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# Metadata interceptor example | ||
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This example shows how to update metadata from unary and streaming interceptors on the server. | ||
Please see | ||
[grpc-metadata.md](https://github.com/grpc/grpc-go/blob/master/Documentation/grpc-metadata.md) | ||
for more information. | ||
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## Try it | ||
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``` | ||
go run server/main.go | ||
``` | ||
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``` | ||
go run client/main.go | ||
``` | ||
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## Explanation | ||
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#### Unary interceptor | ||
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The interceptor can read existing metadata from the RPC context passed to it. | ||
Since Go contexts are immutable, the interceptor will have to create a new context | ||
with updated metadata and pass it to the provided handler. | ||
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```go | ||
func SomeInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) { | ||
// Get the incoming metadata from the RPC context, and add a new | ||
// key-value pair to it. | ||
md, ok := metadata.FromIncomingContext(ctx) | ||
md.Append("key1", "value1") | ||
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// Create a context with the new metadata and pass it to handler. | ||
ctx = metadata.NewIncomingContext(ctx, md) | ||
return handler(ctx, req) | ||
} | ||
``` | ||
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#### Streaming interceptor | ||
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`grpc.ServerStream` does not provide a way to modify its RPC context. The streaming | ||
interceptor therefore needs to implement the `grpc.ServerStream` interface and return | ||
a context with updated metadata. | ||
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The easiest way to do this would be to create a type which embeds the `grpc.ServerStream` | ||
interface and overrides only the `Context()` method to return a context with updated | ||
metadata. The streaming interceptor would then pass this wrapped stream to the provided handler. | ||
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```go | ||
type wrappedStream struct { | ||
grpc.ServerStream | ||
ctx context.Context | ||
} | ||
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func (s *wrappedStream) Context() context.Context { | ||
return s.ctx | ||
} | ||
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func SomeStreamInterceptor(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error { | ||
// Get the incoming metadata from the RPC context, and add a new | ||
// key-value pair to it. | ||
md, ok := metadata.FromIncomingContext(ctx) | ||
md.Append("key1", "value1") | ||
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// Create a context with the new metadata and pass it to handler. | ||
ctx = metadata.NewIncomingContext(ctx, md) | ||
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return handler(srv, &wrappedStream{ss, ctx}) | ||
} | ||
``` |
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/* | ||
* | ||
* Copyright 2022 gRPC 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. | ||
* | ||
*/ | ||
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// Binary client is an example client. | ||
package main | ||
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import ( | ||
"context" | ||
"flag" | ||
"fmt" | ||
"io" | ||
"log" | ||
"time" | ||
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"google.golang.org/grpc" | ||
"google.golang.org/grpc/credentials/insecure" | ||
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pb "google.golang.org/grpc/examples/features/proto/echo" | ||
) | ||
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var addr = flag.String("addr", "localhost:50051", "the address to connect to") | ||
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func callUnaryEcho(ctx context.Context, client pb.EchoClient) { | ||
resp, err := client.UnaryEcho(ctx, &pb.EchoRequest{Message: "hello world"}) | ||
if err != nil { | ||
log.Fatalf("UnaryEcho %v", err) | ||
} | ||
fmt.Println("UnaryEcho: ", resp.Message) | ||
} | ||
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func callBidiStreamingEcho(ctx context.Context, client pb.EchoClient) { | ||
c, err := client.BidirectionalStreamingEcho(ctx) | ||
if err != nil { | ||
log.Fatalf("BidiStreamingEcho %v", err) | ||
} | ||
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if err := c.Send(&pb.EchoRequest{Message: "hello world"}); err != nil { | ||
log.Fatalf("Sending echo request: %v", err) | ||
} | ||
c.CloseSend() | ||
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for { | ||
resp, err := c.Recv() | ||
if err == io.EOF { | ||
break | ||
} | ||
if err != nil { | ||
log.Fatalf("Receiving echo response: %v", err) | ||
} | ||
fmt.Println("BidiStreaming Echo: ", resp.Message) | ||
} | ||
} | ||
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func main() { | ||
flag.Parse() | ||
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conn, err := grpc.Dial(*addr, grpc.WithTransportCredentials(insecure.NewCredentials())) | ||
if err != nil { | ||
log.Fatalf("grpc.Dial(%q): %v", *addr, err) | ||
} | ||
defer conn.Close() | ||
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ec := pb.NewEchoClient(conn) | ||
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ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second) | ||
defer cancel() | ||
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callUnaryEcho(ctx, ec) | ||
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callBidiStreamingEcho(ctx, ec) | ||
} |
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/* | ||
* | ||
* Copyright 2022 gRPC 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. | ||
* | ||
*/ | ||
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// Binary server is an example server. | ||
package main | ||
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import ( | ||
"context" | ||
"flag" | ||
"fmt" | ||
"io" | ||
"log" | ||
"net" | ||
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"google.golang.org/grpc" | ||
"google.golang.org/grpc/codes" | ||
"google.golang.org/grpc/metadata" | ||
"google.golang.org/grpc/status" | ||
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pb "google.golang.org/grpc/examples/features/proto/echo" | ||
) | ||
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var port = flag.Int("port", 50051, "the port to serve on") | ||
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var errMissingMetadata = status.Errorf(codes.InvalidArgument, "no incoming metadata in rpc context") | ||
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type server struct { | ||
pb.UnimplementedEchoServer | ||
} | ||
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func unaryInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) { | ||
md, ok := metadata.FromIncomingContext(ctx) | ||
if !ok { | ||
return nil, errMissingMetadata | ||
} | ||
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md.Append("key1", "value1") | ||
ctx = metadata.NewIncomingContext(ctx, md) | ||
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return handler(ctx, req) | ||
} | ||
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func (s *server) UnaryEcho(ctx context.Context, in *pb.EchoRequest) (*pb.EchoResponse, error) { | ||
fmt.Printf("--- UnaryEcho ---\n") | ||
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md, ok := metadata.FromIncomingContext(ctx) | ||
if !ok { | ||
return nil, status.Errorf(codes.Internal, "UnaryEcho: missing incoming metadata in rpc context") | ||
} | ||
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// Read and print metadata added by the interceptor. | ||
if v, ok := md["key1"]; ok { | ||
fmt.Printf("key1 from metadata: \n") | ||
for i, e := range v { | ||
fmt.Printf(" %d. %s\n", i, e) | ||
} | ||
} | ||
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return &pb.EchoResponse{Message: in.Message}, nil | ||
} | ||
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type wrappedStream struct { | ||
grpc.ServerStream | ||
ctx context.Context | ||
} | ||
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func (s *wrappedStream) Context() context.Context { | ||
return s.ctx | ||
} | ||
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func streamInterceptor(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error { | ||
md, ok := metadata.FromIncomingContext(ss.Context()) | ||
if !ok { | ||
return errMissingMetadata | ||
} | ||
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md.Append("key1", "value1") | ||
ctx := metadata.NewIncomingContext(ss.Context(), md) | ||
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return handler(srv, &wrappedStream{ss, ctx}) | ||
} | ||
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func (s *server) BidirectionalStreamingEcho(stream pb.Echo_BidirectionalStreamingEchoServer) error { | ||
fmt.Printf("--- BidirectionalStreamingEcho ---\n") | ||
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md, ok := metadata.FromIncomingContext(stream.Context()) | ||
if !ok { | ||
return status.Errorf(codes.Internal, "BidirectionalStreamingEcho: missing incoming metadata in rpc context") | ||
} | ||
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// Read and print metadata added by the interceptor. | ||
if v, ok := md["key1"]; ok { | ||
fmt.Printf("key1 from metadata: \n") | ||
for i, e := range v { | ||
fmt.Printf(" %d. %s\n", i, e) | ||
} | ||
} | ||
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// Read requests and send responses. | ||
for { | ||
in, err := stream.Recv() | ||
if err == io.EOF { | ||
return nil | ||
} | ||
if err != nil { | ||
return err | ||
} | ||
if err = stream.Send(&pb.EchoResponse{Message: in.Message}); err != nil { | ||
return err | ||
} | ||
} | ||
} | ||
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func main() { | ||
flag.Parse() | ||
lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port)) | ||
if err != nil { | ||
log.Fatalf("net.Listen() failed: %v", err) | ||
} | ||
fmt.Printf("Server listening at %v\n", lis.Addr()) | ||
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s := grpc.NewServer(grpc.UnaryInterceptor(unaryInterceptor), grpc.StreamInterceptor(streamInterceptor)) | ||
pb.RegisterEchoServer(s, &server{}) | ||
s.Serve(lis) | ||
} |