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FastCGI Developer's Kit
![[[FastCGI]]](../images/fcgi-hd.gif)
FastCGI Developer's Kit
Mark R. Brown
Open Market, Inc.
Document Version: 1.08
11 June 1996
Copyright © 1996 Open Market, Inc. 245 First Street, Cambridge, MA 02142 U.S.A.
Tel: 617-621-9500 Fax: 617-621-1703 URL: http://www.openmarket.com/
$Id: fcgi-devel-kit.htm,v 1.6 2002/02/25 00:42:59 robs Exp $
FastCGI is an open extension to CGI that provides high performance for all Internet applications without the
penalties of Web server APIs.
FastCGI is designed to be layered on top of existing Web server APIs. For instance, the mod_fastcgi
Apache module adds FastCGI support to the Apache server. FastCGI can also be used, with reduced functionality
and reduced performance, on any Web server that supports CGI.
This FastCGI Developer's Kit is designed to make developing FastCGI applications easy. The kit currently
supports FastCGI applications written in C/C++, Perl, Tcl, and Java.
This document:
-
Describes how to configure and build the kit for your development platform.
-
Tells how to write applications using the libraries in the kit.
-
Tells how to run applications using Web servers that support FastCGI or using any Web server and
cgi-fcgi.
The kit includes a technical white paper,
doc/fastcgi-whitepaper/fastcgi.htm. You should read at least the first three sections of the
technical white paper before starting to write FastCGI applications. The performance
paper will help you understand how application design affects performance with FastCGI.
The FastCGI Specification, doc/fcgi-spec.html, defines the interface
between a FastCGI application and a Web server that supports FastCGI. The software in the kit implements the
specification. You don't need to read the specification in order to write applications.
Additional information is provided in the FAQ document, which
contains frequently asked questions about application development using FastCGI, as well as some general
information.
Experience with CGI programming will be extremely valuable in writing FastCGI applications. If you don't
have enough experience with CGI programming, you should read one information on the W3C CGI page.
The kit is a compressed tar (tar.Z) file, distributed via the fastcgi-archives.github.io
Web page. Unpacking the tar file creates a new directory fcgi-devel-kit.
Open the kit's index page, fcgi-devel-kit/index.html, using the "Open File" command in
your Web browser. The index page gives you an overview of the kit structure and helps you navigate the kit.
The index page also contains links that run some example applications, but the applications won't work
when index.html is opened using the "Open File" command because they aren't aren't being
accessed through a Web server.
In order to use the kit in earnest you'll need a Web server that you control, a Web server running with
your user ID. The Web server will be starting FastCGI applications that you will need to debug; this will be a
lot more convenient for you if these processes run with your user ID. It is best to have a Web server that
supports FastCGI. Section 4 discusses Web server issues.
If you can, keep the kit on a file system accessible from your personal workstation, do your builds on your
workstation, and run your Web server on your workstation. If that's not possible, arrange a configuration
such that the kit is accessible from the machine that's going to run your Web server, and build the kit
and your applications on a machine that's configured exactly the same way (same processor architecture,
operating system, etc.) as the machine that's going to run your Web server.
To build the kit you execute this sequence of commands in the fcgi-devel-kit directory:
% ./configure
% make
We've built and exercised the kit on these platforms (listed in alphabetical order):
-
BSD/OS 1.1 (Intel Pentium), gcc
-
Digital UNIX V3.2 148 (Alpha), gcc/cc
-
Hewlett-Packard HP-UX A.09.05 C and B.10.01 A (PA-RISC), gcc/cc
-
IBM AIX 1 4 (RS/6000), gcc
-
Silicon Graphics IRIX 5.3 11091812 (MIPS), gcc
-
Sun Solaris 2.4 and 2.5 (SPARC), gcc/cc
-
Sun SunOS 4.1.4 (SPARC), gcc
Once you've built the kit, follow the directions in Section 4 to bring up your Web
server and run the example applications.
The fcgi_stdio library provides the easiest transition for C CGI programs and C CGI programmers to
FastCGI. Using this library your application can run using either CGI or FastCGI, with the same binary for
both situations.
To introduce the fcgi_stdio library we give a pair of examples: a tiny CGI program and the
translation of this program to FastCGI. These two example programs are included in the kit.
The CGI program is examples/tiny-cgi.c:
#include <stdio.h>
#include <stdlib.h>
void main(void)
{
int count = 0;
printf("Content-type: text/html\r\n"
"\r\n"
"<title>CGI Hello!</title>"
"<h1>CGI Hello!</h1>"
"Request number %d running on host <i>%s</i>\n",
++count, getenv("SERVER_NAME"));
}
The key features of this tiny CGI program are:
-
The program sends data to the Web server by writing to stdout, using printf in this
example. The CGI program first sends a Content-type header, then a small HTML document. The
program includes stdio.h in order to get access to the printf function.
-
The program obtains parameters provided by the Web server by reading environment variables. The CGI program
reads the SERVER_NAME variable using getenv and includes the value in the HTML document.
The program includes stdlib.h in order to get access to the getenv function.
The count variable is degenerate in this example; the CGI program runs a single request, so the
request number is always one. This variable will be more interesting in the FastCGI example.
The corresponding FastCGI program is examples/tiny-fcgi.c:
#include "fcgi_stdio.h"
#include <stdlib.h>
void main(void)
{
int count = 0;
while(FCGI_Accept() >= 0)
printf("Content-type: text/html\r\n"
"\r\n"
"<title>FastCGI Hello!</title>"
"<h1>FastCGI Hello!</h1>"
"Request number %d running on host <i>%s</i>\n",
++count, getenv("SERVER_NAME"));
}
The key features of this tiny FastCGI program are:
-
The program is structured as a loop that begins by calling the function FCGI_Accept. The
FCGI_Accept function blocks until a new request arrives for the program to execute. The program
includes fcgi_stdio.h in order to get access to the FCGI_Accept function.
-
Within the loop, FCGI_Accept creates a CGI-compatible world. printf and getenv
operate just as in the CGI program. stdin and stderr, not used by this tiny program, also
operate just as in a CGI program.
The count variable increments each time through the loop, so the program displays a new request
number each time. You can use the reload button in your browser to demonstrate this, once you've got the
program built and running.
Building the program
If you can build examples/tiny-cgi.c, it will be straightforward for you to build
examples/tiny-fcgi.c. You need to:
-
Add the directory containing the fcgi_stdio.h header to the compiler's include search path.
The kit calls this directory include.
-
Add the library libfcgi.a to the linker's command line so that it will be searched when
linking. The libfcgi.a library implements the functions defined in fcgi_stdio.h. The kit
calls the directory containing this library libfcgi.
-
Determine whether or not the linker on your platform searches the Berkeley socket library by default, and
if not, add linker directives to force this search.
See examples/Makefile (created by configure) for a Makefile that builds both programs.
Autoconf handles the platform-dependent linking issues; to see how, examine configure.in and
examples/Makefile.in.
Running the program
Section 4 is all about how to run FastCGI applications.
You can use CGI to run application binaries built with the fcgi_stdio library. The
FCGI_Accept function tests its environment to determine how the application was invoked. If it was
invoked as a CGI program, the first call to FCGI_Accept is essentially a no-op and the second call returns
-1. In effect, the request loop disappears.
Of course, when a FastCGI application is run using CGI it does not get the benefits of FastCGI. For instance,
the application exits after servicing a single request, so it cannot maintain cached information.
Implementation details
fcgi_stdio.h works by first including stdio.h, then defining macros to replace essentially
all of the types and procedures defined in stdio.h. (stdio.h defines a few procedures that
have nothing to do with FILE *, such as sprintf and sscanf; fcgi_stdio.h
doesn't replace these.) For instance, FILE becomes FCGI_FILE and printf becomes
FCGI_printf. You'll only see these new names if you read fcgi_stdio.h or examine your C
source code after preprocessing.
Here are some consequences of this implementation technique:
-
On some platforms the implementation will break if you include stdio.h after including
fcgi_stdio.h, because stdio.h often defines macros for functions such as getc
and putc. Fortunately, on most platforms stdio.h is protected against multiple includes
by lines near the top of the file that look like
#ifndef _STDIO_H
#define _STDIO_H
The specific symbol used for multiple-include protection, _STDIO_H in this example, varies from
platform to platform. As long as your platform protects stdio.h against multiple includes, you
can forget about this issue.
-
If your application passes FILE * to functions implemented in libraries for which you have source
code, then you'll want to recompile these libraries with fcgi_stdio.h included. Most C
compilers provide a command-line option for including headers in a program being compiled; using such a
compiler feature allows you to rebuild your libraries without making source changes. For instance the gcc
command line
gcc -include /usr/local/include/fcgi_stdio.h wonderlib.c
causes gcc to include fcgi_stdio.h before it even begins to read the module
wonderlib.c.
-
If your application passes FILE * to functions implemented in libraries for which you do not have
source code, then you'll need to include the headers for these libraries before you include
fcgi_stdio.h. You can't pass the stdin, stdout, or stderr streams
produced by FCGI_Accept to any functions implemented by these libraries. You can pass a stream on
a Unix file to a library function by following this pattern:
FILE *myStream = fopen(path, "r");
answer = MungeStream(FCGI_ToFile(myStream));
Here MungeStream is a library function that you can't recompile and FCGI_ToFile is
a macro that converts from FCGI_FILE * to FILE *. The macro FCGI_ToFile is
defined in fcgi_stdio.h.
Converting CGI programs
The main task in converting a CGI program into a FastCGI program is separating the code that needs to execute
once, initializing the program, from the code that needs to run for each request. In our tiny example,
initializing the count variable is outside the loop, while incrementing the count variable
goes inside.
Retained application state may be an issue. You must ensure that any application state created in processing
one request has no unintended effects on later requests. FastCGI offers the possibility of significant
application performance improvements, through caching; it is up to you to make the caches work correctly.
Storage leaks may be an issue. Many CGI programs don't worry about storage leaks because the programs
don't run for long enough for bloating to be a problem. When converting to FastCGI, you can either use a
tool such as Valgrind to discover and fix storage
leaks, or you can run a C garbage collector such as Boehm-Demers-Weiser conservative garbage collector
Limitations
Currently there are some limits to the compatibility provided by the fcgi_stdio library:
Reference documentation
The FCGI_Accept manpage, doc/FCGI_Accept.3, describes the
function in the traditional format.
The FCGI_Finish (doc/FCGI_Finish.3), FCGI_SetExitStatus (doc/FCGI_SetExitStatus.3), and FCGI_StartFilterData (doc/FCGI_StartFilterData.3) manpages
document capabilities of the fcgi-stdio library that are not illustrated above.
The fcgiapp library is a second C library for FastCGI. It does not provide the high degree of source
code compatibility provided by fcgi_stdio; in return, it does not make such heavy use of
#define. fcgi_stdio is implemented as a thin layer on top of fcgiapp.
Applications built using the fcgiapp library cannot run as CGI programs; that feature is provided at
the fcgi_stdio level.
Functions defined in fcgiapp are named using the prefix FCGX_ rather than FCGI_.
For instance, FCGX_Accept is the fcgiapp version of FCGI_Accept.
Documentation of the fcgiapp library takes the form of extensive comments in the header file
include/fcgiapp.h. The sample programs examples/tiny-fcgi2.c and examples/echo2.c
illustrate how to use fcgiapp.
A major advantage of the FastCGI approach to high-performance Web applications is its language-neutrality. CGI
scripts written in popular languages such as Perl and Tcl can be evolved into high-performance FastCGI
applications.
We have produced FastCGI-integrated Perl and Tcl interpreters. Doing so was easy, since Perl and Tcl are
conventional C applications and fcgi_stdio was designed for converting conventional C applications.
Essentially no source code changes were required in these programs; a small amount of code was added in order
to make FCGI_Accept and other FastCGI primitives available in these languages. And because these
interpreters were developed using fcgi_stdio, they run standard Perl and Tcl applications (e.g. CGI
scripts) as well as FastCGI applications.
See the fastcgi-archives.github.io Web page for more information about the Perl and Tcl
libraries.
Here are the Perl and Tcl versions of tiny-fcgi:
#!./perl
use FCGI;
$count = 0;
while(FCGI::accept() >= 0) {
print("Content-type: text/html\r\n\r\n",
"<title>FastCGI Hello! (Perl)</title>\n",
"<h1>FastCGI Hello! (Perl)</h1>\n";
"Request number ", ++$count,
" running on host <i>";$env(SERVER_NAME)</i>");
}
#!./tclsh
set count 0
while {[FCGI_Accept] >= 0 } {
incr count
puts -nonewline "Content-type: text/html\r\n\r\n"
puts "<title>FastCGI Hello! (Tcl)</title>"
puts "<h1>FastCGI Hello! (Tcl)</h1>"
puts "Request number $count running on host <i>$env(SERVER_NAME)</i>"
}
Converting a Perl or Tcl CGI application to FastCGI is not fundamentally different from converting a C CGI
application to FastCGI. You separate the portion of the application that performs one-time initialization from
the portion that performs per-request processing. You put the per-request processing into a loop controlled by
FCGI::accept (Perl) or FCGI_Accept (Tcl).
Java is not just for browser-based applets. It is already suitable for writing some Web server applications,
and its range of applicability will only grow as Java compilers and other Java tools improve. Java's
modules, garbage collection, and threads are especially valuable for writing long-lived application servers.
The FCGIInterface class provides facilities for Java applications analogous to what
fcgi_stdio provides for C applications. Using this library your Java application can run using either
CGI or FastCGI.
The kit includes separate companion document on using FastCGI with Java. The
source code for FastCGI classes is contained in directory java/src and the compiled code in
java/classes.
Here is the Java version of tiny-fcgi:
import FCGIInterface;
class TinyFCGI {
public static void main (String args[]) {
int count = 0;
while(new FCGIInterface().FCGIaccept()>= 0) {
count ++;
System.out.println("Content-type: text/html\r\n\r\n");
System.out.println(
"<title>FastCGI Hello! (Java)</title>");
System.out.println("<h1>FastCGI Hello! (Java)</h1>");
System.out.println(
"request number " + count + " running on host <i>" +
System.getProperty("SERVER_NAME") + "</i>");
}
}
}
For a current listing of Web servers that support FastCGI, see the fastcgi-archives.github.io Web page.
Some of the Web servers that support FastCGI perform management of FastCGI applications. You don't need to
start and stop FastCGI applications; the Web server takes care of this. If an application process should
crash, the Web server restarts it.
Web servers support FastCGI via new configuration directives. Since these directives are server-specific, get
more information from the documentation that accompanies each server.
The program cgi-fcgi allows you to run FastCGI applications using any Web server that supports CGI.
Here is how cgi-fcgi works. cgi-fcgi is a standard CGI program that uses Unix domain or
TCP/IP sockets to communicate with a FastCGI application. cgi-fcgi takes the path name or host/port
name of a listening socket as a parameter and connects to the FastCGI application listening on that
socket. cgi-fcgi then forwards the CGI environment variables and stdin data to the FastCGI
application, and forwards the stdout and stderr data from the FastCGI application to the Web
server. When the FastCGI application signals the end of its response, cgi-fcgi flushes its buffers
and exits.
Obviously, having cgi-fcgi is not as good as having a server with integrated FastCGI support:
-
Communication is slower than with a Web server that avoids the fork/exec overhead on every FastCGI request.
-
cgi-fcgi does not perform application management, so you need to provide this yourself.
-
cgi-fcgi supports only the Responder role.
But cgi-fcgi does allow you to develop applications that retain state in memory between connections,
which often provides a major performance boost over normal CGI. And all the applications you develop using
cgi-fcgi will work with Web servers that have integrated support for FastCGI.
The file examples/tiny-fcgi.cgi demonstrates a way to use cgi-fcgi to run a typical
application, in this case the examples/tiny-fcgi application:
#!../cgi-fcgi/cgi-fcgi -f
-connect sockets/tiny-fcgi tiny-fcgi
On most Unix platforms, executing this command-interpreter file runs cgi-fcgi with arguments
-f and examples/tiny-fcgi.cgi. (Beware: On some Unix platforms, including HP-UX, the first
line of a command-interpreter file cannot contain more than 32 characters, including the newline; you may need
to install the cgi-fcgi application in a standard place like /usr/local/bin or create a
symbolic link to the cgi-fcgi application in the directory containing your application.) The
cgi-fcgi program reads the command-interpreter file and connects to the FastCGI application whose
listening socket is examples/sockets/tiny-fcgi.
Continuing the example, if cgi-fcgi's connection attempt fails, it creates a new process running
the program examples/tiny-fcgi and listening on socket examples/sockets/tiny-fcgi. Then
cgi-fcgi retries the connection attempt, which now should succeed.
The cgi-fcgi program has two other modes of operation. In one mode it connects to applications but
does not start them; in the other it starts applications but does not connect to them. These modes are
required when using TCP/IP. The cgi-fcgi manpage, doc/cgi-fcgi.1,
tells the full story.
To run the example applications using cgi-fcgi, start your Web server and give it the directory
fcgi-devel-kit as the root of its URL space. If the machine running your server is called
bowser and your server is running on port 8888, you'd then open the URL
http://bowser:8888/index.html to reach the kit's index page. Now the links on the index page that
run example applications via cgi-fcgi should be active.
On Digital UNIX 3.0 there's a problem with Unix domain listening sockets on NFS file systems. The symptom
when using cgi-fcgi is an exit status of 38 (ENOTSOCK: socket operation on non-socket), but cgi-fcgi
may dump core in this case when compiled optimized. Work-around: Store your Unix domain listening sockets on a
non NFS file system, upgrade to Digital UNIX 3.2, or use TCP sockets.
On AIX there's a problem with shared listening sockets. The symptoms can include application core dumps
and kernel panic. Work-around: Run a single FastCGI application server per listening socket.
The FastCGI Archives Issues are used for discussions of issues in developing FastCGI
applications, see https://github.com/FastCGI-Archives/fcgi2/issues.
© 1996, Open Market, Inc. / mbrown@openmarket.com
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