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package proxy
import (
"errors"
"google.golang.org/grpc"
)
// StreamPeeker abstracts away the gRPC stream being forwarded so that it can
// be inspected and modified.
type StreamPeeker interface {
// Peek allows a director to peek a messages into the stream without
// removing those messages from the stream that will be forwarded to
// the backend server.
Peek() (Frame, error)
}
// Frame contains a payload that can be optionally modified
type Frame interface {
Modify(payload []byte) error
Payload() []byte
}
type partialStream struct {
frames []*frame // frames encountered in partial stream
err error // error returned by partial stream
}
type peeker struct {
srcStream grpc.ServerStream
consumedStream *partialStream
}
func newPeeker(stream grpc.ServerStream) *peeker {
return &peeker{
srcStream: stream,
consumedStream: &partialStream{},
}
}
// ErrInvalidPeekCount indicates the director function requested an invalid
// peek quanity
var ErrInvalidPeekCount = errors.New("peek count must be greater than zero")
func (p peeker) Peek() (Frame, error) {
frames, err := p.peek(1)
if err != nil {
return nil, err
}
if len(frames) != 1 {
return nil, errors.New("failed to peek 1 message")
}
return frames[0], nil
}
func (p peeker) peek(n uint) ([]*frame, error) {
if n < 1 {
return nil, ErrInvalidPeekCount
}
p.consumedStream.frames = make([]*frame, n)
for i := 0; i < len(p.consumedStream.frames); i++ {
f := &frame{}
if err := p.srcStream.RecvMsg(f); err != nil {
p.consumedStream.err = err
break
}
p.consumedStream.frames[i] = f
}
return p.consumedStream.frames, nil
}
func (f *frame) Payload() []byte {
return f.payload
}
func (f *frame) Modify(payload []byte) error {
f.Lock()
defer f.Unlock()
if f.consumed {
return errors.New("frame has already been consumed")
}
if f.payload == nil {
return errors.New("frame payload is empty")
}
f.payload = payload
return nil
}
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