fix(tracestate): drop right-most member in tracestate

trace/tracestate.go

@@ -179,17 +179,14 @@ func (ts TraceState) Insert(key, value string) (TraceState, error) {
 	}
 
 	cTS := ts.Delete(key)
-	if cTS.Len()+1 > maxListMembers {
-		// TODO (MrAlias): When the second version of the Trace Context
-		// specification is published this needs to not return an error.
-		// Instead it should drop the "right-most" member and insert the new
-		// member at the front.
-		//
-		// https://github.com/w3c/trace-context/pull/448
-		return ts, fmt.Errorf("failed to insert: %w", errMemberNumber)
+	if cTS.Len()+1 <= maxListMembers {
+		cTS.list = append(cTS.list, member{})
 	}
-
-	cTS.list = append(cTS.list, member{})
+	// if tracestate's members > maxListMembers, defaultly
+	// it should drop the "right-most" member and insert the new
+	// member at the front.
+	//
+	// https://github.com/w3c/trace-context/pull/448
 	copy(cTS.list[1:], cTS.list)
 	cTS.list[0] = m
 

trace/tracestate_test.go

@@ -443,14 +443,21 @@ func TestTraceStateInsert(t *testing.T) {
 			err:        errInvalidKey,
 		},
 		{
-			name:       "too many entries",
+			name:       "drop the right-most member(oldest) in queue",
 			tracestate: maxMembers,
 			key:        "keyx",
 			value:      "valx",
-			expected:   maxMembers,
-			err:        errMemberNumber,
-		},
-	}
+			expected: func() TraceState {
+				var traceState TraceState
+				traceState.list = make([]member, 0, len(maxMembers.list))
+				traceState.list = append(traceState.list, member{
+					Key:   "keyx",
+					Value: "valx",
+				})
+				traceState.list = append(traceState.list, maxMembers.list[:len(maxMembers.list)-1]...)
+				return traceState
+			}(),
+		}}
 
 	for _, tc := range testCases {
 		actual, err := tc.tracestate.Insert(tc.key, tc.value)