php json_encode应用分析

发布时间:2020-06-18编辑:脚本学堂
平时输出json,喜欢用 sprintf 拼成json格式,不过听说这样不标准,必须要用json_encode生成的才是标准的json格式。下面哪种是标准的json格式呢?

平时输出json,喜欢用 sprintf 拼成json格式,不过听说这样不标准,必须要用json_encode生成的才是标准的json格式。
下面哪种是标准的json格式呢?
{a : 'abc'}
{'a' : 'abc'}
{a : "abc"}
{"a" : "abc"}

那都知道,只有第四种才是标准的json格式。

我这么做
$ret_json='{"%s":"%s"}';
echo json_encode($ret_json,"a","abc");

必然也符合标准。

既然如此,那我就要刨根问底,json_encode生成的json格式究竟有什么不同?
 

复制代码 代码示例:
static PHP_FUNCTION(json_encode)
{
            zval *parameter;
            smart_str buf = {0};
            long options = 0;
     
            if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "z|l", &parameter, &options) == FAILURE) {
                    return;
            }   
     
            JSON_G(error_code) = PHP_JSON_ERROR_NONE;
     
            php_json_encode(&buf, parameter, options TSRMLS_CC);
     
            ZVAL_STRINGL(return_value, buf.c, buf.len, 1); 
     
            smart_str_free(&buf);
    }

JSON_G(error_code) = PHP_JSON_ERROR_NONE;
是定义的json错误,该错误可以通过json_last_error函数获取,你用过吗?反正我没用过。
php_json_encode是主要的操作
 

复制代码 代码示例:
PHP_JSON_API void php_json_encode(smart_str *buf, zval *val, int options TSRMLS_DC) /* {{{ */
    {
            switch (Z_TYPE_P(val))
            {
                    case IS_NULL:
                            smart_str_appendl(buf, "null", 4); //输出NULL
                            break;
     
                    case IS_BOOL:
                            if (Z_BVAL_P(val)) {
                                    smart_str_appendl(buf, "true", 4);//输出true
                            } else {
                                    smart_str_appendl(buf, "false", 5);//输出false
                            }
                            break;
     
                    case IS_LONG:
                            smart_str_append_long(buf, Z_LVAL_P(val));//输出长整形的值
                            break;
     
                    case IS_DOUBLE:
                            {
                                    char *d = NULL;
                                    int len;
                                    double dbl = Z_DVAL_P(val);
     
                                    if (!zend_isinf(dbl) && !zend_isnan(dbl)) {//非无穷尽
                                            len = spprintf(&d, 0, "%.*k", (int) EG(precision), dbl);
                                            smart_str_appendl(buf, d, len);
                                            efree(d);
                                    } else {
                                            php_error_docref(NULL TSRMLS_CC, E_WARNING, "double %.9g does not conform to the JSON spec, encoded as 0", dbl);
                                            smart_str_appendc(buf, '0');
                                    }
                           }
                            break;
     
                    case IS_STRING://字符串
                            json_escape_string(buf, Z_STRVAL_P(val), Z_STRLEN_P(val), options TSRMLS_CC);
                            break;
     
                    case IS_ARRAY://数组和对象
                    case IS_OBJECT:
                            json_encode_array(buf, &val, options TSRMLS_CC);
                            break;
     
                    default:
                            php_error_docref(NULL TSRMLS_CC, E_WARNING, "type is unsupported, encoded as null");
                            smart_str_appendl(buf, "null", 4);
                            break;
            }
     
            return;
    }

很明显,根据不同的类型,会有相应的case。
最复杂的是 字符串 、数组 、对象这三种类型,数组和对象是同一种操作。
先看看字符串吧,很长,注释直接写在代码里。
 

复制代码 代码示例:
//options应该是5.3版本之后才支持的,由以下常量组成的二进制掩码: JSON_HEX_QUOT, JSON_HEX_TAG, JSON_HEX_AMP, JSON_HEX_APOS, JSON_NUMERIC_CHECK, JSON_PRETTY_PRINT, JSON_UNESCAPED_SLASHES, JSON_FORCE_OBJECT, JSON_UNESCAPED_UNICODE.虽然我没用过。。。
    static void json_escape_string(smart_str *buf, char *s, int len, int options TSRMLS_DC) /* {{{ */
    {
            int pos = 0;
            unsigned short us;
            unsigned short *utf16;
     
            if (len == 0) {//如果长度为0,则直接返回 双引号 ""
                    smart_str_appendl(buf, """", 2);
                    return;
            }
     
            if (options & PHP_JSON_NUMERIC_CHECK) {//检测是否为0-9的数字,如果是数字,那么就会直接把数据作为long或double类型返回。
                    double d;
                    int type;
                    long p;
     
                    if ((type = is_numeric_string(s, len, &p, &d, 0)) != 0) {
                            if (type == IS_LONG) {
                                    smart_str_append_long(buf, p);
                            } else if (type == IS_DOUBLE) {
                                    if (!zend_isinf(d) && !zend_isnan(d)) {
                                            char *tmp;
                                            int l = spprintf(&tmp, 0, "%.*k", (int) EG(precision), d);
                                            smart_str_appendl(buf, tmp, l);
                                            efree(tmp);
                                    } else {
                                            php_error_docref(NULL TSRMLS_CC, E_WARNING, "double %.9g does not conform to the JSON spec, encoded as 0", d);
                                            smart_str_appendc(buf, '0');
                                    }
                            }
                            return;
                    }
     
            }
     
            utf16 = (unsigned short *) safe_emalloc(len, sizeof(unsigned short), 0);
            len = utf8_to_utf16(utf16, s, len); //这里会对你输入的值一次处理转成对应的Dec码,比如1是49,a是97这样的,保存到utf16中。
            if (len <= 0) {//如果len小于0 说明出错。如果用json_encode处理GBK的编码,就会在这里挂掉。
                    if (utf16) {
                            efree(utf16);
                    }
                    if (len < 0) {
                            JSON_G(error_code) = PHP_JSON_ERROR_UTF8;
                            if (!PG(display_errors)) {
                                    php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid UTF-8 sequence in argument");
                            }
                            smart_str_appendl(buf, "null", 4);
                    } else {
                            smart_str_appendl(buf, """", 2);
                    }
                    return;
            }
     
            smart_str_appendc(buf, '"'); //输入 "
     
    //下面这一段代码就是将一些特殊字符转义如 双引号,反斜线等等
            while (pos < len)
            {
                    us = utf16[pos++];
     
                    switch (us)
                    {
                            case '"':
                                    if (options & PHP_JSON_HEX_QUOT) {
                                            smart_str_appendl(buf, "u0022", 6);
                                    } else {
                                            smart_str_appendl(buf, """, 2);
                                    }
                                    break;
     
                            case '':
                                    smart_str_appendl(buf, "\", 2);
                                    break;
    case '/':
                                    smart_str_appendl(buf, "/", 2);
                                    break;
     
                            case 'b':
                                    smart_str_appendl(buf, "b", 2);
                                    break;
     
                            case 'f':
                                    smart_str_appendl(buf, "f", 2);
                                    break;
     
                            case 'n':
                                    smart_str_appendl(buf, "n", 2);
                                    break;
     
                            case 'r':
                                    smart_str_appendl(buf, "r", 2);
                                    break;
     
                            case 't':
                                    smart_str_appendl(buf, "t", 2);
                                    break;
     
                            case '<':
                                    if (options & PHP_JSON_HEX_TAG) {
                                            smart_str_appendl(buf, "u003C", 6);
                                    } else {
                                            smart_str_appendc(buf, '<');
                                    }
                                    break;
     
                            case '>':
                                    if (options & PHP_JSON_HEX_TAG) {
                                            smart_str_appendl(buf, "u003E", 6);
                                    } else {
                                            smart_str_appendc(buf, '>');
    }
                                    break;
     
                            case '&':
                                    if (options & PHP_JSON_HEX_AMP) {
                                            smart_str_appendl(buf, "u0026", 6);
                                    } else {
                                            smart_str_appendc(buf, '&');
                                    }
                                    break;
     
                            case ''':
                                    if (options & PHP_JSON_HEX_APOS) {
                                            smart_str_appendl(buf, "u0027", 6);
                                    } else {
                                            smart_str_appendc(buf, ''');
                                    }
                                    break;
     
                            default: //一直到这里,没有特殊字符就会把值append到buf中
                                    if (us >= ' ' && (us & 127) == us) {
                                            smart_str_appendc(buf, (unsigned char) us);
                                    } else {
                                            smart_str_appendl(buf, "u", 2);
                                            us = REVERSE16(us);
     
                                            smart_str_appendc(buf, digits[us & ((1 << 4) - 1)]);
                                            us >>= 4;
                                            smart_str_appendc(buf, digits[us & ((1 << 4) - 1)]);
                                            us >>= 4;
                                            smart_str_appendc(buf, digits[us & ((1 << 4) - 1)]);
                                            us >>= 4;
                                            smart_str_appendc(buf, digits[us & ((1 << 4) - 1)]);
                                    }
                                    break;
                    }
            }
            smart_str_appendc(buf, '"'); //结束 双引号。 
            efree(utf16);
    }

再来看看数组和对象,也很简单,
 

复制代码 代码示例:
static void json_encode_array(smart_str *buf, zval **val, int options TSRMLS_DC) /* {{{ */
{
            int i, r;
            HashTable *myht;
     
            if (Z_TYPE_PP(val) == IS_ARRAY) {
                    myht = HASH_OF(*val);
                    r = (options & PHP_JSON_FORCE_OBJECT) ? PHP_JSON_OUTPUT_OBJECT : json_determine_array_type(val TSRMLS_CC);
            } else {
                    myht = Z_OBJPROP_PP(val);
                    r = PHP_JSON_OUTPUT_OBJECT;
            }   
     
            if (myht && myht->nApplyCount > 1) {
                    php_error_docref(NULL TSRMLS_CC, E_WARNING, "recursion detected");
                    smart_str_appendl(buf, "null", 4);
                    return;
            }
    //开始标签
            if (r == PHP_JSON_OUTPUT_ARRAY) {
                    smart_str_appendc(buf, '[');
            } else {
                    smart_str_appendc(buf, '{');
            }   
     
            i = myht ? zend_hash_num_elements(myht) : 0;
     
            if (i > 0)
            {
                    char *key;
                    zval **data;
                    ulong index;
                    uint key_len;
                    HashPosition pos;
                    HashTable *tmp_ht;
                    int need_comma = 0;
     
                    zend_hash_internal_pointer_reset_ex(myht, &pos);
    //便利哈希表
                    for (;; zend_hash_move_forward_ex(myht, &pos)) {
                            i = zend_hash_get_current_key_ex(myht, &key, &key_len, &index, 0, &pos);
                            if (i == HASH_KEY_NON_EXISTANT)
                                    break;
     
                            if (zend_hash_get_current_data_ex(myht, (void **) &data, &pos) == SUCCESS) {
                                    tmp_ht = HASH_OF(*data);
                                    if (tmp_ht) {
                                            tmp_ht->nApplyCount++;
                                    }
     
                                    if (r == PHP_JSON_OUTPUT_ARRAY) {
                                            if (need_comma) {
                                                    smart_str_appendc(buf, ',');
                                            } else {
                                                    need_comma = 1;
                                            }
    //将值append到 buf中
                                            php_json_encode(buf, *data, options TSRMLS_CC);
                                    } else if (r == PHP_JSON_OUTPUT_OBJECT) {
                                            if (i == HASH_KEY_IS_STRING) {
                                                    if (key[0] == '' && Z_TYPE_PP(val) == IS_OBJECT) {
                                                            /* Skip protected and private members. */
                                                            if (tmp_ht) {
                                                                    tmp_ht->nApplyCount--;
                                                            }
                                                            continue;
                                                    }
     
                                                    if (need_comma) {
                                                            smart_str_appendc(buf, ',');
                                                    } else {
                                                            need_comma = 1;
                                                    }
     
                                                    json_escape_string(buf, key, key_len - 1, options & ~PHP_JSON_NUMERIC_CHECK TSRMLS_CC);
                                                    smart_str_appendc(buf, ':');
     
                                                    php_json_encode(buf, *data, options TSRMLS_CC);
                                            } else {
                                                    if (need_comma) {
                                                            smart_str_appendc(buf, ',');
                                                    } else {
                                                            need_comma = 1;
                                                    }
     
                                                    smart_str_appendc(buf, '"');
                                                    smart_str_append_long(buf, (long) index);
                                                    smart_str_appendc(buf, '"');
                                                    smart_str_appendc(buf, ':');
     
                                                    php_json_encode(buf, *data, options TSRMLS_CC);
                                            }
                                    }
     
                                    if (tmp_ht) {
                                            tmp_ht->nApplyCount--;
                                    }
                            }
                    }
            }
    //结束标签
            if (r == PHP_JSON_OUTPUT_ARRAY) {
                    smart_str_appendc(buf, ']');
            } else {
                    smart_str_appendc(buf, '}');
            }
    }

通过简单分析,证明了一个问题,跟我上面用sprintf的方法其实是一样的,都是拼接字符串,

而且 为了性能,更应该鼓励用sprintf来拼接json格式,

因为 json_encode会进行很多 循环操作,而且所消耗的性能是线性的 O(n)。