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Protocol Buffers v3.4.0

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Planned Future Changes

  • Preserve unknown fields in proto3: We are going to bring unknown fields back into proto3. In this release, some languages start to support preserving unknown fields in proto3, controlled by flags/options. Some languages also introduce explicit APIs to drop unknown fields for migration. Please read the change log sections by languages for details. See general timeline and plan and issues and discussions

  • Make C++ implementation C++11 only: we plan to require C++11 to build protobuf code starting from 3.5.0 or 3.6.0 release, after unknown fields semantic changes are finished. Please join this github issue to provide your feedback.


  • Extension ranges now accept options and are customizable.
  • reserve keyword now supports max in field number ranges, e.g. reserve 1000 to max;


  • Proto3 messages are now able to preserve unknown fields. The default behavior is still to drop unknowns, which will be flipped in a future release. If you rely on unknowns fields being dropped. Please use Message::DiscardUnknownFields() explicitly.

  • Packable proto3 fields are now packed by default in serialization.

  • Following C++11 features are introduced when C++11 is available:

    • move-constructor and move-assignment are introduced to messages
    • Repeated fields constructor now takes std::initializer_list
    • rvalue setters are introduced for string fields
  • Experimental Table-Driven parsing and serialization available to test. To enable it, pass in table_driven_parsing table_driven_serialization protoc generator flags for C++

    $ protoc --cpp_out=table_driven_parsing,table_driven_serialization:./ test.proto

  • lite generator parameter supported by the generator. Once set, all generated files, use lite runtime regardless of the optimizer_for setting in the .proto file.

  • Various optimizations to make C++ code more performant on PowerPC platform

  • Fixed maps data corruption when the maps are modified by both reflection API and generated API.

  • Deterministic serialization on maps reflection now uses stable sort.

  • file() accessors are introduced to various *Descriptor classes to make writing template function easier.

  • ByteSize() and SpaceUsed() are deprecated.Use ByteSizeLong() and SpaceUsedLong() instead

  • Consistent hash function is used for maps in DEBUG and NDEBUG build.

  • "using namespace std" is removed from stubs/common.h

  • Various performance optimizations and bug fixes


  • Introduced new parser API DiscardUnknownFieldsParser in preparation of proto3 unknown fields preservation change. Users who want to drop unknown fields should migrate to use this new parser API.
    For example:

    Parser<Foo> parser = DiscardUnknownFieldsParser.wrap(Foo.parser());
    Foo foo = parser.parseFrom(input);
  • Introduced new TextFormat API printUnicodeFieldValue() that prints field value without escaping unicode characters.

  • Added, Duration) and, Timestamp).

  • JsonFormat now accepts base64url encoded bytes fields.

  • Optimized CodedInputStream to do less copies when parsing large bytes fields.

  • Optimized TextFormat to allocate less memory when printing.


  • SerializeToString API is changed to SerializeToString(self, **kwargs), deterministic parameter is accepted for deterministic serialization.
  • Added sort_keys parameter in json format to make the output deterministic.
  • Added indent parameter in json format.
  • Added extension support in json format.
  • Added __repr__ support for repeated field in cpp implementation.
  • Added file in FieldDescriptor.
  • Added pretty-print filter to text format.
  • Services and method descriptors are always printed even if generic_service option is turned off.
  • Note: AppEngine 2.5 is deprecated on June 2017 that AppEngine 2.5 will never update protobuf runtime. Users who depend on AppEngine 2.5 should use old protoc.


  • Support PHP generic services. Specify file option php_generic_service=true to enable generating service interface.
  • Message, repeated and map fields setters take value instead of reference.
  • Added map iterator in c extension.
  • Support json  encode/decode.
  • Added more type info in getter/setter phpdoc
  • Fixed the problem that c extension and php implementation cannot be used together.
  • Added file option php_namespace to use custom php namespace instead of package.
  • Added fluent setter.
  • Added descriptor API in runtime for custom encode/decode.
  • Various bug fixes.


  • Fix for GPBExtensionRegistry copying and add tests.
  • Optimize GPBDictionary.m codegen to reduce size of overall library by 46K per architecture.
  • Fix some cases of reading of 64bit map values.
  • Properly error on a tag with field number zero.
  • Preserve unknown fields in proto3 syntax files.
  • Document the exceptions on some of the writing apis.


  • Implemented IReadOnlyDictionary<K,V> in MapField<K,V>
  • Added TryUnpack method for Any message in addition to Unpack.
  • Converted C# projects to MSBuild (csproj) format.


  • Several bug fixes.


  • Added support of field option js_type. Now one can specify the JS type of a 64-bit integer field to be string in the generated code by adding option [jstype = JS_STRING] on the field.