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主要探讨了PHP的大变量的生成过程。另外如果你注意到, 当在表单中提交的input的name中如果有点号的时候, 在PHP中会自动把点号处理成下划线。并且你很想知道这是为什么,在什么时候发生的? 呵呵,本文也就这个问题做了回答。

首先明确一个问题,PHP的变量名中是不能包含点号的。 但是为了处理表单中的点号命名,PHP就会自动把点号(.)转换成下划线(_)。
要知道PHP是怎么处理的,首先我们要了解,$_GET, $_POST, $_COOKIE等变量的构造过程。
在每个请求到来以后,apache处理到response阶段的时候, 会将控制权交给PHP模块, PHP模块会在处理请求之前首先间接调用 php_request_startup (具体调用序列是send_php -> apache_php_module_main -> php_request_startup, 关于这部门可以参看我前面的文章( PHP Life Cycle) , 在php_request_startup中:

   int php_request_startup(TSRMLS_D)
    int retval = SUCCESS;
    signal(SIGCHLD, sigchld_handler);
    if (php_start_sapi() == FAILURE) {
        return FAILURE;
    zend_try {
        PG(during_request_startup) = 1;
        if (PG(expose_php)) {
            sapi_add_header(SAPI_PHP_VERSION_HEADER, sizeof(SAPI_PHP_VERSION_HEADER)-1, 1);
    } zend_catch {
        retval = FAILURE;
    } zend_end_try();
    return retval;

注意其中的php_hash_environment(TSRMLS_C) 函数调用 , 这个函数就是在请求处理前, 初始化请求相关的变量的函数。
这个函数定义在: main/php_variables.c中 , 有兴趣的可以看看:

  int php_hash_environment(TSRMLS_D)
        char *p;
        unsigned char _gpc_flags[5] = {0, 0, 0, 0, 0};
        zend_bool jit_initialization = (PG(auto_globals_jit) && !PG(register_globals) && !PG(register_long_arrays));
        struct auto_global_record {
                char *name;
                uint name_len;
                char *long_name;
                uint long_name_len;
                zend_bool jit_initialization;
        } auto_global_records[] = {
                { "_POST", sizeof("_POST"), "HTTP_POST_VARS", sizeof("HTTP_POST_VARS"), 0 },
                { "_GET", sizeof("_GET"), "HTTP_GET_VARS", sizeof("HTTP_GET_VARS"), 0 },
                { "_COOKIE", sizeof("_COOKIE"), "HTTP_COOKIE_VARS", sizeof("HTTP_COOKIE_VARS"), 0 },
                { "_SERVER", sizeof("_SERVER"), "HTTP_SERVER_VARS", sizeof("HTTP_SERVER_VARS"), 1 },
                { "_ENV", sizeof("_ENV"), "HTTP_ENV_VARS", sizeof("HTTP_ENV_VARS"), 1 },
                { "_FILES", sizeof("_FILES"), "HTTP_POST_FILES", sizeof("HTTP_POST_FILES"), 0 },
        size_t num_track_vars = sizeof(auto_global_records)/sizeof(struct auto_global_record);
        size_t i;
        /* jit_initialization = 0; */
        for (i=0; i<num_track_vars; i++) {
                PG(http_globals)[i] = NULL;
        for (p=PG(variables_order); p && *p; p++) {
                switch(*p) {
                        case 'p':
                        case 'P':
                                if (!_gpc_flags[0] && !SG(headers_sent) && SG(request_info).request_method && !strcasecmp(SG(request_info).request_method, "POST")) {
                                        sapi_module.treat_data(PARSE_POST, NULL, NULL TSRMLS_CC);       /* POST Data */
                                        _gpc_flags[0] = 1;
                                        if (PG(register_globals)) {
                                                php_autoglobal_merge(&EG(symbol_table), Z_ARRVAL_P(PG(http_globals)[TRACK_VARS_POST]) TSRMLS_CC);

到了这里说个题外话, 就是在php.ini中, 可以使用variables_order来控制PHP是否生成某个大变量,已经大变量的生成顺序。
关于顺序,就是说, 如果打开了auto_register_globals的情况下, 如果先处理p,后处理g,那么$_GET['a'],就会覆盖$_POST['a'];
可以看到,离成功不远了,sapi_module.treat_data 也就是php_default_treat_data,
在php_default_treat_data中,对于变量,都调用php_register_variable_safe来注册变量, 而php_register_variable_safe最终会调用php_register_variable_ex:

  PHPAPI void php_register_variable_ex(char *var, zval *val, zval *track_vars_array TSRMLS_DC)
    char *p = NULL;
    char *ip;       /* index pointer */
    char *index, *escaped_index = NULL;
    int var_len, index_len;
    zval *gpc_element, **gpc_element_p;
    zend_bool is_array = 0;
    HashTable *symtable1 = NULL;
    assert(var != NULL);
    if (track_vars_array) {
        symtable1 = Z_ARRVAL_P(track_vars_array);
    } else if (PG(register_globals)) {
        symtable1 = EG(active_symbol_table);
    if (!symtable1) {
        /* Nothing to do */
     * Prepare variable name
    /* ignore leading spaces in the variable name */
    while (*var && *var==' ') {
    /* ensure that we don't have spaces or dots in the variable name (not binary safe) */
    for (p = var; *p; p++) {
        if (*p == ' ' || *p == '.') {
        } else if (*p == '[') {
            is_array = 1;
            ip = p;
            *p = 0;

呵呵,问题的原因找到了, 就是在php_register_variable的时候,会将(.)转换成(_).
最后,再介绍下$_REQUEST变量的生成, 其实很简单, 在php_hash_environment中的最后, 会调用 php_auto_globals_create_request("_REQUEST", sizeof("_REQUEST")-1 TSRMLS_CC)来注册_REQUEST大变量, 在php_auto_globals_create_request("_REQUEST", sizeof("_REQUEST")-1 TSRMLS_CC)中,只是简单的将$_GET, $_POST, $_COOKIE merge起来(G(http_globals)[TRACK_VARS_COOKIE]这部分,可以参看我较早前的) :

static zend_bool php_auto_globals_create_request(char *name, uint name_len TSRMLS_DC)
    zval *form_variables;
    unsigned char _gpc_flags[3] = {0, 0, 0};
    char *p;
    for (p = PG(variables_order); p && *p; p++) {
        switch (*p) {
            case 'g':
            case 'G':
                if (!_gpc_flags[0]) {
                    php_autoglobal_merge(Z_ARRVAL_P(form_variables), Z_ARRVAL_P(PG(http_globals)[TRACK_VARS_GET]) TSRMLS_CC);
                    _gpc_flags[0] = 1;
                break;                                                                                                                    case 'p':
            case 'P':
                if (!_gpc_flags[1]) {
                    php_autoglobal_merge(Z_ARRVAL_P(form_variables), Z_ARRVAL_P(PG(http_globals)[TRACK_VARS_POST]) TSRMLS_CC);
                    _gpc_flags[1] = 1;
            case 'c':
            case 'C':                                                                                                                         if (!_gpc_flags[2]) {
                    php_autoglobal_merge(Z_ARRVAL_P(form_variables), Z_ARRVAL_P(PG(http_globals)[TRACK_VARS_COOKIE]) TSRMLS_CC);
                    _gpc_flags[2] = 1;
    zend_hash_update(&EG(symbol_table), "_REQUEST", sizeof("_REQUEST"), &form_variables, sizeof(zval *), NULL);
    return 0;


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  39. […]     下午睡觉睡不着,起来接着看PHP的内核,想要了解一下PHP中的预定义变量实现过程。对比Laruence的《PHP的GET/POST等大变量生成过程》及TIPI的《第三节 预定义变量》,$_POST、$_GET等预定义变量初始化的过程应该是通过php_request_startup()函数调用php_hash_environment()来进行初始化的。然而找到main/php_variables.c中的php_hash_environment()函数却是如下: […]

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  43. jackywdx
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    #ifdef ZTS
    # define PG(v) TSRMG(core_globals_id, php_core_globals *, v)
    extern PHPAPI int core_globals_id;
    # define PG(v) (core_globals.v)
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  44. jackywdx
    jackywdx November 14, 2008


    • 雪候鸟
      雪候鸟 November 14, 2008

      PG是为了兼容线程安全模式的一种对php_globals的访问包装, 定义在 main/php_globals.h(php 5.x)

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