ipc/ipc_channel_reader_unittest.cc - chromium/src - Git at Google

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "build/build_config.h"

 #include <stddef.h>
 #include <stdint.h>

 #include <limits>
 #include <memory>
 #include <set>

 #include "base/run_loop.h"
 #include "ipc/attachment_broker.h"
 #include "ipc/brokerable_attachment.h"
 #include "ipc/ipc_channel_reader.h"
 #include "ipc/placeholder_brokerable_attachment.h"
 #include "testing/gtest/include/gtest/gtest.h"

 // Whether IPC::Message::FindNext() can determine message size for
 // partial messages. The condition is from FindNext() implementation.
 #if USE_ATTACHMENT_BROKER
 #define MESSAGE_FINDNEXT_PARTIAL 0
 #else
 #define MESSAGE_FINDNEXT_PARTIAL 1
 #endif

 namespace IPC {
 namespace internal {

 namespace {

 #if USE_ATTACHMENT_BROKER

 class MockAttachment : public BrokerableAttachment {
  public:
   MockAttachment() {}
   MockAttachment(BrokerableAttachment::AttachmentId id)
       : BrokerableAttachment(id) {}

 #if defined(OS_POSIX)
   base::PlatformFile TakePlatformFile() override {
     return base::PlatformFile();
   }
 #endif  // OS_POSIX

   BrokerableType GetBrokerableType() const override { return WIN_HANDLE; }

  private:
   ~MockAttachment() override {}
 };

 class MockAttachmentBroker : public AttachmentBroker {
  public:
   typedef std::set<scoped_refptr<BrokerableAttachment>> AttachmentSet;

   bool SendAttachmentToProcess(
       const scoped_refptr<BrokerableAttachment>& attachment,
       base::ProcessId destination_process) override {
     return false;
   }

   bool OnMessageReceived(const Message& message) override { return false; }

   void AddAttachment(scoped_refptr<BrokerableAttachment> attachment) {
     get_attachments()->push_back(attachment);
     NotifyObservers(attachment->GetIdentifier());
   }
 };

 #endif  // USE_ATTACHMENT_BROKER

 class MockChannelReader : public ChannelReader {
  public:
   MockChannelReader()
       : ChannelReader(nullptr), last_dispatched_message_(nullptr) {}

   ReadState ReadData(char* buffer, int buffer_len, int* bytes_read) override {
     if (data_.empty())
       return READ_PENDING;

     size_t read_len = std::min(static_cast<size_t>(buffer_len), data_.size());
     memcpy(buffer, data_.data(), read_len);
     *bytes_read = static_cast<int>(read_len);
     data_.erase(0, read_len);
     return READ_SUCCEEDED;
   }

   bool ShouldDispatchInputMessage(Message* msg) override { return true; }

   bool GetNonBrokeredAttachments(Message* msg) override { return true; }

   bool DidEmptyInputBuffers() override { return true; }

   void HandleInternalMessage(const Message& msg) override {}

   void DispatchMessage(Message* m) override { last_dispatched_message_ = m; }

   base::ProcessId GetSenderPID() override { return base::kNullProcessId; }

   bool IsAttachmentBrokerEndpoint() override { return false; }

   AttachmentBroker* GetAttachmentBroker() override { return broker_; }

   // This instance takes ownership of |m|.
   void AddMessageForDispatch(Message* m) {
     get_queued_messages()->push_back(m);
   }

   Message* get_last_dispatched_message() { return last_dispatched_message_; }

   void set_broker(AttachmentBroker* broker) { broker_ = broker; }

   void AppendData(const void* data, size_t size) {
     data_.append(static_cast<const char*>(data), size);
   }

   void AppendMessageData(const Message& message) {
     AppendData(message.data(), message.size());
   }

  private:
   Message* last_dispatched_message_;
   AttachmentBroker* broker_;
   std::string data_;
 };

 class ExposedMessage: public Message {
  public:
   using Message::Header;
   using Message::header;
 };

 // Payload that makes messages large
 const size_t LargePayloadSize = Channel::kMaximumReadBufferSize * 3 / 2;

 }  // namespace

 #if USE_ATTACHMENT_BROKER

 TEST(ChannelReaderTest, AttachmentAlreadyBrokered) {
   MockAttachmentBroker broker;
   MockChannelReader reader;
   reader.set_broker(&broker);
   scoped_refptr<MockAttachment> attachment(new MockAttachment);
   broker.AddAttachment(attachment);

   Message* m = new Message;
   PlaceholderBrokerableAttachment* needs_brokering_attachment =
       new PlaceholderBrokerableAttachment(attachment->GetIdentifier());
   EXPECT_TRUE(m->WriteAttachment(needs_brokering_attachment));
   reader.AddMessageForDispatch(m);
   EXPECT_EQ(ChannelReader::DISPATCH_FINISHED, reader.DispatchMessages());
   EXPECT_EQ(m, reader.get_last_dispatched_message());
 }

 TEST(ChannelReaderTest, AttachmentNotYetBrokered) {
   std::unique_ptr<base::MessageLoop> message_loop(new base::MessageLoopForIO());

   MockAttachmentBroker broker;
   MockChannelReader reader;
   reader.set_broker(&broker);
   scoped_refptr<MockAttachment> attachment(new MockAttachment);

   Message* m = new Message;
   PlaceholderBrokerableAttachment* needs_brokering_attachment =
       new PlaceholderBrokerableAttachment(attachment->GetIdentifier());
   EXPECT_TRUE(m->WriteAttachment(needs_brokering_attachment));
   reader.AddMessageForDispatch(m);
   EXPECT_EQ(ChannelReader::DISPATCH_WAITING_ON_BROKER,
             reader.DispatchMessages());
   EXPECT_EQ(nullptr, reader.get_last_dispatched_message());

   broker.AddAttachment(attachment);
   base::RunLoop run_loop;
   run_loop.RunUntilIdle();

   EXPECT_EQ(m, reader.get_last_dispatched_message());
 }

 #endif  // USE_ATTACHMENT_BROKER

 #if !USE_ATTACHMENT_BROKER

 // We can determine message size from its header (and hence resize the buffer)
 // only when attachment broker is not used, see IPC::Message::FindNext().

 TEST(ChannelReaderTest, ResizeOverflowBuffer) {
   MockChannelReader reader;

   ExposedMessage::Header header = {};

   header.payload_size = 128 * 1024;
   EXPECT_LT(reader.input_overflow_buf_.capacity(), header.payload_size);
   EXPECT_TRUE(reader.TranslateInputData(
       reinterpret_cast<const char*>(&header), sizeof(header)));

   // Once message header is available we resize overflow buffer to
   // fit the entire message.
   EXPECT_GE(reader.input_overflow_buf_.capacity(), header.payload_size);
 }

 TEST(ChannelReaderTest, InvalidMessageSize) {
   MockChannelReader reader;

   ExposedMessage::Header header = {};

   size_t capacity_before = reader.input_overflow_buf_.capacity();

   // Message is slightly larger than maximum allowed size
   header.payload_size = Channel::kMaximumMessageSize + 1;
   EXPECT_FALSE(reader.TranslateInputData(
       reinterpret_cast<const char*>(&header), sizeof(header)));
   EXPECT_LE(reader.input_overflow_buf_.capacity(), capacity_before);

   // Payload size is negative, overflow is detected by Pickle::PeekNext()
   header.payload_size = static_cast<uint32_t>(-1);
   EXPECT_FALSE(reader.TranslateInputData(
       reinterpret_cast<const char*>(&header), sizeof(header)));
   EXPECT_LE(reader.input_overflow_buf_.capacity(), capacity_before);

   // Payload size is maximum int32_t value
   header.payload_size = std::numeric_limits<int32_t>::max();
   EXPECT_FALSE(reader.TranslateInputData(
       reinterpret_cast<const char*>(&header), sizeof(header)));
   EXPECT_LE(reader.input_overflow_buf_.capacity(), capacity_before);
 }

 #endif  // !USE_ATTACHMENT_BROKER

 TEST(ChannelReaderTest, TrimBuffer) {
   // ChannelReader uses std::string as a buffer, and calls reserve()
   // to trim it to kMaximumReadBufferSize. However, an implementation
   // is free to actually reserve a larger amount.
   size_t trimmed_buffer_size;
   {
     std::string buf;
     buf.reserve(Channel::kMaximumReadBufferSize);
     trimmed_buffer_size = buf.capacity();
   }

   // Buffer is trimmed after message is processed.
   {
     MockChannelReader reader;

     Message message;
     message.WriteString(std::string(LargePayloadSize, 'X'));

     // Sanity check
     EXPECT_TRUE(message.size() > trimmed_buffer_size);

     // Initially buffer is small
     EXPECT_LE(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);

     // Write and process large message
     reader.AppendMessageData(message);
     EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
               reader.ProcessIncomingMessages());

     // After processing large message buffer is trimmed
     EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
   }

   // Buffer is trimmed only after entire message is processed.
   {
     MockChannelReader reader;

     ExposedMessage message;
     message.WriteString(std::string(LargePayloadSize, 'X'));

     // Write and process message header
     reader.AppendData(message.header(), sizeof(ExposedMessage::Header));
     EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
               reader.ProcessIncomingMessages());

 #if MESSAGE_FINDNEXT_PARTIAL
     // We determined message size for the message from its header, so
     // we resized the buffer to fit.
     EXPECT_GE(reader.input_overflow_buf_.capacity(), message.size());
 #else
     // We couldn't determine message size, so we didn't resize the buffer.
 #endif

     // Write and process payload
     reader.AppendData(message.payload(), message.payload_size());
     EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
               reader.ProcessIncomingMessages());

     // But once we process the message, we trim the buffer
     EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
   }

   // Buffer is not trimmed if the next message is also large.
   {
     MockChannelReader reader;

     // Write large message
     Message message1;
     message1.WriteString(std::string(LargePayloadSize * 2, 'X'));
     reader.AppendMessageData(message1);

     // Write header for the next large message
     ExposedMessage message2;
     message2.WriteString(std::string(LargePayloadSize, 'Y'));
     reader.AppendData(message2.header(), sizeof(ExposedMessage::Header));

     // Process messages
     EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
               reader.ProcessIncomingMessages());

 #if MESSAGE_FINDNEXT_PARTIAL
     // We determined message size for the second (partial) message, so
     // we resized the buffer to fit.
     EXPECT_GE(reader.input_overflow_buf_.capacity(), message1.size());
 #else
     // We couldn't determine message size for the second (partial) message,
     // so we trimmed the buffer.
     EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
 #endif
   }

   // Buffer resized appropriately if next message is larger than the first.
   // (Similar to the test above except for the order of messages.)
   {
     MockChannelReader reader;

     // Write large message
     Message message1;
     message1.WriteString(std::string(LargePayloadSize, 'Y'));
     reader.AppendMessageData(message1);

     // Write header for the next even larger message
     ExposedMessage message2;
     message2.WriteString(std::string(LargePayloadSize * 2, 'X'));
     reader.AppendData(message2.header(), sizeof(ExposedMessage::Header));

     // Process messages
     EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
               reader.ProcessIncomingMessages());

 #if MESSAGE_FINDNEXT_PARTIAL
     // We determined message size for the second (partial) message, and
     // resized the buffer to fit it.
     EXPECT_GE(reader.input_overflow_buf_.capacity(), message2.size());
 #else
     // We couldn't determine message size for the second (partial) message,
     // so we trimmed the buffer.
     EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
 #endif
   }

   // Buffer is not trimmed if we've just resized it to accommodate large
   // incoming message.
   {
     MockChannelReader reader;

     // Write small message
     Message message1;
     message1.WriteString(std::string(11, 'X'));
     reader.AppendMessageData(message1);

     // Write header for the next large message
     ExposedMessage message2;
     message2.WriteString(std::string(LargePayloadSize, 'Y'));
     reader.AppendData(message2.header(), sizeof(ExposedMessage::Header));

     EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
               reader.ProcessIncomingMessages());

 #if MESSAGE_FINDNEXT_PARTIAL
     // We determined message size for the second (partial) message, so
     // we resized the buffer to fit.
     EXPECT_GE(reader.input_overflow_buf_.capacity(), message2.size());
 #else
     // We couldn't determine size for the second (partial) message, and
     // first message was small, so we did nothing.
 #endif
   }
 }

 }  // namespace internal
 }  // namespace IPC
	// Copyright 2015 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "build/build_config.h"

	#include <stddef.h>
	#include <stdint.h>

	#include <limits>
	#include <memory>
	#include <set>

	#include "base/run_loop.h"
	#include "ipc/attachment_broker.h"
	#include "ipc/brokerable_attachment.h"
	#include "ipc/ipc_channel_reader.h"
	#include "ipc/placeholder_brokerable_attachment.h"
	#include "testing/gtest/include/gtest/gtest.h"

	// Whether IPC::Message::FindNext() can determine message size for
	// partial messages. The condition is from FindNext() implementation.
	#if USE_ATTACHMENT_BROKER
	#define MESSAGE_FINDNEXT_PARTIAL 0
	#else
	#define MESSAGE_FINDNEXT_PARTIAL 1
	#endif

	namespace IPC {
	namespace internal {

	namespace {

	#if USE_ATTACHMENT_BROKER

	class MockAttachment : public BrokerableAttachment {
	public:
	MockAttachment() {}
	MockAttachment(BrokerableAttachment::AttachmentId id)
	: BrokerableAttachment(id) {}

	#if defined(OS_POSIX)
	base::PlatformFile TakePlatformFile() override {
	return base::PlatformFile();
	}
	#endif // OS_POSIX

	BrokerableType GetBrokerableType() const override { return WIN_HANDLE; }

	private:
	~MockAttachment() override {}
	};

	class MockAttachmentBroker : public AttachmentBroker {
	public:
	typedef std::set<scoped_refptr<BrokerableAttachment>> AttachmentSet;

	bool SendAttachmentToProcess(
	const scoped_refptr<BrokerableAttachment>& attachment,
	base::ProcessId destination_process) override {
	return false;
	}

	bool OnMessageReceived(const Message& message) override { return false; }

	void AddAttachment(scoped_refptr<BrokerableAttachment> attachment) {
	get_attachments()->push_back(attachment);
	NotifyObservers(attachment->GetIdentifier());
	}
	};

	#endif // USE_ATTACHMENT_BROKER

	class MockChannelReader : public ChannelReader {
	public:
	MockChannelReader()
	: ChannelReader(nullptr), last_dispatched_message_(nullptr) {}

	ReadState ReadData(char* buffer, int buffer_len, int* bytes_read) override {
	if (data_.empty())
	return READ_PENDING;

	size_t read_len = std::min(static_cast<size_t>(buffer_len), data_.size());
	memcpy(buffer, data_.data(), read_len);
	*bytes_read = static_cast<int>(read_len);
	data_.erase(0, read_len);
	return READ_SUCCEEDED;
	}

	bool ShouldDispatchInputMessage(Message* msg) override { return true; }

	bool GetNonBrokeredAttachments(Message* msg) override { return true; }

	bool DidEmptyInputBuffers() override { return true; }

	void HandleInternalMessage(const Message& msg) override {}

	void DispatchMessage(Message* m) override { last_dispatched_message_ = m; }

	base::ProcessId GetSenderPID() override { return base::kNullProcessId; }

	bool IsAttachmentBrokerEndpoint() override { return false; }

	AttachmentBroker* GetAttachmentBroker() override { return broker_; }

	// This instance takes ownership of \|m\|.
	void AddMessageForDispatch(Message* m) {
	get_queued_messages()->push_back(m);
	}

	Message* get_last_dispatched_message() { return last_dispatched_message_; }

	void set_broker(AttachmentBroker* broker) { broker_ = broker; }

	void AppendData(const void* data, size_t size) {
	data_.append(static_cast<const char*>(data), size);
	}

	void AppendMessageData(const Message& message) {
	AppendData(message.data(), message.size());
	}

	private:
	Message* last_dispatched_message_;
	AttachmentBroker* broker_;
	std::string data_;
	};

	class ExposedMessage: public Message {
	public:
	using Message::Header;
	using Message::header;
	};

	// Payload that makes messages large
	const size_t LargePayloadSize = Channel::kMaximumReadBufferSize * 3 / 2;

	} // namespace

	#if USE_ATTACHMENT_BROKER

	TEST(ChannelReaderTest, AttachmentAlreadyBrokered) {
	MockAttachmentBroker broker;
	MockChannelReader reader;
	reader.set_broker(&broker);
	scoped_refptr<MockAttachment> attachment(new MockAttachment);
	broker.AddAttachment(attachment);

	Message* m = new Message;
	PlaceholderBrokerableAttachment* needs_brokering_attachment =
	new PlaceholderBrokerableAttachment(attachment->GetIdentifier());
	EXPECT_TRUE(m->WriteAttachment(needs_brokering_attachment));
	reader.AddMessageForDispatch(m);
	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED, reader.DispatchMessages());
	EXPECT_EQ(m, reader.get_last_dispatched_message());
	}

	TEST(ChannelReaderTest, AttachmentNotYetBrokered) {
	std::unique_ptr<base::MessageLoop> message_loop(new base::MessageLoopForIO());

	MockAttachmentBroker broker;
	MockChannelReader reader;
	reader.set_broker(&broker);
	scoped_refptr<MockAttachment> attachment(new MockAttachment);

	Message* m = new Message;
	PlaceholderBrokerableAttachment* needs_brokering_attachment =
	new PlaceholderBrokerableAttachment(attachment->GetIdentifier());
	EXPECT_TRUE(m->WriteAttachment(needs_brokering_attachment));
	reader.AddMessageForDispatch(m);
	EXPECT_EQ(ChannelReader::DISPATCH_WAITING_ON_BROKER,
	reader.DispatchMessages());
	EXPECT_EQ(nullptr, reader.get_last_dispatched_message());

	broker.AddAttachment(attachment);
	base::RunLoop run_loop;
	run_loop.RunUntilIdle();

	EXPECT_EQ(m, reader.get_last_dispatched_message());
	}

	#endif // USE_ATTACHMENT_BROKER

	#if !USE_ATTACHMENT_BROKER

	// We can determine message size from its header (and hence resize the buffer)
	// only when attachment broker is not used, see IPC::Message::FindNext().

	TEST(ChannelReaderTest, ResizeOverflowBuffer) {
	MockChannelReader reader;

	ExposedMessage::Header header = {};

	header.payload_size = 128 * 1024;
	EXPECT_LT(reader.input_overflow_buf_.capacity(), header.payload_size);
	EXPECT_TRUE(reader.TranslateInputData(
	reinterpret_cast<const char*>(&header), sizeof(header)));

	// Once message header is available we resize overflow buffer to
	// fit the entire message.
	EXPECT_GE(reader.input_overflow_buf_.capacity(), header.payload_size);
	}

	TEST(ChannelReaderTest, InvalidMessageSize) {
	MockChannelReader reader;

	ExposedMessage::Header header = {};

	size_t capacity_before = reader.input_overflow_buf_.capacity();

	// Message is slightly larger than maximum allowed size
	header.payload_size = Channel::kMaximumMessageSize + 1;
	EXPECT_FALSE(reader.TranslateInputData(
	reinterpret_cast<const char*>(&header), sizeof(header)));
	EXPECT_LE(reader.input_overflow_buf_.capacity(), capacity_before);

	// Payload size is negative, overflow is detected by Pickle::PeekNext()
	header.payload_size = static_cast<uint32_t>(-1);
	EXPECT_FALSE(reader.TranslateInputData(
	reinterpret_cast<const char*>(&header), sizeof(header)));
	EXPECT_LE(reader.input_overflow_buf_.capacity(), capacity_before);

	// Payload size is maximum int32_t value
	header.payload_size = std::numeric_limits<int32_t>::max();
	EXPECT_FALSE(reader.TranslateInputData(
	reinterpret_cast<const char*>(&header), sizeof(header)));
	EXPECT_LE(reader.input_overflow_buf_.capacity(), capacity_before);
	}

	#endif // !USE_ATTACHMENT_BROKER

	TEST(ChannelReaderTest, TrimBuffer) {
	// ChannelReader uses std::string as a buffer, and calls reserve()
	// to trim it to kMaximumReadBufferSize. However, an implementation
	// is free to actually reserve a larger amount.
	size_t trimmed_buffer_size;
	{
	std::string buf;
	buf.reserve(Channel::kMaximumReadBufferSize);
	trimmed_buffer_size = buf.capacity();
	}

	// Buffer is trimmed after message is processed.
	{
	MockChannelReader reader;

	Message message;
	message.WriteString(std::string(LargePayloadSize, 'X'));

	// Sanity check
	EXPECT_TRUE(message.size() > trimmed_buffer_size);

	// Initially buffer is small
	EXPECT_LE(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);

	// Write and process large message
	reader.AppendMessageData(message);
	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
	reader.ProcessIncomingMessages());

	// After processing large message buffer is trimmed
	EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
	}

	// Buffer is trimmed only after entire message is processed.
	{
	MockChannelReader reader;

	ExposedMessage message;
	message.WriteString(std::string(LargePayloadSize, 'X'));

	// Write and process message header
	reader.AppendData(message.header(), sizeof(ExposedMessage::Header));
	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
	reader.ProcessIncomingMessages());

	#if MESSAGE_FINDNEXT_PARTIAL
	// We determined message size for the message from its header, so
	// we resized the buffer to fit.
	EXPECT_GE(reader.input_overflow_buf_.capacity(), message.size());
	#else
	// We couldn't determine message size, so we didn't resize the buffer.
	#endif

	// Write and process payload
	reader.AppendData(message.payload(), message.payload_size());
	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
	reader.ProcessIncomingMessages());

	// But once we process the message, we trim the buffer
	EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
	}

	// Buffer is not trimmed if the next message is also large.
	{
	MockChannelReader reader;

	// Write large message
	Message message1;
	message1.WriteString(std::string(LargePayloadSize * 2, 'X'));
	reader.AppendMessageData(message1);

	// Write header for the next large message
	ExposedMessage message2;
	message2.WriteString(std::string(LargePayloadSize, 'Y'));
	reader.AppendData(message2.header(), sizeof(ExposedMessage::Header));

	// Process messages
	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
	reader.ProcessIncomingMessages());

	#if MESSAGE_FINDNEXT_PARTIAL
	// We determined message size for the second (partial) message, so
	// we resized the buffer to fit.
	EXPECT_GE(reader.input_overflow_buf_.capacity(), message1.size());
	#else
	// We couldn't determine message size for the second (partial) message,
	// so we trimmed the buffer.
	EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
	#endif
	}

	// Buffer resized appropriately if next message is larger than the first.
	// (Similar to the test above except for the order of messages.)
	{
	MockChannelReader reader;

	// Write large message
	Message message1;
	message1.WriteString(std::string(LargePayloadSize, 'Y'));
	reader.AppendMessageData(message1);

	// Write header for the next even larger message
	ExposedMessage message2;
	message2.WriteString(std::string(LargePayloadSize * 2, 'X'));
	reader.AppendData(message2.header(), sizeof(ExposedMessage::Header));

	// Process messages
	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
	reader.ProcessIncomingMessages());

	#if MESSAGE_FINDNEXT_PARTIAL
	// We determined message size for the second (partial) message, and
	// resized the buffer to fit it.
	EXPECT_GE(reader.input_overflow_buf_.capacity(), message2.size());
	#else
	// We couldn't determine message size for the second (partial) message,
	// so we trimmed the buffer.
	EXPECT_EQ(reader.input_overflow_buf_.capacity(), trimmed_buffer_size);
	#endif
	}

	// Buffer is not trimmed if we've just resized it to accommodate large
	// incoming message.
	{
	MockChannelReader reader;

	// Write small message
	Message message1;
	message1.WriteString(std::string(11, 'X'));
	reader.AppendMessageData(message1);

	// Write header for the next large message
	ExposedMessage message2;
	message2.WriteString(std::string(LargePayloadSize, 'Y'));
	reader.AppendData(message2.header(), sizeof(ExposedMessage::Header));

	EXPECT_EQ(ChannelReader::DISPATCH_FINISHED,
	reader.ProcessIncomingMessages());

	#if MESSAGE_FINDNEXT_PARTIAL
	// We determined message size for the second (partial) message, so
	// we resized the buffer to fit.
	EXPECT_GE(reader.input_overflow_buf_.capacity(), message2.size());
	#else
	// We couldn't determine size for the second (partial) message, and
	// first message was small, so we did nothing.
	#endif
	}
	}

	} // namespace internal
	} // namespace IPC