Protocol Buffers v3.0.0

Version 3.0.0

This change log summarizes all the changes since the last stable release
(v2.6.1). See the last section about changes since v3.0.0-beta-4.

Proto3

• Introduced Protocol Buffers language version 3 (aka proto3).

  When protocol buffers was initially open sourced it implemented Protocol
  Buffers language version 2 (aka proto2), which is why the version number
  started from v2.0.0. From v3.0.0, a new language version (proto3) is
  introduced while the old version (proto2) will continue to be supported.

  The main intent of introducing proto3 is to clean up protobuf before pushing
  the language as the foundation of Google's new API platform. In proto3, the
  language is simplified, both for ease of use and to make it available in a
  wider range of programming languages. At the same time a few features are
  added to better support common idioms found in APIs.

  The following are the main new features in language version 3:

  1. Removal of field presence logic for primitive value fields, removal of
     required fields, and removal of default values. This makes proto3
     significantly easier to implement with open struct representations, as
     in languages like Android Java, Objective C, or Go.
  2. Removal of unknown fields.
  3. Removal of extensions, which are instead replaced by a new standard
     type called Any.
  4. Fix semantics for unknown enum values.
  5. Addition of maps (back-ported to proto2)
  6. Addition of a small set of standard types for representation of time,
     dynamic data, etc (back-ported to proto2)
  7. A well-defined encoding in JSON as an alternative to binary proto
     encoding.

  A new notion "syntax" is introduced to specify whether a .proto file
  uses proto2 or proto3:

  // foo.proto
  syntax = "proto3";
  message Bar {...}
  

  If omitted, the protocol buffer compiler generates a warning and "proto2" is
  used as the default. This warning will be turned into an error in a future
  release.

  We recommend that new Protocol Buffers users use proto3. However, we do not
  generally recommend that existing users migrate from proto2 from proto3 due
  to API incompatibility, and we will continue to support proto2 for a long
  time.

  Other significant changes in proto3.

• Explicit "optional" keyword are disallowed in proto3 syntax, as fields are
  optional by default; required fields are no longer supported.

• Removed non-zero default values and field presence logic for non-message
  fields. e.g. has_xxx() methods are removed; primitive fields set to default
  values (0 for numeric fields, empty for string/bytes fields) will be skipped
  during serialization.

• Group fields are no longer supported in proto3 syntax.

• Changed repeated primitive fields to use packed serialization by default in
  proto3 (implemented for C++, Java, Python in this release). The user can
  still disable packed serialization by setting packed to false for now.

• Added well-known type protos (any.proto, empty.proto, timestamp.proto,
  duration.proto, etc.). Users can import and use these protos just like
  regular proto files. Additional runtime support are available for each
  language.

• Proto3 JSON is supported in several languages (fully supported in C++, Java,
  Python and C# partially supported in Ruby). The JSON spec is defined in the
  proto3 language guide:

  https://developers.google.com/protocol-buffers/docs/proto3#json

  We will publish a more detailed spec to define the exact behavior of
  proto3-conformant JSON serializers and parsers. Until then, do not rely
  on specific behaviors of the implementation if it’s not documented in
  the above spec.

• Proto3 enforces strict UTF-8 checking. Parsing will fail if a string
  field contains non UTF-8 data.

General

• Introduced new language implementations (C#, JavaScript, Ruby, Objective-C)
  to proto3.

• Added support for map fields (implemented in both proto2 and proto3).
  Map fields can be declared using the following syntax:

  message Foo {
    map<string, string> values = 1;
  }
  

  The data of a map field is stored in memory as an unordered map and
  can be accessed through generated accessors.

• Added a "reserved" keyword in both proto2 and proto3 syntax. Users can use
  this keyword to declare reserved field numbers and names to prevent them
  from being reused by other fields in the same message.

  To reserve field numbers, add a reserved declaration in your message:

  message TestMessage {
    reserved 2, 15, 9 to 11, 3;
  }
  

  This reserves field numbers 2, 3, 9, 10, 11 and 15. If a user uses any of
  these as field numbers, the protocol buffer compiler will report an error.

  Field names can also be reserved:

  message TestMessage {
    reserved "foo", "bar";
  }
  

• Added a deterministic serialization API (currently available in C++). The
  deterministic serialization guarantees that given a binary, equal messages
  will be serialized to the same bytes. This allows applications like
  MapReduce to group equal messages based on the serialized bytes. The
  deterministic serialization is, however, NOT canonical across languages; it
  is also unstable across different builds with schema changes due to unknown
  fields. Users who need canonical serialization, e.g. persistent storage in
  a canonical form, fingerprinting, etc, should define their own
  canonicalization specification and implement the serializer using reflection
  APIs rather than relying on this API.

• Added a new field option "json_name". By default proto field names are
  converted to "lowerCamelCase" in proto3 JSON format. This option can be
  used to override this behavior and specify a different JSON name for the
  field.

• Added conformance tests to ensure implementations are following proto3 JSON
  specification.

C++

• Added arena allocation support (for both proto2 and proto3).

  Profiling shows memory allocation and deallocation constitutes a significant
  fraction of CPU-time spent in protobuf code and arena allocation is a
  technique introduced to reduce this cost. With arena allocation, new
  objects are allocated from a large piece of preallocated memory and
  deallocation of these objects is almost free. Early adoption shows 20% to
  50% improvement in some Google binaries.

  To enable arena support, add the following option to your .proto file:

  option cc_enable_arenas = true;
  

  The protocol buffer compiler will generate additional code to make the generated
  message classes work with arenas. This does not change the existing API
  of protobuf messages and does not affect wire format. Your existing code
  should continue to work after adding this option. In the future we will
  make this option enabled by default.

  To actually take advantage of arena allocation, you need to use the arena
  APIs when creating messages. A quick example of using the arena API:

  {
    google::protobuf::Arena arena;
    // Allocate a protobuf message in the arena.
    MyMessage* message = Arena::CreateMessage<MyMessage>(&arena);
    // All submessages will be allocated in the same arena.
    if (!message->ParseFromString(data)) {
      // Deal with malformed input data.
    }
    // Must not delete the message here. It will be deleted automatically
    // when the arena is destroyed.
  }
  

  Currently arena allocation does not work with map fields. Enabling arenas in a .proto
  file containing map fields will result in compile errors in the generated
  code. This will be addressed in a future release.

• Added runtime support for the Any type. To use Any in your proto file, first
  import the definition of Any:

  // foo.proto
  import "google/protobuf/any.proto";
  message Foo {
    google.protobuf.Any any_field = 1;
  }
  message Bar {
    int32 value = 1;
  }
  

  Then in C++ you can access the Any field using PackFrom()/UnpackTo()
  methods:

  Foo foo;
  Bar bar = ...;
  foo.mutable_any_field()->PackFrom(bar);
  ...
  if (foo.any_field().IsType<Bar>()) {
    foo.any_field().UnpackTo(&bar);
    ...
  }
  

• In text format, the entries of a map field will be sorted by key.

• Introduced new utility functions/classes in the google/protobuf/util
  directory:

  • MessageDifferencer: compare two proto messages and report their
    differences.
  • JsonUtil: support converting protobuf binary format to/from JSON.
  • TimeUtil: utility functions to work with well-known types Timestamp
    and Duration.
  • FieldMaskUtil: utility functions to work with FieldMask.

• Introduced a deterministic serialization API in
  CodedOutputStream::SetSerializationDeterministic(bool). See the notes about
  deterministic serialization in the General section.

Java

• Introduced a new util package that will be distributed as a separate
  artifact in maven. It contains:
  • JsonFormat: convert proto messages to/from JSON.
  • Timestamps/Durations: utility functions to work with Timestamp and Duration.
  • FieldMaskUtil: utility functions to work with FieldMask.
• Introduced an ExperimentalApi annotation. Annotated APIs are experimental
  and are subject to change in a backward incompatible way in future releases.
• Introduced zero-copy serialization as an ExperimentalApi
  • Introduction of the ByteOutput interface. This is similar to
    OutputStream but provides semantics for lazy writing (i.e. no
    immediate copy required) of fields that are considered to be immutable.
  • ByteString now supports writing to a ByteOutput, which will directly
    expose the internals of the ByteString (i.e. byte[] or ByteBuffer)
    to the ByteOutput without copying.
  • CodedOutputStream now supports writing to a ByteOutput. ByteString
    instances that are too large to fit in the internal buffer will be
    (lazily) written to the ByteOutput directly.
    ...

Protocol Buffers v3.0.0-beta-4

Version 3.0.0-beta-4

General

• Added a deterministic serialization API for C++. The deterministic
  serialization guarantees that given a binary, equal messages will be
  serialized to the same bytes. This allows applications like MapReduce to
  group equal messages based on the serialized bytes. The deterministic
  serialization is, however, NOT canonical across languages; it is also
  unstable across different builds with schema changes due to unknown fields.
  Users who need canonical serialization, e.g. persistent storage in a
  canonical form, fingerprinting, etc, should define their own
  canonicalization specification and implement the serializer using reflection
  APIs rather than relying on this API.

• Added OneofOptions. You can now define custom options for oneof groups.

  import "google/protobuf/descriptor.proto";
  extend google.protobuf.OneofOptions {
    optional int32 my_oneof_extension = 12345;
  }
  message Foo {
    oneof oneof_group {
      (my_oneof_extension) = 54321;
      ...
    }
  }
  

C++ (beta)

• Introduced a deterministic serialization API in
  CodedOutputStream::SetSerializationDeterministic(bool). See the notes about
  deterministic serialization in the General section.
• Added google::protobuf::Map::swap() to swap two map fields.
• Fixed a memory leak when calling Reflection::ReleaseMessage() on a message
  allocated on arena.
• Improved error reporting when parsing text format protos.
• JSON
  • Added a new parser option to ignore unknown fields when parsing JSON.
  • Added convenient methods for message to/from JSON conversion.
• Various performance optimizations.

Java (beta)

• File option "java_generate_equals_and_hash" is now deprecated. equals() and
  hashCode() methods are generated by default.
• Added a new JSON printer option "omittingInsignificantWhitespace" to produce
  a more compact JSON output. The printer will pretty-print by default.
• Updated Java runtime to be compatible with 2.5.0/2.6.1 generated protos.

Python (beta)

• Added support to pretty print Any messages in text format.
• Added a flag to ignore unknown fields when parsing JSON.
• Bugfix: "@type" field of a JSON Any message is now correctly put before
  other fields.

Objective-C (beta)

• Updated the code to support compiling with more compiler warnings
  enabled. (Issue 1616)
• Exposing more detailed errors for parsing failures. (PR 1623)
• Small (breaking) change to the naming of some methods on the support classes
  for map<>. There were collisions with the system provided KVO support, so
  the names were changed to avoid those issues. (PR 1699)
• Fixed for proper Swift bridging of error handling during parsing. (PR 1712)
• Complete support for generating sources that will go into a Framework and
  depend on generated sources from other Frameworks. (Issue 1457)

C# (beta)

• RepeatedField optimizations.
• Support for .NET Core.
• Minor bug fixes.
• Ability to format a single value in JsonFormatter (advanced usage only).
• Modifications to attributes applied to generated code.

Javascript (alpha)

• Maps now have a real map API instead of being treated as repeated fields.
• Well-known types are now provided in the google-protobuf package, and the
  code generator knows to require() them from that package.
• Bugfix: non-canonical varints are correctly decoded.

Ruby (alpha)

• Accessors for oneof fields now return default values instead of nil.

Java Lite

• Java lite support is removed from protocol compiler. It will be supported
  as a protocol compiler plugin in a separate code branch.

Protocol Buffers v3.0.0-beta-3.1

Fix iOS framework.

Protocol Buffers v3.0.0-beta-3

Version 3.0.0-beta-3

General

• Supported Proto3 lite-runtime in C++/Java for mobile platforms.
• Any type now supports APIs to specify prefixes other than
  type.googleapis.com
• Removed javanano_use_deprecated_package option; Nano will always has its own
  ".nano" package.

C++ (Beta)

• Improved hash maps.
  • Improved hash maps comments. In particular, please note that equal hash
    maps will not necessarily have the same iteration order and
    serialization.
  • Added a new hash maps implementation that will become the default in a
    later release.
• Arenas
  • Several inlined methods in Arena were moved to out-of-line to improve
    build performance and code size.
  • Added SpaceAllocatedAndUsed() to report both space used and allocated
  • Added convenient class UnsafeArenaAllocatedRepeatedPtrFieldBackInserter
• Any
  • Allow custom type URL prefixes in Any packing.
  • TextFormat now expand the Any type rather than printing bytes.
• Performance optimizations and various bug fixes.

Java (Beta)

• Introduced an ExperimentalApi annotation. Annotated APIs are experimental
  and are subject to change in a backward incompatible way in future releases.
• Introduced zero-copy serialization as an ExperimentalApi
  • Introduction of the ByteOutput interface. This is similar to
    OutputStream but provides semantics for lazy writing (i.e. no
    immediate copy required) of fields that are considered to be immutable.
  • ByteString now supports writing to a ByteOutput, which will directly
    expose the internals of the ByteString (i.e. byte[] or ByteBuffer)
    to the ByteOutput without copying.
  • CodedOutputStream now supports writing to a ByteOutput. ByteString
    instances that are too large to fit in the internal buffer will be
    (lazily) written to the ByteOutput directly.
  • This allows applications using large ByteString fields to avoid
    duplication of these fields entirely. Such an application can supply a
    ByteOutput that chains together the chunks received from
    CodedOutputStream before forwarding them onto the IO system.
• Other related changes to CodedOutputStream
  • Additional use of sun.misc.Unsafe where possible to perform fast
    access to byte[] and ByteBuffer values and avoiding unnecessary
    range checking.
  • ByteBuffer-backed CodedOutputStream now writes directly to the
    ByteBuffer rather than to an intermediate array.
• Improved lite-runtime.
  • Lite protos now implement deep equals/hashCode/toString
  • Significantly improved the performance of Builder#mergeFrom() and
    Builder#mergeDelimitedFrom()
• Various bug fixes and small feature enhancement.
  • Fixed stack overflow when in hashCode() for infinite recursive oneofs.
  • Fixed the lazy field parsing in lite to merge rather than overwrite.
  • TextFormat now supports reporting line/column numbers on errors.
  • Updated to add appropriate @OverRide for better compiler errors.

Python (Beta)

• Added JSON format for Any, Struct, Value and ListValue
• "[ ]" is now accepted for both repeated scalar fields and repeated message
  fields in text format parser.
• Numerical field name is now supported in text format.
• Added DiscardUnknownFields API for python protobuf message.

Objective-C (Beta)

• Proto comments now come over as HeaderDoc comments in the generated sources
  so Xcode can pick them up and display them.
• The library headers have been updated to use HeaderDoc comments so Xcode can
  pick them up and display them.
• The per message and per field overhead in both generated code and runtime
  object sizes was reduced.
• Generated code now include deprecated annotations when the proto file
  included them.

C# (Beta)

In general: some changes are breaking, which require regenerating messages.
Most user-written code will not be impacted except for the renaming of enum
values.

• Allow custom type URL prefixes in Any packing, and ignore them when
  unpacking
• protoc is now in a separate NuGet package (Google.Protobuf.Tools)
• New option: internal_access to generate internal classes
• Enum values are now PascalCased, and if there's a prefix which matches the
  name of the enum, that is removed (so an enum COLOR with a value
  COLOR_BLUE would generate a value of just Blue). An option
  (legacy_enum_values) is temporarily available to disable this, but the
  option will be removed for GA.
• json_name option is now honored
• If group tags are encountered when parsing, they are validated more
  thoroughly (although we don't support actual groups)
• NuGet dependencies are better specified
• Breaking: Preconditions is renamed to ProtoPreconditions
• Breaking: GeneratedCodeInfo is renamed to GeneratedClrTypeInfo
• JsonFormatter now allows writing to a TextWriter
• New interface, ICustomDiagnosticMessage to allow more compact
  representations from ToString
• CodedInputStream and CodedOutputStream now implement IDisposable,
  which simply disposes of the streams they were constructed with
• Map fields no longer support null values (in line with other languages)
• Improvements in JSON formatting and parsing

Javascript (Alpha)

• Better support for "bytes" fields: bytes fields can be read as either a
  base64 string or UInt8Array (in environments where TypedArray is supported).
• New support for CommonJS imports. This should make it easier to use the
  JavaScript support in Node.js and tools like WebPack. See js/README.md for
  more information.
• Some significant internal refactoring to simplify and modularize the code.

Ruby (Alpha)

• JSON serialization now properly uses camelCased names, with a runtime option
  that will preserve original names from .proto files instead.
• Well-known types are now included in the distribution.
• Release now includes binary gems for Windows, Mac, and Linux instead of just
  source gems.
• Bugfix for serializing oneofs.

C++/Java Lite (Alpha)

A new "lite" generator parameter was introduced in the protoc for C++ and
Java for Proto3 syntax messages. Example usage:

 ./protoc --cpp_out=lite:$OUTPUT_PATH foo.proto

The protoc will treat the current input and all the transitive dependencies
as LITE. The same generator parameter must be used to generate the
dependencies.

In Proto3 syntax files, "optimized_for=LITE_RUNTIME" is no longer supported.

Protocol Buffers v3.0.0-beta-2

Version 3.0.0-beta-2

General

• Introduced a new language implementation: JavaScript.
• Added a new field option "json_name". By default proto field names are
  converted to "lowerCamelCase" in proto3 JSON format. This option can be
  used to override this behavior and specify a different JSON name for the
  field.
• Added conformance tests to ensure implementations are following proto3 JSON
  specification.

C++ (Beta)

• Various bug fixes and improvements to the JSON support utility:
  • Duplicate map keys in JSON are now rejected (i.e., translation will
    fail).
  • Fixed wire-format for google.protobuf.Value/ListValue.
  • Fixed precision loss when converting google.protobuf.Timestamp.
  • Fixed a bug when parsing invalid UTF-8 code points.
  • Fixed a memory leak.
  • Reduced call stack usage.

Java (Beta)

• Cleaned up some unused methods on CodedOutputStream.
• Presized lists for packed fields during parsing in the lite runtime to
  reduce allocations and improve performance.
• Improved the performance of unknown fields in the lite runtime.
• Introduced UnsafeByteStrings to support zero-copy ByteString creation.
• Various bug fixes and improvements to the JSON support utility:
  • Fixed a thread-safety bug.
  • Added a new option “preservingProtoFieldNames” to JsonFormat.
  • Added a new option “includingDefaultValueFields” to JsonFormat.
  • Updated the JSON utility to comply with proto3 JSON specification.

Python (Beta)

• Added proto3 JSON format utility. It includes support for all field types
  and a few well-known types except for Any and Struct.
• Added runtime support for Any, Timestamp, Duration and FieldMask.
• "[ ]" is now accepted for repeated scalar fields in text format parser.

Objective-C (Beta)

• Various bug-fixes and code tweaks to pass more strict compiler warnings.
• Now has conformance test coverage and is passing all tests.

C# (Beta)

• Various bug-fixes.
• Code generation: Files generated in directories based on namespace.
• Code generation: Include comments from .proto files in XML doc
  comments (naively)
• Code generation: Change organization/naming of "reflection class" (access
  to file descriptor)
• Code generation and library: Add Parser property to MessageDescriptor,
  and introduce a non-generic parser type.
• Library: Added TypeRegistry to support JSON parsing/formatting of Any.
• Library: Added Any.Pack/Unpack support.
• Library: Implemented JSON parsing.

Javascript (Alpha)

• Added proto3 support for JavaScript. The runtime is written in pure
  JavaScript and works in browsers and in Node.js. To generate JavaScript
  code for your proto, invoke protoc with "--js_out". See js/README.md
  for more build instructions.

Protocol Buffers v3.0.0-beta-1

Version 3.0.0-beta-1

Supported languages

• C++/Java/Python/Ruby/Nano/Objective-C/C#

About Beta

• This is the first beta release of protobuf v3.0.0. Not all languages
  have reached beta stage. Languages not marked as beta are still in
  alpha (i.e., be prepared for API breaking changes).

General

• Proto3 JSON is supported in several languages (fully supported in C++
  and Java, partially supported in Ruby/C#). The JSON spec is defined in
  the proto3 language guide:

  https://developers.google.com/protocol-buffers/docs/proto3#json

  We will publish a more detailed spec to define the exact behavior of
  proto3-conformant JSON serializers and parsers. Until then, do not rely
  on specific behaviors of the implementation if it’s not documented in
  the above spec. More specifically, the behavior is not yet finalized for
  the following:

  • Parsing invalid JSON input (e.g., input with trailing commas).
  • Non-camelCase names in JSON input.
  • The same field appears multiple times in JSON input.
  • JSON arrays contain “null” values.
  • The message has unknown fields.

• Proto3 now enforces strict UTF-8 checking. Parsing will fail if a string
  field contains non UTF-8 data.

C++ (Beta)

• Introduced new utility functions/classes in the google/protobuf/util
  directory:
  • MessageDifferencer: compare two proto messages and report their
    differences.
  • JsonUtil: support converting protobuf binary format to/from JSON.
  • TimeUtil: utility functions to work with well-known types Timestamp
    and Duration.
  • FieldMaskUtil: utility functions to work with FieldMask.
• Performance optimization of arena construction and destruction.
• Bug fixes for arena and maps support.
• Changed to use cmake for Windows Visual Studio builds.
• Added Bazel support.

Java (Beta)

• Introduced a new util package that will be distributed as a separate
  artifact in maven. It contains:
  • JsonFormat: convert proto messages to/from JSON.
  • TimeUtil: utility functions to work with Timestamp and Duration.
  • FieldMaskUtil: utility functions to work with FieldMask.
• The static PARSER in each generated message is deprecated, and it will
  be removed in a future release. A static parser() getter is generated
  for each message type instead.
• Performance optimizations for String fields serialization.
• Performance optimizations for Lite runtime on Android:
  • Reduced allocations
  • Reduced method overhead after ProGuarding
  • Reduced code size after ProGuarding

Python (Alpha)

• Removed legacy Python 2.5 support.
• Moved to a single Python 2.x/3.x-compatible codebase, instead of using 2to3.
• Fixed build/tests on Python 2.6, 2.7, 3.3, and 3.4.
  • Pure-Python works on all four.
  • Python/C++ implementation works on all but 3.4, due to changes in the
    Python/C++ API in 3.4.
• Some preliminary work has been done to allow for multiple DescriptorPools
  with Python/C++.

Ruby (Alpha)

• Many bugfixes:
  • fixed parsing/serialization of bytes, sint, sfixed types
  • other parser bugfixes
  • fixed memory leak affecting Ruby 2.2

JavaNano (Alpha)

• JavaNano generated code now will be put in a nano package by default to
  avoid conflicts with Java generated code.

Objective-C (Alpha)

• Added non-null markup to ObjC library. Requires SDK 8.4+ to build.
• Many bugfixes:
  • Removed the class/enum filter.
  • Renamed some internal types to avoid conflicts with the well-known types
    protos.
  • Added missing support for parsing repeated primitive fields in packed or
    unpacked forms.
  • Added *Count for repeated and map<> fields to avoid auto-create when
    checking for them being set.

C# (Alpha)

• Namespace changed to Google.Protobuf (and NuGet package will be named
  correspondingly).
• Target platforms now .NET 4.5 and selected portable subsets only.
• Removed lite runtime.
• Reimplementation to use mutable message types.
• Null references used to represent "no value" for message type fields.
• Proto3 semantics supported; proto2 files are prohibited for C# codegen.
  Most proto3 features supported:
  • JSON formatting (a.k.a. serialization to JSON), including well-known
    types (except for Any).
  • Wrapper types mapped to nullable value types (or string/ByteString
    allowing nullability). JSON parsing is not supported yet.
  • maps
  • oneof
  • enum unknown value preservation

Protocol Buffers v3.0.0-alpha-3

Version 3.0.0-alpha-3 (C++/Java/Python/Ruby/JavaNano/Objective-C/C#)

General

• Introduced two new language implementations (Objective-C, C#) to proto3.

• Explicit "optional" keyword are disallowed in proto3 syntax, as fields are
  optional by default.

• Group fields are no longer supported in proto3 syntax.

• Changed repeated primitive fields to use packed serialization by default in
  proto3 (implemented for C++, Java, Python in this release). The user can
  still disable packed serialization by setting packed to false for now.

• Added well-known type protos (any.proto, empty.proto, timestamp.proto,
  duration.proto, etc.). Users can import and use these protos just like
  regular proto files. Addtional runtime support will be added for them in
  future releases (in the form of utility helper functions, or having them
  replaced by language specific types in generated code).

• Added a "reserved" keyword in both proto2 and proto3 syntax. User can use
  this keyword to declare reserved field numbers and names to prevent them
  from being reused by other fields in the same message.

  To reserve field numbers, add a reserved declaration in your message:

  message TestMessage {
    reserved 2, 15, 9 to 11, 3;
  }
  

  This reserves field numbers 2, 3, 9, 10, 11 and 15. If a user uses any of
  these as field numbers, the protocol buffer compiler will report an error.

  Field names can also be reserved:

  message TestMessage {
    reserved "foo", "bar";
  }
  

• Various bug fixes since 3.0.0-alpha-2

Objective-C

• Objective-C includes a code generator and a native objective-c runtime
  library. By adding “--objc_out” to protoc, the code generator will generate
  a header(.pbobjc.h) and an implementation file(.pbobjc.m) for each proto
  file.

  In this first release, the generated interface provides: enums, messages,
  field support(single, repeated, map, oneof), proto2 and proto3 syntax
  support, parsing and serialization. It’s compatible with ARC and non-ARC
  usage. Besides, user can also access it via the swift bridging header.

  See objectivec/README.md for details.

C#

• C# protobufs are based on project
  https://github.com/jskeet/protobuf-csharp-port. The original project was
  frozen and all the new development will happen here.

• Codegen plugin for C# was completely rewritten to C++ and is now an
  intergral part of protoc.

• Some refactorings and cleanup has been applied to the C# runtime library.

• Only proto2 is supported in C# at the moment, proto3 support is in
  progress and will likely bring significant breaking changes to the API.

  See csharp/README.md for details.

C++

• Added runtime support for Any type. To use Any in your proto file, first
  import the definition of Any:

  // foo.proto
  import "google/protobuf/any.proto";
  message Foo {
    google.protobuf.Any any_field = 1;
  }
  message Bar {
    int32 value = 1;
  }
  

  Then in C++ you can access the Any field using PackFrom()/UnpackTo()
  methods:

  Foo foo;
  Bar bar = ...;
  foo.mutable_any_field()->PackFrom(bar);
  ...
  if (foo.any_field().IsType<Bar>()) {
    foo.any_field().UnpackTo(&bar);
    ...
  }
  

• In text format, entries of a map field will be sorted by key.

Java

• Continued optimizations on the lite runtime to improve performance for
  Android.

Python

• Added map support.
  • maps now have a dict-like interface (msg.map_field[key] = value)
  • existing code that modifies maps via the repeated field interface
    will need to be updated.

Ruby

• Improvements to RepeatedField's emulation of the Ruby Array API.
• Various speedups and internal cleanups.

Protocol Buffers v3.0.0-alpha-2

Version 3.0.0-alpha-2 (C++/Java/Python/Ruby/JavaNano)

General

• Introduced Protocol Buffers language version 3 (aka proto3).

  When protobuf was initially opensourced it implemented Protocol Buffers
  language version 2 (aka proto2), which is why the version number
  started from v2.0.0. From v3.0.0, a new language version (proto3) is
  introduced while the old version (proto2) will continue to be supported.

  The main intent of introducing proto3 is to clean up protobuf before
  pushing the language as the foundation of Google's new API platform.
  In proto3, the language is simplified, both for ease of use and to
  make it available in a wider range of programming languages. At the
  same time a few features are added to better support common idioms
  found in APIs.

  The following are the main new features in language version 3:

  1. Removal of field presence logic for primitive value fields, removal
     of required fields, and removal of default values. This makes proto3
     significantly easier to implement with open struct representations,
     as in languages like Android Java, Objective C, or Go.
  2. Removal of unknown fields.
  3. Removal of extensions, which are instead replaced by a new standard
     type called Any.
  4. Fix semantics for unknown enum values.
  5. Addition of maps.
  6. Addition of a small set of standard types for representation of time,
     dynamic data, etc.
  7. A well-defined encoding in JSON as an alternative to binary proto
     encoding.

  This release (v3.0.0-alpha-2) includes partial proto3 support for C++,
  Java, Python, Ruby and JavaNano. Items 6 (well-known types) and 7
  (JSON format) in the above feature list are not implemented.

  A new notion "syntax" is introduced to specify whether a .proto file
  uses proto2 or proto3:

  // foo.proto
  syntax = "proto3";
  message Bar {...}
  

  If omitted, the protocol compiler will generate a warning and "proto2" will
  be used as the default. This warning will be turned into an error in a
  future release.

  We recommend that new Protocol Buffers users use proto3. However, we do not
  generally recommend that existing users migrate from proto2 from proto3 due
  to API incompatibility, and we will continue to support proto2 for a long
  time.

• Added support for map fields (implemented in proto2 and proto3 C++/Java/JavaNano and proto3 Ruby).

  Map fields can be declared using the following syntax:

  message Foo {
    map<string, string> values = 1;
  }
  

  Data of a map field will be stored in memory as an unordered map and it
  can be accessed through generated accessors.

C++

• Added arena allocation support (for both proto2 and proto3).

  Profiling shows memory allocation and deallocation constitutes a significant
  fraction of CPU-time spent in protobuf code and arena allocation is a
  technique introduced to reduce this cost. With arena allocation, new
  objects will be allocated from a large piece of preallocated memory and
  deallocation of these objects is almost free. Early adoption shows 20% to
  50% improvement in some Google binaries.

  To enable arena support, add the following option to your .proto file:

  option cc_enable_arenas = true;
  

  Protocol compiler will generate additional code to make the generated
  message classes work with arenas. This does not change the existing API
  of protobuf messages and does not affect wire format. Your existing code
  should continue to work after adding this option. In the future we will
  make this option enabled by default.

  To actually take advantage of arena allocation, you need to use the arena
  APIs when creating messages. A quick example of using the arena API:

  {
    google::protobuf::Arena arena;
    // Allocate a protobuf message in the arena.
    MyMessage* message = Arena::CreateMessage<MyMessage>(&arena);
    // All submessages will be allocated in the same arena.
    if (!message->ParseFromString(data)) {
      // Deal with malformed input data.
    }
    // Must not delete the message here. It will be deleted automatically
    // when the arena is destroyed.
  }
  

  Currently arena does not work with map fields. Enabling arena in a .proto
  file containing map fields will result in compile errors in the generated
  code. This will be addressed in a future release.

Python

• Python has received several updates, most notably support for proto3
  semantics in any .proto file that declares syntax="proto3".
  Messages declared in proto3 files no longer represent field presence
  for scalar fields (number, enums, booleans, or strings). You can
  no longer call HasField() for such fields, and they are serialized
  based on whether they have a non-zero/empty/false value.
• One other notable change is in the C++-accelerated implementation.
  Descriptor objects (which describe the protobuf schema and allow
  reflection over it) are no longer duplicated between the Python
  and C++ layers. The Python descriptors are now simple wrappers
  around the C++ descriptors. This change should significantly
  reduce the memory usage of programs that use a lot of message
  types.

Ruby

• We have added proto3 support for Ruby via a native C extension.

  The Ruby extension itself is included in the ruby/ directory, and details on
  building and installing the extension are in ruby/README.md. The extension
  will also be published as a Ruby gem. Code generator support is included as
  part of protoc with the --ruby_out flag.

  The Ruby extension implements a user-friendly DSL to define message types
  (also generated by the code generator from .proto files). Once a message
  type is defined, the user may create instances of the message that behave in
  ways idiomatic to Ruby. For example:

  • Message fields are present as ordinary Ruby properties (getter method
    foo and setter method foo=).
  • Repeated field elements are stored in a container that acts like a native
    Ruby array, and map elements are stored in a container that acts like a
    native Ruby hashmap.
  • The usual well-known methods, such as #to_s, #dup, and the like, are
    present.

  Unlike several existing third-party Ruby extensions for protobuf, this
  extension is built on a "strongly-typed" philosophy: message fields and
  array/map containers will throw exceptions eagerly when values of the
  incorrect type are inserted.

  See ruby/README.md for details.

JavaNano

• JavaNano is a special code generator and runtime library designed especially
  for resource-restricted systems, like Android. It is very resource-friendly
  in both the amount of code and the runtime overhead. Here is an an overview
  of JavaNano features compared with the official Java protobuf:

  • No descriptors or message builders.
  • All messages are mutable; fields are public Java fields.
  • For optional fields only, encapsulation behind setter/getter/hazzer/
    clearer functions is opt-in, which provide proper 'has' state support.
  • For proto2, if not opted in, has state (field presence) is not available.
    Serialization outputs all fields not equal to their defaults.
    The behavior is consistent with proto3 semantics.
  • Required fields (proto2 only) are always serialized.
  • Enum constants are integers; protection against invalid values only
    when parsing from the wire.
  • Enum constants can be generated into container interfaces bearing
    the enum's name (so the referencing code is in Java style).
  • CodedInputByteBufferNano can only take byte[](not InputStream).
  • Similarly CodedOutputByteBufferNano can only write to byte[].
  • Repeated fields are in arrays, not ArrayList or Vector. Null array
    elements are allowed and silently ignored.
  • Full support for serializing/deserializing repeated packed fields.
  • Support extensions (in proto2).
  • Unset messages/groups are null, not an immutable empty default
    instance.
  • toByteArray(...) and mergeFrom(...) are now static functions of
    MessageNano.
  • The 'bytes' type translates to the Java type byte[].

  See javanano/README.txt for details.

Protocol Buffers v3.0.0-alpha-1

Version 3.0.0-alpha-1 (C++/Java)

General

• Introduced Protocol Buffers language version 3 (aka proto3).

  When protobuf was initially opensourced it implemented Protocol Buffers
  language version 2 (aka proto2), which is why the version number
  started from v2.0.0. From v3.0.0, a new language version (proto3) is
  introduced while the old version (proto2) will continue to be supported.

  The main intent of introducing proto3 is to clean up protobuf before
  pushing the language as the foundation of Google's new API platform.
  In proto3, the language is simplified, both for ease of use and to
  make it available in a wider range of programming languages. At the
  same time a few features are added to better support common idioms
  found in APIs.

  The following are the main new features in language version 3:

  1. Removal of field presence logic for primitive value fields, removal
     of required fields, and removal of default values. This makes proto3
     significantly easier to implement with open struct representations,
     as in languages like Android Java, Objective C, or Go.
  2. Removal of unknown fields.
  3. Removal of extensions, which are instead replaced by a new standard
     type called Any.
  4. Fix semantics for unknown enum values.
  5. Addition of maps.
  6. Addition of a small set of standard types for representation of time,
     dynamic data, etc.
  7. A well-defined encoding in JSON as an alternative to binary proto
     encoding.

  This release (v3.0.0-alpha-1) includes partial proto3 support for C++ and
  Java. Items 6 (well-known types) and 7 (JSON format) in the above feature
  list are not impelmented.

  A new notion "syntax" is introduced to specify whether a .proto file
  uses proto2 or proto3:

  // foo.proto
  syntax = "proto3";
  message Bar {...}
  

  If omitted, the protocol compiler will generate a warning and "proto2" will
  be used as the default. This warning will be turned into an error in a
  future release.

  We recommend that new Protocol Buffers users use proto3. However, we do not
  generally recommend that existing users migrate from proto2 from proto3 due
  to API incompatibility, and we will continue to support proto2 for a long
  time.

• Added support for map fields (implemented in C++/Java for both proto2 and
  proto3).

  Map fields can be declared using the following syntax:

  message Foo {
    map<string, string> values = 1;
  }
  

  Data of a map field will be stored in memory as an unordered map and it
  can be accessed through generated accessors.

C++

• Added arena allocation support (for both proto2 and proto3).

  Profiling shows memory allocation and deallocation constitutes a significant
  fraction of CPU-time spent in protobuf code and arena allocation is a
  technique introduced to reduce this cost. With arena allocation, new
  objects will be allocated from a large piece of preallocated memory and
  deallocation of these objects is almost free. Early adoption shows 20% to
  50% improvement in some Google binaries.

  To enable arena support, add the following option to your .proto file:

  option cc_enable_arenas = true;
  

  Protocol compiler will generate additional code to make the generated
  message classes work with arenas. This does not change the existing API
  of protobuf messages and does not affect wire format. Your existing code
  should continue to work after adding this option. In the future we will
  make this option enabled by default.

  To actually take advantage of arena allocation, you need to use the arena
  APIs when creating messages. A quick example of using the arena API:

  {
    google::protobuf::Arena arena;
    // Allocate a protobuf message in the arena.
    MyMessage* message = Arena::CreateMessage<MyMessage>(&arena);
    // All submessages will be allocated in the same arena.
    if (!message->ParseFromString(data)) {
      // Deal with malformed input data.
    }
    // Must not delete the message here. It will be deleted automatically
    // when the arena is destroyed.
  }
  

  Currently arena does not work with map fields. Enabling arena in a .proto
  file containing map fields will result in compile errors in the generated
  code. This will be addressed in a future release.

Protocol Buffers v2.6.1

2014-10-20 version 2.6.1

C++

• Added atomicops support for Solaris.
• Released memory allocated by InitializeDefaultRepeatedFields() and GetEmptyString(). Some memory sanitizers reported them as memory leaks.

Java

• Updated DynamicMessage.setField() to handle repeated enum values correctly.
• Fixed a bug that caused NullPointerException to be thrown when converting manually constructed FileDescriptorProto to FileDescriptor.

Python

• Fixed WhichOneof() to work with de-serialized protobuf messages.
• Fixed a missing file problem of Python C++ implementation.