This package contains a collection of utilities around Google's Protocolbuffer. The functions offered in this packages are widely used across Google's C++ code base and have saved tens of thousands of engineering hours. Some of these functons were originally implemented by the author and later re-implemented or cloned (see below).

The project works with Google's proto library version 27, 28, 29 and 30. Packages are available at Bazel Central Registry and Github.

Parse Proto

• rule: @com_helly25_proto//mbo/proto:parse_text_proto_cc

• namespace: mbo::proto

• ParseTextProtoOrDie(text_proto [, std::source_location])

  • text_proto is a text proto best identified as a raw-string with marker pb or proto.
  • If text_proto cannot be parsed into the receiving proto type, then the function will fail.
  • Prefer this function over template function ParseTextOrDie.

• ParseTextOrDie<Proto>(text_proto [, std::source_location])

  • text_proto is a text proto best identified as a raw-string with marker pb or proto.
  • Proto is the type to produce.
  • If text_proto cannot be parsed as a Proto, then the function will fail.
  • Use this only if the Proto type cannot be inferred by ParserTextProtoOrDie.

• ParseTest<Proto>(text_proto [, std::source_location]) -> absl::StatusOr<Proto>

  • text_proto is a text proto best identified as a raw-string with marker pb or proto.
  • Proto is the type to produce.
  • If text_proto cannot be parse as a Proto, then the function returns a non-absl::OkStatus.
  • Use this function in cases where errors are expected.

Usage

BUILD.bazel:

cc_test(
    name = "test",
    srcs = ["test.cc"],
    deps = ["@com_helly25_proto//mbo/proto:parse_text_proto",]
)

Source test.cc:

#include "mbo/proto/parse_text_proto.h"

using ::mbo::proto::ParseTextProtoOrDie;

TEST(Foo, Test) {
    MyProto msg = ParseTextProtoOrDie(R"pb(
      field: "name"
      what: "Just dump the plain text-proto as C++ raw-string."
      )pb");
    // ...
}

Note:

• In the above example the proto is not manually constructed field by field.
• Instead the text-proto output is directly used as a C++ raw-string.
• Further the C++ raw-string is enclosed in pb markers which some tidy tools identify and use to correctly format the text-proto.
• One of the biggest advantages of these parse function is that their result can be assigned into a const variable.

The ParseTextProtoOrDie function dies if the input text-proto is not valid. That is done because the function emulates type safety this way. That is the author will likely only have to fix this once while many people will read the code. Further, this is test input that is supposed to be correct as is. If the input is of dynamic nature, then ParseText<ProtoType>(std::string_view) has to be used.

Proto Matchers

• rule: @com_helly25_proto//mbo/proto:matchers_cc

• namespace: mbo::proto

• EqualsProto(msg)

  • msg: protocolbuffer Message or string
  • Checks whether msg and the argument are the same proto.
  • If a string is used it is advisable to format the string as a raw-string with 'pb' marker as demonstrated above.

• EqualsProto()

  • 2-tuple polymorphic matcher that can be used for container comparisons.

• EquivToProto(msg)

  • msg: protocolbuffer Message or string
  • Similar to EqualsProto but checks whether msg and the argument are equivalent.
  • Equivalent means that if one side sets a field to the default value and the other side does not have that field specified, then they are equivalent.

• EquivToProto()

  • 2-tuple polymorphic matcher that can be used for container comparisons.

Proto Matcher Wrappers

• Approximately(matcher [, margin [, fraction]])

  • matcher wrapper that allows to compare double and float values with a margin of error.
  • optional margin of error and a relative fraction of error which will make values match if satisfied.

• TreatingNaNsAsEqual(matcher)

  • matcher wrapper that compares floating-point fields such that NaNs are equal

• IgnoringFields(ignore_fields, matcher)

  • matcher wrapper that allows to ignore fields with different values.
  • ignore_fields list of fields to ignore. Fields are specified by their fully qualified names, i.e., the names corresponding to FieldDescriptor.full_name(). (e.g. testing.internal.FooProto2.member).

• IgnoringFieldPaths(ignore_field_paths, matcher)

  • matcher wrapper that allows to ignore fields with different values by their paths.
  • ignore_field_paths list of paths to ignore (e.g. 'field.sub_field.terminal_field').

• IgnoringRepeatedFieldOrdering(matcher)

  • matcher wrapper that allows to ignore the order in which repeated fields are presented.
  • E.g.: IgnoringRepeatedFieldOrdering(EqualsProto(R"pb(x: 1 x: 2)pb")): While the provided proto has the repeated field x specified in the order [1, 2], the matcher will also match if the argument proto has the order reversed.

• Partially(matcher)

  • matcher wrapper that compares only fields present in the expected protobuf. For example,
  • Partially(EqualsProto(p)) will ignore any field that is not set in p when comparing the protobufs.

• WhenDeserialized(matcher)

  • matcher wrapper that matches a string that can be deserialized as a protobuf that matches matcher.

• WhenDeserializedAs<Proto>(matcher)

  • matcher wrapper that matches a string that can be deserialized as a protobuf of type Proto that matches matcher.

Usage

BUILD.bazel:

cc_test(
    name = "test",
    srcs = ["test.cc"],
    deps = ["@com_helly25_proto//mbo/proto:matchers"],
)

Source test.cc:

#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "mbo/proto/matchers.h"

using ::mbo::proto::EqualsProto;
using ::mbo::proto::IgnoringRepeatedFieldOrdering;

TEST(Foo, EqualsProto) {
    MyProto msg;
    msg.set_field("name");
    EXPECT_THAT(msg, EqualsProto(R"pb(
      field: "name"
      )pb"));
}

In the above example EqualsProto takes the text-proto as a C++ raw-string.

The matchers can of course be combined with the parse functions. The below shows how a FunctionUnderTest can be tested. It receives the proto input directly from the parse function and the matcher compares it directly to the expected golden result text-proto. Note how there is no field-by-field processing anywhere. No dstraction from what is being tested and what the expectations are. Or in other words the test avoids misleading and error prone in-test logic. And becasue the function-under-test is called inside the EXPECT_THAT macro the gtest failure messages will show what actually failed (and not something like "Input: temp_var").

#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "mbo/proto/matchers.h"
#include "mbo/proto/parse_text_proto.h"

using ::mbo::proto::EqualsProto;
using ::mbo::proto::IgnoringRepeatedFieldOrdering;
using ::mbo::proto::ParseTextProtoOrDie;

MyProto FunctionUnderTest(const MyProto& proto) {
  return proto;
}

TEST(Foo, Wrapper) {
    const MyProto input = ParseTextProtoOrDie(R"pb(
      number: 1
      number: 2
      number: 3
    )pb");
    EXPECT_THAT(
      FunctionUnderTest(input),
      IgnoringRepeatedFieldOrdering(EqualsProto(R"pb(
        number: 1
        number: 2
        number: 3
      )pb")));
}

Proto Files

• rule: @com_helly25_proto//mbo/proto:file_cc

• namespace: mbo::proto

• class ReadBinaryProtoFile(filename)

  • Reads a binary proto file. Usually using .pb file extension.
  • ProtoType the protocol buffer type to read.
  • filename the filename to read from.
  • Creates a type-erased type that reads the file on access.
  • Supports method interface As and OrDie which take an explicit type argument.

• class ReadTextProtoFile(filename)

  • Reads a text proto file. Usually using .textproto file extension.
  • ProtoType the protocol buffer type to read.
  • filename the filename to read from.
  • Creates a type-erased type that reads the file on access.
  • Supports method interface As and OrDie which take an explicit type argument.

• function WriteBinaryProtoFile(filename, message)

  • Writes a binary proto file. Usually using .pb file extension.
  • filename the filename to read from.
  • message the protocol buffer to write.
  • Returns absl::OkStatus() or an error status.

• function WriteTextProtoFile(filename, message)

  • Writes a text proto file. Usually using .textproto file extension.
  • filename the filename to read from.
  • message the protocol buffer to write.
  • Returns absl::OkStatus() or an error status.

• function HasBinaryProtoExtension(filesname)

  • Returns whether the filename ends with a well-known extension for binary proto files.

• function HasTextProtoExtension(filesname)

  • Returns whether the filename ends with a well-known extension for text proto files.

Usage

#include <filesystem>
#include <iostream>

#include "mbo/proto/file.h"
#include "my_protos/my_proto.pb.h"  # Containing `MyProto`

using ::mbo::proto::ReadBinaryProtoFile;
using ::mbo::proto::ReadTextProtoFile;
using ::mbo::proto::WriteBinaryProtoFile;
using ::mbo::proto::WriteTextProtoFile;

int UseBinaryProto(const MyProto& my_proto, const std::filesystem::path& filename) {
  const auto result = WriteBinaryProtoFile(filename, my_proto);
  if (!auto.ok()) {
    std::cerr << "Error: " << result.status() << "\n";
    return 1;
  }
  // Reading with type-erased interface.
  const absl::StatusOr<MyProto> proto_or_status = ReadBinaryProtoFile(filename);
  if (!proto_or_status.ok()) {
    std::cerr << "Error: " << proto_or_status.status() << "\n";
    return 2;
  }
  // Reading with given template type parameter.
  {
    const auto proto_or_status = ReadBinaryProtoFile::As<MyProto>(filename);
    const auto proto = ReadBinaryProtoFile::OrDie<MyProto>(filename);
  }
  return 0;
}

int UseTextProto(const MyProto& my_proto, const std::filesystem::path& filename) {
  const auto result = WriteTextProtoFile(filename, my_proto);
  if (!auto.ok()) {
    std::cerr << "Error: " << result.status() << "\n";
    return 4;
  }
  // Reading with type-erased interface.
  const absl::StatusOr<MyProto> proto_or_status = ReadTextProtoFile(filename);
  if (!proto_or_status.ok()) {
    std::cerr << "Error: " << proto_or_status.status() << "\n";
    return 8;
  }
  // Reading with given template type parameter.
  {
    const auto proto_or_status = ReadTextProtoFile::As<MyProto>(filename);
    const auto proto = ReadTextProtoFile::OrDie<MyProto>(filename);
  }
  return 0;
}

int main() {
  const MyProto my_proto;
  return UseBinaryProto(my_proto, "my_file.pb") + UseTextProto(my_proto, "my_file.textproto");
}

Installation and requirements

This repository requires a C++20 compiler (in case of MacOS XCode 15 is needed) and Bazel 8 or newer. The project's CI tests a combination of Clang and GCC compilers on Linux/Ubuntu and MacOS. The project can be used with Google's proto libraries in versions [32, 33, 34, 35].

The reliance on a C++20 compiler is because it uses std::source_location since Google's Abseil absl::SourceLocation has not been open sourced.

The project only comes with a Bazel BUILD.bazel file and can be added to other Bazel projects.

The project is formatted with specific clang-format settings which require clang 16+ (in case of MacOs LLVM 16+ can be installed using brew). For simplicity in dev mode the project pulls the appropriate clang tools and can be compiled with those tools using bazel [build|test] --config=clang ....

MODULES.bazel

The project is consumed via Bazel modules (bzlmod); WORKSPACE mode is no longer supported. The BCR version declares the dependency versions this module is pinned to; those can be bumped locally. The protobuf version can be overridden in your own MODULE.bazel (e.g. via single_version_override) to any release the project supports.

Check Releases for details. All that is needed is a bazel_dep instruction with the correct version.

bazel_dep(name = "helly25_proto", version = "0.0.0", repo_name = "com_helly25_proto")

Clone

The clone was made from Google's CPP-proto-builder, of which the project lead is the original author and lead for over a decade. That includes in particular the parse_proto components which were invented in their original form around 2012 and used widely throughout Google.

Parse Proto

The following files were cloned:

cp ../cpp-proto-builder/proto_builder/oss/parse_proto_text.* proto/mbo/proto
cp ../cpp-proto-builder/proto_builder/oss/parse_proto_text_test.cc proto/mbo/proto
cp ../cpp-proto-builder/proto_builder/oss/tests/simple_message.proto proto/mbo/proto
patch <proto/mbo/proto/parse_proto_text.diff

The diff files are available in the repository history.

Proto Matchers

The matchers are part of Google's CPP-proto-builder, (see above). Alternatively this could have been done from:

• FHIR,
• nucleus,
• inazarenko's clone.

The FHIR sources are stripped and the nucleus sources are older and finally inazarenko's clone was modified to remove other Google dependencies which creates the issue that the GoogleTest docs do not apply as for instance the regular expression library is different.

The following files were cloned:

cp ../cpp-proto-builder/proto_builder/oss/testing/proto_test_util.* proto/mbo/testing/proto
patch <proto/mbo/testing/proto_test_util.diff

The diff files are available in the repository history.

The include guards were updated and the namespace changed to testing::proto which allows to import the whole namespace easily. Further logging was switched directly to Abseil logging (this was not an option when I wrote the proto Builder or when it was open sourced).

This clone was established 2023.07.15. The source has since been moved and modified but remains as close to the original source as possible.