golang invalid character 'b' looking for beginning of value

Reason for this eerie error message is :

// When unmarshaling quoted strings, invalid UTF-8 or
// invalid UTF-16 surrogate pairs are not treated as an error.
// Instead, they are replaced by the Unicode replacement
// character U+FFFD.

https://golang.org/src/encoding/json/decode.go

In my case I saved my json as string then parsed it by : stringData = JSON.parse(myJsonString)

I also had the same error another time using gin-context-ShouldBind() (https://godoc.org/github.com/gin-gonic/gin#Context.ShouldBind) and mapping my json to go object: error was because it needs a json as string, so I used : JSON.stringify(jsonObject) when sending my request from front-end part.

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
}

Please Check the request header first. Check the Content-Type. In my cases, it's not an application/JSON. It's application/x-www-form-urlencoded.