php，这个json格式的字符串，为什么json_decode()结果是NULL，而不是预期的数组？

Question

这个json格式的字符串，为什么json_decode()结果是NULL，而不是预期的数组？

$php_input='{"key":"ao_1/f9pbbnam5_0_230502100035.mp3","fname":"ao_1/f9pbbnam5_0_230502100035.mp3","fsize":"234144","avinfo":"{"AttachedPic":null,"Audios":[{"Disposition":{"attached_pic":0},"avg_frame_rate":"0/0","bit_rate":"96000","channels":2,"codec_long_name":"MP3 (MPEG audio layer 3)","codec_name":"mp3","codec_time_base":"1/16000","codec_type":"audio","duration":"19.512000","index":0,"nb_frames":"","profile":"","r_frame_rate":"0/0","sample_fmt":"s16p","sample_rate":"16000","start_time":"0.000000","tags":{}}],"MaxAB":96000,"Subtitles":null,"Videos":null,"audio":{"Disposition":{"attached_pic":0},"avg_frame_rate":"0/0","bit_rate":"96000","channels":2,"codec_long_name":"MP3 (MPEG audio layer 3)","codec_name":"mp3","codec_time_base":"1/16000","codec_type":"audio","duration":"19.512000","index":0,"nb_frames":"","profile":"","r_frame_rate":"0/0","sample_fmt":"s16p","sample_rate":"16000","start_time":"0.000000","tags":{}},"format":{"bit_rate":"96000","duration":"19.512000","format_long_name":"MP2/3 (MPEG audio layer 2/3)","format_name":"mp3","nb_streams":1,"size":"234144","start_time":"0.000000","tags":{}},"subtitle":null,"video":null}","format_name":"mp3","bit_rate":"96000","duration":"19.512000","ext":".mp3"}';

$arr_post=json_decode($php_input,true);
var_dump($arr_post); //输出null

问题出在哪里？

Answer 1

"avinfo" 的值应该是一个字符串，但代码里包含了没有转义的双引号，导致 JSON 解析失败。
看看修复后的：

$php_input='{"key":"ao_1/f9pbbnam5_0_230502100035.mp3","fname":"ao_1/f9pbbnam5_0_230502100035.mp3","fsize":"234144","avinfo":"{\"AttachedPic\":null,\"Audios\":[{\"Disposition\":{\"attached_pic\":0},\"avg_frame_rate\":\"0/0\",\"bit_rate\":\"96000\",\"channels\":2,\"codec_long_name\":\"MP3 (MPEG audio layer 3)\",\"codec_name\":\"mp3\",\"codec_time_base\":\"1/16000\",\"codec_type\":\"audio\",\"duration\":\"19.512000\",\"index\":0,\"nb_frames\":\"\",\"profile\":\"\",\"r_frame_rate\":\"0/0\",\"sample_fmt\":\"s16p\",\"sample_rate\":\"16000\",\"start_time\":\"0.000000\",\"tags\":{}}],\"MaxAB\":96000,\"Subtitles\":null,\"Videos\":null,\"audio\":{\"Disposition\":{\"attached_pic\":0},\"avg_frame_rate\":\"0/0\",\"bit_rate\":\"96000\",\"channels\":2,\"codec_long_name\":\"MP3 (MPEG audio layer 3)\",\"codec_name\":\"mp3\",\"codec_time_base\":\"1/16000\",\"codec_type\":\"audio\",\"duration\":\"19.512000\",\"index\":0,\"nb_frames\":\"\",\"profile\":\"\",\"r_frame_rate\":\"0/0\",\"sample_fmt\":\"s16p\",\"sample_rate\":\"16000\",\"start_time\":\"0.000000\",\"tags\":{}},\"format\":{\"bit_rate\":\"96000\",\"duration\":\"19.512000\",\"format_long_name\":\"MP2/3 (MPEG audio layer 2/3)\",\"format_name\":\"mp3\",\"nb_streams\":1,\"size\":\"234144\",\"start_time\":\"0.000000\",\"tags\":{}},\"subtitle\":null,\"video\":null}","format_name":"mp3","bit_rate":"96000","duration":"19.512000","ext":".mp3"}';

$arr_post=json_decode($php_input,true);
var_dump($arr_post); //输出数组

不需要手动的方法：

$data = [
    "key" => "ao_1/f9pbbnam5_0_230502100035.mp3",
    "fname" => "ao_1/f9pbbnam5_0_230502100035.mp3",
    "fsize" => "234144",
    "avinfo" => [
        "AttachedPic" => null,
        "Audios" => [
            [
                "Disposition" => ["attached_pic" => 0],
                "avg_frame_rate" => "0/0",
                "bit_rate" => "96000",
                "channels" => 2,
                "codec_long_name" => "MP3 (MPEG audio layer 3)",
                "codec_name" => "mp3",
                "codec_time_base" => "1/16000",
                "codec_type" => "audio",
                "duration" => "19.512000",
                "index" => 0,
                "nb_frames" => "",
                "profile" => "",
                "r_frame_rate" => "0/0",
                "sample_fmt" => "s16p",
                "sample_rate" => "16000",
                "start_time" => "0.000000",
                "tags" => [],
            ]
        ],
        // ... 其他数据
    ],
    "format_name" => "mp3",
    "bit_rate" => "96000",
    "duration" => "19.512000",
    "ext" => ".mp3",
];

$php_input = json_encode($data);

$arr_post = json_decode($php_input, true);
var_dump($arr_post); //输出数组

用 preg_replace_callback()

$php_input = '{"key":"ao_1/f9pbbnam5_0_230502100035.mp3","fname":"ao_1/f9pbbnam5_0_230502100035.mp3","fsize":"234144","avinfo":"{"AttachedPic":null,"Audios":[{"Disposition":{"attached_pic":0},"avg_frame_rate":"0/0","bit_rate":"96000","channels":2,"codec_long_name":"MP3 (MPEG audio layer 3)","codec_name":"mp3","codec_time_base":"1/16000","codec_type":"audio","duration":"19.512000","index":0,"nb_frames":"","profile":"","r_frame_rate":"0/0","sample_fmt":"s16p","sample_rate":"16000","start_time":"0.000000","tags":{}}],"MaxAB":96000,"Subtitles":null,"Videos":null,"audio":{"Disposition":{"attached_pic":0},"avg_frame_rate":"0/0","bit_rate":"96000","channels":2,"codec_long_name":"MP3 (MPEG audio layer 3)","codec_name":"mp3","codec_time_base":"1/16000","codec_type":"audio","duration":"19.512000","index":0,"nb_frames":"","profile":"","r_frame_rate":"0/0","sample_fmt":"s16p","sample_rate":"16000","start_time":"0.000000","tags":{}},"format":{"bit_rate":"96000","duration":"19.512000","format_long_name":"MP2/3 (MPEG audio layer 2/3)","format_name":"mp3","nb_streams":1,"size":"234144","start_time":"0.000000","tags":{}},"subtitle":null,"video":null}","format_name":"mp3","bit_rate":"96000","duration":"19.512000","ext":".mp3"}';

$php_input_fixed = preg_replace_callback(
    '/"avinfo":"(.*?)"/',
    function ($matches) {
        return '"avinfo":"' . str_replace('"', '\\"', $matches[1]) . '"';
    },
    $php_input
);

$arr_post = json_decode($php_input_fixed, true);
var_dump($arr_post);