PHP中JSON解析错误排查
概述
今天遇到在接收一个接口返回的时候，对返回的json字符串进行json_decode的时候返回null。但是返回的字符串打印到日志中确实是一个json格式的。在json.cn上也是可以正常格式化的。尝试很多次之后。通过 json_last_error_msg() 拿到了返回错误信息：Syntax error。 通过搜索终于查找到解决方案：
$content = trim($content, "\xEF\xBB\xBF");
$data = json_decode($content, true);
错误的原因是因为返回的字符串带了UTF8编码的BOM头。即\xEF\xBB\xBF，通过trim()将其修剪掉即可。
总结
PHP 中的json_decode,json_encode在遇到错误的时候，不会抛异常或者返回错误信息。我们可以通过json_last_error()获取最新的错误码，或者通过json_last_error_msg()来获取错误信息，再去排查问题。
JSON error codes
| Value | Constant | Meaning | Availability |
|---|---|---|---|
| 0 | JSON_ERROR_NONE | No error has occurred | |
| 1 | JSON_ERROR_DEPTH | The maximum stack depth has been exceeded | |
| 2 | JSON_ERROR_STATE_MISMATCH | Invalid or malformed JSON | |
| 3 | JSON_ERROR_CTRL_CHAR | Control character error, possibly incorrectly encoded | |
| 4 | JSON_ERROR_SYNTAX | Syntax error | |
| 5 | JSON_ERROR_UTF8 | Malformed UTF-8 characters, possibly incorrectly encoded | PHP 5.3.3 |
| 6 | JSON_ERROR_RECURSION | One or more recursive references in the value to be encoded | PHP 5.5.0 |
| 7 | JSON_ERROR_INF_OR_NAN | One or more NAN or INF values in the value to be encoded | PHP 5.5.0 |
| 8 | JSON_ERROR_UNSUPPORTED_TYPE | A value of a type that cannot be encoded was given | PHP 5.5.0 |
| 9 | JSON_ERROR_INVALID_PROPERTY_NAME | A property name that cannot be encoded was given | PHP 7.0.0 |
| 10 | JSON_ERROR_UTF16 | Malformed UTF-16 characters, possibly incorrectly encoded | PHP 7.0.0 |