| // Copyright 2020 The LUCI Authors. |
| // |
| // 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. |
| |
| package grpcutil |
| |
| import ( |
| "context" |
| |
| "google.golang.org/grpc" |
| ) |
| |
| // ChainUnaryServerInterceptors chains multiple interceptors together. |
| // |
| // The first one becomes the outermost, and the last one becomes the |
| // innermost, i.e. `ChainUnaryServerInterceptors(a, b, c)(h) === a(b(c(h)))`. |
| // |
| // nil-valued interceptors are silently skipped. |
| func ChainUnaryServerInterceptors(interceptors ...grpc.UnaryServerInterceptor) grpc.UnaryServerInterceptor { |
| switch { |
| case len(interceptors) == 0: |
| // Noop interceptor. |
| return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) { |
| return handler(ctx, req) |
| } |
| case interceptors[0] == nil: |
| // Skip nils. |
| return ChainUnaryServerInterceptors(interceptors[1:]...) |
| case len(interceptors) == 1: |
| // No need to actually chain anything. |
| return interceptors[0] |
| default: |
| return combinator(interceptors[0], ChainUnaryServerInterceptors(interceptors[1:]...)) |
| } |
| } |
| |
| // combinator is an interceptor that chains just two interceptors together. |
| func combinator(first, second grpc.UnaryServerInterceptor) grpc.UnaryServerInterceptor { |
| return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) { |
| return first(ctx, req, info, func(ctx context.Context, req interface{}) (interface{}, error) { |
| return second(ctx, req, info, handler) |
| }) |
| } |
| } |