JNIHelp.cpp - platform/libnativehelper - Git at Google

 /*
  * Copyright (C) 2006 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #if defined(__ANDROID__)
 /* libnativehelper is built by NDK 19 in one variant, which doesn't yet have the GNU strerror_r. */
 #undef _GNU_SOURCE
 /* ...but this code uses asprintf, which is a BSD/GNU extension. */
 #define _BSD_SOURCE
 #endif

 #define LOG_TAG "JNIHelp"

 #include <nativehelper/JniConstants.h>
 #include <nativehelper/JNIHelp.h>
 #include "ALog-priv.h"

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>

 #include <string>

 /**
  * Equivalent to ScopedLocalRef, but for C_JNIEnv instead. (And slightly more powerful.)
  */
 template<typename T>
 class scoped_local_ref {
 public:
     explicit scoped_local_ref(C_JNIEnv* env, T localRef = NULL)
     : mEnv(env), mLocalRef(localRef)
     {
     }

     ~scoped_local_ref() {
         reset();
     }

     void reset(T localRef = NULL) {
         if (mLocalRef != NULL) {
             (*mEnv)->DeleteLocalRef(reinterpret_cast<JNIEnv*>(mEnv), mLocalRef);
             mLocalRef = localRef;
         }
     }

     T get() const {
         return mLocalRef;
     }

 private:
     C_JNIEnv* const mEnv;
     T mLocalRef;

     DISALLOW_COPY_AND_ASSIGN(scoped_local_ref);
 };

 static jclass findClass(C_JNIEnv* env, const char* className) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
     return (*env)->FindClass(e, className);
 }

 extern "C" int jniRegisterNativeMethods(C_JNIEnv* env, const char* className,
     const JNINativeMethod* gMethods, int numMethods)
 {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

     ALOGV("Registering %s's %d native methods...", className, numMethods);

     scoped_local_ref<jclass> c(env, findClass(env, className));
     if (c.get() == NULL) {
         char* tmp;
         const char* msg;
         if (asprintf(&tmp,
                      "Native registration unable to find class '%s'; aborting...",
                      className) == -1) {
             // Allocation failed, print default warning.
             msg = "Native registration unable to find class; aborting...";
         } else {
             msg = tmp;
         }
         e->FatalError(msg);
     }

     if ((*env)->RegisterNatives(e, c.get(), gMethods, numMethods) < 0) {
         char* tmp;
         const char* msg;
         if (asprintf(&tmp, "RegisterNatives failed for '%s'; aborting...", className) == -1) {
             // Allocation failed, print default warning.
             msg = "RegisterNatives failed; aborting...";
         } else {
             msg = tmp;
         }
         e->FatalError(msg);
     }

     return 0;
 }

 /*
  * Returns a human-readable summary of an exception object.  The buffer will
  * be populated with the "binary" class name and, if present, the
  * exception message.
  */
 static bool getExceptionSummary(C_JNIEnv* env, jthrowable exception, std::string& result) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

     /* get the name of the exception's class */
     scoped_local_ref<jclass> exceptionClass(env, (*env)->GetObjectClass(e, exception)); // can't fail
     scoped_local_ref<jclass> classClass(env,
             (*env)->GetObjectClass(e, exceptionClass.get())); // java.lang.Class, can't fail
     jmethodID classGetNameMethod =
             (*env)->GetMethodID(e, classClass.get(), "getName", "()Ljava/lang/String;");
     scoped_local_ref<jstring> classNameStr(env,
             (jstring) (*env)->CallObjectMethod(e, exceptionClass.get(), classGetNameMethod));
     if (classNameStr.get() == NULL) {
         (*env)->ExceptionClear(e);
         result = "<error getting class name>";
         return false;
     }
     const char* classNameChars = (*env)->GetStringUTFChars(e, classNameStr.get(), NULL);
     if (classNameChars == NULL) {
         (*env)->ExceptionClear(e);
         result = "<error getting class name UTF-8>";
         return false;
     }
     result += classNameChars;
     (*env)->ReleaseStringUTFChars(e, classNameStr.get(), classNameChars);

     /* if the exception has a detail message, get that */
     jmethodID getMessage =
             (*env)->GetMethodID(e, exceptionClass.get(), "getMessage", "()Ljava/lang/String;");
     scoped_local_ref<jstring> messageStr(env,
             (jstring) (*env)->CallObjectMethod(e, exception, getMessage));
     if (messageStr.get() == NULL) {
         return true;
     }

     result += ": ";

     const char* messageChars = (*env)->GetStringUTFChars(e, messageStr.get(), NULL);
     if (messageChars != NULL) {
         result += messageChars;
         (*env)->ReleaseStringUTFChars(e, messageStr.get(), messageChars);
     } else {
         result += "<error getting message>";
         (*env)->ExceptionClear(e); // clear OOM
     }

     return true;
 }

 /*
  * Returns an exception (with stack trace) as a string.
  */
 static bool getStackTrace(C_JNIEnv* env, jthrowable exception, std::string& result) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

     scoped_local_ref<jclass> stringWriterClass(env, findClass(env, "java/io/StringWriter"));
     if (stringWriterClass.get() == NULL) {
         return false;
     }

     jmethodID stringWriterCtor = (*env)->GetMethodID(e, stringWriterClass.get(), "<init>", "()V");
     jmethodID stringWriterToStringMethod =
             (*env)->GetMethodID(e, stringWriterClass.get(), "toString", "()Ljava/lang/String;");

     scoped_local_ref<jclass> printWriterClass(env, findClass(env, "java/io/PrintWriter"));
     if (printWriterClass.get() == NULL) {
         return false;
     }

     jmethodID printWriterCtor =
             (*env)->GetMethodID(e, printWriterClass.get(), "<init>", "(Ljava/io/Writer;)V");

     scoped_local_ref<jobject> stringWriter(env,
             (*env)->NewObject(e, stringWriterClass.get(), stringWriterCtor));
     if (stringWriter.get() == NULL) {
         return false;
     }

     scoped_local_ref<jobject> printWriter(env,
             (*env)->NewObject(e, printWriterClass.get(), printWriterCtor, stringWriter.get()));
     if (printWriter.get() == NULL) {
         return false;
     }

     scoped_local_ref<jclass> exceptionClass(env, (*env)->GetObjectClass(e, exception)); // can't fail
     jmethodID printStackTraceMethod =
             (*env)->GetMethodID(e, exceptionClass.get(), "printStackTrace", "(Ljava/io/PrintWriter;)V");
     (*env)->CallVoidMethod(e, exception, printStackTraceMethod, printWriter.get());

     if ((*env)->ExceptionCheck(e)) {
         return false;
     }

     scoped_local_ref<jstring> messageStr(env,
             (jstring) (*env)->CallObjectMethod(e, stringWriter.get(), stringWriterToStringMethod));
     if (messageStr.get() == NULL) {
         return false;
     }

     const char* utfChars = (*env)->GetStringUTFChars(e, messageStr.get(), NULL);
     if (utfChars == NULL) {
         return false;
     }

     result = utfChars;

     (*env)->ReleaseStringUTFChars(e, messageStr.get(), utfChars);
     return true;
 }

 extern "C" int jniThrowException(C_JNIEnv* env, const char* className, const char* msg) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

     if ((*env)->ExceptionCheck(e)) {
         /* TODO: consider creating the new exception with this as "cause" */
         scoped_local_ref<jthrowable> exception(env, (*env)->ExceptionOccurred(e));
         (*env)->ExceptionClear(e);

         if (exception.get() != NULL) {
             std::string text;
             getExceptionSummary(env, exception.get(), text);
             ALOGW("Discarding pending exception (%s) to throw %s", text.c_str(), className);
         }
     }

     scoped_local_ref<jclass> exceptionClass(env, findClass(env, className));
     if (exceptionClass.get() == NULL) {
         ALOGE("Unable to find exception class %s", className);
         /* ClassNotFoundException now pending */
         return -1;
     }

     if ((*env)->ThrowNew(e, exceptionClass.get(), msg) != JNI_OK) {
         ALOGE("Failed throwing '%s' '%s'", className, msg);
         /* an exception, most likely OOM, will now be pending */
         return -1;
     }

     return 0;
 }

 int jniThrowExceptionFmt(C_JNIEnv* env, const char* className, const char* fmt, va_list args) {
     char msgBuf[512];
     vsnprintf(msgBuf, sizeof(msgBuf), fmt, args);
     return jniThrowException(env, className, msgBuf);
 }

 int jniThrowNullPointerException(C_JNIEnv* env, const char* msg) {
     return jniThrowException(env, "java/lang/NullPointerException", msg);
 }

 int jniThrowRuntimeException(C_JNIEnv* env, const char* msg) {
     return jniThrowException(env, "java/lang/RuntimeException", msg);
 }

 int jniThrowIOException(C_JNIEnv* env, int errnum) {
     char buffer[80];
     const char* message = jniStrError(errnum, buffer, sizeof(buffer));
     return jniThrowException(env, "java/io/IOException", message);
 }

 static std::string jniGetStackTrace(C_JNIEnv* env, jthrowable exception) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

     scoped_local_ref<jthrowable> currentException(env, (*env)->ExceptionOccurred(e));
     if (exception == NULL) {
         exception = currentException.get();
         if (exception == NULL) {
           return "<no pending exception>";
         }
     }

     if (currentException.get() != NULL) {
         (*env)->ExceptionClear(e);
     }

     std::string trace;
     if (!getStackTrace(env, exception, trace)) {
         (*env)->ExceptionClear(e);
         getExceptionSummary(env, exception, trace);
     }

     if (currentException.get() != NULL) {
         (*env)->Throw(e, currentException.get()); // rethrow
     }

     return trace;
 }

 void jniLogException(C_JNIEnv* env, int priority, const char* tag, jthrowable exception) {
     std::string trace(jniGetStackTrace(env, exception));
     __android_log_write(priority, tag, trace.c_str());
 }

 const char* jniStrError(int errnum, char* buf, size_t buflen) {
 #if __GLIBC__
     // Note: glibc has a nonstandard strerror_r that returns char* rather than POSIX's int.
     // char *strerror_r(int errnum, char *buf, size_t n);
     return strerror_r(errnum, buf, buflen);
 #else
     int rc = strerror_r(errnum, buf, buflen);
     if (rc != 0) {
         // (POSIX only guarantees a value other than 0. The safest
         // way to implement this function is to use C++ and overload on the
         // type of strerror_r to accurately distinguish GNU from POSIX.)
         snprintf(buf, buflen, "errno %d", errnum);
     }
     return buf;
 #endif
 }

 jobject jniCreateFileDescriptor(C_JNIEnv* env, int fd) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
     JniConstants::init(e);
     static jmethodID ctor = e->GetMethodID(JniConstants::fileDescriptorClass, "<init>", "()V");
     jobject fileDescriptor = (*env)->NewObject(e, JniConstants::fileDescriptorClass, ctor);
     // NOTE: NewObject ensures that an OutOfMemoryError will be seen by the Java
     // caller if the alloc fails, so we just return NULL when that happens.
     if (fileDescriptor != NULL)  {
         jniSetFileDescriptorOfFD(env, fileDescriptor, fd);
     }
     return fileDescriptor;
 }

 int jniGetFDFromFileDescriptor(C_JNIEnv* env, jobject fileDescriptor) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
     JniConstants::init(e);
     static jfieldID fid = e->GetFieldID(JniConstants::fileDescriptorClass, "descriptor", "I");
     if (fileDescriptor != NULL) {
         return (*env)->GetIntField(e, fileDescriptor, fid);
     } else {
         return -1;
     }
 }

 void jniSetFileDescriptorOfFD(C_JNIEnv* env, jobject fileDescriptor, int value) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
     JniConstants::init(e);
     static jfieldID fid = e->GetFieldID(JniConstants::fileDescriptorClass, "descriptor", "I");
     (*env)->SetIntField(e, fileDescriptor, fid, value);
 }

 jobject jniGetReferent(C_JNIEnv* env, jobject ref) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
     JniConstants::init(e);
     static jmethodID get = e->GetMethodID(JniConstants::referenceClass, "get", "()Ljava/lang/Object;");
     return (*env)->CallObjectMethod(e, ref, get);
 }

 jstring jniCreateString(C_JNIEnv* env, const jchar* unicodeChars, jsize len) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
     return (*env)->NewString(e, unicodeChars, len);
 }
	/*
	* Copyright (C) 2006 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#if defined(__ANDROID__)
	/* libnativehelper is built by NDK 19 in one variant, which doesn't yet have the GNU strerror_r. */
	#undef _GNU_SOURCE
	/* ...but this code uses asprintf, which is a BSD/GNU extension. */
	#define _BSD_SOURCE
	#endif

	#define LOG_TAG "JNIHelp"

	#include <nativehelper/JniConstants.h>
	#include <nativehelper/JNIHelp.h>
	#include "ALog-priv.h"

	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <assert.h>

	#include <string>

	/**
	* Equivalent to ScopedLocalRef, but for C_JNIEnv instead. (And slightly more powerful.)
	*/
	template<typename T>
	class scoped_local_ref {
	public:
	explicit scoped_local_ref(C_JNIEnv* env, T localRef = NULL)
	: mEnv(env), mLocalRef(localRef)
	{
	}

	~scoped_local_ref() {
	reset();
	}

	void reset(T localRef = NULL) {
	if (mLocalRef != NULL) {
	(mEnv)->DeleteLocalRef(reinterpret_cast<JNIEnv>(mEnv), mLocalRef);
	mLocalRef = localRef;
	}
	}

	T get() const {
	return mLocalRef;
	}

	private:
	C_JNIEnv* const mEnv;
	T mLocalRef;

	DISALLOW_COPY_AND_ASSIGN(scoped_local_ref);
	};

	static jclass findClass(C_JNIEnv* env, const char* className) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
	return (*env)->FindClass(e, className);
	}

	extern "C" int jniRegisterNativeMethods(C_JNIEnv* env, const char* className,
	const JNINativeMethod* gMethods, int numMethods)
	{
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

	ALOGV("Registering %s's %d native methods...", className, numMethods);

	scoped_local_ref<jclass> c(env, findClass(env, className));
	if (c.get() == NULL) {
	char* tmp;
	const char* msg;
	if (asprintf(&tmp,
	"Native registration unable to find class '%s'; aborting...",
	className) == -1) {
	// Allocation failed, print default warning.
	msg = "Native registration unable to find class; aborting...";
	} else {
	msg = tmp;
	}
	e->FatalError(msg);
	}

	if ((*env)->RegisterNatives(e, c.get(), gMethods, numMethods) < 0) {
	char* tmp;
	const char* msg;
	if (asprintf(&tmp, "RegisterNatives failed for '%s'; aborting...", className) == -1) {
	// Allocation failed, print default warning.
	msg = "RegisterNatives failed; aborting...";
	} else {
	msg = tmp;
	}
	e->FatalError(msg);
	}

	return 0;
	}

	/*
	* Returns a human-readable summary of an exception object. The buffer will
	* be populated with the "binary" class name and, if present, the
	* exception message.
	*/
	static bool getExceptionSummary(C_JNIEnv* env, jthrowable exception, std::string& result) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

	/* get the name of the exception's class */
	scoped_local_ref<jclass> exceptionClass(env, (*env)->GetObjectClass(e, exception)); // can't fail
	scoped_local_ref<jclass> classClass(env,
	(*env)->GetObjectClass(e, exceptionClass.get())); // java.lang.Class, can't fail
	jmethodID classGetNameMethod =
	(*env)->GetMethodID(e, classClass.get(), "getName", "()Ljava/lang/String;");
	scoped_local_ref<jstring> classNameStr(env,
	(jstring) (*env)->CallObjectMethod(e, exceptionClass.get(), classGetNameMethod));
	if (classNameStr.get() == NULL) {
	(*env)->ExceptionClear(e);
	result = "<error getting class name>";
	return false;
	}
	const char* classNameChars = (*env)->GetStringUTFChars(e, classNameStr.get(), NULL);
	if (classNameChars == NULL) {
	(*env)->ExceptionClear(e);
	result = "<error getting class name UTF-8>";
	return false;
	}
	result += classNameChars;
	(*env)->ReleaseStringUTFChars(e, classNameStr.get(), classNameChars);

	/* if the exception has a detail message, get that */
	jmethodID getMessage =
	(*env)->GetMethodID(e, exceptionClass.get(), "getMessage", "()Ljava/lang/String;");
	scoped_local_ref<jstring> messageStr(env,
	(jstring) (*env)->CallObjectMethod(e, exception, getMessage));
	if (messageStr.get() == NULL) {
	return true;
	}

	result += ": ";

	const char* messageChars = (*env)->GetStringUTFChars(e, messageStr.get(), NULL);
	if (messageChars != NULL) {
	result += messageChars;
	(*env)->ReleaseStringUTFChars(e, messageStr.get(), messageChars);
	} else {
	result += "<error getting message>";
	(*env)->ExceptionClear(e); // clear OOM
	}

	return true;
	}

	/*
	* Returns an exception (with stack trace) as a string.
	*/
	static bool getStackTrace(C_JNIEnv* env, jthrowable exception, std::string& result) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

	scoped_local_ref<jclass> stringWriterClass(env, findClass(env, "java/io/StringWriter"));
	if (stringWriterClass.get() == NULL) {
	return false;
	}

	jmethodID stringWriterCtor = (*env)->GetMethodID(e, stringWriterClass.get(), "<init>", "()V");
	jmethodID stringWriterToStringMethod =
	(*env)->GetMethodID(e, stringWriterClass.get(), "toString", "()Ljava/lang/String;");

	scoped_local_ref<jclass> printWriterClass(env, findClass(env, "java/io/PrintWriter"));
	if (printWriterClass.get() == NULL) {
	return false;
	}

	jmethodID printWriterCtor =
	(*env)->GetMethodID(e, printWriterClass.get(), "<init>", "(Ljava/io/Writer;)V");

	scoped_local_ref<jobject> stringWriter(env,
	(*env)->NewObject(e, stringWriterClass.get(), stringWriterCtor));
	if (stringWriter.get() == NULL) {
	return false;
	}

	scoped_local_ref<jobject> printWriter(env,
	(*env)->NewObject(e, printWriterClass.get(), printWriterCtor, stringWriter.get()));
	if (printWriter.get() == NULL) {
	return false;
	}

	scoped_local_ref<jclass> exceptionClass(env, (*env)->GetObjectClass(e, exception)); // can't fail
	jmethodID printStackTraceMethod =
	(*env)->GetMethodID(e, exceptionClass.get(), "printStackTrace", "(Ljava/io/PrintWriter;)V");
	(*env)->CallVoidMethod(e, exception, printStackTraceMethod, printWriter.get());

	if ((*env)->ExceptionCheck(e)) {
	return false;
	}

	scoped_local_ref<jstring> messageStr(env,
	(jstring) (*env)->CallObjectMethod(e, stringWriter.get(), stringWriterToStringMethod));
	if (messageStr.get() == NULL) {
	return false;
	}

	const char* utfChars = (*env)->GetStringUTFChars(e, messageStr.get(), NULL);
	if (utfChars == NULL) {
	return false;
	}

	result = utfChars;

	(*env)->ReleaseStringUTFChars(e, messageStr.get(), utfChars);
	return true;
	}

	extern "C" int jniThrowException(C_JNIEnv* env, const char* className, const char* msg) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

	if ((*env)->ExceptionCheck(e)) {
	/* TODO: consider creating the new exception with this as "cause" */
	scoped_local_ref<jthrowable> exception(env, (*env)->ExceptionOccurred(e));
	(*env)->ExceptionClear(e);

	if (exception.get() != NULL) {
	std::string text;
	getExceptionSummary(env, exception.get(), text);
	ALOGW("Discarding pending exception (%s) to throw %s", text.c_str(), className);
	}
	}

	scoped_local_ref<jclass> exceptionClass(env, findClass(env, className));
	if (exceptionClass.get() == NULL) {
	ALOGE("Unable to find exception class %s", className);
	/* ClassNotFoundException now pending */
	return -1;
	}

	if ((*env)->ThrowNew(e, exceptionClass.get(), msg) != JNI_OK) {
	ALOGE("Failed throwing '%s' '%s'", className, msg);
	/* an exception, most likely OOM, will now be pending */
	return -1;
	}

	return 0;
	}

	int jniThrowExceptionFmt(C_JNIEnv* env, const char* className, const char* fmt, va_list args) {
	char msgBuf[512];
	vsnprintf(msgBuf, sizeof(msgBuf), fmt, args);
	return jniThrowException(env, className, msgBuf);
	}

	int jniThrowNullPointerException(C_JNIEnv* env, const char* msg) {
	return jniThrowException(env, "java/lang/NullPointerException", msg);
	}

	int jniThrowRuntimeException(C_JNIEnv* env, const char* msg) {
	return jniThrowException(env, "java/lang/RuntimeException", msg);
	}

	int jniThrowIOException(C_JNIEnv* env, int errnum) {
	char buffer[80];
	const char* message = jniStrError(errnum, buffer, sizeof(buffer));
	return jniThrowException(env, "java/io/IOException", message);
	}

	static std::string jniGetStackTrace(C_JNIEnv* env, jthrowable exception) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);

	scoped_local_ref<jthrowable> currentException(env, (*env)->ExceptionOccurred(e));
	if (exception == NULL) {
	exception = currentException.get();
	if (exception == NULL) {
	return "<no pending exception>";
	}
	}

	if (currentException.get() != NULL) {
	(*env)->ExceptionClear(e);
	}

	std::string trace;
	if (!getStackTrace(env, exception, trace)) {
	(*env)->ExceptionClear(e);
	getExceptionSummary(env, exception, trace);
	}

	if (currentException.get() != NULL) {
	(*env)->Throw(e, currentException.get()); // rethrow
	}

	return trace;
	}

	void jniLogException(C_JNIEnv* env, int priority, const char* tag, jthrowable exception) {
	std::string trace(jniGetStackTrace(env, exception));
	__android_log_write(priority, tag, trace.c_str());
	}

	const char* jniStrError(int errnum, char* buf, size_t buflen) {
	#if __GLIBC__
	// Note: glibc has a nonstandard strerror_r that returns char* rather than POSIX's int.
	// char strerror_r(int errnum, char buf, size_t n);
	return strerror_r(errnum, buf, buflen);
	#else
	int rc = strerror_r(errnum, buf, buflen);
	if (rc != 0) {
	// (POSIX only guarantees a value other than 0. The safest
	// way to implement this function is to use C++ and overload on the
	// type of strerror_r to accurately distinguish GNU from POSIX.)
	snprintf(buf, buflen, "errno %d", errnum);
	}
	return buf;
	#endif
	}

	jobject jniCreateFileDescriptor(C_JNIEnv* env, int fd) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
	JniConstants::init(e);
	static jmethodID ctor = e->GetMethodID(JniConstants::fileDescriptorClass, "<init>", "()V");
	jobject fileDescriptor = (*env)->NewObject(e, JniConstants::fileDescriptorClass, ctor);
	// NOTE: NewObject ensures that an OutOfMemoryError will be seen by the Java
	// caller if the alloc fails, so we just return NULL when that happens.
	if (fileDescriptor != NULL) {
	jniSetFileDescriptorOfFD(env, fileDescriptor, fd);
	}
	return fileDescriptor;
	}

	int jniGetFDFromFileDescriptor(C_JNIEnv* env, jobject fileDescriptor) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
	JniConstants::init(e);
	static jfieldID fid = e->GetFieldID(JniConstants::fileDescriptorClass, "descriptor", "I");
	if (fileDescriptor != NULL) {
	return (*env)->GetIntField(e, fileDescriptor, fid);
	} else {
	return -1;
	}
	}

	void jniSetFileDescriptorOfFD(C_JNIEnv* env, jobject fileDescriptor, int value) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
	JniConstants::init(e);
	static jfieldID fid = e->GetFieldID(JniConstants::fileDescriptorClass, "descriptor", "I");
	(*env)->SetIntField(e, fileDescriptor, fid, value);
	}

	jobject jniGetReferent(C_JNIEnv* env, jobject ref) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
	JniConstants::init(e);
	static jmethodID get = e->GetMethodID(JniConstants::referenceClass, "get", "()Ljava/lang/Object;");
	return (*env)->CallObjectMethod(e, ref, get);
	}

	jstring jniCreateString(C_JNIEnv* env, const jchar* unicodeChars, jsize len) {
	JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
	return (*env)->NewString(e, unicodeChars, len);
	}