balancer: set RPC metadata in address attributes, instead of Metadata field (#4041)

This metadata will be sent with all RPCs on the created SubConn
8 files changed
tree: 45fe0a2fab7326e459a2abaad4c2ffe1f1e5b198
  1. .github/
  2. attributes/
  3. backoff/
  4. balancer/
  5. benchmark/
  6. binarylog/
  7. channelz/
  8. cmd/
  9. codes/
  10. connectivity/
  11. credentials/
  12. Documentation/
  13. encoding/
  14. examples/
  15. grpclog/
  16. health/
  17. internal/
  18. interop/
  19. keepalive/
  20. metadata/
  21. peer/
  22. profiling/
  23. reflection/
  24. resolver/
  25. security/
  26. serviceconfig/
  27. stats/
  28. status/
  29. stress/
  30. tap/
  31. test/
  32. testdata/
  33. xds/
  34. .travis.yml
  36. backoff.go
  37. balancer_conn_wrappers.go
  38. balancer_conn_wrappers_test.go
  39. balancer_switching_test.go
  40. call.go
  41. call_test.go
  42. clientconn.go
  43. clientconn_state_transition_test.go
  44. clientconn_test.go
  46. codec.go
  47. codec_test.go
  50. dialoptions.go
  51. doc.go
  52. go.mod
  53. go.sum
  55. grpc_test.go
  57. interceptor.go
  60. Makefile
  61. picker_wrapper.go
  62. picker_wrapper_test.go
  63. pickfirst.go
  64. pickfirst_test.go
  65. preloader.go
  68. resolver_conn_wrapper.go
  69. resolver_conn_wrapper_test.go
  70. rpc_util.go
  71. rpc_util_test.go
  72. server.go
  73. server_test.go
  74. service_config.go
  75. service_config_test.go
  76. stream.go
  77. trace.go
  78. trace_test.go
  79. version.go


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The Go implementation of gRPC: A high performance, open source, general RPC framework that puts mobile and HTTP/2 first. For more information see the Go gRPC docs, or jump directly into the quick start.



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import ""

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$ go get -u
package unrecognized import path "" (https fetch: Get dial tcp i/o timeout)

To build Go code, there are several options:

  • Set up a VPN and access through that.

  • Without Go module support: git clone the repo manually:

    git clone $GOPATH/src/

    You will need to do the same for all of grpc's dependencies in, e.g.

  • With Go module support: it is possible to use the replace feature of go mod to create aliases for packages. In your project's directory:

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    go mod tidy
    go mod vendor
    go build -mod=vendor

    Again, this will need to be done for all transitive dependencies hosted on as well. For details, refer to golang/go issue #28652.

Compiling error, undefined: grpc.SupportPackageIsVersion

If you are using Go modules:

Ensure your gRPC-Go version is required at the appropriate version in the same module containing the generated .pb.go files. For example, SupportPackageIsVersion6 needs v1.27.0, so in your go.mod file:

module <your module name>

require ( v1.27.0

If you are not using Go modules:

Update the proto package, gRPC package, and rebuild the .proto files:

go get -u{proto,protoc-gen-go}
go get -u
protoc --go_out=plugins=grpc:. *.proto

How to turn on logging

The default logger is controlled by environment variables. Turn everything on like this:


The RPC failed with error "code = Unavailable desc = transport is closing"

This error means the connection the RPC is using was closed, and there are many possible reasons, including:

  1. mis-configured transport credentials, connection failed on handshaking
  2. bytes disrupted, possibly by a proxy in between
  3. server shutdown
  4. Keepalive parameters caused connection shutdown, for example if you have configured your server to terminate connections regularly to trigger DNS lookups. If this is the case, you may want to increase your MaxConnectionAgeGrace, to allow longer RPC calls to finish.

It can be tricky to debug this because the error happens on the client side but the root cause of the connection being closed is on the server side. Turn on logging on both client and server, and see if there are any transport errors.