Revert "Make all "grpc-" metadata field names reserved (#1391)" (#1400)

This reverts commit 3ddcdc268d88595eb2f3721f7dc87970a6c3ab6e.

transport/http_util.go

@@ -121,14 +121,19 @@ func isReservedHeader(hdr string) bool {
 	if hdr != "" && hdr[0] == ':' {
 		return true
 	}
-	if strings.HasPrefix(hdr, "grpc-") {
-		return true
-	}
 	switch hdr {
-	case "content-type", "te":
+	case "content-type",
+		"grpc-message-type",
+		"grpc-encoding",
+		"grpc-message",
+		"grpc-status",
+		"grpc-timeout",
+		"grpc-status-details-bin",
+		"te":
 		return true
+	default:
+		return false
 	}
-	return false
 }
 
 // isWhitelistedPseudoHeader checks whether hdr belongs to HTTP2 pseudoheaders

transport/transport_test.go

@@ -1577,7 +1577,7 @@ func TestIsReservedHeader(t *testing.T) {
 		{"grpc-encoding", true},
 		{"grpc-message", true},
 		{"grpc-status", true},
-		{"grpc-anything-else99999", true},
+		{"grpc-timeout", true},
 		{"te", true},
 	}
 	for _, tt := range tests {