PHP 输出控制

　　以apache2 的mod_php5模块为例，通过php_ap2_register_hook()函数来注册钩子，pre_config，post_config，child_init是启动挂钩，它们在服务器启动时调用，handler 是请求钩子，挂钩到apache 的一次请求。很自然的，要在apache启动和请求的时候，分别完成不同的工作。　　

void php_ap2_register_hook(apr_pool_t *p){	ap_hook_pre_config(php_pre_config, NULL, NULL, APR_HOOK_MIDDLE);	ap_hook_post_config(php_apache_server_startup, NULL, NULL, APR_HOOK_MIDDLE);	ap_hook_handler(php_handler, NULL, NULL, APR_HOOK_MIDDLE);	ap_hook_child_init(php_apache_child_init, NULL, NULL, APR_HOOK_MIDDLE);}

　在php_apache_server_startup中

static intphp_apache_server_startup(apr_pool_t *pconf, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *s){	void *data = NULL;	const char *userdata_key = "apache2hook_post_config";	/* Apache will load, unload and then reload a DSO module. This	 * prevents us from starting PHP until the second load. */	apr_pool_userdata_get(&data, userdata_key, s->process->pool);	if (data == NULL) {		/* We must use set() here and *not* setn(), otherwise the		 * static string pointed to by userdata_key will be mapped		 * to a different location when the DSO is reloaded and the		 * pointers won't match, causing get() to return NULL when		 * we expected it to return non-NULL. */		apr_pool_userdata_set((const void *)1, userdata_key, apr_pool_cleanup_null, s->process->pool);		return OK;	}	/* Set up our overridden path. */	if (apache2_php_ini_path_override) {		apache2_sapi_module.php_ini_path_override = apache2_php_ini_path_override;	}#ifdef ZTS	tsrm_startup(1, 1, 0, NULL);#endif	sapi_startup(&apache2_sapi_module);//完成sapi的启动，初始化全局变量等	apache2_sapi_module.startup(&apache2_sapi_module);//通过调用_sapi_module_struct的startup函数，注册apache sapi module 一系列函数	apr_pool_cleanup_register(pconf, NULL, php_apache_server_shutdown, apr_pool_cleanup_null);	php_apache_add_version(pconf);	return OK;}

　　随后又会调用php_module_startup来启动作为apache一个模块的PHP,初始化一些PHP的状态，函数等等。这篇文章要用到的代码为：

int php_module_startup(sapi_module_struct *sf, zend_module_entry *additional_modules, uint num_additional_modules){	zend_utility_functions zuf;。。。//省略部分代码       php_output_startup();//初始化PHP的输出函数	zuf.error_function = php_error_cb;	zuf.printf_function = php_printf;	zuf.write_function = php_body_write_wrapper;//PHP的默认输出函数	zuf.fopen_function = php_fopen_wrapper_for_zend;	zuf.message_handler = php_message_handler_for_zend;	zuf.block_interruptions = sapi_module.block_interruptions;	zuf.unblock_interruptions = sapi_module.unblock_interruptions;	zuf.get_configuration_directive = php_get_configuration_directive_for_zend;	zuf.ticks_function = php_run_ticks;	zuf.on_timeout = php_on_timeout;	zuf.stream_open_function = php_stream_open_for_zend;	zuf.vspprintf_function = vspprintf;	zuf.getenv_function = sapi_getenv;	zuf.resolve_path_function = php_resolve_path_for_zend;	zend_startup(&zuf, NULL TSRMLS_CC);。。。//省略部分代码}

　　PHPAPI void php_output_startup(void)->static void php_output_init_globals(php_output_globals *output_globals_p TSRMLS_DC)

此时PHP的默认一系列输出函数为：　　

static void php_output_init_globals(php_output_globals *output_globals_p TSRMLS_DC){	OG(php_body_write) = php_default_output_func;	OG(php_header_write) = php_default_output_func;	OG(implicit_flush) = 0;	OG(output_start_filename) = NULL;	OG(output_start_lineno) = 0;}

　

/* {{{ php_default_output_func */PHPAPI int php_default_output_func(const char *str, uint str_len TSRMLS_DC){	fwrite(str, 1, str_len, stderr);//默认输出到标准错误/* See http://support.microsoft.com/kb/190351 */#ifdef PHP_WIN32	fflush(stderr);#endif	return str_len;}

　　上述情况是发生在apache启动的时候，初始化PHP的过程，在每一次请求过程中，显然输出函数不对。跟踪函数php_handler->php_apache_request_ctor->php_request_startup-> php_output_activate,在这个函数中：

PHPAPI void php_output_activate(TSRMLS_D){	OG(php_body_write) = php_ub_body_write;//输出函数	OG(php_header_write) = sapi_module.ub_write;	OG(ob_nesting_level) = 0;	OG(ob_lock) = 0;	OG(disable_output) = 0;	OG(output_start_filename) = NULL;	OG(output_start_lineno) = 0;}PHPAPI int php_ub_body_write(const char *str, uint str_length TSRMLS_DC){	int result = 0;	if (SG(request_info).headers_only) {		if(SG(headers_sent)) {			return 0;		}		php_header(TSRMLS_C);		zend_bailout();	}	if (php_header(TSRMLS_C)) {		if (zend_is_compiling(TSRMLS_C)) {			OG(output_start_filename) = zend_get_compiled_filename(TSRMLS_C);			OG(output_start_lineno) = zend_get_compiled_lineno(TSRMLS_C);		} else if (zend_is_executing(TSRMLS_C)) {			OG(output_start_filename) = zend_get_executed_filename(TSRMLS_C);			OG(output_start_lineno) = zend_get_executed_lineno(TSRMLS_C);		}		OG(php_body_write) = php_ub_body_write_no_header;//输出函数重新赋值		result = php_ub_body_write_no_header(str, str_length TSRMLS_CC);	}	return result;}PHPAPI int php_ub_body_write_no_header(const char *str, uint str_length TSRMLS_DC){	int result;	if (OG(disable_output)) {		return 0;	}	result = OG(php_header_write)(str, str_length TSRMLS_CC);//实际上调用的是OG(php_header_write)也就是sapi_module.ub_write为apache的函数	if (OG(implicit_flush)) {		sapi_flush(TSRMLS_C);	}	return result;}

　　这样一来结果就了然了，在PHP启动的时候，输出函数指向的fd是stderr,在每一次请求的时候，再将函数指针指向apache的输出函数。

　　在zend_startup的时候会有：　　

ZEND_API zend_write_func_t zend_write;zend_write = (zend_write_func_t) utility_functions->write_function;

　　在实际使用的时候，以echo为例，最终会调用：

ZEND_API int zend_print_zval(zval *expr, int indent) /* {{{ */{	return zend_print_zval_ex(zend_write, expr, indent);//zend_write为实际调用的指针函数}

 想了一下PHP在请求的时候，可以动态的指定输出函数，这样更加方便SAPI层的接口编写，这个输出函数的控制权力在server端才合理，但是PHP在自身上面包装了很多层，不知道是不是命名和年代久远的关系。