Annotation of libwww/Library/src/HTFormat.html, revision 2.52
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")
162:
163: #define WWW_FTP_LNST HTAtom_for("text/x-ftp-lnst")
164: #define WWW_FTP_LIST HTAtom_for("text/x-ftp-list")
165:
166: #define WWW_NNTP_LIST HTAtom_for("text/x-nntp-list")
167: #define WWW_NNTP_OVER HTAtom_for("text/x-nntp-over")
168: #define WWW_NNTP_HEAD HTAtom_for("text/x-nntp-head")
2.28 frystyk 169: </PRE>
170:
2.50 frystyk 171: <H4>Add a Presenter</H4>
172:
173: This function creates a presenter object and adds to the list of
174: conversions.
2.31 frystyk 175:
2.1 timbl 176: <DL>
2.31 frystyk 177: <DT>conversions
178: <DD>The list of <CODE>conveters</CODE> and <CODE>presenters</CODE>
2.50 frystyk 179: <DT>rep_in
2.42 frystyk 180: <DD>the MIME-style format name
2.50 frystyk 181: <DT>rep_out
182: <DD>is the resulting content-type after the conversion
183: <DT>converter
184: <DD>is the routine to call which actually does the conversion
2.1 timbl 185: <DT>quality
2.31 frystyk 186: <DD>A degradation faction [0..1]
2.1 timbl 187: <DT>maxbytes
2.31 frystyk 188: <DD>A limit on the length acceptable as input (0 infinite)
2.1 timbl 189: <DT>maxsecs
2.31 frystyk 190: <DD>A limit on the time user will wait (0 for infinity)
2.1 timbl 191: </DL>
192:
2.31 frystyk 193: <PRE>
2.49 frystyk 194: extern void HTPresentation_add (HTList * conversions,
195: CONST char * representation,
196: CONST char * command,
197: CONST char * test_command,
198: double quality,
199: double secs,
200: double secs_per_byte);
2.31 frystyk 201: </PRE>
2.1 timbl 202:
2.50 frystyk 203: <H4>Delete a list of Presenters</H4>
204:
205: <PRE>
206: extern void HTPresentation_deleteAll (HTList * list);
207: </PRE>
208:
209: <H4>Add a Converter</H4>
210:
211: This function creates a presenter object and adds to the list of
212: conversions.
2.1 timbl 213:
214: <DL>
2.31 frystyk 215: <DT>conversions
216: <DD>The list of <CODE>conveters</CODE> and <CODE>presenters</CODE>
2.1 timbl 217: <DT>rep_in
2.42 frystyk 218: <DD>the MIME-style format name
2.1 timbl 219: <DT>rep_out
2.31 frystyk 220: <DD>is the resulting content-type after the conversion
2.1 timbl 221: <DT>converter
2.31 frystyk 222: <DD>is the routine to call which actually does the conversion
223: <DT>quality
224: <DD>A degradation faction [0..1]
225: <DT>maxbytes
226: <DD>A limit on the length acceptable as input (0 infinite)
227: <DT>maxsecs
228: <DD>A limit on the time user will wait (0 for infinity)
2.1 timbl 229: </DL>
230:
231: <PRE>
2.49 frystyk 232: extern void HTConversion_add (HTList * conversions,
233: CONST char * rep_in,
234: CONST char * rep_out,
235: HTConverter * converter,
236: double quality,
237: double secs,
238: double secs_per_byte);
2.42 frystyk 239: </PRE>
240:
2.50 frystyk 241: <H4>Delete a list of Converters</H4>
242:
243: <PRE>
244: extern void HTConversion_deleteAll (HTList * list);
245: </PRE>
246:
2.42 frystyk 247: <A NAME="Encoding"><H3>Registration of Accepted Content Encodings</H3></A>
248:
249: Encodings are the HTTP extension of transfer encodings. Encodings
2.50 frystyk 250: include compress, gzip etc.
2.42 frystyk 251:
252: <PRE>
253: typedef struct _HTAcceptNode {
254: HTAtom * atom;
255: double quality;
256: } HTAcceptNode;
257: </PRE>
258:
259: <H4>Predefined Encoding Types</H4>
260:
261: <PRE>
262: #define WWW_ENC_7BIT HTAtom_for("7bit")
263: #define WWW_ENC_8BIT HTAtom_for("8bit")
264: #define WWW_ENC_BINARY HTAtom_for("binary")
265: #define WWW_ENC_BASE64 HTAtom_for("base64")
266: #define WWW_ENC_COMPRESS HTAtom_for("compress")
267: #define WWW_ENC_GZIP HTAtom_for("gzip")
268: </PRE>
269:
270: <H4>Register an Encoding</H4>
271:
272: <PRE>
2.50 frystyk 273: extern void HTEncoding_add (HTList * list,
274: CONST char * enc,
275: double quality);
2.42 frystyk 276: </PRE>
2.31 frystyk 277:
2.50 frystyk 278: <H4>Delete a list of Encoders</H4>
2.31 frystyk 279:
2.50 frystyk 280: <PRE>
2.51 frystyk 281: extern void HTEncoding_deleteAll (HTList * list);
2.50 frystyk 282: </PRE>
283:
284: <H3><A NAME="charset">Accepted Charsets</A></H3>
2.31 frystyk 285:
2.42 frystyk 286: <H4>Register a Charset</H4>
287:
288: <PRE>
2.50 frystyk 289: extern void HTCharset_add (HTList * list,
290: CONST char * charset,
291: double quality);
2.42 frystyk 292: </PRE>
293:
2.50 frystyk 294: <H4>Delete a list of Charsets</H4>
2.42 frystyk 295:
2.50 frystyk 296: <PRE>
297: extern void HTCharset_deleteAll (HTList * list);
298: </PRE>
299:
300: <A NAME="Language"><H3>Accepted Content Languages</H3></A>
2.31 frystyk 301:
2.42 frystyk 302: <H4>Register a Language</H4>
2.31 frystyk 303:
304: <PRE>
2.50 frystyk 305: extern void HTLanguage_add (HTList * list,
306: CONST char * lang,
307: double quality);
308: </PRE>
309:
310: <H4>Delete a list of Languages</H4>
311:
312: <PRE>
2.51 frystyk 313: extern void HTLanguage_deleteAll (HTList * list);
2.50 frystyk 314: </PRE>
315:
316: <A NAME="global"><H2>Global Registrations</H2></A>
317:
318: There are two places where these preferences can be registered: in a
319: <EM>global</EM> list valid for <B>all</B> requests and a
320: <EM>local</EM> list valid for a particular request only. These are
321: valid for <EM>all</EM> requests. See the <A HREF="HTReq.html">Request
322: Manager</A> fro local sets.
323:
2.51 frystyk 324: <H3>Converters and Presenters</H3>
2.50 frystyk 325:
326: The <EM>global</EM> list of specific conversions which the format
327: manager can do in order to fulfill the request. There is also a <A
328: HREF="HTReq.html"><EM>local</EM></A> list of conversions which
329: contains a generic set of possible conversions.
330:
331: <PRE>
332: extern void HTFormat_setConversion (HTList *list);
333: extern HTList * HTFormat_conversion (void);
2.31 frystyk 334: </PRE>
335:
2.50 frystyk 336: <H3>Content Encodings</H3>
2.42 frystyk 337:
2.50 frystyk 338: <PRE>
339: extern void HTFormat_setEncoding (HTList *list);
340: extern HTList * HTFormat_encoding (void);
341: </PRE>
2.1 timbl 342:
2.51 frystyk 343: <H3>Content Languages</H3>
2.50 frystyk 344:
345: <PRE>
346: extern void HTFormat_setLanguage (HTList *list);
347: extern HTList * HTFormat_language (void);
348: </PRE>
2.42 frystyk 349:
2.51 frystyk 350: <H3>Content Charsets</H3>
2.1 timbl 351:
2.31 frystyk 352: <PRE>
2.50 frystyk 353: extern void HTFormat_setCharset (HTList *list);
354: extern HTList * HTFormat_charset (void);
2.31 frystyk 355: </PRE>
356:
2.50 frystyk 357: <H3>Delete All Global Lists</H3>
2.42 frystyk 358:
2.50 frystyk 359: This is a convenience function that might make life easier.
2.34 frystyk 360:
361: <PRE>
2.50 frystyk 362: extern void HTFormat_deleteAll (void);
2.34 frystyk 363: </PRE>
2.31 frystyk 364:
365: <A NAME="Rank"><H2>Ranking of Accepted Formats</H2></A>
366:
2.36 frystyk 367: This function is used when the best match among several possible
368: documents is to be found as a function of the accept headers sent in
369: the client request.
2.31 frystyk 370:
371: <PRE>
2.42 frystyk 372: typedef struct _HTContentDescription {
373: char * filename;
374: HTAtom * content_type;
375: HTAtom * content_language;
376: HTAtom * content_encoding;
377: int content_length;
378: double quality;
379: } HTContentDescription;
380:
2.52 ! frystyk 381: extern BOOL HTRank (HTList * possibilities,
! 382: HTList * accepted_content_types,
! 383: HTList * accepted_content_languages,
! 384: HTList * accepted_content_encodings);
2.1 timbl 385: </PRE>
2.31 frystyk 386:
2.42 frystyk 387: <H2><A NAME="z3">The Stream Stack</A></H2>
2.31 frystyk 388:
389: This is the routine which actually sets up the conversion. It
390: currently checks only for direct conversions, but multi-stage
391: conversions are forseen. It takes a stream into which the output
392: should be sent in the final format, builds the conversion stack, and
393: returns a stream into which the data in the input format should be
2.42 frystyk 394: fed. If <CODE>guess</CODE> is true and input format is
2.31 frystyk 395: <CODE>www/unknown</CODE>, try to guess the format by looking at the
396: first few bytes of the stream. <P>
2.1 timbl 397:
2.31 frystyk 398: <PRE>
2.52 ! frystyk 399: extern HTStream * HTStreamStack (HTFormat rep_in,
! 400: HTFormat rep_out,
! 401: HTStream * output_stream,
! 402: HTRequest * request,
! 403: BOOL guess);
2.1 timbl 404: </PRE>
2.31 frystyk 405:
2.42 frystyk 406: <H2>Cost of a Stream Stack</H2>
2.31 frystyk 407:
408: Must return the cost of the same stack which HTStreamStack would set
2.1 timbl 409: up.
410:
2.31 frystyk 411: <PRE>
2.52 ! frystyk 412: extern double HTStackValue (HTList * conversions,
! 413: HTFormat format_in,
! 414: HTFormat format_out,
! 415: double initial_value,
! 416: long int length);
2.31 frystyk 417:
2.42 frystyk 418: #endif /* HTFORMAT */
2.38 frystyk 419: </PRE>
420:
2.42 frystyk 421: End of declaration module
2.31 frystyk 422:
423: </BODY>
2.10 timbl 424: </HTML>
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