fix: concurrent writes to headers of http_response (#804)

inputs/http_response/http_response.go

@@ -91,6 +91,10 @@ func (ins *Instance) Init() error {
 	if ins.HTTPCommonConfig.Headers == nil {
 		ins.HTTPCommonConfig.Headers = make(map[string]string)
 	}
+	// compatible with old config
+	for i := 0; i < len(ins.Headers); i += 2 {
+		ins.HTTPCommonConfig.Headers[ins.Headers[i]] = ins.Headers[i+1]
+	}
 	if len(ins.ExpectResponseRegularExpression) > 0 {
 		ins.regularExpression = regexp.MustCompile(ins.ExpectResponseRegularExpression)
 	}
@@ -241,11 +245,6 @@ func (ins *Instance) httpGather(target string) (map[string]string, map[string]in
 	if err != nil {
 		return nil, nil, err
 	}
-
-	// compatible with old config
-	for i := 0; i < len(ins.Headers); i += 2 {
-		ins.HTTPCommonConfig.Headers[ins.Headers[i]] = ins.Headers[i+1]
-	}
 	ins.SetHeaders(request)
 
 	// Start Timer