Talk about your understanding of Zend SAPIs (Zend SAPI Internals), sapissapi

SAPI: Server abstraction API, students who have studied PHP architecture should know the importance of this stuff , which provides an interface that allows PHP to interact with other applications. This article will not introduce each PHP SAPI in detail, but will only explain the mechanism of SAPI for the simplest CGI SAPI.

First, let’s take a look at the architecture diagram of PHP:

Figure 1 PHP Architecture

SAPI provides an interface for external communication. For PHP5.2, many kinds of SAPI are provided by default. The common ones are mod_php5 for Apache, CGI, ISAPI for IIS, and Shell CLI. This article starts from CGI SAPI Let’s start by introducing the mechanism of SAPI. Although CGI is simple, don't worry, it contains most of the content, enough to give you a deep understanding of how SAPI works.

To define a SAPI, you must first define a sapi_module_struct, see PHP-SRC/sapi/cgi/cgi_main.c:

 */
static sapi_module_struct cgi_sapi_module = {
#if PHP_FASTCGI
 "cgi-fcgi",      /* name */
 "CGI/FastCGI",     /* pretty name */
#else
 "cgi",       /* name */
 "CGI",       /* pretty name */
#endif
 
 php_cgi_startup,    /* startup */
 php_module_shutdown_wrapper, /* shutdown */
 
 NULL,       /* activate */
 sapi_cgi_deactivate,   /* deactivate */
 
 sapi_cgibin_ub_write,   /* unbuffered write */
 sapi_cgibin_flush,    /* flush */
 NULL,       /* get uid */
 sapi_cgibin_getenv,    /* getenv */
 
 php_error,      /* error handler */
 
 NULL,       /* header handler */
 sapi_cgi_send_headers,   /* send headers handler */
 NULL,       /* send header handler */
 
 sapi_cgi_read_post,    /* read POST data */
 sapi_cgi_read_cookies,   /* read Cookies */
 
 sapi_cgi_register_variables, /* register server variables */
 sapi_cgi_log_message,   /* Log message */
 NULL,       /* Get request time */
 
 STANDARD_SAPI_MODULE_PROPERTIES
};

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This structure contains some constants, such as name, which will be used when we call php_info(). Some initialization, closing functions, and some function pointers are used to tell Zend how to obtain and output data.

1. php_cgi_startup, when an application calls PHP, this function will be called. For CGI, it simply calls PHP’s initialization function:

 static int php_cgi_startup(sapi_module_struct *sapi_module)
{
 if (php_module_startup(sapi_module, NULL, 0) == FAILURE) {
  return FAILURE;
 }
 return SUCCESS;
}

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2. php_module_shutdown_wrapper, a simple wrapper for PHP shutdown function. Just simply call php_module_shutdown;

3. PHP will handle some initialization and resource allocation transactions at each request. This part is what the activate field is to be defined. From the above structure, we can see that for CGI, it does not provide an initialization handle. For mod_php, it's different. He needs to register the resource destructor in the apache pool, apply for space, initialize environment variables, and so on.

4. sapi_cgi_deactivate, this is the function corresponding to activate. As the name suggests, it will provide a handler to handle the finishing work. For CGI, it simply refreshes the buffer to ensure that the user can complete the process before Zend is closed. Get all output data:

 static int sapi_cgi_deactivate(TSRMLS_D)
{
 /* flush only when SAPI was started. The reasons are:
  1. SAPI Deactivate is called from two places: module init and request shutdown
  2. When the first call occurs and the request is not set up, flush fails on
   FastCGI.
 */
 if (SG(sapi_started)) {
  sapi_cgibin_flush(SG(server_context));
 }
 return SUCCESS;
}

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5. sapi_cgibin_ub_write, this handler tells Zend how to output data. For mod_php, this function provides an interface for writing response data, while for CGI, it simply writes to stdout:

static inline size_t sapi_cgibin_single_write(const char *str, uint str_length TSRMLS_DC)
{
#ifdef PHP_WRITE_STDOUT
 long ret;
#else
 size_t ret;
#endif
#if PHP_FASTCGI
 if (fcgi_is_fastcgi()) {
  fcgi_request *request = (fcgi_request*) SG(server_context);
  long ret = fcgi_write(request, FCGI_STDOUT, str, str_length);
  if (ret <= 0) {
   return 0;
  }
  return ret;
 }
#endif
#ifdef PHP_WRITE_STDOUT
 ret = write(STDOUT_FILENO, str, str_length);
 if (ret <= 0) return 0;
 return ret;
#else
 ret = fwrite(str, 1, MIN(str_length, 16384), stdout);
 return ret;
#endif
}
static int sapi_cgibin_ub_write(const char *str, uint str_length TSRMLS_DC)
{
 const char *ptr = str;
 uint remaining = str_length;
 size_t ret;
 while (remaining > 0) {
  ret = sapi_cgibin_single_write(ptr, remaining TSRMLS_CC);
  if (!ret) {
   php_handle_aborted_connection();
   return str_length - remaining;
  }
  ptr += ret;
  remaining -= ret;
 }
 return str_length;
}

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The real writing logic is stripped out in order to simply implement a fastcgi-compatible writing method.

6. sapi_cgibin_flush, this is the function handle provided to zend to refresh the cache. For CGI, it is just a simple call to fflush provided by the system;

7.NULL, this part is used to allow Zend to verify the state of a script file to be executed to determine whether the file has execution permissions, etc. CGI does not provide this.

8. sapi_cgibin_getenv, provides Zend with an interface to find environment variables based on name. For mod_php5, when we call getenv in the script, this handle will be called indirectly. For CGI, because its operating mechanism is very similar to CLI, the direct call parent is Shell, so it simply calls genenv:

provided by the system.

static char *sapi_cgibin_getenv(char *name, size_t name_len TSRMLS_DC)
{
#if PHP_FASTCGI
 /* when php is started by mod_fastcgi, no regular environment
  is provided to PHP. It is always sent to PHP at the start
  of a request. So we have to do our own lookup to get env
  vars. This could probably be faster somehow. */
 if (fcgi_is_fastcgi()) {
  fcgi_request *request = (fcgi_request*) SG(server_context);
  return fcgi_getenv(request, name, name_len);
 }
#endif
 /* if cgi, or fastcgi and not found in fcgi env
  check the regular environment */
 return getenv(name);
}

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9. php_error, error handling function. Here, let me make a few digressions. Last time I saw the php maillist mentioned that the error handling mechanism of PHP is completely OO, that is, rewriting this function handle makes it possible whenever When an error occurs, an exception is thrown. CGI simply calls the error handling function provided by PHP.

10. This function will be called when we call PHP's header() function, which is not provided for CGI.

11. sapi_cgi_send_headers, this function will be called when the header is actually sent, generally speaking, before any output is to be sent:

static int sapi_cgi_send_headers(sapi_headers_struct *sapi_headers TSRMLS_DC)
{
 char buf[SAPI_CGI_MAX_HEADER_LENGTH];
 sapi_header_struct *h;
 zend_llist_position pos;
 if (SG(request_info).no_headers == 1) {
  return SAPI_HEADER_SENT_SUCCESSFULLY;
 }
 if (cgi_nph || SG(sapi_headers).http_response_code != 200)
 {
  int len;
  if (rfc2616_headers && SG(sapi_headers).http_status_line) {
   len = snprintf(buf, SAPI_CGI_MAX_HEADER_LENGTH,
       "%s\r\n", SG(sapi_headers).http_status_line);
   if (len > SAPI_CGI_MAX_HEADER_LENGTH) {
    len = SAPI_CGI_MAX_HEADER_LENGTH;
   }
  } else {
   len = sprintf(buf, "Status: %d\r\n", SG(sapi_headers).http_response_code);
  }
  PHPWRITE_H(buf, len);
 }
 h = (sapi_header_struct*)zend_llist_get_first_ex(&sapi_headers->headers, &pos);
 while (h) {
  /* prevent CRLFCRLF */
  if (h->header_len) {
   PHPWRITE_H(h->header, h->header_len);
   PHPWRITE_H("\r\n", 2);
  }
  h = (sapi_header_struct*)zend_llist_get_next_ex(&sapi_headers->headers, &pos);
 }
 PHPWRITE_H("\r\n", 2);
 return SAPI_HEADER_SENT_SUCCESSFULLY;
 }

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12. NULL, this is used to send each header separately, CGI does not provide it

13. sapi_cgi_read_post, this handle specifies how to obtain POST data. If you have done CGI programming, we know that CGI reads POST DATA from stdin,

static int sapi_cgi_read_post(char *buffer, uint count_bytes TSRMLS_DC)
{
 uint read_bytes=0, tmp_read_bytes;
#if PHP_FASTCGI
 char *pos = buffer;
#endif
 count_bytes = MIN(count_bytes, (uint) SG(request_info).content_length - SG(read_post_bytes));
 while (read_bytes < count_bytes) {
#if PHP_FASTCGI
  if (fcgi_is_fastcgi()) {
   fcgi_request *request = (fcgi_request*) SG(server_context);
   tmp_read_bytes = fcgi_read(request, pos, count_bytes - read_bytes);
   pos += tmp_read_bytes;
  } else {
   tmp_read_bytes = read(0, buffer + read_bytes, count_bytes - read_bytes);
  }
#else
  tmp_read_bytes = read(0, buffer + read_bytes, count_bytes - read_bytes);
#endif
  if (tmp_read_bytes <= 0) {
   break;
  }
  read_bytes += tmp_read_bytes;
 }
 return read_bytes;
}

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14. sapi_cgi_read_cookies, this is the same as the function above, except to get the cookie value:

static char *sapi_cgi_read_cookies(TSRMLS_D)
{
 return sapi_cgibin_getenv((char *) "HTTP_COOKIE", sizeof("HTTP_COOKIE")-1 TSRMLS_CC);
}

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15. sapi_cgi_register_variables, this function provides an interface for adding variables to the $_SERVER variable. For CGI, a PHP_SELF is registered so that we can access $_SERVER['PHP_SELF'] in the script. Get

This request_uri:

static void sapi_cgi_register_variables(zval *track_vars_array TSRMLS_DC)
{
 /* In CGI mode, we consider the environment to be a part of the server
  * variables
  */
 php_import_environment_variables(track_vars_array TSRMLS_CC);
 /* Build the special-case PHP_SELF variable for the CGI version */
 php_register_variable("PHP_SELF", (SG(request_info).request_uri &#63; SG(request_info).request_uri : ""), track_vars_array TSRMLS_CC);
}

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16. sapi_cgi_log_message, used to output error messages. For CGI, it is simply output to stderr:

static void sapi_cgi_log_message(char *message)
{
#if PHP_FASTCGI
 if (fcgi_is_fastcgi() && fcgi_logging) {
  fcgi_request *request;
  TSRMLS_FETCH();
  request = (fcgi_request*) SG(server_context);
  if (request) {
   int len = strlen(message);
   char *buf = malloc(len+2);
   memcpy(buf, message, len);
   memcpy(buf + len, "\n", sizeof("\n"));
   fcgi_write(request, FCGI_STDERR, buf, len+1);
   free(buf);
  } else {
   fprintf(stderr, "%s\n", message);
  }
  /* ignore return code */
 } else
#endif /* PHP_FASTCGI */
 fprintf(stderr, "%s\n", message);
}

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After analysis, we have understood how a SAPI is implemented. After analyzing CGI, we can also imagine the implementation mechanism of SAPI such as mod_php, embed and so on. :)

How about this article? Is this article very detailed? I hope you like it.