server/prpc: updated server according to protocol

server/prpc/server.go

Index: server/prpc/server.go
diff --git a/server/prpc/server.go b/server/prpc/server.go
index df43971e712a79a6b1a1ac4ed34302ea92bf26fd..0732adea009e79bb6bbaf18ded97519de2fffb62 100644
--- a/server/prpc/server.go
+++ b/server/prpc/server.go
@@ -5,6 +5,7 @@
 package prpc
 
 import (
+	"fmt"
 	"net/http"
 	"sort"
 	"sync"
@@ -12,7 +13,9 @@ import (
 	"github.com/julienschmidt/httprouter"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
 
+	"github.com/luci/luci-go/common/logging"
 	"github.com/luci/luci-go/server/auth"
 	"github.com/luci/luci-go/server/middleware"
 )
@@ -74,7 +77,8 @@ func (s *Server) authenticate(base middleware.Base) middleware.Base {
 			c = auth.SetAuthenticator(c, a)
 			c, err := a.Authenticate(c, r)
 			if err != nil {
-				writeError(c, w, withStatus(err, http.StatusUnauthorized))
+				res := errResponse(codes.Unauthenticated, http.StatusUnauthorized, err.Error())
+				res.write(c, w)
 				return
 			}
 			h(c, w, r, p)
@@ -82,8 +86,9 @@ func (s *Server) authenticate(base middleware.Base) middleware.Base {
 	}
 }
 
-// InstallHandlers installs HTTP POST handlers at
-// /prpc/{service_name}/{method_name} for all registered services.
+// InstallHandlers installs HTTP handlers at /prpc/:service/:method.
+// See https://godoc.org/github.com/luci/luci-go/common/prpc#hdr-Protocol
+// for pRPC protocol.
 func (s *Server) InstallHandlers(r *httprouter.Router, base middleware.Base) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -92,11 +97,52 @@ func (s *Server) InstallHandlers(r *httprouter.Router, base middleware.Base) {
 		base = s.authenticate(base)
 	}
 
-	for _, service := range s.services {
-		for _, m := range service.methods {
-			m.InstallHandlers(r, base)
-		}
+	const path = "/prpc/:service/:method"
+	handle := base(s.handle)
+	r.POST(path, handle)

[dnj (Google), 2016/01/26 16:13:57]

Do we need to support all of these methods? I thought we were only doing POST.
If not, leave the others for httprouter to 404.

Is StatusMethodNotAllowed important here? If so, we're not setting the Allow
headers accordingly. I don't think there's any value in returning
MethodNotAllowed over 404, though, so let's just not register endpoints we don't
have.

[nodir, 2016/01/26 18:01:07]

We had this discussion and decided to handle all methods and include grpc code
in the response.
Included Allow in response.

[dnj, 2016/01/26 18:50:27]

Seems pointless, but OK. IMO either a client knows what it's doing (POST,
protocol, etc.) or it doesn't, and in the latter case this won't help it at all.
I see no value at all to being partially RESTful. We're abusing HTTP/POST here
to implement RPC. I don't think there's any value in trying to have conformance
in this single minor area, moreso b/c basically nothing at all will consume this
response code meaningfully.

If you're going to do this, implement a simple separate handle method that
returns StatusMethodNotAllowed.

r.POST(path, handle)
r.GET(path, handleNotAllowed)
etc.

[nodir, 2016/01/26 19:06:09]

ah, Server.handle was exported at some point, that's why it checked method. 
Anyway, removed other methods and updated protocol.

+	r.GET(path, handle)
+	r.PUT(path, handle)
+	r.DELETE(path, handle)
+	r.PATCH(path, handle)
+}
+
+// handle handles RPCs.
+// See https://godoc.org/github.com/luci/luci-go/common/prpc#hdr-Protocol
+// for pRPC protocol.
+func (s *Server) handle(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params) {
+	res := s.respond(c, w, r, p)

[dnj (Google), 2016/01/26 16:13:57]

nit: pull service/method out of params up front, then pass them to respond().

[nodir, 2016/01/26 18:01:07]

Done.

+
+	c = logging.SetFields(c, logging.Fields{
+		"Service": p.ByName("service"),
+		"Method":  p.ByName("method"),
+	})
+	res.write(c, w)
+}
+
+func (s *Server) respond(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params) *response {
+	if r.Method != "POST" {
+		return errResponse(codes.Unimplemented, http.StatusMethodNotAllowed, "HTTP method must be POST")
 	}
+
+	serviceName := p.ByName("service")
+	service := s.services[serviceName]
+	if service == nil {
+		return errResponse(
+			codes.Unimplemented,
+			http.StatusNotImplemented,
+			fmt.Sprintf("service %q is not implemented", serviceName))
+	}
+
+	methodName := p.ByName("method")
+	method := service.methods[methodName]
+	if method == nil {
+		return errResponse(
+			codes.Unimplemented,
+			http.StatusNotImplemented,
+			fmt.Sprintf("method %q in service %q is not implemented", methodName, serviceName))
+	}
+
+	return method.handle(c, w, r)
 }
 
 // ServiceNames returns a sorted list of full names of all registered services.