Add support for the detailed error model

Motivation:

A common extension to gRPC is a the detailed error model. While not a
standard gRPC feature it is widely used. The standard error model only
allows for a status code and message to be propagated to the client. The
detailed error model allows users to use a common set of structured
errors and send them to the client in metadata. The model uses the
'google.rpc.Status' protobuf message to describe the error and any error
details.

Modifications:

- Update the fetch and generate protobuf scripts to get and build the
  relevant standard protobuf messages.
- Add `ErrorDetails` which is a container for common error types. Each
  of the error types maps to one a standard error detail from the
  detailed error model.
- Add a `GoogleRPCStatus` error which maps to the 'google.rpc.Status'
  protobuf. This also conforms to `RPCErrorConvertible` so gRPC will
  automaticlly turn it into an appropriate status and metadata.
- Add a helper for unpacking the `GoogleRPCStatus` from an `RPCError`.

Result:

Support for the detailed error mode.

Author: glbrntt

dev/protos/fetch.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+## Copyright 2024, gRPC Authors All rights reserved.
+##
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+##     http://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+
+set -eu
+
+here="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+upstream="$here/upstream"
+
+# Create a temporary directory for the repo checkouts.
+checkouts="$(mktemp -d)"
+
+# Clone the google protos into the staging area.
+git clone --depth 1 https://github.com/googleapis/googleapis.git "$checkouts/googleapis"
+
+# Remove the old protos.
+rm -rf "$upstream"
+
+# Copy over the googleapis protos.
+mkdir -p "$upstream/google/rpc"
+cp -rp "$checkouts/googleapis/google/rpc/error_details.proto" "$upstream/google/rpc/error_details.proto"
+cp -rp "$checkouts/googleapis/google/rpc/code.proto" "$upstream/google/rpc/code.proto"
+cp -rp "$checkouts/googleapis/google/rpc/status.proto" "$upstream/google/rpc/status.proto"

dev/protos/generate.sh

@@ -19,13 +19,84 @@ here="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 root="$here/../.."
 protoc=$(which protoc)
 
+# Checkout and build the plugins.
+swift build --package-path "$root" --product protoc-gen-swift
+swift build --package-path "$root" --product protoc-gen-grpc-swift
+
+# Grab the plugin paths.
+bin_path=$(swift build --package-path "$root" --show-bin-path)
+protoc_gen_swift="$bin_path/protoc-gen-swift"
+protoc_gen_grpc_swift="$bin_path/protoc-gen-grpc-swift"
+
+# Generates gRPC by invoking protoc with the gRPC Swift plugin.
+# Parameters:
+# - $1: .proto file
+# - $2: proto path
+# - $3: output path
+# - $4 onwards: options to forward to the plugin
+function generate_grpc {
+  local proto=$1
+  local args=("--plugin=$protoc_gen_grpc_swift" "--proto_path=${2}" "--grpc-swift_out=${3}")
+
+  for option in "${@:4}"; do
+    args+=("--grpc-swift_opt=$option")
+  done
+
+  invoke_protoc "${args[@]}" "$proto"
+}
+
+# Generates messages by invoking protoc with the Swift plugin.
+# Parameters:
+# - $1: .proto file
+# - $2: proto path
+# - $3: output path
+# - $4 onwards: options to forward to the plugin
+function generate_message {
+  local proto=$1
+  local args=("--plugin=$protoc_gen_swift" "--proto_path=$2" "--swift_out=$3")
+
+  for option in "${@:4}"; do
+    args+=("--swift_opt=$option")
+  done
+
+  invoke_protoc "${args[@]}" "$proto"
+}
+
 function invoke_protoc {
   # Setting -x when running the script produces a lot of output, instead boil
   # just echo out the protoc invocations.
   echo "$protoc" "$@"
   "$protoc" "$@"
 }
 
+#- DETAILED ERROR -------------------------------------------------------------
+
+function generate_rpc_error_details {
+  local protos output
+
+  protos=(
+    "$here/upstream/google/rpc/status.proto"
+    "$here/upstream/google/rpc/code.proto"
+    "$here/upstream/google/rpc/error_details.proto"
+  )
+  output="$root/Sources/GRPCProtobuf/Errors/Generated"
+
+  for proto in "${protos[@]}"; do
+    generate_message "$proto" "$(dirname "$proto")" "$output" "Visibility=Internal" "UseAccessLevelOnImports=true"
+  done
+}
+
+#- DETAILED ERROR Tests -------------------------------------------------------
+
+function generate_error_service {
+  local proto output
+  proto="$here/local/error-service.proto"
+  output="$root/Tests/GRPCProtobufTests/Errors/Generated"
+
+  generate_message "$proto" "$(dirname "$proto")" "$output" "Visibility=Internal" "UseAccessLevelOnImports=true"
+  generate_grpc "$proto" "$(dirname "$proto")" "$output" "Visibility=Internal" "UseAccessLevelOnImports=true"
+}
+
 #- DESCRIPTOR SETS ------------------------------------------------------------
 
 function generate_test_service_descriptor_set {
@@ -72,7 +143,13 @@ function generate_wkt_service_descriptor_set {
 
 #------------------------------------------------------------------------------
 
-# Descriptor sets
+# Detailed error model
+generate_rpc_error_details
+
+# Service for testing error details
+generate_error_service
+
+# Descriptor sets for tests
 generate_test_service_descriptor_set
 generate_foo_service_descriptor_set
 generate_bar_service_descriptor_set