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<html><head><title>FastCGI Programmer's Guide - Chapter 2, Developing FastCGI Applications in C</title></head>
<body bgcolor=#ffffff>
 
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<a name="3659">
<center><h1>2 Developing FastCGI <br>Applications in C</h1></center>
</a><a name="917"></a>
This chapter explains how to code FastCGI applications in C and how to build them into executables. <p>
<a name="4230"></a>
If you are converting a CGI application into a FastCGI application, in many cases you will only need to add a few lines of code. For more complex applications, you may also need to rearrange some code.<p>
<a name="5371">
<h1> The I/O Libraries</h1>
</a><a name="5384"></a>
The FastCGI Software Development Kit that accompanies Open Market WebServer 2.0 includes I/O libraries to simplify the job of converting existing CGI applications to FastCGI or writing new FastCGI applications. There are two libraries in the kit: fcgi_stdio and fcgiapp. You must include one of these header files in your program:<p>
<ul><a name="5386"></a>
<li><code>fcgi_stdio.h</code>
<a name="4237"></a>
<li><code>fcgiapp.h</code>
</ul><a name="4199"></a>
The <code>fcgi_stdio</code> library is a layer on top of the <code>fcgiapp</code> library, and we recommend strongly that you use it, both for converting existing CGI applications and for writing new FastCGI applications. The fcgi_stdio library offers several advantages:<p>
<ul><a name="5811"></a>
<li>Simplicity: there are only 3 new API calls to learn
<a name="5828"></a>
<li>Familiarity: If you are converting a CGI application to FastCGI, you will find few changes between CGI and FastCGI. We designed our library to make the job of building a FastCGI application as similar as possible to that of building a FastCGI application: you use the same environment variables, same techniques for parsing query strings, the same I/O routines, and so on. 
<a name="5817"></a>
<li>Convenience: the library provides full binary compatibility between CGI and FastCGI. That is, you can run the same binary as either CGI or FastCGI. 
</ul><a name="5399"></a>
The fcgiapp library is more specific to FastCGI, without trying to provide the veneer of familiarity with CGI. This manual describes the fcgi_stdio library; the fcgiapp library is documented in the header files that accompany the development kit. <p>
<a name="5847">
<h1> Code Structure</h1>
</a><a name="4240"></a>
To structure code for FastCGI, you separate your code into two sections:<p>
<ul><a name="4200"></a>
<li>Initialization section, which is executed only once.
<a name="4201"></a>
<li>Response loop section, which gets executed every time the FastCGI script gets called.
</ul><a name="4202"></a>
A response loop typically has the following format:<p>
<pre><a name="4203">
while (FCGI_Accept() &gt;= 0) {
</a>
<a name="4204">
# body of response loop
</a>
<a name="4205">
}
</a>
</pre><a name="4206"></a>
The <code>FCGI_Accept</code> blocks until a client request comes in, and then returns 0. If there is a system failure, or the system administrator terminates the process, Accept will return -1. <p>
<a name="5852"></a>
If the application was invoked as a CGI program, the first call to Accept returns 0 and the second always returns -1, producing CGI behavior. (See <a href="apaman.htm#95860">"FCGI_Accept (3)" on page &#32;21</a> for details.)<p>
<a name="5909"></a>
Also note that the CGI world encourages small scripts, whereas FastCGI encourages combining scripts. You may choose to rethink the overall structure of your applications to take better advantage of FastCGI performance gains.<p>
<a name="5373">
<h1> Example 1: TinyFastCGI</h1>
</a><a name="4263">
Here is a simple example of a responder FastCGI application written in C:<p>
<pre>
#include "fcgi_stdio.h" /* fcgi library; put it first*/<br>#include &lt;stdlib.h&gt;

int count;

void initialize(void)
{
  count=0;
}

void main(void)
{
/* Initialization. */  
  initialize();

/* Response loop. */
  while (FCGI_Accept() &gt;= 0)   {
    printf("Content-type: text/html\r\n"
           "\r\n"
           "&lt;title&gt;FastCGI Hello! (C, fcgi_stdio library)&lt;/title&gt;"
           "&lt;h1&gt;FastCGI Hello! (C, fcgi_stdio library)&lt;/h1&gt;"
           "Request number %d running on host &lt;i&gt;%s&lt;/i&gt;\n",
            ++count, getenv("SERVER_HOSTNAME"));
  }
}
</pre>
<h1> Example 2: Prime Number Generator</h1>
</a><a name="4182"></a>
Consider a responder application that generates the n-th prime number. <p>
<a name="5217"></a>
A CGI application would have no efficient way of solving this problem. For example, if the user asks for the 50,000th prime number, a CGI application would have to calculate the first prime number, then the second, and so on, up until the 50,000th. The application would then terminate, taking with it all its hard-earned calculations. If a client then asks for the 49,000th prime number, the server will have to spawn a new CGI application which will have to start calculating prime numbers from scratch.<p>
<a name="4315"></a>
FastCGI applications can be much more efficient at this sort of problem, since they can maintain state. A FastCGI application can calculate an extensive table of prime numbers in its initialization phase and then keep the table around indefinitely. Whenever a client requests a particular prime number, the response loop merely needs to look it up in the table. <p>
<a name="4343"></a>
Here is the code for the prime number example:<p>
<pre>
#include "fcgi_stdio.h"
#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;

#define POTENTIALLY_PRIME 0
#define COMPOSITE 1
#define VALS_IN_SIEVE_TABLE 1000000
#define MAX_NUMBER_OF_PRIME_NUMBERS 78600 

/* All initialized to POTENTIALLY_PRIME */
long int  sieve_table[VALS_IN_SIEVE_TABLE]; 
long int  prime_table[MAX_NUMBER_OF_PRIME_NUMBERS];  
/* Use Sieve of Erastothenes method of building 
   a prime number table. */
void
initialize_prime_table(void)
{
 long int prime_counter=1;
 long int current_prime=2, c, d; 
  
  prime_table[prime_counter]=current_prime;

  while (current_prime &lt; VALS_IN_SIEVE_TABLE)   {
   /* Mark off composite numbers. */
     for (c = current_prime; c &lt;= VALS_IN_SIEVE_TABLE; 
          c += current_prime)  {
        sieve_table[c] = COMPOSITE;  
     }

   /* Find the next prime number. */
     for (d=current_prime+1; sieve_table[d] == COMPOSITE; d++); 
   /* Put the new prime number into the table. */ 
     prime_table[++prime_counter]=d; 
     current_prime=d;
  }
}


void main(void)
{
    char *query_string;
    long int n;

    initialize_prime_table();

    while(FCGI_Accept() &gt;= 0) {
        /*
         * Produce the necessary HTTP header.
         */
        printf("Content-type: text/html\r\n"
               "\r\n");
        /*
         * Produce the constant part of the HTML document.
         */
        printf("&lt;title&gt;Prime FastCGI&lt;/title&gt;\n"
               "&lt;h1&gt;Prime FastCGI&lt;/h1&gt;\n");
        /*
         * Read the query string and produce the variable part
         * of the HTML document.
         */
        query_string = getenv("QUERY_STRING");
        if(query_string == NULL) {
            printf("Usage: Specify a positive number in the query string.\n");
        } else {
            query_string = strchr(query_string, `=') + 1;
            n = strtol(query_string);
            if(n &lt; 1) {
                printf("The query string `%s' is not a positive number.\n",
                       query_string);
            } else if(n &gt; MAX_NUMBER_OF_PRIME_NUMBERS) {
                printf("The number %d is too large for this program.\n", n);
            } else
                printf("The %ldth prime number is %ld.\n", prime_table[n]);
            }
        }
    } /* while FCGI_Accept */
}
</pre><a name="5349"></a>
This application has a noticeable start up cost while it initializes the table, but subsequent accesses are fast.<p>
<a name="5151">
<h1> Building</h1>
</a><a name="4630"></a>
This section explains how to build and debug FastCGI applications written in C.<p>
<a name="4629"></a>
The C preprocessor needs to know the location of the <code>fcgi_stdio.h</code> header file, which is at the following pathname:<p>
<pre><a name="4642">
<em>$toolkit</em>/include/fcgi_stdio.h
</a>
</pre><a name="4645"></a>
where <em>$toolkit</em> symbolizes the directory in which you have installed the Software Development Kit for FastCGI. <p>
<a name="4760"></a>
The linker needs to know the location of the <code>libfcgi.a</code> library file, which is at the following pathname:<p>
<pre><a name="4647">
<em>$toolkit</em>/libfcgi/libfcgi.a 
</a>
</pre><a name="4648"></a>
If your linker does not search the Berkeley socket library, then you must add linker directives to force this search.<p>
<a name="4773"></a>
We provide a sample application <code>Makefile</code> at the following pathname: <p>
<pre><a name="4649">
<em>$toolkit</em>/examples/Makefile
</a>
</pre><a name="4652"></a>
This <code>Makefile</code> contains the necessary rules and pathnames to build the C FastCGI applications accompanying the toolkit. To build all the applications, type:<p>
<pre><a name="4653">
$ ./configure<br>$ make 
</a>
</pre><a name="4190">
<h1> Memory Leaks</h1>
</a><a name="4178"></a>
Memory leaks are seldom a problem in CGI programming because CGI applications rarely run long enough to be concerned with leaks. However, memory leaks can become a problem in FastCGI applications, particularly if each call to a popular FastCGI application causes additional memory to leak. <p>
<a name="4785"></a>
When converting to FastCGI, you can either use a tool such as Purify from Pure Software to discover and fix storage leaks or you can run a C garbage collector such as Great Circle from Geodesic Systems. <p>
<a name="4972"></a>
<p>

<hr><br>
 
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Commit	Line	Data
6791223e	1	<html><head><title>FastCGI Programmer's Guide - Chapter 2, Developing FastCGI Applications in C</title></head>
0198fd3c	2	<body bgcolor=#ffffff>
	3
	4	<a href="cover.htm">[Top]</a> <a href="ch1intro.htm">[Prev]</a> <a href="ch3perl.htm">[Next]</a> <a href="ap_guida.htm">[Bottom]</a>
	5	<hr><br>
	6
	7	<a name="3659">
	8	<center><h1>2 Developing FastCGI <br>Applications in C</h1></center>
6791223e	9	</a><a name="917"></a>
0198fd3c	10	This chapter explains how to code FastCGI applications in C and how to build them into executables. <p>
6791223e	11	<a name="4230"></a>
0198fd3c	12	If you are converting a CGI application into a FastCGI application, in many cases you will only need to add a few lines of code. For more complex applications, you may also need to rearrange some code.<p>
6791223e	13	<a name="5371">
0198fd3c	14	<h1> The I/O Libraries</h1>
6791223e	15	</a><a name="5384"></a>
0198fd3c	16	The FastCGI Software Development Kit that accompanies Open Market WebServer 2.0 includes I/O libraries to simplify the job of converting existing CGI applications to FastCGI or writing new FastCGI applications. There are two libraries in the kit: fcgi_stdio and fcgiapp. You must include one of these header files in your program:<p>
6791223e	17	<ul><a name="5386"></a>
0198fd3c	18	<li><code>fcgi_stdio.h</code>
6791223e	19	<a name="4237"></a>
0198fd3c	20	<li><code>fcgiapp.h</code>
6791223e	21	</ul><a name="4199"></a>
0198fd3c	22	The <code>fcgi_stdio</code> library is a layer on top of the <code>fcgiapp</code> library, and we recommend strongly that you use it, both for converting existing CGI applications and for writing new FastCGI applications. The fcgi_stdio library offers several advantages:<p>
6791223e	23	<ul><a name="5811"></a>
0198fd3c	24	<li>Simplicity: there are only 3 new API calls to learn
6791223e	25	<a name="5828"></a>
0198fd3c	26	<li>Familiarity: If you are converting a CGI application to FastCGI, you will find few changes between CGI and FastCGI. We designed our library to make the job of building a FastCGI application as similar as possible to that of building a FastCGI application: you use the same environment variables, same techniques for parsing query strings, the same I/O routines, and so on.
6791223e	27	<a name="5817"></a>
0198fd3c	28	<li>Convenience: the library provides full binary compatibility between CGI and FastCGI. That is, you can run the same binary as either CGI or FastCGI.
6791223e	29	</ul><a name="5399"></a>
0198fd3c	30	The fcgiapp library is more specific to FastCGI, without trying to provide the veneer of familiarity with CGI. This manual describes the fcgi_stdio library; the fcgiapp library is documented in the header files that accompany the development kit. <p>
6791223e	31	<a name="5847">
0198fd3c	32	<h1> Code Structure</h1>
6791223e	33	</a><a name="4240"></a>
0198fd3c	34	To structure code for FastCGI, you separate your code into two sections:<p>
6791223e	35	<ul><a name="4200"></a>
0198fd3c	36	<li>Initialization section, which is executed only once.
6791223e	37	<a name="4201"></a>
0198fd3c	38	<li>Response loop section, which gets executed every time the FastCGI script gets called.
6791223e	39	</ul><a name="4202"></a>
0198fd3c	40	A response loop typically has the following format:<p>
6791223e	41	<pre><a name="4203">
0198fd3c	42	while (FCGI_Accept() >= 0) {
	43	</a>
	44	<a name="4204">
	45	# body of response loop
	46	</a>
	47	<a name="4205">
	48	}
	49	</a>
6791223e	50	</pre><a name="4206"></a>
0198fd3c	51	The <code>FCGI_Accept</code> blocks until a client request comes in, and then returns 0. If there is a system failure, or the system administrator terminates the process, Accept will return -1. <p>
6791223e	52	<a name="5852"></a>
0198fd3c	53	If the application was invoked as a CGI program, the first call to Accept returns 0 and the second always returns -1, producing CGI behavior. (See <a href="apaman.htm#95860">"FCGI_Accept (3)" on page 21</a> for details.)<p>
6791223e	54	<a name="5909"></a>
0198fd3c	55	Also note that the CGI world encourages small scripts, whereas FastCGI encourages combining scripts. You may choose to rethink the overall structure of your applications to take better advantage of FastCGI performance gains.<p>
6791223e	56	<a name="5373">
0198fd3c	57	<h1> Example 1: TinyFastCGI</h1>
	58	</a><a name="4263">
	59	Here is a simple example of a responder FastCGI application written in C:<p>
	60	<pre>
	61	#include "fcgi_stdio.h" /* fcgi library; put it first*/<br>#include <stdlib.h>
	62
	63	int count;
	64
	65	void initialize(void)
	66	{
	67	count=0;
	68	}
	69
	70	void main(void)
	71	{
	72	/* Initialization. */
	73	initialize();
	74
	75	/* Response loop. */
	76	while (FCGI_Accept() >= 0) {
	77	printf("Content-type: text/html\r\n"
	78	"\r\n"
	79	"<title>FastCGI Hello! (C, fcgi_stdio library)</title>"
	80	"<h1>FastCGI Hello! (C, fcgi_stdio library)</h1>"
	81	"Request number %d running on host <i>%s</i>\n",
	82	++count, getenv("SERVER_HOSTNAME"));
	83	}
	84	}
	85	</pre>
	86	<h1> Example 2: Prime Number Generator</h1>
6791223e	87	</a><a name="4182"></a>
0198fd3c	88	Consider a responder application that generates the n-th prime number. <p>
6791223e	89	<a name="5217"></a>
0198fd3c	90	A CGI application would have no efficient way of solving this problem. For example, if the user asks for the 50,000th prime number, a CGI application would have to calculate the first prime number, then the second, and so on, up until the 50,000th. The application would then terminate, taking with it all its hard-earned calculations. If a client then asks for the 49,000th prime number, the server will have to spawn a new CGI application which will have to start calculating prime numbers from scratch.<p>
6791223e	91	<a name="4315"></a>
0198fd3c	92	FastCGI applications can be much more efficient at this sort of problem, since they can maintain state. A FastCGI application can calculate an extensive table of prime numbers in its initialization phase and then keep the table around indefinitely. Whenever a client requests a particular prime number, the response loop merely needs to look it up in the table. <p>
6791223e	93	<a name="4343"></a>
0198fd3c	94	Here is the code for the prime number example:<p>
	95	<pre>
	96	#include "fcgi_stdio.h"
	97	#include <stdlib.h>
	98	#include <string.h>
	99
	100	#define POTENTIALLY_PRIME 0
	101	#define COMPOSITE 1
	102	#define VALS_IN_SIEVE_TABLE 1000000
	103	#define MAX_NUMBER_OF_PRIME_NUMBERS 78600
	104
	105	/* All initialized to POTENTIALLY_PRIME */
	106	long int sieve_table[VALS_IN_SIEVE_TABLE];
	107	long int prime_table[MAX_NUMBER_OF_PRIME_NUMBERS];
	108	/* Use Sieve of Erastothenes method of building
	109	a prime number table. */
	110	void
	111	initialize_prime_table(void)
	112	{
	113	long int prime_counter=1;
	114	long int current_prime=2, c, d;
	115
	116	prime_table[prime_counter]=current_prime;
	117
	118	while (current_prime < VALS_IN_SIEVE_TABLE) {
	119	/* Mark off composite numbers. */
	120	for (c = current_prime; c <= VALS_IN_SIEVE_TABLE;
	121	c += current_prime) {
	122	sieve_table[c] = COMPOSITE;
	123	}
	124
	125	/* Find the next prime number. */
	126	for (d=current_prime+1; sieve_table[d] == COMPOSITE; d++);
	127	/* Put the new prime number into the table. */
	128	prime_table[++prime_counter]=d;
	129	current_prime=d;
	130	}
	131	}
	132
	133
	134	void main(void)
	135	{
	136	char *query_string;
	137	long int n;
	138
	139	initialize_prime_table();
	140
	141	while(FCGI_Accept() >= 0) {
	142	/*
	143	* Produce the necessary HTTP header.
	144	*/
	145	printf("Content-type: text/html\r\n"
	146	"\r\n");
	147	/*
	148	* Produce the constant part of the HTML document.
	149	*/
	150	printf("<title>Prime FastCGI</title>\n"
	151	"<h1>Prime FastCGI</h1>\n");
	152	/*
	153	* Read the query string and produce the variable part
	154	* of the HTML document.
	155	*/
	156	query_string = getenv("QUERY_STRING");
	157	if(query_string == NULL) {
158	printf("Usage: Specify a positive number in the query string.\n");
159	} else {
160	query_string = strchr(query_string, `=') + 1;
161	n = strtol(query_string);
162	if(n < 1) {
163	printf("The query string `%s' is not a positive number.\n",
164	query_string);
165	} else if(n > MAX_NUMBER_OF_PRIME_NUMBERS) {
166	printf("The number %d is too large for this program.\n", n);
167	} else
168	printf("The %ldth prime number is %ld.\n", prime_table[n]);
169	}
170	}
171	} /* while FCGI_Accept */
172	}
6791223e	173	</pre><a name="5349"></a>
0198fd3c	174	This application has a noticeable start up cost while it initializes the table, but subsequent accesses are fast.<p>
6791223e	175	<a name="5151">
0198fd3c	176	<h1> Building</h1>
6791223e	177	</a><a name="4630"></a>
0198fd3c	178	This section explains how to build and debug FastCGI applications written in C.<p>
6791223e	179	<a name="4629"></a>
0198fd3c	180	The C preprocessor needs to know the location of the <code>fcgi_stdio.h</code> header file, which is at the following pathname:<p>
6791223e	181	<pre><a name="4642">
0198fd3c	182	<em>$toolkit</em>/include/fcgi_stdio.h
0198fd3c	183	</a>
6791223e	184	</pre><a name="4645"></a>
0198fd3c	185	where <em>$toolkit</em> symbolizes the directory in which you have installed the Software Development Kit for FastCGI. <p>
6791223e	186	<a name="4760"></a>
0198fd3c	187	The linker needs to know the location of the <code>libfcgi.a</code> library file, which is at the following pathname:<p>
6791223e	188	<pre><a name="4647">
0198fd3c	189	<em>$toolkit</em>/libfcgi/libfcgi.a
0198fd3c	190	</a>
6791223e	191	</pre><a name="4648"></a>
0198fd3c	192	If your linker does not search the Berkeley socket library, then you must add linker directives to force this search.<p>
6791223e	193	<a name="4773"></a>
0198fd3c	194	We provide a sample application <code>Makefile</code> at the following pathname: <p>
6791223e	195	<pre><a name="4649">
0198fd3c	196	<em>$toolkit</em>/examples/Makefile
0198fd3c	197	</a>
6791223e	198	</pre><a name="4652"></a>
0198fd3c	199	This <code>Makefile</code> contains the necessary rules and pathnames to build the C FastCGI applications accompanying the toolkit. To build all the applications, type:<p>
6791223e	200	<pre><a name="4653">
0198fd3c	201	$ ./configure<br>$ make
	202	</a>
	203	</pre><a name="4190">
	204	<h1> Memory Leaks</h1>
6791223e	205	</a><a name="4178"></a>
0198fd3c	206	Memory leaks are seldom a problem in CGI programming because CGI applications rarely run long enough to be concerned with leaks. However, memory leaks can become a problem in FastCGI applications, particularly if each call to a popular FastCGI application causes additional memory to leak. <p>
6791223e	207	<a name="4785"></a>
0198fd3c	208	When converting to FastCGI, you can either use a tool such as Purify from Pure Software to discover and fix storage leaks or you can run a C garbage collector such as Great Circle from Geodesic Systems. <p>
6791223e	209	<a name="4972"></a>
0198fd3c	210	<p>
6791223e	211
0198fd3c	212	<hr><br>
	213
	214	<a href="cover.htm">[Top]</a> <a href="ch1intro.htm">[Prev]</a> <a href="ch3perl.htm">[Next]</a> <a href="ap_guida.htm">[Bottom]</a>
	215	<hr><br>
	216
	217
	218	<!-- This file was created with Quadralay WebWorks Publisher 3.0.3 -->
	219	<!-- -->
	220	<!-- For more information on how this document, and how the rest of -->
	221	<!-- this server was created, email yourEmail@xyzcorp.com -->
	222	<!-- -->
	223	<!-- Last updated: 04/15/96 08:00:16 -->
	224
	225	</body>
	226	</html>