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Merge pull request #4 from smira/one2many-1
Proxying one to many: first iteration
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,276 @@ | ||
| // Copyright 2019 Andrey Smirnov. All Rights Reserved. | ||
| // See LICENSE for licensing terms. | ||
|
|
||
| package proxy | ||
|
|
||
| import ( | ||
| "errors" | ||
| "fmt" | ||
| "io" | ||
|
|
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| "github.com/hashicorp/go-multierror" | ||
|
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| "google.golang.org/grpc" | ||
| "google.golang.org/grpc/codes" | ||
| "google.golang.org/grpc/status" | ||
| ) | ||
|
|
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| func (s *handler) handlerMulti(serverStream grpc.ServerStream, backendConnections []backendConnection) error { | ||
| // wrap the stream for safe concurrent access | ||
| serverStream = &ServerStreamWrapper{ServerStream: serverStream} | ||
|
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| s2cErrChan := s.forwardServerToClientsMulti(serverStream, backendConnections) | ||
| var c2sErrChan chan error | ||
|
|
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| if true { // TODO: if unary | ||
| c2sErrChan = s.forwardClientsToServerMultiUnary(backendConnections, serverStream) | ||
| } else { | ||
| c2sErrChan = s.forwardClientsToServerMultiStreaming(backendConnections, serverStream) | ||
| } | ||
|
|
||
| for i := 0; i < 2; i++ { | ||
| select { | ||
| case s2cErr := <-s2cErrChan: | ||
| if s2cErr == io.EOF { | ||
| // this is the happy case where the sender has encountered io.EOF, and won't be sending anymore./ | ||
| // the clientStream>serverStream may continue pumping though. | ||
| for i := range backendConnections { | ||
| if backendConnections[i].clientStream != nil { | ||
| backendConnections[i].clientStream.CloseSend() //nolint: errcheck | ||
| } | ||
| } | ||
| break | ||
| } else { | ||
| // however, we may have gotten a receive error (stream disconnected, a read error etc) in which case we need | ||
| // to cancel the clientStream to the backend, let all of its goroutines be freed up by the CancelFunc and | ||
| // exit with an error to the stack | ||
| return status.Errorf(codes.Internal, "failed proxying s2c: %v", s2cErr) | ||
| } | ||
| case c2sErr := <-c2sErrChan: | ||
| // c2sErr will contain RPC error from client code. If not io.EOF return the RPC error as server stream error. | ||
| if c2sErr != io.EOF { | ||
| return c2sErr | ||
| } | ||
| return nil | ||
| } | ||
| } | ||
| return status.Errorf(codes.Internal, "gRPC proxying should never reach this stage.") | ||
| } | ||
|
|
||
| // formatError tries to format error from upstream as message to the client | ||
| func (s *handler) formatError(src *backendConnection, backendErr error) ([]byte, error) { | ||
| payload, err := src.backend.BuildError(backendErr) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("error building error for %s: %w", src.backend, err) | ||
| } | ||
|
|
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| if payload == nil { | ||
| err = backendErr | ||
| } | ||
|
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| return payload, err | ||
| } | ||
|
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| // sendError tries to deliver error back to the client via dst | ||
| // | ||
| // if sendError fails to deliver the error, error is returned | ||
| // if sendError successfully delivers the error, nil is returned | ||
| func (s *handler) sendError(src *backendConnection, dst grpc.ServerStream, backendErr error) error { | ||
| payload, err := s.formatError(src, backendErr) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| f := &frame{payload: payload} | ||
| if err = dst.SendMsg(f); err != nil { | ||
| return fmt.Errorf("error sending error back: %w", err) | ||
| } | ||
|
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| return nil | ||
| } | ||
|
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| // one:many proxying, unary call version (merging results) | ||
| func (s *handler) forwardClientsToServerMultiUnary(sources []backendConnection, dst grpc.ServerStream) chan error { | ||
| ret := make(chan error, 1) | ||
|
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| payloadCh := make(chan []byte, len(sources)) | ||
| errCh := make(chan error, len(sources)) | ||
|
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| for i := 0; i < len(sources); i++ { | ||
| go func(src *backendConnection) { | ||
| errCh <- func() error { | ||
| f := &frame{} | ||
| for j := 0; ; j++ { | ||
| if err := src.clientStream.RecvMsg(f); err != nil { | ||
| if err == io.EOF { | ||
| // This happens when the clientStream has nothing else to offer (io.EOF), returned a gRPC error. In those two | ||
| // cases we may have received Trailers as part of the call. In case of other errors (stream closed) the trailers | ||
| // will be nil. | ||
| dst.SetTrailer(src.clientStream.Trailer()) | ||
| return nil | ||
| } | ||
|
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| payload, err := s.formatError(src, err) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| payloadCh <- payload | ||
| return nil | ||
| } | ||
| if j == 0 { | ||
| // This is a bit of a hack, but client to server headers are only readable after first client msg is | ||
| // received but must be written to server stream before the first msg is flushed. | ||
| // This is the only place to do it nicely. | ||
| md, err := src.clientStream.Header() | ||
| if err != nil { | ||
| payload, err := s.formatError(src, err) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| payloadCh <- payload | ||
| return nil | ||
| } | ||
|
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| if err := dst.SetHeader(md); err != nil { | ||
| return fmt.Errorf("error setting headers from client %s: %w", src.backend, err) | ||
| } | ||
| } | ||
|
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| var err error | ||
| f.payload, err = src.backend.AppendInfo(f.payload) | ||
| if err != nil { | ||
| return fmt.Errorf("error appending info for %s: %w", src.backend, err) | ||
| } | ||
|
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| payloadCh <- f.payload | ||
| } | ||
| }() | ||
| }(&sources[i]) | ||
| } | ||
|
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| go func() { | ||
| var multiErr *multierror.Error | ||
|
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| for range sources { | ||
| multiErr = multierror.Append(multiErr, <-errCh) | ||
| } | ||
|
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| if multiErr.ErrorOrNil() != nil { | ||
| ret <- multiErr.ErrorOrNil() | ||
| return | ||
| } | ||
|
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| close(payloadCh) | ||
|
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| var merged []byte | ||
| for b := range payloadCh { | ||
| merged = append(merged, b...) | ||
| } | ||
|
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| ret <- dst.SendMsg(&frame{payload: merged}) | ||
| }() | ||
|
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| return ret | ||
| } | ||
|
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| // one:many proxying, streaming version (no merge) | ||
| func (s *handler) forwardClientsToServerMultiStreaming(sources []backendConnection, dst grpc.ServerStream) chan error { | ||
| ret := make(chan error, 1) | ||
|
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| errCh := make(chan error, len(sources)) | ||
|
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| for i := range sources { | ||
| go func(src *backendConnection) { | ||
| errCh <- func() error { | ||
| if src.connError != nil { | ||
| return s.sendError(src, dst, src.connError) | ||
| } | ||
|
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| f := &frame{} | ||
| for j := 0; ; j++ { | ||
| if err := src.clientStream.RecvMsg(f); err != nil { | ||
| if err == io.EOF { | ||
| // This happens when the clientStream has nothing else to offer (io.EOF), returned a gRPC error. In those two | ||
| // cases we may have received Trailers as part of the call. In case of other errors (stream closed) the trailers | ||
| // will be nil. | ||
| dst.SetTrailer(src.clientStream.Trailer()) | ||
| return nil | ||
| } | ||
| return s.sendError(src, dst, fmt.Errorf("error reading from client stream %s: %w", src.backend, err)) | ||
| } | ||
| if j == 0 { | ||
| // This is a bit of a hack, but client to server headers are only readable after first client msg is | ||
| // received but must be written to server stream before the first msg is flushed. | ||
| // This is the only place to do it nicely. | ||
| md, err := src.clientStream.Header() | ||
| if err != nil { | ||
| return s.sendError(src, dst, fmt.Errorf("error getting headers from client stream %s: %w", src.backend, err)) | ||
| } | ||
| if err := dst.SetHeader(md); err != nil { | ||
| return fmt.Errorf("error setting headers from client %s: %w", src.backend, err) | ||
| } | ||
| } | ||
|
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||
| var err error | ||
| f.payload, err = src.backend.AppendInfo(f.payload) | ||
| if err != nil { | ||
| return fmt.Errorf("error appending info for %s: %w", src.backend, err) | ||
| } | ||
|
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| if err = dst.SendMsg(f); err != nil { | ||
| return fmt.Errorf("error sending back to server from %s: %w", src.backend, err) | ||
| } | ||
| } | ||
|
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| }() | ||
| }(&sources[i]) | ||
| } | ||
|
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| go func() { | ||
| var multiErr *multierror.Error | ||
|
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| for range sources { | ||
| multiErr = multierror.Append(multiErr, <-errCh) | ||
| } | ||
|
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| ret <- multiErr.ErrorOrNil() | ||
| }() | ||
|
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| return ret | ||
| } | ||
|
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| func (s *handler) forwardServerToClientsMulti(src grpc.ServerStream, destinations []backendConnection) chan error { | ||
| ret := make(chan error, 1) | ||
| go func() { | ||
| f := &frame{} | ||
| for { | ||
| if err := src.RecvMsg(f); err != nil { | ||
| ret <- err | ||
| return | ||
| } | ||
|
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| liveDestinations := 0 | ||
| for i := range destinations { | ||
| if destinations[i].clientStream == nil || destinations[i].connError != nil { | ||
| continue | ||
| } | ||
|
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| if err := destinations[i].clientStream.SendMsg(f); err != nil { | ||
| // TODO: race with reading connError (?) | ||
| // skip this or keep using? | ||
| destinations[i].connError = err | ||
| } else { | ||
| liveDestinations++ | ||
| } | ||
| } | ||
|
|
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| if liveDestinations == 0 { | ||
| ret <- errors.New("no backend connections to forward to are available") | ||
| return | ||
| } | ||
| } | ||
| }() | ||
| return ret | ||
| } |
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