Annotation of libwww/Library/src/HTFormat.html, revision 2.10
2.10 ! timbl 1: <HTML>
! 2: <HEAD>
2.1 timbl 3: <TITLE>HTFormat: The format manager in the WWW Library</TITLE>
2.10 ! timbl 4: <NEXTID N="z11">
! 5: </HEAD>
2.1 timbl 6: <BODY>
7: <H1>Manage different document formats</H1>Here we describe the functions of
8: the HTFormat module which handles
9: conversion between different data
10: representations. (In MIME parlance,
11: a representation is known as a content-type.
2.2 timbl 12: In WWW the term "format" is often
2.1 timbl 13: used as it is shorter).<P>
14: This module is implemented by <A
2.10 ! timbl 15: NAME="z0" HREF="HTFormat.c">HTFormat.c</A>
2.7 timbl 16: . This hypertext document is used
17: to generate the <A
2.10 ! timbl 18: NAME="z8" HREF="HTFormat.h">HTFormat.h</A> inlude
2.9 timbl 19: file. Part of the <A
2.10 ! timbl 20: NAME="z10" HREF="Overview.html">WWW library</A> .
2.1 timbl 21: <H2>Preamble</H2>
22: <PRE>#ifndef HTFORMAT_H
23: #define HTFORMAT_H
24:
25: #include "HTUtils.h"
26: #include <A
2.10 ! timbl 27: NAME="z7" HREF="HTStream.html">"HTStream.h"</A>
2.1 timbl 28: #include "HTAtom.h"
2.2 timbl 29: #include "HTList.h"
2.1 timbl 30:
31: #ifdef SHORT_NAMES
32: #define HTOutputSource HTOuSour
33: #define HTOutputBinary HTOuBina
34: #endif
35:
36: </PRE>
37: <H2>The HTFormat type</H2>We use the HTAtom object for holding
38: representations. This allows faster
39: manipulation (comparison and copying)
40: that if we stayed with strings.
41: <PRE>typedef HTAtom * HTFormat;
42:
43: </PRE>These macros (which used to be constants)
44: define some basic internally referenced
2.2 timbl 45: representations. The www/xxx ones
2.1 timbl 46: are of course not MIME standard.<P>
47: www/source is an output format which
48: leaves the input untouched. It is
49: useful for diagnostics, and for users
50: who want to see the original, whatever
51: it is.
52: <PRE> /* Internal ones */
53: #define WWW_SOURCE HTAtom_for("www/source") /* Whatever it was originally*/
54:
55: </PRE>www/present represents the user's
56: perception of the document. If you
57: convert to www/present, you present
58: the material to the user.
59: <PRE>#define WWW_PRESENT HTAtom_for("www/present") /* The user's perception */
60:
61: </PRE>The message/rfc822 format means a
62: MIME message or a plain text message
63: with no MIME header. This is what
64: is returned by an HTTP server.
65: <PRE>#define WWW_MIME HTAtom_for("www/mime") /* A MIME message */
2.10 ! timbl 66:
2.1 timbl 67: </PRE>www/print is like www/present except
68: it represents a printed copy.
69: <PRE>#define WWW_PRINT HTAtom_for("www/print") /* A printed copy */
70:
2.10 ! timbl 71: </PRE>www/unknown is a really unknown type.
! 72: Some default action is appropriate.
! 73: <PRE>#define WWW_UNKNOWN HTAtom_for("www/unknown")
! 74:
! 75: </PRE>These are regular MIME types:
! 76: <PRE>#define WWW_PLAINTEXT HTAtom_for("text/plain")
2.1 timbl 77: #define WWW_POSTSCRIPT HTAtom_for("application/postscript")
78: #define WWW_RICHTEXT HTAtom_for("application/rtf")
2.10 ! timbl 79: #define WWW_AUDIO HTAtom_for("audio/basic")
2.1 timbl 80: #define WWW_HTML HTAtom_for("text/html")
81: #define WWW_BINARY HTAtom_for("application/binary")
2.7 timbl 82:
2.1 timbl 83: </PRE>We must include the following file
84: after defining HTFormat, to which
2.10 ! timbl 85: it makes reference.
! 86: <H2>The HTEncoding type</H2>
! 87: <PRE>typedef HTAtom* HTEncoding;
! 88:
! 89: </PRE>The following are values for the
! 90: MIME types:
! 91: <PRE>#define WWW_ENC_7BIT HTAtom_for("7bit")
! 92: #define WWW_ENC_8BIT HTAtom_for("8bit")
! 93: #define WWW_ENC_BINARY HTAtom_for("binary")
! 94:
! 95: </PRE>We also add
! 96: <PRE>#define WWW_ENC_COMPRESS HTAtom_for("compress")
! 97:
! 98: #include "HTAnchor.h"
2.1 timbl 99:
100: </PRE>
101: <H2>The HTPresentation and HTConverter
102: types</H2>This HTPresentation structure represents
103: a possible conversion algorithm from
104: one format to annother. It includes
105: a pointer to a conversion routine.
106: The conversion routine returns a
107: stream to which data should be fed.
108: See also <A
2.10 ! timbl 109: NAME="z5" HREF="#z3">HTStreamStack</A> which scans
2.1 timbl 110: the list of registered converters
111: and calls one. See the <A
2.10 ! timbl 112: NAME="z6" HREF="HTInit.html">initialisation
2.1 timbl 113: module</A> for a list of conversion routines.
114: <PRE>typedef struct _HTPresentation HTPresentation;
115:
2.2 timbl 116: typedef HTStream * HTConverter PARAMS((
2.1 timbl 117: HTPresentation * pres,
118: HTParentAnchor * anchor,
119: HTStream * sink));
120:
121: struct _HTPresentation {
122: HTAtom* rep; /* representation name atmoized */
123: HTAtom* rep_out; /* resulting representation */
2.2 timbl 124: HTConverter *converter; /* The routine to gen the stream stack */
2.1 timbl 125: char * command; /* MIME-format string */
126: float quality; /* Between 0 (bad) and 1 (good) */
127: float secs;
128: float secs_per_byte;
129: };
130:
131: </PRE>The list of presentations is kept
132: by this module. It is also scanned
133: by modules which want to know the
134: set of formats supported. for example.
135: <PRE>extern HTList * HTPresentations;
136:
137: </PRE>
138: <H2>HTSetPresentation: Register a system
139: command to present a format</H2>
2.8 timbl 140: <H3>On entry,</H3>
2.1 timbl 141: <DL>
142: <DT>rep
143: <DD> is the MIME - style format name
144: <DT>command
145: <DD> is the MAILCAP - style command
146: template
147: <DT>quality
148: <DD> A degradation faction 0..1
149: <DT>maxbytes
150: <DD> A limit on the length acceptable
151: as input (0 infinite)
152: <DT>maxsecs
153: <DD> A limit on the time user
154: will wait (0 for infinity)
155: </DL>
156:
157: <PRE>extern void HTSetPresentation PARAMS((
158: CONST char * representation,
159: CONST char * command,
160: float quality,
161: float secs,
162: float secs_per_byte
163: ));
164:
165:
166: </PRE>
167: <H2>HTSetConversion: Register a converstion
168: routine</H2>
2.8 timbl 169: <H3>On entry,</H3>
2.1 timbl 170: <DL>
171: <DT>rep_in
172: <DD> is the content-type input
173: <DT>rep_out
174: <DD> is the resulting content-type
175: <DT>converter
176: <DD> is the routine to make
177: the stream to do it
178: </DL>
179:
180: <PRE>
181: extern void HTSetConversion PARAMS((
182: CONST char * rep_in,
183: CONST char * rep_out,
2.2 timbl 184: HTConverter * converter,
2.1 timbl 185: float quality,
186: float secs,
187: float secs_per_byte
188: ));
189:
190:
191: </PRE>
192: <H2><A
2.10 ! timbl 193: NAME="z3">HTStreamStack: Create a stack of
2.1 timbl 194: streams</A></H2>This is the routine which actually
195: sets up the conversion. It currently
196: checks only for direct conversions,
2.8 timbl 197: but multi-stage conversions are forseen.
2.2 timbl 198: It takes a stream into which the
2.1 timbl 199: output should be sent in the final
200: format, builds the conversion stack,
201: and returns a stream into which the
202: data in the input format should be
203: fed. The anchor is passed because
204: hypertxet objects load information
205: into the anchor object which represents
206: them.
207: <PRE>extern HTStream * HTStreamStack PARAMS((
208: HTFormat format_in,
209: HTFormat format_out,
210: HTStream* stream_out,
211: HTParentAnchor* anchor));
212:
213: </PRE>
214: <H2>HTStackValue: Find the cost of a
215: filter stack</H2>Must return the cost of the same
216: stack which HTStreamStack would set
217: up.
2.8 timbl 218: <H3>On entry,</H3>
2.1 timbl 219: <DL>
220: <DT>format_in
221: <DD> The fomat of the data to
222: be converted
223: <DT>format_out
224: <DD> The format required
225: <DT>initial_value
226: <DD> The intrinsic "value"
227: of the data before conversion on
228: a scale from 0 to 1
229: <DT>length
230: <DD> The number of bytes expected
231: in the input format
232: </DL>
233:
234: <PRE>extern float HTStackValue PARAMS((
235: HTFormat format_in,
236: HTFormat rep_out,
237: float initial_value,
238: long int length));
239:
240: #define NO_VALUE_FOUND -1e20 /* returned if none found */
241:
242: </PRE>
243: <H2><A
2.10 ! timbl 244: NAME="z1">HTCopy: Copy a socket to a stream</A></H2>This is used by the protocol engines
2.6 secret 245: to send data down a stream, typically
2.1 timbl 246: one which has been generated by HTStreamStack.
247: <PRE>extern void HTCopy PARAMS((
248: int file_number,
249: HTStream* sink));
250:
251:
2.6 secret 252: </PRE>
253: <H2><A
2.10 ! timbl 254: NAME="c6">HTFileCopy: Copy a file to a stream</A></H2>This is used by the protocol engines
2.6 secret 255: to send data down a stream, typically
2.7 timbl 256: one which has been generated by HTStreamStack.
257: It is currently called by <A
2.10 ! timbl 258: NAME="z9" HREF="#c7">HTParseFile</A>
2.6 secret 259: <PRE>extern void HTFileCopy PARAMS((
260: FILE* fp,
261: HTStream* sink));
262:
263:
2.7 timbl 264: </PRE>
265: <H2><A
2.10 ! timbl 266: NAME="c2">HTCopyNoCR: Copy a socket to a stream,
2.7 timbl 267: stripping CR characters.</A></H2>It is slower than <A
2.10 ! timbl 268: NAME="z2" HREF="#z1">HTCopy</A> .
2.1 timbl 269: <PRE>
270: extern void HTCopyNoCR PARAMS((
271: int file_number,
272: HTStream* sink));
273:
274:
275: </PRE>
276: <H2>Clear input buffer and set file number</H2>This routine and the one below provide
277: simple character input from sockets.
278: (They are left over from the older
279: architecure and may not be used very
280: much.) The existence of a common
281: routine and buffer saves memory space
282: in small implementations.
283: <PRE>extern void HTInitInput PARAMS((int file_number));
284:
285: </PRE>
286: <H2>Get next character from buffer</H2>
287: <PRE>extern char HTGetChararcter NOPARAMS;
288:
289:
290: </PRE>
291: <H2>HTParseSocket: Parse a socket given
292: its format</H2>This routine is called by protocol
293: modules to load an object. uses<A
2.10 ! timbl 294: NAME="z4" HREF="#z3">
2.1 timbl 295: HTStreamStack</A> and the copy routines
296: above. Returns HT_LOADED if succesful,
297: <0 if not.
298: <PRE>extern int HTParseSocket PARAMS((
299: HTFormat format_in,
300: HTFormat format_out,
301: HTParentAnchor *anchor,
302: int file_number,
2.6 secret 303: HTStream* sink));
304:
305: </PRE>
306: <H2><A
2.10 ! timbl 307: NAME="c1">HTParseFile: Parse a File through
2.7 timbl 308: a file pointer</A></H2>This routine is called by protocols
309: modules to load an object. uses<A
2.10 ! timbl 310: NAME="z4" HREF="#z3"> HTStreamStack</A>
2.7 timbl 311: and <A
2.10 ! timbl 312: NAME="c7" HREF="#c6">HTFileCopy</A> . Returns HT_LOADED
2.7 timbl 313: if succesful, <0 if not.
2.6 secret 314: <PRE>extern int HTParseFile PARAMS((
315: HTFormat format_in,
316: HTFormat format_out,
317: HTParentAnchor *anchor,
318: FILE *fp,
2.1 timbl 319: HTStream* sink));
2.8 timbl 320:
321: </PRE>
322: <H2>HTFormatInit: Set up default presentations
323: and conversions</H2>These are defined in HTInit.c or
324: HTSInit.c if these have been replaced.
325: If you don't call this routine, and
326: you don't define any presentations,
327: then this routine will automatically
328: be called the first time a conversion
329: is needed. However, if you explicitly
330: add some conversions (eg using HTLoadRules)
331: then you may want also to explicitly
332: call this to get the defaults as
333: well.
334: <PRE>extern void HTFormatInit NOPARAMS;
2.1 timbl 335:
336: </PRE>
337: <H2>Epilogue</H2>
338: <PRE>extern BOOL HTOutputSource; /* Flag: shortcut parser */
339: #endif
340:
2.7 timbl 341: </PRE>end</A></BODY>
2.10 ! timbl 342: </HTML>
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