server/prpc: updated server according to protocol

server/prpc/response.go

Index: server/prpc/response.go
diff --git a/server/prpc/response.go b/server/prpc/response.go
new file mode 100644
index 0000000000000000000000000000000000000000..bca03893ad2845cbf25769a053254fc984775e16
--- /dev/null
+++ b/server/prpc/response.go
@@ -0,0 +1,78 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package prpc
+
+import (
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"golang.org/x/net/context"
+	"google.golang.org/grpc/codes"
+
+	"github.com/luci/luci-go/common/logging"
+	"github.com/luci/luci-go/common/prpc"
+)
+
+var newLineBytes = []byte{'\n'}
+
+// response is a pRPC server response.
+// All pRPC responses must be written using write.
+type response struct {
+	code   codes.Code // defaults to OK
+	status int        // defaults to status derived from code.
+	header http.Header
+	body   []byte
+}
+
+// errResponse creates a response with an error.
+func errResponse(code codes.Code, status int, format string, a ...interface{}) *response {
+	return &response{
+		code:   code,
+		status: status,
+		header: http.Header{
+			headerContentType: []string{"text/plain"},
+		},
+		body: []byte(fmt.Sprintf(format+"\n", a...)),
+	}
+}
+
+// escapeFmt escapes format characters in a string destined for a format
+// parameter. This is used to sanitize externally-supplied strings that are
+// passed verbatim into errResponse.
+func escapeFmt(s string) string {
+	return strings.Replace(s, "%", "%%", -1)
+}
+
+// write writes r to w.
+func (r *response) write(c context.Context, w http.ResponseWriter) {
+	body := r.body
+	switch r.code {
+	case codes.Internal, codes.Unknown:
+		// res.body is error message.
+		logging.Fields{
+			"code": r.code,
+		}.Errorf(c, "%s", body)
+		body = []byte("Internal Server Error\n")
+	}
+
+	for h, vs := range r.header {
+		w.Header()[h] = vs
+	}
+	w.Header().Set(prpc.HeaderGRPCCode, strconv.Itoa(int(r.code)))
+
+	status := r.status
+	if status == 0 {
+		status = codeStatus(r.code)
+	}
+	w.WriteHeader(status)
+
+	if _, err := w.Write(body); err != nil {
+		logging.WithError(err).Errorf(c, "Could not respond")
+		// The header is already written. There is nothing more we can do.
+		return
+	}
+}