What to do if php json_decode parsing fails

php Solution to json_decode parsing failure: 1. Obtain the error code through json_last_error and other functions; 2. Eliminate illegal utf8 characters according to the utf8 encoding range.

The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer

php json_decode parsing failure manage?

php json_decode parsing failure and error handling

Under normal circumstances, after obtaining a piece of json content, directly json_decode($content, true) is converted into an array Come and use it, it’s very convenient.
However, if there is something wrong with the interface that provides you with json content, and the json provided is not standard or simply has errors, then you have to find a way to find the problem.
Let’s take a look at the manul of json_encode first
https://www.php.net/manual/en/function.json-last-error.php

Returns NULL on failure

 //  $json = '{"a":1,"b":2,"c":3,"d":4,"e":5, "name":"Corwien"}'; 
 $json = '{"a":1,"b":2,"c":3,"d":4,"e":5, "name":}';  //错误的json格式
 $result = json_decode($json, true);
  if(!$result)
  {
        //error handle ,错误处理
        $ret = json_last_error();
        print_r($ret);   //打印为： 4,查错误信息表，可知是语法错误
        
  }   

json_last_error错误msg对照表：
0 = JSON_ERROR_NONE
1 = JSON_ERROR_DEPTH
2 = JSON_ERROR_STATE_MISMATCH
3 = JSON_ERROR_CTRL_CHAR
4 = JSON_ERROR_SYNTAX
5 = JSON_ERROR_UTF8

How do we know where we went wrong?

1. Get the error code

php has a json_last_error function, see
https://www.php.net/manual/en/function.json -last-error.php

It will return an error code to tell us what went wrong.
Can’t understand the error code? You can use json_last_error_msg, see
https://www.php.net/manual/en/function.json-last-error-msg.php

But json_last_error_msg is only available in php >= 5.5.0 It only exists in different versions. If the version is lower, just define one yourself.

2. The lower version of php json error codes are incomplete

However, if you pay attention to the manual, you will find that many of the error codes defined in json_last_error are only available in the higher version. Yes, lower versions of php are out of service. For example, the JSON_ERROR_UTF8 error code clearly tells us that there are illegal utf8 characters in the json string, but it only exists in Php >= 5.3.3. The tragedy is that my php is 5.3.2....

所以，如果你的json_last_error返回的是JSON_ERROR_NONE（0） ，并不是说没有错误，而只是这个错误在你的低版本php中没有定义。再说，没有错误怎么会失败呢....

If the json format is wrong, no matter how low the version of php is, it will tell you JSON_ERROR_SYNTAX, so the first possibility is JSON_ERROR_NONE. Think about illegal utf8 strings.

3. How to deal with illegal utf8 characters in json

According to the encoding range of utf8, illegal utf8 characters can be eliminated.
See https://magp.ie/2011/01/06/remove-non-utf8-characters-from-string-with-php/

//reject overly long 2 byte sequences, as well as characters above U+10000 and replace with ?
$some_string = preg_replace('/[\x00-\x08\x10\x0B\x0C\x0E-\x19\x7F]'.
 '|[\x00-\x7F][\x80-\xBF]+'.
 '|([\xC0\xC1]|[\xF0-\xFF])[\x80-\xBF]*'.
 '|[\xC2-\xDF]((?![\x80-\xBF])|[\x80-\xBF]{2,})'.
 '|[\xE0-\xEF](([\x80-\xBF](?![\x80-\xBF]))|(?![\x80-\xBF]{2})|[\x80-\xBF]{3,})/S',
 '?', $some_string );
 
//reject overly long 3 byte sequences and UTF-16 surrogates and replace with ?
$some_string = preg_replace('/\xE0[\x80-\x9F][\x80-\xBF]'.
 '|\xED[\xA0-\xBF][\x80-\xBF]/S','?', $some_string );

Here are the illegal characters replaced with? , change it yourself as needed.

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