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Overview ¶
Package proxy provides a reverse proxy handler for gRPC.
The implementation allows a `grpc.Server` to pass a received ServerStream to a ClientStream without understanding the semantics of the messages exchanged. It basically provides a transparent reverse-proxy.
This package is intentionally generic, exposing a `StreamDirector` function that allows users of this package to implement whatever logic of backend-picking, dialing and service verification to perform.
See examples on documented functions.
Index ¶
- Variables
- func CodecWithParent(fallback encoding.Codec) encoding.Codec
- func NewCodec() encoding.Codec
- func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, ...)
- func RegisterStreamHandlers(server *grpc.Server, serviceName string, ...)
- func TransparentHandler(director StreamDirector) grpc.StreamHandler
- type Destination
- type StreamDirector
- type StreamParameters
- type StreamPeeker
Examples ¶
Constants ¶
This section is empty.
Variables ¶
var ErrInvalidPeekCount = errors.New("peek count must be greater than zero")
ErrInvalidPeekCount indicates the director function requested an invalid peek quanity
Functions ¶
func CodecWithParent ¶
CodecWithParent returns a proxying encoding.Codec with a user provided codec as parent.
This codec is *crucial* to the functioning of the proxy. It allows the proxy server to be oblivious to the schema of the forwarded messages. It basically treats a gRPC message frame as raw bytes. However, if the server handler, or the client caller are not proxy-internal functions it will fall back to trying to decode the message using a fallback codec.
func NewCodec ¶
NewCodec returns a proxying encoding.Codec with the default protobuf codec as parent.
See CodecWithParent.
func RegisterService ¶
func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, methodNames ...string)
RegisterService sets up a proxy handler for a particular gRPC service and method. The behaviour is the same as if you were registering a handler method, e.g. from a codegenerated pb.go file.
This can *only* be used if the `server` also uses grpcproxy.CodecForServer() ServerOption.
Example ¶
package main
import (
"gitlab.com/gitlab-org/gitaly/v14/internal/praefect/grpc-proxy/proxy"
"google.golang.org/grpc"
)
var director proxy.StreamDirector
func main() {
// A gRPC server with the proxying codec enabled.
server := grpc.NewServer(grpc.ForceServerCodec(proxy.NewCodec()))
// Register a TestService with 4 of its methods explicitly.
proxy.RegisterService(server, director,
"mwitkow.testproto.TestService",
"PingEmpty", "Ping", "PingError", "PingList")
}
Output:
func RegisterStreamHandlers ¶
func RegisterStreamHandlers(server *grpc.Server, serviceName string, streamers map[string]grpc.StreamHandler)
RegisterStreamHandlers sets up stream handlers for a set of gRPC methods for a given service. streamers is a map of method to grpc.StreamHandler eg:
streamHandler := func(srv interface{}, stream ServerStream) error {
/** do some stuff **/
return nil
}
RegisterStreamHandlers(grpcServer, "MyGrpcService", map[string]grpc.StreamHandler{"Method1": streamHandler}) note: multiple calls with the same serviceName will result in a fatal
func TransparentHandler ¶
func TransparentHandler(director StreamDirector) grpc.StreamHandler
TransparentHandler returns a handler that attempts to proxy all requests that are not registered in the server. The indented use here is as a transparent proxy, where the server doesn't know about the services implemented by the backends. It should be used as a `grpc.UnknownServiceHandler`.
This can *only* be used if the `server` also uses grpcproxy.CodecForServer() ServerOption.
Example ¶
package main
import (
"gitlab.com/gitlab-org/gitaly/v14/internal/praefect/grpc-proxy/proxy"
"google.golang.org/grpc"
)
var director proxy.StreamDirector
func main() {
grpc.NewServer(
grpc.ForceServerCodec(proxy.NewCodec()),
grpc.UnknownServiceHandler(proxy.TransparentHandler(director)))
}
Output:
Types ¶
type Destination ¶
type Destination struct {
// Ctx is the context used for the connection.
Ctx context.Context
// Conn is the GRPC client connection.
Conn *grpc.ClientConn
// Msg is the initial message which shall be sent to the destination. This is used in order
// to allow for re-writing the header message.
Msg []byte
// ErrHandler is invoked when proxying to the destination fails. It can be used to swallow
// errors in case proxying failures are considered to be non-fatal. If all errors are
// swallowed, the proxied RPC will be successful.
ErrHandler func(error) error
}
Destination contains a client connection as well as a rewritten protobuf message
type StreamDirector ¶
type StreamDirector func(ctx context.Context, fullMethodName string, peeker StreamPeeker) (*StreamParameters, error)
StreamDirector returns a gRPC ClientConn to be used to forward the call to.
The presence of the `Context` allows for rich filtering, e.g. based on Metadata (headers). If no handling is meant to be done, a `codes.NotImplemented` gRPC error should be returned.
The context returned from this function should be the context for the *outgoing* (to backend) call. In case you want to forward any Metadata between the inbound request and outbound requests, you should do it manually. However, you *must* propagate the cancel function (`context.WithCancel`) of the inbound context to the one returned.
It is worth noting that the StreamDirector will be fired *after* all server-side stream interceptors are invoked. So decisions around authorization, monitoring etc. are better to be handled there.
See the rather rich example.
Example ¶
Provide sa simple example of a director that shields internal services and dials a staging or production backend. This is a *very naive* implementation that creates a new connection on every request. Consider using pooling.
package main
import (
"context"
"strings"
"gitlab.com/gitlab-org/gitaly/v14/internal/metadata"
"gitlab.com/gitlab-org/gitaly/v14/internal/praefect/grpc-proxy/proxy"
"google.golang.org/grpc"
"google.golang.org/grpc/codes"
grpc_metadata "google.golang.org/grpc/metadata"
"google.golang.org/grpc/status"
)
var director proxy.StreamDirector
func main() {
director = func(ctx context.Context, fullMethodName string, _ proxy.StreamPeeker) (*proxy.StreamParameters, error) {
// Make sure we never forward internal services.
if strings.HasPrefix(fullMethodName, "/com.example.internal.") {
return nil, status.Errorf(codes.Unimplemented, "Unknown method")
}
md, ok := grpc_metadata.FromIncomingContext(ctx)
if ok {
// Decide on which backend to dial
if val, exists := md[":authority"]; exists && val[0] == "staging.api.example.com" {
// Make sure we use DialContext so the dialing can be cancelled/time out together with the context.
conn, err := grpc.DialContext(ctx, "api-service.staging.svc.local", grpc.WithDefaultCallOptions(grpc.ForceCodec(proxy.NewCodec())))
return proxy.NewStreamParameters(proxy.Destination{
Conn: conn,
Ctx: metadata.IncomingToOutgoing(ctx),
}, nil, nil, nil), err
} else if val, exists := md[":authority"]; exists && val[0] == "api.example.com" {
conn, err := grpc.DialContext(ctx, "api-service.prod.svc.local", grpc.WithDefaultCallOptions(grpc.ForceCodec(proxy.NewCodec())))
return proxy.NewStreamParameters(proxy.Destination{
Conn: conn,
Ctx: metadata.IncomingToOutgoing(ctx),
}, nil, nil, nil), err
}
}
return nil, status.Errorf(codes.Unimplemented, "Unknown method")
}
}
Output:
type StreamParameters ¶
type StreamParameters struct {
// contains filtered or unexported fields
}
StreamParameters encapsulates streaming parameters the praefect coordinator returns to the proxy handler
func NewStreamParameters ¶
func NewStreamParameters(primary Destination, secondaries []Destination, reqFinalizer func() error, callOpts []grpc.CallOption) *StreamParameters
NewStreamParameters returns a new instance of StreamParameters
func (*StreamParameters) CallOptions ¶
func (s *StreamParameters) CallOptions() []grpc.CallOption
CallOptions returns call options
func (*StreamParameters) Primary ¶
func (s *StreamParameters) Primary() Destination
nolint: revive,stylecheck // This is unintentionally missing documentation.
func (*StreamParameters) RequestFinalizer ¶
func (s *StreamParameters) RequestFinalizer() error
RequestFinalizer calls the request finalizer
func (*StreamParameters) Secondaries ¶
func (s *StreamParameters) Secondaries() []Destination
nolint: revive,stylecheck // This is unintentionally missing documentation.
type StreamPeeker ¶
type StreamPeeker interface {
// Peek allows a director to peek one message into the request stream without
// removing those messages from the stream that will be forwarded to
// the backend server.
Peek() (frame []byte, _ error)
}
StreamPeeker abstracts away the gRPC stream being forwarded so that it can be inspected and modified.
Source Files