len);
+        self.vec.extend(iter);
+        self.len = self.vec.len();
+    }
+}
+
+impl<'a, T: Copy + 'a> Extend<&'a T> for RepeatedField<T> {
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+        self.vec.truncate(self.len);
+        self.vec.extend(iter);
+        self.len = self.vec.len();
+    }
+}
+
 impl<T: fmt::Debug> fmt::Debug for RepeatedField<T> {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -508,4 +536,28 @@
         v.clear();
         assert_eq!("".to_string(), *v.push_default());
     }
+
+    #[test]
+    fn extend_values() {
+        let mut r = RepeatedField::new();
+        r.push(10);
+        r.push(20);
+        r.clear();
+        // self-check
+        assert_eq!(2, r.vec.len());
+        r.extend(vec![30, 40]);
+        assert_eq!(&[30, 40][..], &r);
+    }
+
+    #[test]
+    fn extend_copy() {
+        let mut r = RepeatedField::new();
+        r.push(10);
+        r.push(20);
+        r.clear();
+        // self-check
+        assert_eq!(2, r.vec.len());
+        r.extend(&[30, 40]);
+        assert_eq!(&[30, 40][..], &r);
+    }
 }
diff --git a/src/rt.rs b/src/rt.rs
index 3bb0280..fca1254 100644
--- a/src/rt.rs
+++ b/src/rt.rs
@@ -6,27 +6,26 @@
 use std::hash::Hash;
 
 #[cfg(feature = "bytes")]
-use crate::chars::Chars;
-#[cfg(feature = "bytes")]
 use bytes::Bytes;
 
+#[cfg(feature = "bytes")]
+use crate::chars::Chars;
 use crate::coded_input_stream::CodedInputStream;
 use crate::coded_output_stream::CodedOutputStream;
 use crate::enums::ProtobufEnum;
 use crate::error::ProtobufError;
 use crate::error::ProtobufResult;
 use crate::error::WireError;
+pub use crate::lazy_v2::LazyV2;
 use crate::message::*;
 use crate::repeated::RepeatedField;
 use crate::singular::SingularField;
 use crate::singular::SingularPtrField;
 use crate::types::*;
-use crate::zigzag::*;
-
-pub use crate::lazy_v2::LazyV2;
 use crate::unknown::UnknownFields;
 use crate::wire_format;
 use crate::wire_format::WireType;
+use crate::zigzag::*;
 
 /// Given `u64` value compute varint encoded length.
 pub fn compute_raw_varint64_size(value: u64) -> u32 {
diff --git a/src/rustproto.rs b/src/rustproto.rs
index 83854e4..75df067 100644
--- a/src/rustproto.rs
+++ b/src/rustproto.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
@@ -59,6 +59,8 @@
     pub const carllerche_bytes_for_bytes_field: crate::ext::ExtFieldOptional<crate::descriptor::FieldOptions, crate::types::ProtobufTypeBool> = crate::ext::ExtFieldOptional { field_number: 17011, phantom: ::std::marker::PhantomData };
 
     pub const carllerche_bytes_for_string_field: crate::ext::ExtFieldOptional<crate::descriptor::FieldOptions, crate::types::ProtobufTypeBool> = crate::ext::ExtFieldOptional { field_number: 17012, phantom: ::std::marker::PhantomData };
+
+    pub const serde_rename_all: crate::ext::ExtFieldOptional<crate::descriptor::EnumOptions, crate::types::ProtobufTypeString> = crate::ext::ExtFieldOptional { field_number: 17032, phantom: ::std::marker::PhantomData };
 }
 
 static file_descriptor_proto_data: &'static [u8] = b"\
@@ -94,92 +96,98 @@
     s_for_bytes_field\x18\xf3\x84\x01\x20\x01(\x08\x12\x1d.google.protobuf.F\
     ieldOptionsR\x1ccarllercheBytesForBytesField:i\n!carllerche_bytes_for_st\
     ring_field\x18\xf4\x84\x01\x20\x01(\x08\x12\x1d.google.protobuf.FieldOpt\
-    ionsR\x1dcarllercheBytesForStringFieldJ\xf2\x13\n\x06\x12\x04\0\07\x01\n\
-    \x08\n\x01\x0c\x12\x03\0\0\x12\n\t\n\x02\x03\0\x12\x03\x02\0*\nh\n\x01\
-    \x02\x12\x03\x07\0\x122^\x20see\x20https://github.com/gogo/protobuf/blob\
-    /master/gogoproto/gogo.proto\n\x20for\x20the\x20original\x20idea\n\n\t\n\
-    \x01\x07\x12\x04\t\0\x1b\x01\n7\n\x02\x07\0\x12\x03\x0b\x04+\x1a,\x20Whe\
-    n\x20true,\x20oneof\x20field\x20is\x20generated\x20public\n\n\n\n\x03\
-    \x07\0\x02\x12\x03\t\x07\"\n\n\n\x03\x07\0\x04\x12\x03\x0b\x04\x0c\n\n\n\
-    \x03\x07\0\x05\x12\x03\x0b\r\x11\n\n\n\x03\x07\0\x01\x12\x03\x0b\x12\"\n\
-    \n\n\x03\x07\0\x03\x12\x03\x0b%*\nI\n\x02\x07\x01\x12\x03\r\x04,\x1a>\
-    \x20When\x20true\x20all\x20fields\x20are\x20public,\x20and\x20not\x20acc\
-    essors\x20generated\n\n\n\n\x03\x07\x01\x02\x12\x03\t\x07\"\n\n\n\x03\
-    \x07\x01\x04\x12\x03\r\x04\x0c\n\n\n\x03\x07\x01\x05\x12\x03\r\r\x11\n\n\
-    \n\x03\x07\x01\x01\x12\x03\r\x12#\n\n\n\x03\x07\x01\x03\x12\x03\r&+\nP\n\
-    \x02\x07\x02\x12\x03\x0f\x041\x1aE\x20When\x20false,\x20`get_`,\x20`set_\
-    `,\x20`mut_`\x20etc.\x20accessors\x20are\x20not\x20generated\n\n\n\n\x03\
-    \x07\x02\x02\x12\x03\t\x07\"\n\n\n\x03\x07\x02\x04\x12\x03\x0f\x04\x0c\n\
-    \n\n\x03\x07\x02\x05\x12\x03\x0f\r\x11\n\n\n\x03\x07\x02\x01\x12\x03\x0f\
-    \x12(\n\n\n\x03\x07\x02\x03\x12\x03\x0f+0\n2\n\x02\x07\x03\x12\x03\x11\
-    \x049\x1a'\x20Use\x20`bytes::Bytes`\x20for\x20`bytes`\x20fields\n\n\n\n\
-    \x03\x07\x03\x02\x12\x03\t\x07\"\n\n\n\x03\x07\x03\x04\x12\x03\x11\x04\
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+    \x07#\n\n\n\x03\x07\x10\x04\x12\x032\x04\x0c\n\n\n\x03\x07\x10\x05\x12\
+    \x032\r\x11\n\n\n\x03\x07\x10\x01\x12\x032\x12*\n\n\n\x03\x07\x10\x03\
+    \x12\x032-2\n2\n\x02\x07\x11\x12\x034\x04;\x1a'\x20Use\x20`bytes::Bytes`\
+    \x20for\x20`bytes`\x20fields\n\n\n\n\x03\x07\x11\x02\x12\x03.\x07#\n\n\n\
+    \x03\x07\x11\x04\x12\x034\x04\x0c\n\n\n\x03\x07\x11\x05\x12\x034\r\x11\n\
+    \n\n\x03\x07\x11\x01\x12\x034\x122\n\n\n\x03\x07\x11\x03\x12\x0345:\n3\n\
+    \x02\x07\x12\x12\x036\x04<\x1a(\x20Use\x20`bytes::Bytes`\x20for\x20`stri\
+    ng`\x20fields\n\n\n\n\x03\x07\x12\x02\x12\x03.\x07#\n\n\n\x03\x07\x12\
+    \x04\x12\x036\x04\x0c\n\n\n\x03\x07\x12\x05\x12\x036\r\x11\n\n\n\x03\x07\
+    \x12\x01\x12\x036\x123\n\n\n\x03\x07\x12\x03\x12\x0366;\n\t\n\x01\x07\
+    \x12\x049\0<\x01\n/\n\x02\x07\x13\x12\x03;\x04-\x1a$\x20use\x20rename_al\
+    l\x20attribute\x20for\x20serde\n\n\n\n\x03\x07\x13\x02\x12\x039\x07\"\n\
+    \n\n\x03\x07\x13\x04\x12\x03;\x04\x0c\n\n\n\x03\x07\x13\x05\x12\x03;\r\
+    \x13\n\n\n\x03\x07\x13\x01\x12\x03;\x14$\n\n\n\x03\x07\x13\x03\x12\x03;'\
+    ,\
 ";
 
 static file_descriptor_proto_lazy: crate::rt::LazyV2<crate::descriptor::FileDescriptorProto> = crate::rt::LazyV2::INIT;
diff --git a/src/singular.rs b/src/singular.rs
index ef04d2f..1b7e28d 100644
--- a/src/singular.rs
+++ b/src/singular.rs
@@ -1,6 +1,3 @@
-#[cfg(feature = "with-serde")]
-use serde;
-
 use std::default::Default;
 use std::fmt;
 use std::hash::Hash;
@@ -8,6 +5,9 @@
 use std::mem;
 use std::option;
 
+#[cfg(feature = "with-serde")]
+use serde;
+
 use crate::clear::Clear;
 
 /// Like `Option<T>`, but keeps the actual element on `clear`.
@@ -341,7 +341,9 @@
     /// Get contained data, consume self. Return default value for type if this is empty.
     #[inline]
     pub fn unwrap_or_default(mut self) -> T {
-        self.value.clear();
+        if !self.set {
+            self.value.clear();
+        }
         self.value
     }
 
@@ -577,4 +579,16 @@
         x.set_default();
         assert_eq!(0, x.as_ref().unwrap().b);
     }
+
+    #[test]
+    fn unwrap_or_default() {
+        assert_eq!(
+            "abc",
+            SingularField::some("abc".to_owned()).unwrap_or_default()
+        );
+        assert_eq!("", SingularField::<String>::none().unwrap_or_default());
+        let mut some = SingularField::some("abc".to_owned());
+        some.clear();
+        assert_eq!("", some.unwrap_or_default());
+    }
 }
diff --git a/src/text_format/lexer/lexer_impl.rs b/src/text_format/lexer/lexer_impl.rs
index f824a7a..ae9035a 100644
--- a/src/text_format/lexer/lexer_impl.rs
+++ b/src/text_format/lexer/lexer_impl.rs
@@ -605,7 +605,7 @@
             if let Some(c) = self.next_char_if_in("+-") {
                 s.push(c);
             }
-            s.push(self.next_char_expect(is_digit_1_9, LexerError::IncorrectJsonNumber)?);
+            s.push(self.next_char_expect(is_digit, LexerError::IncorrectJsonNumber)?);
             while let Some(c) = self.next_char_if(is_digit) {
                 s.push(c);
             }
@@ -716,4 +716,11 @@
         let mess = lex(msg, |p| p.next_token_inner());
         assert_eq!(Token::FloatLit(12.3), mess);
     }
+
+    #[test]
+    fn test_lexer_float_lit_leading_zeros_in_exp() {
+        let msg = r#"1e00009"#;
+        let mess = lex(msg, |p| p.next_token_inner());
+        assert_eq!(Token::FloatLit(1_000_000_000.0), mess);
+    }
 }
diff --git a/src/text_format/lexer/str_lit.rs b/src/text_format/lexer/str_lit.rs
index caa98f1..15ffa5b 100644
--- a/src/text_format/lexer/str_lit.rs
+++ b/src/text_format/lexer/str_lit.rs
@@ -1,8 +1,9 @@
+use std::fmt;
+use std::string::FromUtf8Error;
+
 use super::lexer_impl::Lexer;
 use super::lexer_impl::LexerError;
 use crate::text_format::lexer::ParserLanguage;
-use std::fmt;
-use std::string::FromUtf8Error;
 
 #[derive(Debug)]
 pub enum StrLitDecodeError {
diff --git a/src/text_format/mod.rs b/src/text_format/mod.rs
index 7af03e4..2fa9a16 100644
--- a/src/text_format/mod.rs
+++ b/src/text_format/mod.rs
@@ -19,13 +19,14 @@
 //! protobuf implementations, including `protoc` command which can decode
 //! and encode messages using text format.
 
-use crate::message::Message;
-use crate::reflect::ReflectFieldRef;
-use crate::reflect::ReflectValueRef;
 use std;
 use std::fmt;
 use std::fmt::Write;
 
+use crate::message::Message;
+use crate::reflect::ReflectFieldRef;
+use crate::reflect::ReflectValueRef;
+
 mod print;
 
 // Used by text format parser and by pure-rust codegen parsed
diff --git a/src/types.rs b/src/types.rs
index d9bbb10..20244a1 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -4,10 +4,10 @@
 use std::mem;
 
 #[cfg(feature = "bytes")]
-use crate::chars::Chars;
-#[cfg(feature = "bytes")]
 use bytes::Bytes;
 
+#[cfg(feature = "bytes")]
+use crate::chars::Chars;
 use crate::coded_input_stream::CodedInputStream;
 use crate::coded_output_stream::CodedOutputStream;
 use crate::enums::ProtobufEnum;
diff --git a/src/unknown.rs b/src/unknown.rs
index fb0cf45..dd67033 100644
--- a/src/unknown.rs
+++ b/src/unknown.rs
@@ -1,15 +1,17 @@
-use crate::clear::Clear;
-use crate::wire_format;
-use crate::zigzag::encode_zig_zag_32;
-use crate::zigzag::encode_zig_zag_64;
 use std::collections::hash_map;
 use std::collections::hash_map::DefaultHasher;
 use std::collections::HashMap;
 use std::default::Default;
+use std::hash::BuildHasherDefault;
 use std::hash::Hash;
 use std::hash::Hasher;
 use std::slice;
 
+use crate::clear::Clear;
+use crate::wire_format;
+use crate::zigzag::encode_zig_zag_32;
+use crate::zigzag::encode_zig_zag_64;
+
 /// Unknown value.
 ///
 /// See [`UnknownFields`](crate::UnknownFields) for the explanations.
@@ -169,10 +171,19 @@
 #[derive(Clone, PartialEq, Eq, Debug, Default)]
 pub struct UnknownFields {
     /// The map.
-    // option is needed, because HashMap constructor performs allocation,
-    // and very expensive
+    //
+    // `Option` is needed, because HashMap constructor performs allocation,
+    // and very expensive.
+    //
+    // We use "default hasher" to make iteration order deterministic.
+    // Which is used to make codegen output deterministic in presence of unknown fields
+    // (e. g. file options are represented as unknown fields).
+    // Using default hasher is suboptimal, because it makes unknown fields less safe.
+    // Note, Google Protobuf C++ simply uses linear map (which can exploitable the same way),
+    // and Google Protobuf Java uses tree map to store unknown fields
+    // (which is more expensive than hashmap).
     // TODO: hide
-    pub fields: Option<Box<HashMap<u32, UnknownValues>>>,
+    pub fields: Option<Box<HashMap<u32, UnknownValues, BuildHasherDefault<DefaultHasher>>>>,
 }
 
 /// Very simple hash implementation of `Hash` for `UnknownFields`.
@@ -301,11 +312,12 @@
 
 #[cfg(test)]
 mod test {
-    use super::UnknownFields;
     use std::collections::hash_map::DefaultHasher;
     use std::hash::Hash;
     use std::hash::Hasher;
 
+    use super::UnknownFields;
+
     #[test]
     fn unknown_fields_hash() {
         let mut unknown_fields_1 = UnknownFields::new();
@@ -329,4 +341,23 @@
 
         assert_eq!(hash(&unknown_fields_1), hash(&unknown_fields_2));
     }
+
+    #[test]
+    fn unknown_fields_iteration_order_deterministic() {
+        let mut u_1 = UnknownFields::new();
+        let mut u_2 = UnknownFields::new();
+        for u in &mut [&mut u_1, &mut u_2] {
+            u.add_fixed32(10, 20);
+            u.add_varint(30, 40);
+            u.add_fixed64(50, 60);
+            u.add_length_delimited(70, Vec::new());
+            u.add_varint(80, 90);
+            u.add_fixed32(11, 22);
+            u.add_fixed64(33, 44);
+        }
+
+        let items_1: Vec<_> = u_1.iter().collect();
+        let items_2: Vec<_> = u_2.iter().collect();
+        assert_eq!(items_1, items_2);
+    }
 }
diff --git a/src/varint.rs b/src/varint.rs
index 1f1cb1c..8e542bc 100644
--- a/src/varint.rs
+++ b/src/varint.rs
@@ -1,17 +1,21 @@
+use std::mem::MaybeUninit;
+
+use crate::misc::maybe_uninit_write;
+
 /// Encode u64 as varint.
 /// Panics if buffer length is less than 10.
 #[inline]
-pub fn encode_varint64(mut value: u64, buf: &mut [u8]) -> usize {
+pub fn encode_varint64(mut value: u64, buf: &mut [MaybeUninit<u8>]) -> usize {
     assert!(buf.len() >= 10);
 
     unsafe {
         let mut i = 0;
         while (value & !0x7F) > 0 {
-            *buf.get_unchecked_mut(i) = ((value & 0x7F) | 0x80) as u8;
+            maybe_uninit_write(buf.get_unchecked_mut(i), ((value & 0x7F) | 0x80) as u8);
             value >>= 7;
             i += 1;
         }
-        *buf.get_unchecked_mut(i) = value as u8;
+        maybe_uninit_write(buf.get_unchecked_mut(i), value as u8);
         i + 1
     }
 }
@@ -19,17 +23,17 @@
 /// Encode u32 value as varint.
 /// Panics if buffer length is less than 5.
 #[inline]
-pub fn encode_varint32(mut value: u32, buf: &mut [u8]) -> usize {
+pub fn encode_varint32(mut value: u32, buf: &mut [MaybeUninit<u8>]) -> usize {
     assert!(buf.len() >= 5);
 
     unsafe {
         let mut i = 0;
         while (value & !0x7F) > 0 {
-            *buf.get_unchecked_mut(i) = ((value & 0x7F) | 0x80) as u8;
+            maybe_uninit_write(buf.get_unchecked_mut(i), ((value & 0x7F) | 0x80) as u8);
             value >>= 7;
             i += 1;
         }
-        *buf.get_unchecked_mut(i) = value as u8;
+        maybe_uninit_write(buf.get_unchecked_mut(i), value as u8);
         i + 1
     }
 }
diff --git a/src/well_known_types/any.rs b/src/well_known_types/any.rs
index f306202..e46065f 100644
--- a/src/well_known_types/any.rs
+++ b/src/well_known_types/any.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/api.rs b/src/well_known_types/api.rs
index 34798b4..ef97015 100644
--- a/src/well_known_types/api.rs
+++ b/src/well_known_types/api.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/duration.rs b/src/well_known_types/duration.rs
index ec82f78..822061a 100644
--- a/src/well_known_types/duration.rs
+++ b/src/well_known_types/duration.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/empty.rs b/src/well_known_types/empty.rs
index 5c69487..d55e517 100644
--- a/src/well_known_types/empty.rs
+++ b/src/well_known_types/empty.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/field_mask.rs b/src/well_known_types/field_mask.rs
index 9d1f8f6..e98eb53 100644
--- a/src/well_known_types/field_mask.rs
+++ b/src/well_known_types/field_mask.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/source_context.rs b/src/well_known_types/source_context.rs
index 55c1ab4..646e87d 100644
--- a/src/well_known_types/source_context.rs
+++ b/src/well_known_types/source_context.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/struct_pb.rs b/src/well_known_types/struct_pb.rs
index 222d712..5f18a42 100644
--- a/src/well_known_types/struct_pb.rs
+++ b/src/well_known_types/struct_pb.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/timestamp.rs b/src/well_known_types/timestamp.rs
index d0f7903..25e7acf 100644
--- a/src/well_known_types/timestamp.rs
+++ b/src/well_known_types/timestamp.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/type_pb.rs b/src/well_known_types/type_pb.rs
index d6c06cc..14bfdb2 100644
--- a/src/well_known_types/type_pb.rs
+++ b/src/well_known_types/type_pb.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
diff --git a/src/well_known_types/wrappers.rs b/src/well_known_types/wrappers.rs
index 11edf4c..4e056c7 100644
--- a/src/well_known_types/wrappers.rs
+++ b/src/well_known_types/wrappers.rs
@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.22.0. Do not edit
+// This file is generated by rust-protobuf 2.26.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702