Annotation of libwww/Library/src/HTFormat.html, revision 2.53
2.10 timbl 1: <HTML>
2: <HEAD>
2.45 frystyk 3: <TITLE>Format Negotiation Manager</TITLE>
2.52 frystyk 4: <!-- Changed by: Henrik Frystyk Nielsen, 5-Nov-1995 -->
2.15 timbl 5: <NEXTID N="z18">
2.10 timbl 6: </HEAD>
2.1 timbl 7: <BODY>
2.27 frystyk 8:
2.31 frystyk 9: <H1>The Format Manager</H1>
2.33 frystyk 10:
11: <PRE>
12: /*
2.41 frystyk 13: ** (c) COPYRIGHT MIT 1995.
2.33 frystyk 14: ** Please first read the full copyright statement in the file COPYRIGH.
15: */
16: </PRE>
2.31 frystyk 17:
18: Here we describe the functions of the HTFormat module which handles
19: conversion between different data representations. (In MIME parlance,
20: a representation is known as a content-type. In <A
2.46 frystyk 21: HREF="http://www.w3.org/pub/WWW/TheProject.html">WWW</A> the
2.31 frystyk 22: term <EM>format</EM> is often used as it is shorter). The content of
23: this module is:
24:
25: <UL>
2.42 frystyk 26: <LI><A HREF="#converter">Converters</A>
2.50 frystyk 27: <LI><A HREF="#user">Generic preferences (media type, language, charset etc.)</A>
28: <LI><A HREF="#global">Global Preferences</A>
2.42 frystyk 29: <LI><A HREF="#Rank">Content Negotiation</A>
2.31 frystyk 30: <LI><A HREF="#z3">The Stream Stack</A>
31: </UL>
32:
33: This module is implemented by <A HREF="HTFormat.c">HTFormat.c</A>, and
2.49 frystyk 34: it is a part of the <A HREF="http://www.w3.org/pub/WWW/Library/"> W3C
35: Reference Library</A>.
2.27 frystyk 36:
2.31 frystyk 37: <PRE>
38: #ifndef HTFORMAT_H
2.1 timbl 39: #define HTFORMAT_H
40:
2.31 frystyk 41: #include <A HREF="HTUtils.html">"HTUtils.h"</A>
42: #include <A HREF="HTStream.html">"HTStream.h"</A>
43: #include <A HREF="HTAtom.html">"HTAtom.h"</A>
44: #include <A HREF="HTList.html">"HTList.h"</A>
2.42 frystyk 45: #include <A HREF="HTAnchor.html">"HTAnchor.h"</A>
2.47 frystyk 46: #include <A HREF="HTReq.html">"HTReq.h"</A>
2.31 frystyk 47: </PRE>
2.1 timbl 48:
2.42 frystyk 49: <A NAME="converter"><H2>Stream Converters</H2></A>
2.18 luotonen 50:
2.42 frystyk 51: A <CODE><A NAME="z12">converter</A></CODE> is a stream with a special
52: set of parameters and which is registered as capable of converting
53: from a MIME type to something else (maybe another MIME-type). A
54: converter is defined to be a function returning a stream and accepting
55: the following parameters. The content type elements are atoms for
56: which we have defined a prototype.
2.18 luotonen 57:
2.31 frystyk 58: <PRE>
2.52 frystyk 59: typedef HTStream * HTConverter (HTRequest * request,
60: void * param,
61: HTFormat input_format,
62: HTFormat output_format,
63: HTStream * output_stream);
2.42 frystyk 64: </PRE>
2.18 luotonen 65:
2.50 frystyk 66: <A NAME="user"><H2>Generic Preferences</H2></A>
2.31 frystyk 67:
2.42 frystyk 68: The Library contains functionality for letting the application (or
69: user) express the preferences for the rendition of a given data object
70: when issuing a request. The categories supported are:
71:
72: <UL>
73: <LI>Content type (media type)
74: <LI>Encoding
75: <LI>Language
76: <LI>Charset
77: </UL>
2.17 luotonen 78:
2.42 frystyk 79: <A NAME="FormatTypes"><H3>Registration of Accepted Content Types</H3></A>
2.17 luotonen 80:
2.42 frystyk 81: A <CODE>presenter</CODE> is a module (possibly an external program)
82: which can present a graphic object of a certain MIME type to the
83: user. That is, <CODE>presenters</CODE> are normally used to present
84: objects that the <CODE>converters</CODE> are not able to handle. Data
85: is transferred to the external program using for example the <A
86: HREF="HTFWrite.html">HTSaveAndExecute</A> stream which writes to a
87: local file. Both presenters and converters are of the type <A
88: HREF="#converter">HTConverter</A>.
2.31 frystyk 89:
90: <PRE>
2.42 frystyk 91: typedef struct _HTPresentation {
92: HTFormat rep; /* representation name atomized */
93: HTFormat rep_out; /* resulting representation */
94: HTConverter *converter; /* The routine to gen the stream stack */
95: char * command; /* MIME-format string */
96: char * test_command; /* MIME-format string */
97: double quality; /* Between 0 (bad) and 1 (good) */
98: double secs;
99: double secs_per_byte;
100: } HTPresentation;
2.28 frystyk 101: </PRE>
102:
2.42 frystyk 103: <H4>Predefined Content Types</H4>
2.28 frystyk 104:
2.42 frystyk 105: These macros (which used to be constants) define some basic internally
106: referenced representations. The <CODE>www/xxx</CODE> ones are of
2.52 frystyk 107: course not MIME standard. They are internal representations used in
108: the Library but they can't be exported to other apps!
2.28 frystyk 109:
110: <PRE>
111: #define WWW_SOURCE HTAtom_for("*/*") /* Whatever it was originally */
112: </PRE>
113:
2.52 frystyk 114: <CODE>WWW_SOURCE</CODE> is an output format which leaves the input
115: untouched. In case we are receiving a MIME like message (like for
116: example in HTTP/1.x) the source is only considered to be the raw body
117: data. The HTTP status line and all headers are stripped out. It is
118: useful for diagnostics, and for users who want to see the original,
119: whatever it is.
2.10 timbl 120:
2.28 frystyk 121: <PRE>
122: #define WWW_PRESENT HTAtom_for("www/present") /* The user's perception */
123: </PRE>
124:
2.52 frystyk 125: <CODE>WWW_PRESENT</CODE> represents the user's perception of the
126: document. If you convert to <CODE>WWW_PRESENT</CODE>, you present the
127: material to the user.
2.28 frystyk 128:
129: <PRE>
2.52 frystyk 130: #define WWW_UNKNOWN HTAtom_for("www/unknown")
2.28 frystyk 131: </PRE>
132:
2.52 frystyk 133: <CODE>WWW_UNKNOWN</CODE> is a really unknown type. It differs from the
134: real MIME type <EM>"application/octet-stream"</EM> in that we haven't
135: even tried to figure out the content type at this point.<P>
2.28 frystyk 136:
2.31 frystyk 137: These are regular MIME types defined. Others can be added!
2.28 frystyk 138:
139: <PRE>
2.52 frystyk 140: #define WWW_HTML HTAtom_for("text/html")
2.28 frystyk 141: #define WWW_PLAINTEXT HTAtom_for("text/plain")
2.52 frystyk 142:
143: #define WWW_MIME HTAtom_for("message/rfc822")
144:
2.10 timbl 145: #define WWW_AUDIO HTAtom_for("audio/basic")
2.52 frystyk 146:
2.26 frystyk 147: #define WWW_VIDEO HTAtom_for("video/mpeg")
2.52 frystyk 148:
2.38 frystyk 149: #define WWW_GIF HTAtom_for("image/gif")
2.52 frystyk 150: #define WWW_PNG HTAtom_for("image/png")
151:
152: #define WWW_BINARY HTAtom_for("application/octet-stream")
153: #define WWW_POSTSCRIPT HTAtom_for("application/postscript")
154: #define WWW_RICHTEXT HTAtom_for("application/rtf")
2.48 frystyk 155: </PRE>
156:
2.52 frystyk 157: We also have some MIME types that come from the various protocols when
158: we convert from ASCII to HTML.
2.48 frystyk 159:
160: <PRE>
161: #define WWW_GOPHER_MENU HTAtom_for("text/x-gopher")
2.53 ! frystyk 162: #define WWW_CSO_SEARCH HTAtom_for("text/x-cso")
2.48 frystyk 163:
164: #define WWW_FTP_LNST HTAtom_for("text/x-ftp-lnst")
165: #define WWW_FTP_LIST HTAtom_for("text/x-ftp-list")
166:
167: #define WWW_NNTP_LIST HTAtom_for("text/x-nntp-list")
168: #define WWW_NNTP_OVER HTAtom_for("text/x-nntp-over")
169: #define WWW_NNTP_HEAD HTAtom_for("text/x-nntp-head")
2.28 frystyk 170: </PRE>
171:
2.50 frystyk 172: <H4>Add a Presenter</H4>
173:
174: This function creates a presenter object and adds to the list of
175: conversions.
2.31 frystyk 176:
2.1 timbl 177: <DL>
2.31 frystyk 178: <DT>conversions
179: <DD>The list of <CODE>conveters</CODE> and <CODE>presenters</CODE>
2.50 frystyk 180: <DT>rep_in
2.42 frystyk 181: <DD>the MIME-style format name
2.50 frystyk 182: <DT>rep_out
183: <DD>is the resulting content-type after the conversion
184: <DT>converter
185: <DD>is the routine to call which actually does the conversion
2.1 timbl 186: <DT>quality
2.31 frystyk 187: <DD>A degradation faction [0..1]
2.1 timbl 188: <DT>maxbytes
2.31 frystyk 189: <DD>A limit on the length acceptable as input (0 infinite)
2.1 timbl 190: <DT>maxsecs
2.31 frystyk 191: <DD>A limit on the time user will wait (0 for infinity)
2.1 timbl 192: </DL>
193:
2.31 frystyk 194: <PRE>
2.49 frystyk 195: extern void HTPresentation_add (HTList * conversions,
196: CONST char * representation,
197: CONST char * command,
198: CONST char * test_command,
199: double quality,
200: double secs,
201: double secs_per_byte);
2.31 frystyk 202: </PRE>
2.1 timbl 203:
2.50 frystyk 204: <H4>Delete a list of Presenters</H4>
205:
206: <PRE>
207: extern void HTPresentation_deleteAll (HTList * list);
208: </PRE>
209:
210: <H4>Add a Converter</H4>
211:
212: This function creates a presenter object and adds to the list of
213: conversions.
2.1 timbl 214:
215: <DL>
2.31 frystyk 216: <DT>conversions
217: <DD>The list of <CODE>conveters</CODE> and <CODE>presenters</CODE>
2.1 timbl 218: <DT>rep_in
2.42 frystyk 219: <DD>the MIME-style format name
2.1 timbl 220: <DT>rep_out
2.31 frystyk 221: <DD>is the resulting content-type after the conversion
2.1 timbl 222: <DT>converter
2.31 frystyk 223: <DD>is the routine to call which actually does the conversion
224: <DT>quality
225: <DD>A degradation faction [0..1]
226: <DT>maxbytes
227: <DD>A limit on the length acceptable as input (0 infinite)
228: <DT>maxsecs
229: <DD>A limit on the time user will wait (0 for infinity)
2.1 timbl 230: </DL>
231:
232: <PRE>
2.49 frystyk 233: extern void HTConversion_add (HTList * conversions,
234: CONST char * rep_in,
235: CONST char * rep_out,
236: HTConverter * converter,
237: double quality,
238: double secs,
239: double secs_per_byte);
2.42 frystyk 240: </PRE>
241:
2.50 frystyk 242: <H4>Delete a list of Converters</H4>
243:
244: <PRE>
245: extern void HTConversion_deleteAll (HTList * list);
246: </PRE>
247:
2.42 frystyk 248: <A NAME="Encoding"><H3>Registration of Accepted Content Encodings</H3></A>
249:
250: Encodings are the HTTP extension of transfer encodings. Encodings
2.50 frystyk 251: include compress, gzip etc.
2.42 frystyk 252:
253: <PRE>
254: typedef struct _HTAcceptNode {
255: HTAtom * atom;
256: double quality;
257: } HTAcceptNode;
258: </PRE>
259:
260: <H4>Predefined Encoding Types</H4>
261:
262: <PRE>
263: #define WWW_ENC_7BIT HTAtom_for("7bit")
264: #define WWW_ENC_8BIT HTAtom_for("8bit")
265: #define WWW_ENC_BINARY HTAtom_for("binary")
266: #define WWW_ENC_BASE64 HTAtom_for("base64")
267: #define WWW_ENC_COMPRESS HTAtom_for("compress")
268: #define WWW_ENC_GZIP HTAtom_for("gzip")
269: </PRE>
270:
271: <H4>Register an Encoding</H4>
272:
273: <PRE>
2.50 frystyk 274: extern void HTEncoding_add (HTList * list,
275: CONST char * enc,
276: double quality);
2.42 frystyk 277: </PRE>
2.31 frystyk 278:
2.50 frystyk 279: <H4>Delete a list of Encoders</H4>
2.31 frystyk 280:
2.50 frystyk 281: <PRE>
2.51 frystyk 282: extern void HTEncoding_deleteAll (HTList * list);
2.50 frystyk 283: </PRE>
284:
285: <H3><A NAME="charset">Accepted Charsets</A></H3>
2.31 frystyk 286:
2.42 frystyk 287: <H4>Register a Charset</H4>
288:
289: <PRE>
2.50 frystyk 290: extern void HTCharset_add (HTList * list,
291: CONST char * charset,
292: double quality);
2.42 frystyk 293: </PRE>
294:
2.50 frystyk 295: <H4>Delete a list of Charsets</H4>
2.42 frystyk 296:
2.50 frystyk 297: <PRE>
298: extern void HTCharset_deleteAll (HTList * list);
299: </PRE>
300:
301: <A NAME="Language"><H3>Accepted Content Languages</H3></A>
2.31 frystyk 302:
2.42 frystyk 303: <H4>Register a Language</H4>
2.31 frystyk 304:
305: <PRE>
2.50 frystyk 306: extern void HTLanguage_add (HTList * list,
307: CONST char * lang,
308: double quality);
309: </PRE>
310:
311: <H4>Delete a list of Languages</H4>
312:
313: <PRE>
2.51 frystyk 314: extern void HTLanguage_deleteAll (HTList * list);
2.50 frystyk 315: </PRE>
316:
317: <A NAME="global"><H2>Global Registrations</H2></A>
318:
319: There are two places where these preferences can be registered: in a
320: <EM>global</EM> list valid for <B>all</B> requests and a
321: <EM>local</EM> list valid for a particular request only. These are
322: valid for <EM>all</EM> requests. See the <A HREF="HTReq.html">Request
323: Manager</A> fro local sets.
324:
2.51 frystyk 325: <H3>Converters and Presenters</H3>
2.50 frystyk 326:
327: The <EM>global</EM> list of specific conversions which the format
328: manager can do in order to fulfill the request. There is also a <A
329: HREF="HTReq.html"><EM>local</EM></A> list of conversions which
330: contains a generic set of possible conversions.
331:
332: <PRE>
333: extern void HTFormat_setConversion (HTList *list);
334: extern HTList * HTFormat_conversion (void);
2.31 frystyk 335: </PRE>
336:
2.50 frystyk 337: <H3>Content Encodings</H3>
2.42 frystyk 338:
2.50 frystyk 339: <PRE>
340: extern void HTFormat_setEncoding (HTList *list);
341: extern HTList * HTFormat_encoding (void);
342: </PRE>
2.1 timbl 343:
2.51 frystyk 344: <H3>Content Languages</H3>
2.50 frystyk 345:
346: <PRE>
347: extern void HTFormat_setLanguage (HTList *list);
348: extern HTList * HTFormat_language (void);
349: </PRE>
2.42 frystyk 350:
2.51 frystyk 351: <H3>Content Charsets</H3>
2.1 timbl 352:
2.31 frystyk 353: <PRE>
2.50 frystyk 354: extern void HTFormat_setCharset (HTList *list);
355: extern HTList * HTFormat_charset (void);
2.31 frystyk 356: </PRE>
357:
2.50 frystyk 358: <H3>Delete All Global Lists</H3>
2.42 frystyk 359:
2.50 frystyk 360: This is a convenience function that might make life easier.
2.34 frystyk 361:
362: <PRE>
2.50 frystyk 363: extern void HTFormat_deleteAll (void);
2.34 frystyk 364: </PRE>
2.31 frystyk 365:
366: <A NAME="Rank"><H2>Ranking of Accepted Formats</H2></A>
367:
2.36 frystyk 368: This function is used when the best match among several possible
369: documents is to be found as a function of the accept headers sent in
370: the client request.
2.31 frystyk 371:
372: <PRE>
2.42 frystyk 373: typedef struct _HTContentDescription {
374: char * filename;
375: HTAtom * content_type;
376: HTAtom * content_language;
377: HTAtom * content_encoding;
378: int content_length;
379: double quality;
380: } HTContentDescription;
381:
2.52 frystyk 382: extern BOOL HTRank (HTList * possibilities,
383: HTList * accepted_content_types,
384: HTList * accepted_content_languages,
385: HTList * accepted_content_encodings);
2.1 timbl 386: </PRE>
2.31 frystyk 387:
2.42 frystyk 388: <H2><A NAME="z3">The Stream Stack</A></H2>
2.31 frystyk 389:
390: This is the routine which actually sets up the conversion. It
391: currently checks only for direct conversions, but multi-stage
392: conversions are forseen. It takes a stream into which the output
393: should be sent in the final format, builds the conversion stack, and
394: returns a stream into which the data in the input format should be
2.42 frystyk 395: fed. If <CODE>guess</CODE> is true and input format is
2.31 frystyk 396: <CODE>www/unknown</CODE>, try to guess the format by looking at the
397: first few bytes of the stream. <P>
2.1 timbl 398:
2.31 frystyk 399: <PRE>
2.52 frystyk 400: extern HTStream * HTStreamStack (HTFormat rep_in,
401: HTFormat rep_out,
402: HTStream * output_stream,
403: HTRequest * request,
404: BOOL guess);
2.1 timbl 405: </PRE>
2.31 frystyk 406:
2.42 frystyk 407: <H2>Cost of a Stream Stack</H2>
2.31 frystyk 408:
409: Must return the cost of the same stack which HTStreamStack would set
2.1 timbl 410: up.
411:
2.31 frystyk 412: <PRE>
2.52 frystyk 413: extern double HTStackValue (HTList * conversions,
414: HTFormat format_in,
415: HTFormat format_out,
416: double initial_value,
417: long int length);
2.31 frystyk 418:
2.42 frystyk 419: #endif /* HTFORMAT */
2.38 frystyk 420: </PRE>
421:
2.42 frystyk 422: End of declaration module
2.31 frystyk 423:
424: </BODY>
2.10 timbl 425: </HTML>
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