blob: b55731297020f070f9fa4437c1cbb34e48c4372d [file] [log] [blame]
// Copyright 2016 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 "net/log/file_net_log_observer.h"
#include <algorithm>
#include <memory>
#include <string>
#include <utility>
#include "base/bind.h"
#include "base/containers/queue.h"
#include "base/files/file.h"
#include "base/files/file_util.h"
#include "base/json/json_writer.h"
#include "base/logging.h"
#include "base/memory/ptr_util.h"
#include "base/numerics/clamped_math.h"
#include "base/sequenced_task_runner.h"
#include "base/strings/string_number_conversions.h"
#include "base/synchronization/lock.h"
#include "base/task/post_task.h"
#include "base/task/thread_pool.h"
#include "base/values.h"
#include "net/log/net_log_capture_mode.h"
#include "net/log/net_log_entry.h"
#include "net/log/net_log_util.h"
#include "net/url_request/url_request_context.h"
namespace {
// Number of events that can build up in |write_queue_| before a task is posted
// to the file task runner to flush them to disk.
const int kNumWriteQueueEvents = 15;
// TODO(eroman): Should use something other than 10 for number of files?
const int kDefaultNumFiles = 10;
scoped_refptr<base::SequencedTaskRunner> CreateFileTaskRunner() {
// The tasks posted to this sequenced task runner do synchronous File I/O for
// the purposes of writing NetLog files.
// These intentionally block shutdown to ensure the log file has finished
// being written.
return base::ThreadPool::CreateSequencedTaskRunner(
{base::MayBlock(), base::TaskPriority::USER_VISIBLE,
// Truncates a file, also reseting the seek position.
void TruncateFile(base::File* file) {
if (!file->IsValid())
file->Seek(base::File::FROM_BEGIN, 0);
// Opens |path| in write mode.
base::File OpenFileForWrite(const base::FilePath& path) {
base::File result(path,
base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE);
LOG_IF(ERROR, !result.IsValid()) << "Failed opening: " << path.value();
return result;
// Helper that writes data to a file. |file->IsValid()| may be false,
// in which case nothing will be written. Returns the number of bytes
// successfully written (may be less than input data in case of errors).
size_t WriteToFile(base::File* file,
base::StringPiece data1,
base::StringPiece data2 = base::StringPiece(),
base::StringPiece data3 = base::StringPiece()) {
size_t bytes_written = 0;
if (file->IsValid()) {
// Append each of data1, data2 and data3.
if (!data1.empty())
bytes_written +=
std::max(0, file->WriteAtCurrentPos(, data1.size()));
if (!data2.empty())
bytes_written +=
std::max(0, file->WriteAtCurrentPos(, data2.size()));
if (!data3.empty())
bytes_written +=
std::max(0, file->WriteAtCurrentPos(, data3.size()));
return bytes_written;
// Copies all of the data at |source_path| and appends it to |destination_file|,
// then deletes |source_path|.
void AppendToFileThenDelete(const base::FilePath& source_path,
base::File* destination_file,
char* read_buffer,
size_t read_buffer_size) {
base::ScopedFILE source_file(base::OpenFile(source_path, "rb"));
if (!source_file)
// Read |source_path|'s contents in chunks of read_buffer_size and append
// to |destination_file|.
size_t num_bytes_read;
while ((num_bytes_read =
fread(read_buffer, 1, read_buffer_size, source_file.get())) > 0) {
base::StringPiece(read_buffer, num_bytes_read));
// Now that it has been copied, delete the source file.
base::FilePath SiblingInprogressDirectory(const base::FilePath& log_path) {
return log_path.AddExtension(FILE_PATH_LITERAL(".inprogress"));
} // namespace
namespace net {
// Used to store events to be written to file.
using EventQueue = base::queue<std::unique_ptr<std::string>>;
// WriteQueue receives events from FileNetLogObserver on the main thread and
// holds them in a queue until they are drained from the queue and written to
// file on the file task runner.
// WriteQueue contains the resources shared between the main thread and the
// file task runner. |lock_| must be acquired to read or write to |queue_| and
// |memory_|.
// WriteQueue is refcounted and should be destroyed once all events on the
// file task runner have finished executing.
class FileNetLogObserver::WriteQueue
: public base::RefCountedThreadSafe<WriteQueue> {
// |memory_max| indicates the maximum amount of memory that the virtual write
// queue can use. If |memory_| exceeds |memory_max_|, the |queue_| of events
// is overwritten.
explicit WriteQueue(uint64_t memory_max);
// Adds |event| to |queue_|. Also manages the size of |memory_|; if it
// exceeds |memory_max_|, then old events are dropped from |queue_| without
// being written to file.
// Returns the number of events in the |queue_|.
size_t AddEntryToQueue(std::unique_ptr<std::string> event);
// Swaps |queue_| with |local_queue|. |local_queue| should be empty, so that
// |queue_| is emptied. Resets |memory_| to 0.
void SwapQueue(EventQueue* local_queue);
friend class base::RefCountedThreadSafe<WriteQueue>;
// Queue of events to be written, shared between main thread and file task
// runner. Main thread adds events to the queue and the file task runner
// drains them and writes the events to file.
// |lock_| must be acquired to read or write to this.
EventQueue queue_;
// Tracks how much memory is being used by the virtual write queue.
// Incremented in AddEntryToQueue() when events are added to the
// buffer, and decremented when SwapQueue() is called and the file task
// runner's local queue is swapped with the shared write queue.
// |lock_| must be acquired to read or write to this.
uint64_t memory_;
// Indicates the maximum amount of memory that the |queue_| is allowed to
// use.
const uint64_t memory_max_;
// Protects access to |queue_| and |memory_|.
// A lock is necessary because |queue_| and |memory_| are shared between the
// file task runner and the main thread. NetLog's lock protects OnAddEntry(),
// which calls AddEntryToQueue(), but it does not protect access to the
// observer's member variables. Thus, a race condition exists if a thread is
// calling OnAddEntry() at the same time that the file task runner is
// accessing |memory_| and |queue_| to write events to file. The |queue_| and
// |memory_| counter are necessary to bound the amount of memory that is used
// for the queue in the event that the file task runner lags significantly
// behind the main thread in writing events to file.
base::Lock lock_;
// FileWriter is responsible for draining events from a WriteQueue and writing
// them to disk. FileWriter can be constructed on any thread, and
// afterwards is only accessed on the file task runner.
class FileNetLogObserver::FileWriter {
// If max_event_file_size == kNoLimit, then no limit is enforced.
FileWriter(const base::FilePath& log_path,
const base::FilePath& inprogress_dir_path,
base::Optional<base::File> pre_existing_log_file,
uint64_t max_event_file_size,
size_t total_num_event_files,
scoped_refptr<base::SequencedTaskRunner> task_runner);
// Writes |constants_value| to disk and opens the events array (closed in
// Stop()).
void Initialize(std::unique_ptr<base::Value> constants_value);
// Closes the events array opened in Initialize() and writes |polled_data| to
// disk. If |polled_data| cannot be converted to proper JSON, then it
// is ignored.
void Stop(std::unique_ptr<base::Value> polled_data);
// Drains |queue_| from WriteQueue into a local file queue and writes the
// events in the queue to disk.
void Flush(scoped_refptr<WriteQueue> write_queue);
// Deletes all netlog files. It is not valid to call any method of
// FileNetLogObserver after DeleteAllFiles().
void DeleteAllFiles();
void FlushThenStop(scoped_refptr<WriteQueue> write_queue,
std::unique_ptr<base::Value> polled_data);
// Returns true if there is no file size bound to enforce.
// When operating in unbounded mode, the implementation is optimized to stream
// writes to a single file, rather than chunking them across temporary event
// files.
bool IsUnbounded() const;
bool IsBounded() const;
// Increments |current_event_file_number_|, and updates all state relating to
// the current event file (open file handle, num bytes written, current file
// number).
void IncrementCurrentEventFile();
// Returns the path to the event file having |index|. This looks like
// "LOGDIR/event_file_<index>.json".
base::FilePath GetEventFilePath(size_t index) const;
// Gets the file path where constants are saved at the start of
// logging. This looks like "LOGDIR/constants.json".
base::FilePath GetConstantsFilePath() const;
// Gets the file path where the final data is written at the end of logging.
// This looks like "LOGDIR/end_netlog.json".
base::FilePath GetClosingFilePath() const;
// Returns the corresponding index for |file_number|. File "numbers" are a
// monotonically increasing identifier that start at 1 (a value of zero means
// it is uninitialized), whereas the file "index" is a bounded value that
// wraps and identifies the file path to use.
// Keeping track of the current number rather than index makes it a bit easier
// to assemble a file at the end, since it is unambiguous which paths have
// been used/re-used.
size_t FileNumberToIndex(size_t file_number) const;
// Writes |constants_value| to a file.
static void WriteConstantsToFile(std::unique_ptr<base::Value> constants_value,
base::File* file);
// Writes |polled_data| to a file.
static void WritePolledDataToFile(std::unique_ptr<base::Value> polled_data,
base::File* file);
// If any events were written (wrote_event_bytes_), rewinds |file| by 2 bytes
// in order to overwrite the trailing ",\n" that was written by the last event
// line.
void RewindIfWroteEventBytes(base::File* file) const;
// Concatenates all the log files to assemble the final
// |final_log_file_|. This single "stitched" file is what other
// log ingesting tools expect.
void StitchFinalLogFile();
// Creates the .inprogress directory used by bounded mode.
void CreateInprogressDirectory();
// The file the final netlog is written to. In bounded mode this is mostly
// written to once logging is stopped, whereas in unbounded mode events will
// be directly written to it.
base::File final_log_file_;
// If non-empty, this is the path to |final_log_file_| created and owned
// by FileWriter itself (rather than passed in to Create*PreExisting
// methods of FileNetLogObserver).
const base::FilePath final_log_path_;
// Path to a (temporary) directory where files are written in bounded mode.
// When logging is stopped these files are stitched together and written
// to the final log path.
const base::FilePath inprogress_dir_path_;
// Holds the numbered events file where data is currently being written to.
// The file path of this file is GetEventFilePath(current_event_file_number_).
// The file may be !IsValid() if an error previously occurred opening the
// file, or logging has been stopped.
base::File current_event_file_;
uint64_t current_event_file_size_;
// Indicates the total number of netlog event files allowed.
// (The files GetConstantsFilePath() and GetClosingFilePath() do
// not count against the total.)
const size_t total_num_event_files_;
// Counter for the events file currently being written into. See
// FileNumberToIndex() for an explanation of what "number" vs "index" mean.
size_t current_event_file_number_;
// Indicates the maximum size of each individual events file. May be kNoLimit
// to indicate that it can grow arbitrarily large.
const uint64_t max_event_file_size_;
// Whether any bytes were written for events. This is used to properly format
// JSON (events list shouldn't end with a comma).
bool wrote_event_bytes_;
// Task runner for doing file operations.
const scoped_refptr<base::SequencedTaskRunner> task_runner_;
std::unique_ptr<FileNetLogObserver> FileNetLogObserver::CreateBounded(
const base::FilePath& log_path,
uint64_t max_total_size,
std::unique_ptr<base::Value> constants) {
return CreateInternal(log_path, SiblingInprogressDirectory(log_path),
base::nullopt, max_total_size, kDefaultNumFiles,
std::unique_ptr<FileNetLogObserver> FileNetLogObserver::CreateUnbounded(
const base::FilePath& log_path,
std::unique_ptr<base::Value> constants) {
return CreateInternal(log_path, base::FilePath(), base::nullopt, kNoLimit,
kDefaultNumFiles, std::move(constants));
const base::FilePath& inprogress_dir_path,
base::File output_file,
uint64_t max_total_size,
std::unique_ptr<base::Value> constants) {
return CreateInternal(base::FilePath(), inprogress_dir_path,
max_total_size, kDefaultNumFiles, std::move(constants));
base::File output_file,
std::unique_ptr<base::Value> constants) {
return CreateInternal(base::FilePath(), base::FilePath(),
kNoLimit, kDefaultNumFiles, std::move(constants));
FileNetLogObserver::~FileNetLogObserver() {
if (net_log()) {
// StopObserving was not called.
file_task_runner_->DeleteSoon(FROM_HERE, file_writer_.release());
void FileNetLogObserver::StartObserving(NetLog* net_log,
NetLogCaptureMode capture_mode) {
net_log->AddObserver(this, capture_mode);
void FileNetLogObserver::StopObserving(std::unique_ptr<base::Value> polled_data,
base::OnceClosure optional_callback) {
base::OnceClosure bound_flush_then_stop =
base::Unretained(file_writer_.get()), write_queue_,
// Note that PostTaskAndReply() requires a non-null closure.
if (!optional_callback.is_null()) {
} else {
file_task_runner_->PostTask(FROM_HERE, std::move(bound_flush_then_stop));
void FileNetLogObserver::OnAddEntry(const NetLogEntry& entry) {
std::unique_ptr<std::string> json(new std::string);
*json = SerializeNetLogValueToJson(entry.ToValue());
size_t queue_size = write_queue_->AddEntryToQueue(std::move(json));
// If events build up in |write_queue_|, trigger the file task runner to drain
// the queue. Because only 1 item is added to the queue at a time, if
// queue_size > kNumWriteQueueEvents a task has already been posted, or will
// be posted.
if (queue_size == kNumWriteQueueEvents) {
base::Unretained(file_writer_.get()), write_queue_));
std::unique_ptr<FileNetLogObserver> FileNetLogObserver::CreateBoundedForTests(
const base::FilePath& log_path,
uint64_t max_total_size,
size_t total_num_event_files,
std::unique_ptr<base::Value> constants) {
return CreateInternal(log_path, SiblingInprogressDirectory(log_path),
base::nullopt, max_total_size, total_num_event_files,
std::unique_ptr<FileNetLogObserver> FileNetLogObserver::CreateInternal(
const base::FilePath& log_path,
const base::FilePath& inprogress_dir_path,
base::Optional<base::File> pre_existing_log_file,
uint64_t max_total_size,
size_t total_num_event_files,
std::unique_ptr<base::Value> constants) {
DCHECK_GT(total_num_event_files, 0u);
scoped_refptr<base::SequencedTaskRunner> file_task_runner =
const uint64_t max_event_file_size =
max_total_size == kNoLimit ? kNoLimit
: max_total_size / total_num_event_files;
// The FileWriter uses a soft limit to write events to file that allows
// the size of the file to exceed the limit, but the WriteQueue uses a hard
// limit which the size of |WriteQueue::queue_| cannot exceed. Thus, the
// FileWriter may write more events to file than can be contained by
// the WriteQueue if they have the same size limit. The maximum size of the
// WriteQueue is doubled to allow |WriteQueue::queue_| to hold enough events
// for the FileWriter to fill all files. As long as all events have
// sizes <= the size of an individual event file, the discrepancy between the
// hard limit and the soft limit will not cause an issue.
// TODO(dconnol): Handle the case when the WriteQueue still doesn't
// contain enough events to fill all files, because of very large events
// relative to file size.
std::unique_ptr<FileWriter> file_writer(new FileWriter(
log_path, inprogress_dir_path, std::move(pre_existing_log_file),
max_event_file_size, total_num_event_files, file_task_runner));
uint64_t write_queue_memory_max =
base::MakeClampedNum<uint64_t>(max_total_size) * 2;
return base::WrapUnique(new FileNetLogObserver(
file_task_runner, std::move(file_writer),
base::WrapRefCounted(new WriteQueue(write_queue_memory_max)),
scoped_refptr<base::SequencedTaskRunner> file_task_runner,
std::unique_ptr<FileWriter> file_writer,
scoped_refptr<WriteQueue> write_queue,
std::unique_ptr<base::Value> constants)
: file_task_runner_(std::move(file_task_runner)),
file_writer_(std::move(file_writer)) {
if (!constants)
constants = base::Value::ToUniquePtrValue(GetNetConstants());
FROM_HERE, base::BindOnce(&FileNetLogObserver::FileWriter::Initialize,
FileNetLogObserver::WriteQueue::WriteQueue(uint64_t memory_max)
: memory_(0), memory_max_(memory_max) {}
size_t FileNetLogObserver::WriteQueue::AddEntryToQueue(
std::unique_ptr<std::string> event) {
base::AutoLock lock(lock_);
memory_ += event->size();
while (memory_ > memory_max_ && !queue_.empty()) {
// Delete oldest events in the queue.
memory_ -= queue_.front()->size();
return queue_.size();
void FileNetLogObserver::WriteQueue::SwapQueue(EventQueue* local_queue) {
base::AutoLock lock(lock_);
memory_ = 0;
FileNetLogObserver::WriteQueue::~WriteQueue() = default;
const base::FilePath& log_path,
const base::FilePath& inprogress_dir_path,
base::Optional<base::File> pre_existing_log_file,
uint64_t max_event_file_size,
size_t total_num_event_files,
scoped_refptr<base::SequencedTaskRunner> task_runner)
: final_log_path_(log_path),
task_runner_(std::move(task_runner)) {
DCHECK_EQ(pre_existing_log_file.has_value(), log_path.empty());
DCHECK_EQ(IsBounded(), !inprogress_dir_path.empty());
if (pre_existing_log_file.has_value()) {
// pre_existing_log_file.IsValid() being false is fine.
final_log_file_ = std::move(pre_existing_log_file.value());
FileNetLogObserver::FileWriter::~FileWriter() = default;
void FileNetLogObserver::FileWriter::Initialize(
std::unique_ptr<base::Value> constants_value) {
// Open the final log file, and keep it open for the duration of logging (even
// in bounded mode).
if (!final_log_path_.empty())
final_log_file_ = OpenFileForWrite(final_log_path_);
if (IsBounded()) {
base::File constants_file = OpenFileForWrite(GetConstantsFilePath());
WriteConstantsToFile(std::move(constants_value), &constants_file);
} else {
WriteConstantsToFile(std::move(constants_value), &final_log_file_);
void FileNetLogObserver::FileWriter::Stop(
std::unique_ptr<base::Value> polled_data) {
// Write out the polled data.
if (IsBounded()) {
base::File closing_file = OpenFileForWrite(GetClosingFilePath());
WritePolledDataToFile(std::move(polled_data), &closing_file);
} else {
WritePolledDataToFile(std::move(polled_data), &final_log_file_);
// If operating in bounded mode, the events were written to separate files
// within |inprogress_dir_path_|. Assemble them into the final destination
// file.
if (IsBounded())
// Ensure the final log file has been flushed.
void FileNetLogObserver::FileWriter::Flush(
scoped_refptr<FileNetLogObserver::WriteQueue> write_queue) {
EventQueue local_file_queue;
while (!local_file_queue.empty()) {
base::File* output_file;
// If in bounded mode, output events to the current event file. Otherwise
// output events to the final log path.
if (IsBounded()) {
if (current_event_file_number_ == 0 ||
current_event_file_size_ >= max_event_file_size_) {
output_file = &current_event_file_;
} else {
output_file = &final_log_file_;
size_t bytes_written =
WriteToFile(output_file, *local_file_queue.front(), ",\n");
wrote_event_bytes_ |= bytes_written > 0;
// Keep track of the filesize for current event file when in bounded mode.
if (IsBounded())
current_event_file_size_ += bytes_written;
void FileNetLogObserver::FileWriter::DeleteAllFiles() {
if (IsBounded()) {
// Only delete |final_log_file_| if it was created internally.
// (If it was provided as a base::File by the caller, don't try to delete it).
if (!final_log_path_.empty())
void FileNetLogObserver::FileWriter::FlushThenStop(
scoped_refptr<FileNetLogObserver::WriteQueue> write_queue,
std::unique_ptr<base::Value> polled_data) {
bool FileNetLogObserver::FileWriter::IsUnbounded() const {
return max_event_file_size_ == kNoLimit;
bool FileNetLogObserver::FileWriter::IsBounded() const {
return !IsUnbounded();
void FileNetLogObserver::FileWriter::IncrementCurrentEventFile() {
current_event_file_ = OpenFileForWrite(
current_event_file_size_ = 0;
base::FilePath FileNetLogObserver::FileWriter::GetEventFilePath(
size_t index) const {
DCHECK_LT(index, total_num_event_files_);
return inprogress_dir_path_.AppendASCII(
"event_file_" + base::NumberToString(index) + ".json");
base::FilePath FileNetLogObserver::FileWriter::GetConstantsFilePath() const {
return inprogress_dir_path_.AppendASCII("constants.json");
base::FilePath FileNetLogObserver::FileWriter::GetClosingFilePath() const {
return inprogress_dir_path_.AppendASCII("end_netlog.json");
size_t FileNetLogObserver::FileWriter::FileNumberToIndex(
size_t file_number) const {
DCHECK_GT(file_number, 0u);
// Note that "file numbers" start at 1 not 0.
return (file_number - 1) % total_num_event_files_;
void FileNetLogObserver::FileWriter::WriteConstantsToFile(
std::unique_ptr<base::Value> constants_value,
base::File* file) {
// Print constants to file and open events array.
std::string json = SerializeNetLogValueToJson(*constants_value);
WriteToFile(file, "{\"constants\":", json, ",\n\"events\": [\n");
void FileNetLogObserver::FileWriter::WritePolledDataToFile(
std::unique_ptr<base::Value> polled_data,
base::File* file) {
// Close the events array.
WriteToFile(file, "]");
// Write the polled data (if any).
if (polled_data) {
std::string polled_data_json;
base::JSONWriter::Write(*polled_data, &polled_data_json);
if (!polled_data_json.empty())
WriteToFile(file, ",\n\"polledData\": ", polled_data_json, "\n");
// Close the log.
WriteToFile(file, "}\n");
void FileNetLogObserver::FileWriter::RewindIfWroteEventBytes(
base::File* file) const {
if (file->IsValid() && wrote_event_bytes_) {
// To be valid JSON the events array should not end with a comma. If events
// were written though, they will have been terminated with "\n," so strip
// it before closing the events array.
file->Seek(base::File::FROM_END, -2);
void FileNetLogObserver::FileWriter::StitchFinalLogFile() {
// Make sure all the events files are flushed (as will read them next).
// Allocate a 64K buffer used for reading the files. At most kReadBufferSize
// bytes will be in memory at a time.
const size_t kReadBufferSize = 1 << 16; // 64KiB
std::unique_ptr<char[]> read_buffer(new char[kReadBufferSize]);
if (final_log_file_.IsValid()) {
// Truncate the final log file.
// Append the constants file.
AppendToFileThenDelete(GetConstantsFilePath(), &final_log_file_,
read_buffer.get(), kReadBufferSize);
// Iterate over the events files, from oldest to most recent, and append
// them to the final destination. Note that "file numbers" start at 1 not 0.
size_t end_filenumber = current_event_file_number_ + 1;
size_t begin_filenumber =
current_event_file_number_ <= total_num_event_files_
? 1
: end_filenumber - total_num_event_files_;
for (size_t filenumber = begin_filenumber; filenumber < end_filenumber;
++filenumber) {
&final_log_file_, read_buffer.get(),
// Account for the final event line ending in a ",\n". Strip it to form
// valid JSON.
// Append the polled data.
AppendToFileThenDelete(GetClosingFilePath(), &final_log_file_,
read_buffer.get(), kReadBufferSize);
// Delete the inprogress directory (and anything that may still be left inside
// it).
void FileNetLogObserver::FileWriter::CreateInprogressDirectory() {
// If an output file couldn't be created, either creation of intermediate
// files will also fail (if they're in a sibling directory), or are they are
// hidden somewhere the user would be unlikely to find them, so there is
// little reason to progress.
if (!final_log_file_.IsValid())
if (!base::CreateDirectory(inprogress_dir_path_)) {
LOG(WARNING) << "Failed creating directory: "
<< inprogress_dir_path_.value();
// It is OK if the path is wrong due to encoding - this is really just a
// convenience display for the user in understanding what the file means.
std::string in_progress_path = inprogress_dir_path_.AsUTF8Unsafe();
// Since |final_log_file_| will not be written to until the very end, leave
// some data in it explaining that the real data is currently in the
// .inprogress directory. This ordinarily won't be visible (overwritten when
// stopping) however if logging does not end gracefully the comments are
// useful for recovery.
&final_log_file_, "Logging is in progress writing data to:\n ",
"That data will be stitched into a single file (this one) once logging\n"
"has stopped.\n"
"If logging was interrupted, you can stitch a NetLog file out of the\n"
".inprogress directory manually using:\n"
std::string SerializeNetLogValueToJson(const base::Value& value) {
// Omit trailing ".0" when printing a DOUBLE that is representable as a 64-bit
// integer. This makes the values returned by NetLogNumberValue() look more
// pleasant (for representing integers between 32 and 53 bits large).
std::string json;
bool ok = base::JSONWriter::WriteWithOptions(value, options, &json);
// Serialization shouldn't fail. However it can if a consumer has passed a
// parameter of type BINARY, since JSON serialization can't handle that.
return json;
} // namespace net