golang无效字符'b'寻找值的开始

Question

I am trying to post a json with xml message inside it. However it returns

invalid character 'b' looking for beginning of value

I think the possible reason is that I am trying to marshal the returns body which is not in json format.

func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
    log.Printf("Requesting %v %v%v
", req.Method, req.URL.Host, req.URL.Path)
    start := time.Now()

    res, err := s.HTTPClient.Do(req)

    if debug {
        log.Printf("Completed in %v
", time.Since(start))
    }

    if err != nil {
        log.Printf("Request to sakura failed: %v
", err)
        return err
    }
    defer res.Body.Close()

    resBody, err := ioutil.ReadAll(res.Body)
    if err != nil {
        log.Printf("Cannot parse sakura response: %v
", err)
        return err
    }

    if debug {
        log.Printf("sakura response: %q
", resBody)
    }

    if v != nil {
        return json.Unmarshal(resBody, v)
    }

    return nil
}

The error happened at this line

return json.Unmarshal(resBody, v)

Answer 1

The error indicates that the server did not return a valid JSON response. I suggest adding the following code to debug the issue:

err := json.Unmarshal(resBody, v)
if err != nil {
    log.Printf("error decoding sakura response: %v", err)
    if e, ok := err.(*json.SyntaxError); ok {
        log.Printf("syntax error at byte offset %d", e.Offset)
    }
    log.Printf("sakura response: %q", resBody)
    return err
}