This file is indexed.

/usr/share/doc/swi-prolog-doc/UserGuide/httpd.html is in swi-prolog-doc 5.6.59-2.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

<HTML>
<HEAD>
<TITLE>Programming in XPCE/Prolog: Section 11.9</TITLE><LINK REL=home HREF="index.html">
<LINK REL=contents HREF="Contents.html">
<LINK REL=index HREF="DocIndex.html">
<LINK REL=summary HREF="summary.html">
<LINK REL=previous HREF="dragdrop.html">
<LINK REL=next HREF="docrender.html">
<STYLE type="text/css">
/* Style sheet for SWI-Prolog latex2html
*/

dd.defbody
{ margin-bottom: 1em;
}

dt.pubdef
{ background-color: #c5e1ff;
}

pre.code
{ margin-left: 1.5em;
margin-right: 1.5em;
border: 1px dotted;
padding-top: 5px;
padding-left: 5px;
padding-bottom: 5px;
background-color: #f8f8f8;
}

div.navigate
{ text-align: center;
background-color: #f0f0f0;
border: 1px dotted;
padding: 5px;
}

div.title
{ text-align: center;
padding-bottom: 1em;
font-size: 200%;
font-weight: bold;
}

div.author
{ text-align: center;
font-style: italic;
}

div.abstract
{ margin-top: 2em;
background-color: #f0f0f0;
border: 1px dotted;
padding: 5px;
margin-left: 10%; margin-right:10%;
}

div.abstract-title
{ text-align: center;
padding: 5px;
font-size: 120%;
font-weight: bold;
}

div.toc-h1
{ font-size: 200%;
font-weight: bold;
}

div.toc-h2
{ font-size: 120%;
font-weight: bold;
margin-left: 2em;
}

div.toc-h3
{ font-size: 100%;
font-weight: bold;
margin-left: 4em;
}

div.toc-h4
{ font-size: 100%;
margin-left: 6em;
}

span.sec-nr
{ 
}

span.sec-title
{ 
}

span.pred-ext
{ font-weight: bold;
}

/* Footnotes */

sup.fn { color: blue; text-decoration: underline; }
span.fn-text: { display: none; }
sup.fn span {display: none;}
sup:hover span 
{ display: block !important;
position: absolute; top: auto; left: auto; width: 80%;
color: #000; background: white;
border: 2px solid;
padding: 5px; margin: 10px; z-index: 100;
font-size: smaller;
}
</STYLE>
</HEAD>
<BODY BGCOLOR="white">
<DIV class="navigate"><A class="nav" href="index.html"><IMG SRC="home.gif" BORDER=0 ALT="Home"></A>
<A class="nav" href="Contents.html"><IMG SRC="index.gif" BORDER=0 ALT="Contents"></A>
<A class="nav" href="DocIndex.html"><IMG SRC="yellow_pages.gif" BORDER=0 ALT="Index"></A>
<A class="nav" href="summary.html"><IMG SRC="info.gif" BORDER=0 ALT="Summary"></A>
<A class="nav" href="dragdrop.html"><IMG SRC="prev.gif" BORDER=0 ALT="Previous"></A>
<A class="nav" href="docrender.html"><IMG SRC="next.gif" BORDER=0 ALT="Next"></A>
</DIV>

<H2><A NAME="sec:11.9"><SPAN class="sec-nr">11.9</SPAN> <SPAN class="sec-title">Playing 
WEB (HTTP) server</SPAN></A></H2>

<A NAME="sec:httpd"></A>

<P>Web presentation has attractive features. It is well accepted, 
standardised (if you stick to the basics) and network-transparent. Many 
people think you need a web-server like
<A class="url" href="http://www.apache.org">Apache</A> with some sort of 
server-scripting (<A NAME="idx:CGI:530">CGI</A>) to realise a server. 
This is not true. Any application capable of elementary TCP/IP 
communication can easily act as a web-server.

<P>Using <font size=-1>XPCE</font> for this task may be attractive for a 
number of reasons.

<P>
<UL>
<LI><I>Prototyping</I><BR>
As the <font size=-1>XPCE/P</font>rolog running on your desktop is the 
server you can use the full debugging capabilities of Prolog to debug 
your server application.

<P>
<LI><I>Including graphics</I><BR>
<font size=-1>XPCE</font> can generate GIF and JPEG images for your 
web-pages on the fly. You can include <font size=-1>XPCE</font> <A class="" href="summary.html#class:graphical">graphical</A> 
objects directly in the output and have the server library handle the 
required transformations.

<P>
<LI><I>Remote presentation</I><BR>
<font size=-1>XPCE</font> can be used as <A NAME="idx:groupware:531">groupware</A> 
server, presenting state of the applications and allowing remote users 
to interact using their web-browser<SUP class="fn">13<SPAN class="fn-text">Using 
the Unix/X11 version <font size=-1>XPCE</font> can manage windows on 
multiple desktops. For MS-Windows users this is not supported.</SPAN></SUP>

<P>
<LI><I>Report generation</I><BR>
Applications may to use HTML as framework for report generation. Though 
rather weak in its expressiveness, the advantage is the wide support on 
presentation and distribution applications.
</UL>

<P>We start with a small demo, illustrating frames and text.

<P><A NAME="fig:httpd"></A>
<CENTER>
<IMG SRC="httpd.gif">
</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Figure 28 : </B>Mozilla showing <font size=-1>XPCE</font> generated 
figure</TABLE>

<PRE class="code">
:- module(my_httpd,
          [ go/1
          ]).
:- use_module(library(pce)).
:- use_module(library('http/httpd')).
:- use_module(library('http/html_write')).
:- use_module(library('draw/importpl')).

%       Create server at Port
<A NAME="idx:go1:532"></A>
go(Port) :-
        new(_, my_httpd(Port)).
<A NAME="idx:myhttpd:533"></A>
:- pce_begin_class(my_httpd, httpd, "Demo Web server").</PRE>

<P><B><CODE>-&gt;</CODE>request</B> is sent after the super-class has 
received a complete request header. We get the `path' and have a Prolog 
predicate generating the replies.

<PRE class="code"><A NAME="idx:myhttpdsendrequest:534"></A>
request(HTTPD, Request:sheet) :-&gt;
        "A request came in."::
        get(Request, path, Path),
        reply(Path, HTTPD).

:- discontiguous
        reply/2.</PRE>

<P><B><CODE>-&gt;</CODE>reply_html</B> takes &lt;<VAR>Module</VAR>&gt;:&lt;<VAR>DCGRuleSet</VAR>&gt; 
to formulate a reply. This uses the html_write library, converting a 
complex Prolog term into a formatted HTML document. The complex term can 
invoke additional DCG rulesets, providing nicely structured 
content-generation.

<PRE class="code">
reply('/', HTTPD) :- !,
        send(HTTPD, reply_html, my_httpd:frames).

frames --&gt;
        html(html([ head(title('Demo')),
                    frameset([cols('25%,75%')],
                             [ frame([ src('/index'),
                                       name(index)
                                     ]),
                               frame([ src('/blank'),
                                       name(body)
                                     ])
                             ])
                  ])).

<A NAME="idx:reply2:535"></A>
reply('/blank', HTTPD) :-
        send(HTTPD, reply_html, my_httpd:blank).

blank --&gt;
        page(title('Blank'),
             []).
<A NAME="idx:reply2:536"></A>
reply('/index', HTTPD) :-
        send(HTTPD, reply_html, my_httpd:index).

index --&gt;
        page(title('Index'),
             [ a([ href('/text'), target(body) ],
                 [ 'Show text' ]),
               br([]),
               a([ href('/picture'), target(body) ],
                 [ 'Show picture' ])
             ]).
<A NAME="idx:reply2:537"></A>
reply('/text', HTTPD) :-
        send(HTTPD, reply_html, my_httpd:text).

text --&gt;
        page(title('Text'),
             [ p(['Just showing a little text'])
             ]).</PRE>

<P>Reply a graphical object. The server translates the graphical to a 
GIF or JPEG bitmap and provides the proper HTTP reply header. You can 
also embed graphicals into the HTML structures used above.

<P>The drawing itself is exported from the demo program PceDraw and 
turned into an XPCE graphical using the support library draw/importpl.

<PRE class="code"><A NAME="idx:reply2:538"></A>
reply('/picture', HTTPD) :-
        make_picture(Gr),
        send(HTTPD, reply, Gr, 'image/gif').
<A NAME="idx:makepicture1:539"></A>
make_picture(Dev) :-
        new(Dev, device),
        drawing(xpcenetscape, Drawing),
        realise_drawing(Dev, Drawing).

%       Drawing imported from PceDraw

drawing(xpcenetscape,
        [ compound(new(A, figure),
                   drawing([ display(box(137, 74)+radius(17),
                                     point(0, 0)),
                             display(text('XPCE', center, normal),
                                     point(52, 30))
                           ]),
                   point(163, 183)),
          compound(new(B, figure),
                   drawing([ display(box(137, 74)+radius(17),
                                     point(0, 0)),
                             display(text('Netscape', center, normal),
                                     point(42, 30))
                           ]),
                   point(350, 183)),
          connect(connection(A,
                             B,
                             handle(w, h/2, link, east),
                             handle(0, h/2, link, west)) +
                    arrows(both))
        ]).

:- pce_end_class(my_httpd).</PRE>

<H3><A NAME="sec:11.9.1"><SPAN class="sec-nr">11.9.1</SPAN> <SPAN class="sec-title">Class <B>httpd</B></SPAN></A></H3>

<P>The library <CODE>library(http/httpd)</CODE> defines the class <B>httpd</B>. 
This subclass of <A class="" href="summary.html#class:socket">socket</A> 
deals with most of the HTTP protocol details, breaking down HTTP 
requests and encapsulating responses with the proper headers. The class 
itself is an <EM>abstract</EM> class, a subclass needs to be created and 
some of the <EM>virtual methods</EM> needs to be refined to arrive at a 
useful application.

<DL>
<DT><STRONG>httpd -&gt;initialise:</STRONG> <VAR>Port:[int]</VAR></DT>
<DD class="defbody">
Create a server and bind it to <VAR>Port</VAR>. If <VAR>Port</VAR> is 
omitted a free port is chosen. With a specified port, 8080 is a commonly 
used alternative to the standard 80 used by web-servers. If you have a 
web-server running on the same machine you may can generate a page on 
your website redirecting a page to this server. The URI of this server 
is <TT>http://&lt;<VAR>host</VAR>&gt;/&lt;<VAR>Port</VAR>&gt;</TT>.</DD>
<DT><STRONG>httpd -&gt;accepted:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
This is sent after a connection has been accepted. The system 
implementation logs the new connection if debugging is enabled. You can 
refine or redefine this method, asking for the <A NAME="idx:socketgetpeername:540"></A>`<B>socket<CODE>&lt;-</CODE>peer_name</B>' 
and sending <B><CODE>-&gt;</CODE>free</B> to the socket if you want to 
restrict access.</DD>
<DT><STRONG>httpd -&gt;request:</STRONG> <VAR>Data:sheet</VAR></DT>
<DD class="defbody">
This is sent from <B><CODE>-&gt;</CODE>input</B> after a complete 
request-header is received.
<B><CODE>-&gt;</CODE>input</B> decodes the header-fields, places them in <VAR>Data</VAR> 
and then calls <B><CODE>-&gt;</CODE>request</B>. The attribute-names in 
the sheet are downcase versions of the case-insensitive request fields 
of the HTTP header. In addition, the following fields are defined:

<P>
<CENTER>
<TABLE BORDER=2 FRAME=box RULES=groups>
<TR VALIGN=top><TD COLSPAN=2 ALIGN=center><B>Fields that are always 
present</B></TR>
<TBODY>
<TR VALIGN=top><TD>request</TD><TD><CODE>GET</CODE>, <CODE>POST</CODE>, 
etc. I.e. the first word of the request-header. In most cases this will 
be
<CODE>GET</CODE>. </TD></TR>
<TR VALIGN=top><TD>path</TD><TD>The `path' part of the request. This is 
normally used to decide on the response. If the path contains a ? 
(question mark) this and the remaining data are removed and decoded to 
the `form' attribute. </TD></TR>
<TR VALIGN=top><TD>form</TD><TD>If the request is a <CODE>GET</CODE> 
request with form-data, the form attribute contains another sheet 
holding the decoded form-data. Otherwise <B><CODE>&lt;-</CODE>form</B> 
holds <A NAME="idx:nil:541"></A><B>@nil</B>. </TD></TR>
<TR VALIGN=top><TD>http_version</TD><TD>Version of the HTTP protocol 
used by the client. Normally
<CODE>1.0</CODE> or <CODE>1.1</CODE>. </TD></TR>
<TBODY>
<TR VALIGN=top><TD COLSPAN=2 ALIGN=center><B>Other fields</B></TR>
<TBODY>
<TR VALIGN=top><TD>user</TD><TD>If authorisation data is present, this 
contains the user-name. If this field is present, the password field is 
present too. </TD></TR>
<TR VALIGN=top><TD>password</TD><TD>Contains the decoded password 
supplied by the user. </TD></TR>
</TABLE>

</CENTER>

<P>After decoding the request, the user should compose a response and 
use
<B><CODE>-&gt;</CODE>reply</B> or <B><CODE>-&gt;</CODE>reply_html</B> to 
return the response to the client.</DD>
<DT><STRONG>httpd -&gt;reply:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
Send a reply. This method or <B><CODE>-&gt;</CODE>reply_html</B> is 
normally activated at the end of the user's <B><CODE>-&gt;</CODE>request</B> 
implementation. Data is one of:

<P>
<UL>
<LI><I>A string or source_sink</I><BR>
If the reply is a <A class="" href="summary.html#class:string">string</A>, <A class="" href="summary.html#class:text_buffer">text_buffer</A>, <A class="" href="summary.html#class:resource">resource</A> 
or <A class="" href="summary.html#class:file">file</A>, the data in this 
object will be returned. Unless otherwise specified <B><CODE>-&gt;</CODE>reply</B> 
assumes the data has <A NAME="idx:mimetype:542">mime-type</A> <CODE>text/plain</CODE>.

<P>
<LI><I>A pixmap</I><BR>
If the reply is a <A class="" href="summary.html#class:pixmap">pixmap</A> 
(or can be converted automatically, for example any <A class="" href="summary.html#class:graphical">graphical</A>), 
this image is encoded as GIF or JPEG and sent with the corresponding <A NAME="idx:imagegif:543">image/gif</A> 
or <A NAME="idx:imagejpeg:544">image/jpeg</A> mime-type. For more 
information on image save-types, see <A NAME="idx:imagesendsavein:545"></A>`<B>image<CODE>-&gt;</CODE>save_in</B>'.
</UL>

<P><VAR>Type</VAR> is the mimi-type returned and tells the browser what 
to do with the data. This should correspond with the content of <VAR>Data</VAR>. 
For example, you can return a PNG picture from a file using

<PRE class="code">
        send(HTTPD, reply, file('pict.png'), 'image/png'),
</PRE>

<P><VAR>Status</VAR> is used to tell the client in a formal way how the 
request was processed. The default is <CODE>200 OK</CODE>. See the 
methods below for returning other values.

<P><VAR>Header</VAR> is a <A class="" href="summary.html#class:sheet">sheet</A> 
holding additional name-value pairs. If present, they are simply added 
to the end of the reply-header. For example if you want to prevent the 
browser caching the result you can use

<PRE class="code">
        send(HTTPD, reply, ...,
             sheet(attribute('Cache-Control', 'no-cache'))),
</PRE>

</DD>
<DT><STRONG>httpd -&gt;reply_html:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
Uses the <CODE>library(http/html_write)</CODE> library to translate <VAR>Term</VAR> 
into HTML text using DCG rules and then invokes <B><CODE>-&gt;</CODE>reply</B> 
using the <VAR>Type</VAR>
<CODE>text/html</CODE>. <VAR>Status</VAR> and <VAR>Header</VAR> are 
passed unmodified to <B><CODE>-&gt;</CODE>reply</B>.
</DD>
</DL>

<P>In addition to the principal methods above, a number of methods are 
defined for dealing with abnormal replies such as denying permission, 
etc.

<DL>
<DT><STRONG>httpd -&gt;forbidden:</STRONG> <VAR>What:[name]</VAR></DT>
<DD class="defbody">
Replies with a <CODE>403 Forbidden</CODE> message. <VAR>What</VAR> may 
be provided to indicate what is forbidden. Default is the path from the 
current
<B><CODE>&lt;-</CODE>request</B>.</DD>
<DT><STRONG>httpd -&gt;authorization_required:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
Challenges the user to provide a name and password. The only method 
provided is <CODE>Basic</CODE>. <VAR>Realm</VAR> tells the user for 
which service permission is requested. On all subsequence contacts from 
this client to this server the <B><CODE>-&gt;</CODE>request</B> data 
contains the <CODE>user</CODE> and
<CODE>password</CODE> fields. The demo implementation of <B><CODE>-&gt;</CODE>request</B> 
in
<B>httpd</B> contains the following example code:

<PRE class="code">
request(S, Header:sheet) :-&gt;
        "Process a request.  The argument is the header"::
        (   get(Header, path, '/no')
        -&gt;  send(S, forbidden, '/no')
        ;   get(Header, path, '/maybe')
        -&gt;  (   get(Header, value, user, jan),
                get(Header, value, password, test)
            -&gt;  send(S, reply, 'You hacked me')
            ;   send(S, authorization_required)
            )
        ;   send(S, reply, 'Nice try')
        ).</PRE>

</DD>
<DT><STRONG>httpd -&gt;not_found:</STRONG> <VAR>What:[char_array]</VAR></DT>
<DD class="defbody">
Reply with a <CODE>404 Not Found</CODE> message, using the request-path 
as default for <VAR>What</VAR>.</DD>
<DT><STRONG>httpd -&gt;moved:</STRONG> <VAR>Where:char_array</VAR></DT>
<DD class="defbody">
Reply with a <CODE>301 Moved Permanently</CODE>. Normally the client 
will retry the request using the URL returned in <VAR>Where</VAR>.</DD>
<DT><STRONG>httpd -&gt;server_error:</STRONG> <VAR>What:[char_array]</VAR></DT>
<DD class="defbody">
Reply with a <CODE>500 Internal Server</CODE> using `<VAR>What</VAR> as 
additional information to the user. This is the default reply if <B><CODE>-&gt;</CODE>request</B> 
fails or raised an exception.
</DD>
</DL>

<P></BODY></HTML>