improve logger middleware error value logging

Author: aldas

middleware/logger.go

@@ -5,7 +5,6 @@ package middleware
 
 import (
 	"bytes"
-	"encoding/json"
 	"io"
 	"strconv"
 	"strings"
@@ -375,10 +374,7 @@ func LoggerWithConfig(config LoggerConfig) echo.MiddlewareFunc {
 					return buf.WriteString(s)
 				case "error":
 					if err != nil {
-						// Error may contain invalid JSON e.g. `"`
-						b, _ := json.Marshal(err.Error())
-						b = b[1 : len(b)-1]
-						return buf.Write(b)
+						return writeJSONSafeString(buf, err.Error())
 					}
 				case "latency":
 					l := stop.Sub(start)

middleware/logger_test.go

@@ -47,6 +47,21 @@ func TestLoggerDefaultMW(t *testing.T) {
 			whenError: errors.New("error"),
 			expect:    `{"time":"2020-04-28T01:26:40Z","id":"","remote_ip":"192.0.2.1","host":"example.com","method":"GET","uri":"/","user_agent":"","status":500,"error":"error","latency":1,"latency_human":"1µs","bytes_in":0,"bytes_out":36}` + "\n",
 		},
+		{
+			name:      "error with invalid UTF-8 sequences",
+			whenError: errors.New("invalid data: \xFF\xFE"),
+			expect:    `{"time":"2020-04-28T01:26:40Z","id":"","remote_ip":"192.0.2.1","host":"example.com","method":"GET","uri":"/","user_agent":"","status":500,"error":"invalid data: \ufffd\ufffd","latency":1,"latency_human":"1µs","bytes_in":0,"bytes_out":36}` + "\n",
+		},
+		{
+			name:      "error with JSON special characters (quotes and backslashes)",
+			whenError: errors.New(`error with "quotes" and \backslash`),
+			expect:    `{"time":"2020-04-28T01:26:40Z","id":"","remote_ip":"192.0.2.1","host":"example.com","method":"GET","uri":"/","user_agent":"","status":500,"error":"error with \"quotes\" and \\backslash","latency":1,"latency_human":"1µs","bytes_in":0,"bytes_out":36}` + "\n",
+		},
+		{
+			name:      "error with control characters (newlines and tabs)",
+			whenError: errors.New("error\nwith\nnewlines\tand\ttabs"),
+			expect:    `{"time":"2020-04-28T01:26:40Z","id":"","remote_ip":"192.0.2.1","host":"example.com","method":"GET","uri":"/","user_agent":"","status":500,"error":"error\nwith\nnewlines\tand\ttabs","latency":1,"latency_human":"1µs","bytes_in":0,"bytes_out":36}` + "\n",
+		},
 		{
 			name:           "ok, remote_ip from X-Real-Ip header",
 			whenHeader:     map[string]string{echo.HeaderXRealIP: "127.0.0.1"},