Use a conventional JSON POST API rather than go net/rpc

net/rpc doesn't automatically handle reconnecting and we have better
logging and metrics infrastructure for monitoring HTTP apis.

src/github.com/matrix-org/dendrite/roomserver/api/query.go

@@ -1,7 +1,11 @@
 package api
 
 import (
+	"bytes"
+	"encoding/json"
+	"fmt"
 	"github.com/matrix-org/gomatrixserverlib"
+	"net/http"
 )
 
 // StateKeyTuple is a pair of an event type and state_key.
@@ -38,34 +42,53 @@ type RoomserverQueryAPI interface {
 	) error
 }
 
-// RPCServer is used to register a roomserver implementation with an RPC server.
-type RPCServer interface {
-	RegisterName(name string, rcvr interface{}) error
+// RoomserverQueryLatestEventsAndStatePath is the HTTP path for the QueryLatestEventsAndState API.
+const RoomserverQueryLatestEventsAndStatePath = "/api/Roomserver/QueryLatestEventsAndState"
+
+// NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
+// If httpClient is nil then it uses the http.DefaultClient
+func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client) RoomserverQueryAPI {
+	if httpClient == nil {
+		httpClient = http.DefaultClient
+	}
+	return &httpRoomserverQueryAPI{roomserverURL, *httpClient}
 }
 
-// RegisterRoomserverQueryAPI registers a RoomserverQueryAPI implementation with an RPC server.
-func RegisterRoomserverQueryAPI(rpcServer RPCServer, roomserver RoomserverQueryAPI) error {
-	return rpcServer.RegisterName("Roomserver", roomserver)
-}
-
-// RPCClient is used to invoke roomserver APIs on a remote server.
-type RPCClient interface {
-	Call(serviceMethod string, args interface{}, reply interface{}) error
-}
-
-// NewRoomserverQueryAPIFromClient creates a new query API from an RPC client.
-func NewRoomserverQueryAPIFromClient(client RPCClient) RoomserverQueryAPI {
-	return &remoteRoomserver{client}
-}
-
-type remoteRoomserver struct {
-	client RPCClient
+type httpRoomserverQueryAPI struct {
+	roomserverURL string
+	httpClient    http.Client
 }
 
 // QueryLatestEventsAndState implements RoomserverQueryAPI
-func (r *remoteRoomserver) QueryLatestEventsAndState(
+func (h *httpRoomserverQueryAPI) QueryLatestEventsAndState(
 	request *QueryLatestEventsAndStateRequest,
 	response *QueryLatestEventsAndStateResponse,
 ) error {
-	return r.client.Call("Roomserver.QueryLatestEventsAndState", request, response)
+	apiURL := h.roomserverURL + RoomserverQueryLatestEventsAndStatePath
+	return postJSON(h.httpClient, apiURL, request, response)
+}
+
+func postJSON(httpClient http.Client, apiURL string, request, response interface{}) error {
+	jsonBytes, err := json.Marshal(request)
+	if err != nil {
+		return err
+	}
+	res, err := httpClient.Post(apiURL, "application/json", bytes.NewReader(jsonBytes))
+	if res != nil {
+		defer res.Body.Close()
+	}
+	if err != nil {
+		return err
+	}
+	if res.StatusCode != 200 {
+		var errorBody struct {
+			Message string `json:"message"`
+		}
+		if err = json.NewDecoder(res.Body).Decode(&errorBody); err != nil {
+			return err
+		} else {
+			return fmt.Errorf("api: %d: %s", res.StatusCode, errorBody.Message)
+		}
+	}
+	return json.NewDecoder(res.Body).Decode(response)
 }

src/github.com/matrix-org/dendrite/roomserver/query/query.go

@@ -1,8 +1,12 @@
 package query
 
 import (
+	"encoding/json"
 	"fmt"
 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/util"
+	"github.com/prometheus/client_golang/prometheus"
+	"net/http"
 )
 
 // RoomserverQueryAPI is an implemenation of RoomserverQueryAPI
@@ -16,3 +20,24 @@ func (r *RoomserverQueryAPI) QueryLatestEventsAndState(
 ) error {
 	return fmt.Errorf("Not Implemented")
 }
+
+func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
+	servMux.Handle(
+		api.RoomserverQueryLatestEventsAndStatePath,
+		makeAPI("query_latest_events_and_state", func(req *http.Request) util.JSONResponse {
+			var request api.QueryLatestEventsAndStateRequest
+			var response api.QueryLatestEventsAndStateResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.QueryLatestEventsAndState(&request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: 200, JSON: &response}
+		}),
+	)
+}
+
+func makeAPI(metric string, apiFunc func(req *http.Request) util.JSONResponse) http.Handler {
+	return prometheus.InstrumentHandler(metric, util.MakeJSONAPI(util.NewJSONRequestHandler(apiFunc)))
+}

src/github.com/matrix-org/dendrite/roomserver/roomserver-integration-tests/main.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
-	"net/rpc"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -210,12 +209,8 @@ func testRoomServer(input []string, wantOutput []string) {
 	cmd.Stderr = os.Stderr
 
 	gotOutput, err := runAndReadFromTopic(cmd, outputTopic, 1, func() {
-		client, err := rpc.DialHTTP("tcp", roomserverAddr)
-		if err != nil {
-			panic(err)
-		}
-		queryAPI := api.NewRoomserverQueryAPIFromClient(client)
-		if err = queryAPI.QueryLatestEventsAndState(
+		queryAPI := api.NewRoomserverQueryAPIHTTP("http://"+roomserverAddr, nil)
+		if err := queryAPI.QueryLatestEventsAndState(
 			&api.QueryLatestEventsAndStateRequest{},
 			&api.QueryLatestEventsAndStateResponse{},
 		); err != nil {

src/github.com/matrix-org/dendrite/roomserver/roomserver/roomserver.go

@@ -2,13 +2,11 @@ package main
 
 import (
 	"fmt"
-	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/roomserver/input"
 	"github.com/matrix-org/dendrite/roomserver/query"
 	"github.com/matrix-org/dendrite/roomserver/storage"
 	sarama "gopkg.in/Shopify/sarama.v1"
 	"net/http"
-	"net/rpc"
 	"os"
 	"strings"
 )
@@ -51,11 +49,7 @@ func main() {
 
 	queryAPI := query.RoomserverQueryAPI{}
 
-	if err = api.RegisterRoomserverQueryAPI(rpc.DefaultServer, &queryAPI); err != nil {
-		panic(err)
-	}
-
-	rpc.HandleHTTP()
+	queryAPI.SetupHTTP(http.DefaultServeMux)
 
 	fmt.Println("Started roomserver")
 

vendor/manifest

@@ -98,7 +98,7 @@
 		{
 			"importpath": "github.com/matrix-org/util",
 			"repository": "https://github.com/matrix-org/util",
-			"revision": "ccef6dc7c24a7c896d96b433a9107b7c47ecf828",
+			"revision": "28bd7491c8aafbf346ca23821664f0f9911ef52b",
 			"branch": "master"
 		},
 		{

vendor/src/github.com/matrix-org/util/context.go

@@ -25,11 +25,13 @@ func GetRequestID(ctx context.Context) string {
 // ctxValueLogger is the key to extract the logrus Logger.
 const ctxValueLogger = contextKeys("logger")
 
-// GetLogger retrieves the logrus logger from the supplied context. Returns nil if there is no logger.
+// GetLogger retrieves the logrus logger from the supplied context. Always returns a logger,
+// even if there wasn't one originally supplied.
 func GetLogger(ctx context.Context) *log.Entry {
 	l := ctx.Value(ctxValueLogger)
 	if l == nil {
-		return nil
+		// Always return a logger so callers don't need to constantly nil check.
+		return log.WithField("context", "missing")
 	}
 	return l.(*log.Entry)
 }

vendor/src/github.com/matrix-org/util/json.go

@@ -58,6 +58,21 @@ type JSONRequestHandler interface {
 	OnIncomingRequest(req *http.Request) JSONResponse
 }
 
+// jsonRequestHandlerWrapper is a wrapper to allow in-line functions to conform to util.JSONRequestHandler
+type jsonRequestHandlerWrapper struct {
+	function func(req *http.Request) JSONResponse
+}
+
+// OnIncomingRequest implements util.JSONRequestHandler
+func (r *jsonRequestHandlerWrapper) OnIncomingRequest(req *http.Request) JSONResponse {
+	return r.function(req)
+}
+
+// NewJSONRequestHandler converts the given OnIncomingRequest function into a JSONRequestHandler
+func NewJSONRequestHandler(f func(req *http.Request) JSONResponse) JSONRequestHandler {
+	return &jsonRequestHandlerWrapper{f}
+}
+
 // Protect panicking HTTP requests from taking down the entire process, and log them using
 // the correct logger, returning a 500 with a JSON response rather than abruptly closing the
 // connection. The http.Request MUST have a ctxValueLogger.

vendor/src/github.com/matrix-org/util/json_test.go

@@ -164,8 +164,8 @@ func TestGetLogger(t *testing.T) {
 
 	noLoggerInReq, _ := http.NewRequest("GET", "http://example.com/foo", nil)
 	ctxLogger = GetLogger(noLoggerInReq.Context())
-	if ctxLogger != nil {
-		t.Errorf("TestGetLogger wanted nil logger, got '%v'", ctxLogger)
+	if ctxLogger == nil {
+		t.Errorf("TestGetLogger wanted logger, got nil")
 	}
 }