refactor: provide better public API, enforce proxying mode

Provide more clear public API with options, also enforce proxying mode
with options (not by looking at number of backends).

One2one and one2many have some differences: one2one is transparent and
oen2many might inject additional metadata, wrap errors and responses,
etc., so if client expects one2many format, it should get it even with
one upstream.

Also provide method to guess streamed methods via function so any policy
can be implemented (inspecting grpc server description, looking at
method name prefix/suffix, etc.)

No functional changes, just shuffling code around.

Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>

.github/workflows/go.yml

@@ -37,6 +37,7 @@ jobs:
       with:
         token: ${{secrets.CODECOV_TOKEN}}
         file: ./coverage.txt
+      if: github.event_name == 'push'
 
   lint:
     name: Lint

README.md

@@ -74,7 +74,10 @@ locally:
 ```go
 server := grpc.NewServer(
     grpc.CustomCodec(proxy.Codec()),
-    grpc.UnknownServiceHandler(proxy.TransparentHandler(director)))
+    grpc.UnknownServiceHandler(
+        proxy.TransparentHandler(director),
+        proxy.WithMode(proxy.One2One),
+    ))
 pb_test.RegisterTestServiceServer(server, &testImpl{})
 ```
 

proxy/DOC.md

@@ -46,26 +46,26 @@ nolint: staticcheck
 #### func  RegisterService
 
 ```go
-func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, methodNames ...string)
+func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, options ...Option)
 ```
 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,
+method. The behavior 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()
+This can *only* be used if the `server` also uses grpc.CustomCodec()
 ServerOption.
 
 #### func  TransparentHandler
 
 ```go
-func TransparentHandler(director StreamDirector) grpc.StreamHandler
+func TransparentHandler(director StreamDirector, options ...Option) 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()
+This can *only* be used if the `server` also uses grpc.CustomCodec()
 ServerOption.
 
 #### type Backend
@@ -115,6 +115,127 @@ When proxying one-to-many and aggregating results, Backend might be used to
 append additional fields to upstream response to support more complicated
 proxying.
 
+#### type Mode
+
+```go
+type Mode int
+```
+
+Mode specifies proxying mode: one2one (transparent) or one2many (aggregation,
+error wrapping).
+
+```go
+const (
+	One2One Mode = iota
+	One2Many
+)
+```
+Mode constants.
+
+#### type Option
+
+```go
+type Option func(*handlerOptions)
+```
+
+Option configures gRPC proxy
+
+#### func  WithMethodNames
+
+```go
+func WithMethodNames(methodNames ...string) Option
+```
+WithMethodNames configures list of method names to proxy for non-transparent
+handler.
+
+#### func  WithMode
+
+```go
+func WithMode(mode Mode) Option
+```
+WithMode sets proxying mode: One2One or One2Many.
+
+Default mode is One2One.
+
+#### func  WithStreamedDetector
+
+```go
+func WithStreamedDetector(detector StreamedDetectorFunc) Option
+```
+WithStreamedDetector configures a function to detect streamed methods.
+
+This is only important for one2many proxying.
+
+#### func  WithStreamedMethodNames
+
+```go
+func WithStreamedMethodNames(streamedMethodNames ...string) Option
+```
+WithStreamedMethodNames configures list of streamed method names.
+
+This is only important for one2many proxying. This option can't be used with
+TransparentHandler.
+
+#### type ServerStreamWrapper
+
+```go
+type ServerStreamWrapper struct {
+	grpc.ServerStream
+}
+```
+
+ServerStreamWrapper wraps grpc.ServerStream and adds locking to send path
+
+#### func (*ServerStreamWrapper) SendHeader
+
+```go
+func (wrapper *ServerStreamWrapper) SendHeader(md metadata.MD) error
+```
+SendHeader sends the header metadata. The provided md and headers set by
+SetHeader() will be sent. It fails if called multiple times.
+
+#### func (*ServerStreamWrapper) SendMsg
+
+```go
+func (wrapper *ServerStreamWrapper) SendMsg(m interface{}) error
+```
+SendMsg sends a message. On error, SendMsg aborts the stream and the error is
+returned directly.
+
+SendMsg blocks until:
+
+    - There is sufficient flow control to schedule m with the transport, or
+    - The stream is done, or
+    - The stream breaks.
+
+SendMsg does not wait until the message is received by the client. An untimely
+stream closure may result in lost messages.
+
+It is safe to have a goroutine calling SendMsg and another goroutine calling
+RecvMsg on the same stream at the same time, but it is not safe to call SendMsg
+on the same stream in different goroutines.
+
+#### func (*ServerStreamWrapper) SetHeader
+
+```go
+func (wrapper *ServerStreamWrapper) SetHeader(md metadata.MD) error
+```
+SetHeader sets the header metadata. It may be called multiple times. When call
+multiple times, all the provided metadata will be merged. All the metadata will
+be sent out when one of the following happens:
+
+    - ServerStream.SendHeader() is called;
+    - The first response is sent out;
+    - An RPC status is sent out (error or success).
+
+#### func (*ServerStreamWrapper) SetTrailer
+
+```go
+func (wrapper *ServerStreamWrapper) SetTrailer(md metadata.MD)
+```
+SetTrailer sets the trailer metadata which will be sent with the RPC status.
+When called more than once, all the provided metadata will be merged.
+
 #### type SingleBackend
 
 ```go
@@ -186,3 +307,12 @@ stream interceptors are invoked. So decisions around authorization, monitoring
 etc. are better to be handled there.
 
 See the rather rich example.
+
+#### type StreamedDetectorFunc
+
+```go
+type StreamedDetectorFunc func(fullMethodName string) bool
+```
+
+StreamedDetectorFunc reports is gRPC is doing streaming (only for one2many
+proxying).

proxy/examples_test.go

@@ -25,8 +25,10 @@ func ExampleRegisterService() {
 	// Register a TestService with 4 of its methods explicitly.
 	proxy.RegisterService(server, director,
 		"talos.testproto.TestService",
-		[]string{"PingEmpty", "Ping", "PingError", "PingList"},
-		[]string{"PingList"})
+		proxy.WithMode(proxy.One2Many),
+		proxy.WithMethodNames("PingEmpty", "Ping", "PingError", "PingList"),
+		proxy.WithStreamedMethodNames("PingList"),
+	)
 }
 
 func ExampleTransparentHandler() {