api/handler/rpc: improvements and fixes (#1535)

* api/handler/rpc: fix empty body case
* api/handler/rpc: copy all request headers to metadata

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

api/handler/rpc/rpc.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"io"
 	"net/http"
+	"net/textproto"
 	"strconv"
 	"strings"
 
@@ -119,6 +120,13 @@ func (h *rpcHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	// fill contex with http headers
 	md["Host"] = r.Host
+	md["Method"] = r.Method
+	// get canonical headers
+	for k, _ := range r.Header {
+		// may be need to get all values for key like r.Header.Values() provide in go 1.14
+		md[textproto.CanonicalMIMEHeaderKey(k)] = r.Header.Get(k)
+	}
+
 	// merge context with overwrite
 	cx = metadata.MergeContext(cx, md, true)
 
@@ -384,8 +392,6 @@ func requestPayload(r *http.Request) ([]byte, error) {
 		}
 		if b := buf.Bytes(); len(b) > 0 {
 			bodybuf = b
-		} else {
-			return []byte{}, nil
 		}
 		if bodydst == "" || bodydst == "*" {
 			if out, err = jsonpatch.MergeMergePatches(out, bodybuf); err == nil {