Add a gRPC API (#577)

This adds a gRPC API alongside the existing gob API.

It is enabled whenever the RPC setting is enabled. I didn't think it made sense to have a separate setting to enable it. It is only used when a gRPC request is detected (Content-Type: application/grpc). Eventually, we should likely open a separate port for gRPC traffic, but this should be okay for now.

In order to minimize the footprint of this change, we only use the protobuf definitions in the RPC layer. They are translated to/from the existing go types. This results in a small perf penalty.

BUILD.bazel

@@ -21,6 +21,7 @@ go_library(
     name = "zoekt",
     srcs = [
         "api.go",
+        "api_proto.go",
         "bits.go",
         "btree.go",
         "contentprovider.go",
@@ -45,12 +46,15 @@ go_library(
     importpath = "github.com/sourcegraph/zoekt",
     visibility = ["//visibility:public"],
     deps = [
+        "//grpc/v1:grpc",
         "//query",
         "@com_github_edsrzf_mmap_go//:mmap-go",
         "@com_github_go_enry_go_enry_v2//:go-enry",
         "@com_github_go_enry_go_enry_v2//data",
         "@com_github_grafana_regexp//:regexp",
         "@com_github_rs_xid//:xid",
+        "@org_golang_google_protobuf//types/known/durationpb",
+        "@org_golang_google_protobuf//types/known/timestamppb",
     ] + select({
         "@io_bazel_rules_go//go/platform:aix": [
             "@org_golang_x_sys//unix",
@@ -98,6 +102,7 @@ go_library(
 go_test(
     name = "zoekt_test",
     srcs = [
+        "api_proto_test.go",
         "api_test.go",
         "bits_test.go",
         "btree_test.go",
@@ -114,12 +119,15 @@ go_test(
     ],
     data = [":testdata"],
     embed = [":zoekt"],
+    embedsrcs = ["//testdata:search_result_1.pb"],  #keep
     deps = [
+        "//grpc/v1:grpc",
         "//query",
         "@com_github_google_go_cmp//cmp",
         "@com_github_google_go_cmp//cmp/cmpopts",
         "@com_github_grafana_regexp//:regexp",
         "@com_github_kylelemons_godebug//pretty",
         "@com_github_roaringbitmap_roaring//:roaring",
+        "@org_golang_google_protobuf//proto",
     ],
 )

WORKSPACE

@@ -49,7 +49,7 @@ http_archive(
 
 # Go toolchain setup
 load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")
-load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies", "go_repository")
+load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies")
 load("//:deps.bzl", "go_dependencies")
 
 # gazelle:repository_macro deps.bzl%go_dependencies

api.go

@@ -525,7 +525,7 @@ func (r RepositoryBranch) String() string {
 
 // Repository holds repository metadata.
 type Repository struct {
-	// Sourcergaph's repository ID
+	// Sourcegraph's repository ID
 	ID uint32
 
 	// The repository name