Add a buffered SkStream class.
This is used by Android to buffer an input stream which may not
otherwise be able to rewind.
Add a test for the new class.
R=bungeman@google.com, mtklein@google.com, reed@google.com
Review URL: https://codereview.chromium.org/23717055
git-svn-id: http://skia.googlecode.com/svn/trunk/src@11488 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/utils/SkFrontBufferedStream.cpp b/utils/SkFrontBufferedStream.cpp
new file mode 100644
index 0000000..12030da
--- /dev/null
+++ b/utils/SkFrontBufferedStream.cpp
@@ -0,0 +1,147 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkFrontBufferedStream.h"
+
+SkStreamRewindable* SkFrontBufferedStream::Create(SkStream* stream, size_t bufferSize) {
+ if (NULL == stream) {
+ return NULL;
+ }
+ return SkNEW_ARGS(SkFrontBufferedStream, (stream, bufferSize));
+}
+
+SkFrontBufferedStream::SkFrontBufferedStream(SkStream* stream, size_t bufferSize)
+ : fStream(SkRef(stream))
+ , fOffset(0)
+ , fBufferedSoFar(0)
+ , fBufferSize(bufferSize)
+ , fBuffer(bufferSize) {}
+
+bool SkFrontBufferedStream::isAtEnd() const {
+ if (fOffset < fBufferedSoFar) {
+ // Even if the underlying stream is at the end, this stream has been
+ // rewound after buffering, so it is not at the end.
+ return false;
+ }
+
+ return fStream->isAtEnd();
+}
+
+bool SkFrontBufferedStream::rewind() {
+ // Only allow a rewind if we have not exceeded the buffer.
+ if (fOffset <= fBufferSize) {
+ fOffset = 0;
+ return true;
+ }
+ return false;
+}
+
+bool SkFrontBufferedStream::hasLength() const {
+ return fStream->hasLength();
+}
+
+size_t SkFrontBufferedStream::getLength() const {
+ return fStream->getLength();
+}
+
+size_t SkFrontBufferedStream::readFromBuffer(char* dst, size_t size) {
+ SkASSERT(fOffset < fBufferedSoFar);
+ // Some data has already been copied to fBuffer. Read up to the
+ // lesser of the size requested and the remainder of the buffered
+ // data.
+ const size_t bytesToCopy = SkTMin(size, fBufferedSoFar - fOffset);
+ if (dst != NULL) {
+ memcpy(dst, fBuffer + fOffset, bytesToCopy);
+ }
+
+ // Update fOffset to the new position. It is guaranteed to be
+ // within the buffered data.
+ fOffset += bytesToCopy;
+ SkASSERT(fOffset <= fBufferedSoFar);
+
+ return bytesToCopy;
+}
+
+size_t SkFrontBufferedStream::bufferAndWriteTo(char* dst, size_t size) {
+ SkASSERT(size > 0);
+ SkASSERT(fOffset >= fBufferedSoFar);
+ // Data needs to be buffered. Buffer up to the lesser of the size requested
+ // and the remainder of the max buffer size.
+ const size_t bytesToBuffer = SkTMin(size, fBufferSize - fBufferedSoFar);
+ char* buffer = fBuffer + fOffset;
+ const size_t buffered = fStream->read(buffer, bytesToBuffer);
+
+ fBufferedSoFar += buffered;
+ fOffset = fBufferedSoFar;
+ SkASSERT(fBufferedSoFar <= fBufferSize);
+
+ // Copy the buffer to the destination buffer and update the amount read.
+ if (dst != NULL) {
+ memcpy(dst, buffer, buffered);
+ }
+
+ return buffered;
+}
+
+size_t SkFrontBufferedStream::readDirectlyFromStream(char* dst, size_t size) {
+ SkASSERT(size > 0);
+ // If we get here, we have buffered all that can be buffered.
+ SkASSERT(fBufferSize == fBufferedSoFar && fOffset >= fBufferSize);
+
+ const size_t bytesReadDirectly = fStream->read(dst, size);
+ fOffset += bytesReadDirectly;
+
+ // If we have read past the end of the buffer, rewinding is no longer
+ // supported, so we can go ahead and free the memory.
+ if (bytesReadDirectly > 0) {
+ fBuffer.reset(0);
+ }
+
+ return bytesReadDirectly;
+}
+
+size_t SkFrontBufferedStream::read(void* voidDst, size_t size) {
+ // Cast voidDst to a char* for easy addition.
+ char* dst = reinterpret_cast<char*>(voidDst);
+ SkDEBUGCODE(const size_t totalSize = size;)
+ const size_t start = fOffset;
+
+ // First, read any data that was previously buffered.
+ if (fOffset < fBufferedSoFar) {
+ const size_t bytesCopied = this->readFromBuffer(dst, size);
+
+ // Update the remaining number of bytes needed to read
+ // and the destination buffer.
+ size -= bytesCopied;
+ SkASSERT(size + (fOffset - start) == totalSize);
+ if (dst != NULL) {
+ dst += bytesCopied;
+ }
+ }
+
+ // Buffer any more data that should be buffered, and copy it to the
+ // destination.
+ if (size > 0 && fBufferedSoFar < fBufferSize) {
+ const size_t buffered = this->bufferAndWriteTo(dst, size);
+
+ // Update the remaining number of bytes needed to read
+ // and the destination buffer.
+ size -= buffered;
+ SkASSERT(size + (fOffset - start) == totalSize);
+ if (dst != NULL) {
+ dst += buffered;
+ }
+ }
+
+ if (size > 0 && !fStream->isAtEnd()) {
+ const size_t bytesReadDirectly = this->readDirectlyFromStream(dst, size);
+ SkDEBUGCODE(size -= bytesReadDirectly;)
+ SkASSERT(size + (fOffset - start) == totalSize);
+ }
+
+ return fOffset - start;
+}
