mirror of https://github.com/grpc/grpc-go.git
71 lines
2.2 KiB
Markdown
71 lines
2.2 KiB
Markdown
# Metadata interceptor example
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This example shows how to update metadata from unary and streaming interceptors on the server.
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Please see
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[grpc-metadata.md](https://github.com/grpc/grpc-go/blob/master/Documentation/grpc-metadata.md)
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for more information.
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## Try it
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```
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go run server/main.go
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```
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```
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go run client/main.go
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```
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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.
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Since Go contexts are immutable, the interceptor will have to create a new context
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with updated metadata and pass it to the provided handler.
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```go
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func SomeInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
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// Get the incoming metadata from the RPC context, and add a new
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// key-value pair to it.
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md, ok := metadata.FromIncomingContext(ctx)
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md.Append("key1", "value1")
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// Create a context with the new metadata and pass it to handler.
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ctx = metadata.NewIncomingContext(ctx, md)
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return handler(ctx, req)
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}
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```
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#### Streaming interceptor
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`grpc.ServerStream` does not provide a way to modify its RPC context. The streaming
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interceptor therefore needs to implement the `grpc.ServerStream` interface and return
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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`
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interface and overrides only the `Context()` method to return a context with updated
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metadata. The streaming interceptor would then pass this wrapped stream to the provided handler.
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```go
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type wrappedStream struct {
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grpc.ServerStream
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ctx context.Context
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}
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func (s *wrappedStream) Context() context.Context {
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return s.ctx
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}
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func SomeStreamInterceptor(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
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// Get the incoming metadata from the RPC context, and add a new
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// key-value pair to it.
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md, ok := metadata.FromIncomingContext(ctx)
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md.Append("key1", "value1")
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// Create a context with the new metadata and pass it to handler.
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ctx = metadata.NewIncomingContext(ctx, md)
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return handler(srv, &wrappedStream{ss, ctx})
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}
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```
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