gRPC gateway Bazel build rules

[achew22]

I'm using the normal bazel go rules (http://bazel.io/docs/be/go.html) and I've started looking into creating a build rule for Bazel so the output from grpc-gateway can be depended upon directly. I have a sneaking suspicion that you're using Bazel in some of your projects. Do you have any tricks/tips for getting everything set up in Bazel? Would you be willing to put a sample in the examples folder of how you're doing this?

[yugui]

@achew22 No, I don't have a good example since I am just trying Bazel in a small project which does not use grpc-gateway.
But I agree that it would be useful if we have a Skylark macro like grpc_gateway_library or grpc_gateway_binary

[ivucica]

The following is from a project that's not opensourced (yet), so I can't point to the exact rules. One limiting factor is that I also have custom Go rules (based on Kythe's rules) and haven't gotten around to reworking Bazel's Go rules (see bazelbuild/bazel#828). Because the build rule for //vendor:protoc-gen-gprc-gateway is too dependent on custom Go rules that are too fragile and messy to be shared, I'm not sharing them here.

Instead I'll try to describe my approach enough to get interested people started.

This is my genrule() in the BUILD file for the Bazel package containing file scheduler.proto:

genrule(
    name = "scheduler_pb_gw",
    srcs = [
        "scheduler.proto",
        "//vendor:github.com/gengo/grpc-gateway/third_party/googleapis/google/api/annotations.proto",
        "//vendor:github.com/gengo/grpc-gateway/third_party/googleapis/google/api/http.proto",
        "//vendor:github.com/gogo/protobuf/protobuf/google/protobuf/descriptor.proto"],
    outs = ["scheduler.pb.gw.go"],
    cmd = (
        "$(location @protobuf//:protoc) " +
        " --grpc-gateway_out=logtostderr=true:$$(dirname $@)" +
        " -I$$(dirname $$(dirname $$(dirname $(location //vendor:github.com/gengo/grpc-gateway/third_party/googleapis/google/api/annotations.proto)))):$$(dirname $$(dirname $$(dirname $(location //vendor:github.com/gogo/protobuf/protobuf/google/protobuf/descriptor.proto)))):." +
        " --plugin=protoc-gen-grpc-gateway=$(location //vendor:protoc-gen-grpc-gateway)" +
        " --proto_path=$$(dirname $(location scheduler.proto)):$$(dirname \"$@\")" +
        " $(location scheduler.proto); mv \"$$(dirname \"$@\")\"/scheduler/\"$$(basename \"$@\")\" \"$@\""),
    message = "Processing proto file with grpc-gateway",
    tools = [
        "@protobuf//:protoc",
        "//vendor:protoc-gen-grpc-gateway",
    ]
)

The WORKSPACE defines external repository protobuf. While ordinarily one would specify a git_repository() rule, I am already using vendoring + externals:

local_repository(
    name = "protobuf",
    path = __workspace_dir__ + "/vendor/github.com/google/protobuf",
)

I'm using a genrule() here because it was easier than writing a proper Skylark rule. Even this genrule() is quite hacky.

[yugui]

@ivucica Thank you for sharing that.

Although I'm not going to write the skylark rule by myself very soon, but it is definitely on my to-do list.
Also I'm happy to accept PRs for the rule. In both cases, your genrule will be quite helpful.

[pcj]

I've posted a preliminary implementation of grpc_gateway_proto_library in rules_protobuf that:

• builds the grpc-gateway runtime and associated libraries,
• builds the protoc-gen-grpc-gateway plugin,
• invokes the plugin
• compiles the *.pb.gw.go files into a go_library

Hopefully we can accomplish easy grpc-gateway support in bazel. Feedback or contributions welcome.