Skylark macro to generate an objc_library from protos

Still needed:
- Use compiled protoc.
- Work with multiple proto sources.
- Work with proto sources in nested dirs.

grpc.bzl

+
+def _lower_underscore_to_upper_camel(str):
+  humps = []
+  for hump in str.split('_'):
+    humps += [hump[0].upper() + hump[1:]]
+  return "".join(humps)
+
+def objc_grpc_library(name, srcs, visibility=None):
+  basename = srcs[0].split('/')[-1]
+  filename = basename[:-6] # remove .proto suffix
+  filename = _lower_underscore_to_upper_camel(filename)
+
+  protoc_command = "protoc -I . "
+  srcs_params = ""
+  for src in srcs:
+    srcs_params += " $(location %s)" % (src)
+
+  # Messages
+  protoc_messages_flags = "--objc_out=$(GENDIR)"
+  native.genrule(
+    name = name + "_mesages_codegen",
+    srcs = srcs,
+    outs = [
+      filename + ".pbobjc.h",
+      filename + ".pbobjc.m",
+    ],
+    cmd = protoc_command + protoc_messages_flags + srcs_params,
+  )
+  native.objc_library(
+    name = name + "_messages",
+    hdrs = [
+      ":" + filename + ".pbobjc.h",
+    ],
+    includes = ["."],
+    non_arc_srcs = [
+      ":" + filename + ".pbobjc.m",
+    ],
+    deps = [
+      "//external:protobuf_objc",
+    ],
+  )
+
+  # Services
+  protoc_services_flags = "--grpc_out=$(GENDIR) --plugin=protoc-gen-grpc=$(location //external:grpc_protoc_plugin_objc)"
+  native.genrule(
+    name = name + "_codegen",
+    srcs = srcs + ["//external:grpc_protoc_plugin_objc"],
+    outs = [
+      filename + ".pbrpc.h",
+      filename + ".pbrpc.m",
+    ],
+    cmd = protoc_command + protoc_services_flags + srcs_params,
+  )
+  native.objc_library(
+    name = name,
+    hdrs = [
+      ":" + filename + ".pbrpc.h",
+    ],
+    includes = ["."],
+    srcs = [
+      ":" + filename + ".pbrpc.m",
+    ],
+    deps = [
+      ":" + name + "_messages",
+      "//external:proto_objc_rpc",
+    ],
+    visibility = visibility,
+  )