doc/fcgi-tcl.htm

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   5          Integrating FastCGI with Tcl
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  21       <DIV CLASS="c1">
  22          <A HREF="http://fastcgi.com"><IMG BORDER="0" SRC="../images/fcgi-hd.gif" ALT="[[FastCGI]]"></A>
  23       </DIV>
  24       <BR CLEAR="all">
  25       <DIV CLASS="c1">
  26          <H3>
  27             Integrating FastCGI with Tcl
  28          </H3>
  29       </DIV>
  30       <!--Copyright (c) 1996 Open Market, Inc.                                    -->
  31       <!--See the file "LICENSE.TERMS" for information on usage and redistribution-->
  32       <!--of this file, and for a DISCLAIMER OF ALL WARRANTIES.                   -->
  33       <P CLASS="c2">
  34          Michael S. Shanzer<BR>
  35          Open Market, Inc.<BR>
  36          <EM>19 January 1995</EM>
  37       </P>
  38       <H5 CLASS="c3">
  39          Copyright &copy; 1996 Open Market, Inc. 245 First Street, Cambridge, MA 02142 U.S.A.<BR>
  40          Tel: 617-621-9500 Fax: 617-621-1703 URL: <A HREF=
  41          "http://www.openmarket.com/">http://www.openmarket.com/</A><BR>
  42          $Id: fcgi-tcl.htm,v 1.4 2002/02/25 00:42:59 robs Exp $<BR>
  43       </H5>
  44       <HR>
  45       <H3>
  46          <A NAME="S1">1. Introduction</A>
  47       </H3>
  48       <P>
  49          Tcl (tool command language) is an embeddable scripting language that&#39;s often used for CGI programming. Tcl
  50          is freely available as a source kit.
  51       </P>
  52       <P>
  53          We&#39;ve built a Tcl interpreter that runs as a FastCGI application. Our purpose in doing so was twofold:
  54       </P>
  55       <UL>
  56          <LI>
  57             <I>Create a useful artifact.</I> Open Market has written many CGI applications using Tcl. Now we&#39;d like
  58             to turn them into FastCGI applications.
  59             <P>
  60             </P>
  61          </LI>
  62          <LI>
  63             <I>Demonstrate how easy it is to integrate FastCGI with an existing program.</I> The Tcl interpreter is a
  64             substantial program, so integrating FastCGI with the Tcl interpreter is a good test of the
  65             <TT>fcgi_stdio</TT> compatability library.
  66          </LI>
  67       </UL>
  68       <P>
  69          We&#39;ve succeeded on both counts. We now have a platform for migrating our Tcl-based CGI applications to
  70          FastCGI. And the integration required a very small effort. The only source code change to the Tcl interpreter
  71          was the routine addition of a handful of new commands: <TT>FCGI_Accept</TT>, <TT>FCGI_Finish</TT>,
  72          <TT>FCGI_SetExitStatus</TT>, and <TT>FCGI_StartFilterData</TT>.
  73       </P>
  74       <P>
  75          The FastCGI-integrated Tcl interpreter works as usual when run from a shell or as a CGI program. You don&#39;t
  76          need two Tcls, one for FastCGI and one for other uses.
  77       </P>
  78       <P>
  79          The remainder of this document gives a recipe you can follow to build FastCGI into Tcl, explains what&#39;s
  80          happening in the recipe, and illustrates the use of FastCGI Tcl with an example program.
  81       </P>
  82       <P>
  83       </P>
  84       <H3>
  85          <A NAME="S2">2. Recipe</A>
  86       </H3>
  87       <P>
  88          Here are the assumptions embedded in the following recipe:
  89       </P>
  90       <UL>
  91          <LI>
  92             You are building Tcl 7.4p3, the current stable Tcl release as this is written. You unpack the Tcl kit into
  93             a directory <TT>tcl7.4</TT> that&#39;s a sibling of the FastCGI kit directory <TT>fcgi-devel-kit</TT>.
  94             <P>
  95             </P>
  96          </LI>
  97          <LI>
  98             You have gcc version 2.7 installed on your system, and use it in the build. gcc is convenient because it
  99             supports the <TT>-include</TT> command-line option that instructs the C preprocessor to include a specific
 100             file before processing any other include files. This allows you to include <TT>fcgi_stdio.h</TT> without
 101             modifying Tcl source files. (The reason for specifying gcc version 2.7 is that I have experienced bad
 102             behavior with an earlier version and the <TT>-include</TT> flag -- the C preprocessor died with SIGABRT.)
 103             <P>
 104             </P>
 105          </LI>
 106          <LI>
 107             You have GNU autoconf installed on your system. If you don&#39;t have GNU autoconf, you will have to make
 108             certain edits by hand and repeat these edits for each build platform.<BR>
 109             <BR>
 110          </LI>
 111       </UL>
 112       <P>
 113          If those are valid assumptions, follow these steps:
 114       </P>
 115       <OL>
 116          <LI>
 117             <I>Build the FastCGI Developer&#39;s Kit.</I> Tcl needs to link against <TT>libfcgi.a</TT>, so <A HREF=
 118             "fcgi-devel-kit.htm#S2">build the FastCGI Developer&#39;s Kit</A> in order to create this library for your
 119             platform.
 120             <P>
 121             </P>
 122          </LI>
 123          <LI>
 124             <I>Pull the Tcl 7.4p3 kit.</I> You&#39;ll need the files <A HREF=
 125             "ftp://ftp.smli.com/pub/tcl/tcl7.4.tar.Z">tcl7.4.tar.Z</A>, <A HREF=
 126             "ftp://ftp.smli.com/pub/tcl/tcl7.4p1.patch.gz">tcl7.4p1.patch.gz</A>, <A HREF=
 127             "ftp://ftp.smli.com/pub/tcl/tcl7.4p2.patch.gz">tcl7.4p2.patch.gz</A>, and <A HREF=
 128             "ftp://ftp.smli.com/pub/tcl/tcl7.4p3.patch.gz">tcl7.4p3.patch.gz</A>. (Some older Netscape browsers
 129             can&#39;t perform these retrievals because of a protocol conflict between Netscape and Sun&#39;s firewall.)
 130             <P>
 131                Unpack the tar file in the parent directory of the FastCGI kit directory you used in the previous step,
 132                so that the directories <TT>tcl7.4</TT> and <TT>fcgi-devel-kit</TT> are siblings. After unpacking the
 133                tar file, follow the directions in the <TT>README</TT> to apply the patches.
 134             </P>
 135             <P>
 136                The <A HREF="http://www.sunlabs.com:80/research/tcl/">Sun Labs Tcl/Tk Project Page</A> contains a wealth
 137                of information on Tcl, including up to date information on the latest kits.
 138             </P>
 139             <P>
 140             </P>
 141          </LI>
 142          <LI>
 143             <I>Copy the files <TT>tclFCGI.c</TT>, <TT>tclAppInit.c</TT>, <TT>Makefile.in</TT>, and
 144             <TT>configure.in</TT> from the FastCGI kit.</I>
 145 <PRE>
 146     &gt; cd tcl7.4
 147     &gt; mv tclAppInit.c tclAppInit.c.orig
 148     &gt; mv Makefile.in.orig Makefile.in.orig.orig
 149     &gt; mv Makefile.in Makefile.in.orig
 150     &gt; mv configure.in configure.in.orig
 151     &gt; cp ../fcgi-devel-kit/tcl/tcl7.4/* .
 152     &gt; cp ../fcgi-devel-kit/tcl/common/* .
 153 </PRE>
 154          </LI>
 155          <LI>
 156             <I>Create a new <TT>configure</TT> script.</I>
 157 <PRE>
 158     &gt; autoconf
 159 </PRE>
 160          </LI>
 161          <LI>
 162             <I>Configure and build.</I>
 163 <PRE>
 164     &gt; ./configure
 165     &gt; make
 166 </PRE>
 167             The <TT>make</TT> creates the Tcl interpreter <TT>tclsh</TT> and library archive <TT>libtcl.a</TT> (for
 168             embedding Tcl in your own C applications). The Tcl <TT>README</TT> file explains how you can experiment
 169             with <TT>tclsh</TT> without installing it in a standard place.<BR>
 170             <BR>
 171          </LI>
 172       </OL>
 173       <H3>
 174          <A NAME="S3">3. Recipe Explained</A>
 175       </H3>
 176       <P>
 177          The recipe alone is fine if you are using Tcl 7.4p3, you have gcc version 2.7, and you have GNU autoconf. In
 178          case one or more of these assumptions doesn&#39;t hold for you, and to illuminate how little work was involved
 179          in integrating FastCGI, here&#39;s an explanation of how and why you would modify the files
 180          <TT>tclAppInit.c</TT>, <TT>Makefile.in</TT>, and <TT>configure.in</TT> from the Tcl kit.
 181       </P>
 182       <UL>
 183          <LI>
 184             <TT>tclAppInit.c</TT>:
 185             <P>
 186             </P>
 187             <UL>
 188                <LI>
 189                   Add the following three lines of code to the function <TT>Tcl_AppInit</TT> after the call to
 190                   <TT>Tcl_Init</TT> and after the comment about calling init procedures:
 191 <PRE>
 192     if (FCGI_Init(interp) == TCL_ERROR) {
 193         return TCL_ERROR;
 194     }
 195 </PRE>
 196                   This registers four Tcl commands (<TT>FCGI_Accept</TT>, <TT>FCGI_Finish</TT>,
 197                   <TT>FCGI_SetExitStatus</TT>, and <TT>FCGI_StartFilterData</TT>), implemented in <TT>tclFCGI.c</TT>,
 198                   with the Tcl interpreter.
 199                   <P>
 200                   </P>
 201                </LI>
 202             </UL>
 203          </LI>
 204          <LI>
 205             <TT>Makefile.in</TT>:
 206             <P>
 207             </P>
 208             <UL>
 209                <LI>
 210                   Add <TT>tclFCGI.o</TT> to the <TT>GENERIC_OBJS</TT> variable, and add <TT>tclFCGI.c</TT> to the
 211                   <TT>SRCS</TT> variable.
 212                   <P>
 213                      This builds the FastCGI Tcl commands and links them into the Tcl interpreter.
 214                   </P>
 215                   <P>
 216                   </P>
 217                </LI>
 218                <LI>
 219                   Add <TT>-I../fcgi-devel-kit/include -include ../fcgi-devel-kit/include/fcgi_stdio.h</TT> to the
 220                   <TT>CFLAGS</TT> variable.
 221                   <P>
 222                      This includes <TT>fcgi_stdio.h</TT> when compiling C code for the Tcl interpreter, overriding the
 223                      normal <TT>stdio</TT> types, variables, and functions.
 224                   </P>
 225                   <P>
 226                   </P>
 227                </LI>
 228                <LI>
 229                   Add <TT>../fcgi-devel-kit/libfcgi/libfcgi.a</TT> before the <TT>@LIBS@</TT> part of the <TT>LIBS</TT>
 230                   variable.
 231                   <P>
 232                      This links the implementation of <TT>fcgi_stdio.h</TT> into the Tcl interpreter, for use by the
 233                      <TT>FCGI_accept</TT> command and any code that uses <TT>stdio</TT> variables or calls
 234                      <TT>stdio</TT> functions.
 235                   </P>
 236                   <P>
 237                   </P>
 238                </LI>
 239             </UL>
 240             <P>
 241                The last two edits will vary if you use a compiler other than gcc or install the <TT>tcl7.4</TT>
 242                directory somewhere else in relation to the <TT>fcgi-devel-kit</TT> directory.
 243             </P>
 244             <P>
 245             </P>
 246          </LI>
 247          <LI>
 248             <TT>configure.in</TT>:
 249             <P>
 250             </P>
 251             <UL>
 252                <LI>
 253                   Replace the lines
 254 <PRE>
 255 AC_C_CROSS
 256 CC=${CC-cc}
 257 </PRE>
 258                   with the lines
 259 <PRE>
 260 AC_PROG_CC
 261 AC_C_CROSS
 262 </PRE>
 263                   This selects gcc in preference to other C compilers.
 264                   <P>
 265                   </P>
 266                </LI>
 267                <LI>
 268                   Add the following lines just after the <TT>AC_SUBST(CC)</TT> line:
 269 <PRE>
 270 AC_CHECK_LIB(socket, main, [LIBS=&quot;$LIBS -lsocket&quot;])
 271 AC_CHECK_LIB(nsl, main, [LIBS=&quot;$LIBS -lnsl&quot;])
 272 AC_SUBST(LIBS)
 273 </PRE>
 274                   This ensures that the socket libraries used by FastCGI are linked into the Tcl interpreter.
 275                   <P>
 276                   </P>
 277                </LI>
 278             </UL>
 279             If GNU autoconf is not available to you, you&#39;ll leave <TT>configure.in</TT> alone and perform the
 280             following steps:
 281             <P>
 282             </P>
 283             <UL>
 284                <LI>
 285                   Execute
 286 <PRE>
 287     &gt; SETENV CC gcc
 288 </PRE>
 289                   before running <TT>configure</TT>.
 290                   <P>
 291                   </P>
 292                </LI>
 293                <LI>
 294                   If you are running on a SVR4-derived Unix platform, edit <TT>Makefile</TT> to add <TT>-lsocket
 295                   -lnsl</TT> to the <TT>LIBS</TT> value after running <TT>configure</TT>.
 296                   <P>
 297                   </P>
 298                </LI>
 299             </UL>
 300             If you ever re-run <TT>configure</TT>, you&#39;ll need to repeat these steps.
 301             <P>
 302             </P>
 303          </LI>
 304       </UL>
 305       <H3>
 306          <A NAME="S4">4. Writing FastCGI applications in Tcl</A>
 307       </H3>
 308       <P>
 309          The Tcl program <TT>tcl/tiny-tcl-fcgi</TT> performs the same function as the C program
 310          <TT>examples/tiny-fcgi.c</TT> that&#39;s used as an example in the <A HREF="fcgi-devel-kit.htm#S3.1.1">FastCGI
 311          Developer&#39;s Kit document</A>. Here&#39;s what the Tcl version looks like:
 312       </P>
 313       <P>
 314       </P>
 315 <PRE>
 316 #!./tclsh
 317 set count 0
 318 while {[FCGI_Accept] &gt;= 0 } {
 319     incr count
 320     puts -nonewline &quot;Content-type: text/html\r\n\r\n&quot;
 321     puts &quot;&lt;title&gt;FastCGI Hello! (Tcl)&lt;/title&gt;&quot;
 322     puts &quot;&lt;h1&gt;FastCGI Hello! (Tcl)&lt;/h1&gt;&quot;
 323     puts &quot;Request number $count running on host &lt;i&gt;$env(SERVER_NAME)&lt;/i&gt;&quot;
 324 }
 325 </PRE>
 326       <P>
 327          If you&#39;ve built Tcl according to the recipe and you have a Web server set up to run FastCGI applications,
 328          load the FastCGI Developer&#39;s Kit Index Page in that server and run this Tcl application now.
 329       </P>
 330       <P>
 331          The script invokes Tcl indirectly via the symbolic link <TT>examples/tclsh</TT>. It does this because HP-UX
 332          has a limit of 32 characters for the first line of a command-interpreter file such as
 333          <TT>examples/tiny-tcl-fcgi</TT>. If you run on HP-UX you won&#39;t want to sprinkle symbolic links to
 334          <TT>tclsh</TT> everywhere, so you should install <TT>tclsh</TT> with a shorter pathname than
 335          <TT>/usr/local/tcl7.4-fcgi/bin/tclsh7.4</TT>.
 336       </P>
 337       <P>
 338          The Tcl command <TT>FCGI_Accept</TT> treats the initial environment differently than the C function
 339          <TT>FCGI_Accept</TT>. The first call to the C function <TT>FCGI_Accept</TT> replaces the initial environment
 340          with the environment of the first request. The first call to the Tcl command <TT>FCGI_Accept</TT> adds the
 341          variable bindings of the first request to the bindings present in the initial environment. So when the first
 342          call to <TT>FCGI_Accept</TT> returns, bindings from the initial environment are still there (unless, due to
 343          naming conflicts, some of them have been overwritten by the first request). The next call to
 344          <TT>FCGI_Accept</TT> removes the bindings made on the previous call before adding a new set for the request
 345          just accepted, again preserving the initial environment.
 346       </P>
 347       <P>
 348          The FastCGI-integrated <TT>tclsh</TT> also includes commands <TT>FCGI_Finish</TT>,
 349          <TT>FCGI_SetExitStatus</TT>, and <TT>FCGI_StartFilterData</TT> that correspond to C functions in
 350          <TT>fcgi_stdio.h</TT>; see the manpages for full information.
 351       </P>
 352       <P>
 353          Converting a Tcl CGI application to FastCGI is not fundamentally different from converting a C CGI
 354          application. You separate the portion of the application that performs one-time initialization from the
 355          portion that performs per-request processing. You put the per-request processing into a loop controlled by
 356          <TT>FCGI_Accept</TT>.
 357       </P>
 358       <P>
 359       </P>
 360       <HR>
 361       <ADDRESS>
 362          <A HREF="mailto:shanzer@openmarket.com">Mike Shanzer // shanzer@openmarket.com</A>
 363       </ADDRESS>
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