Annotation of libwww/Library/src/HTFormat.html, revision 2.13
2.10 timbl 1: <HTML>
2: <HEAD>
2.1 timbl 3: <TITLE>HTFormat: The format manager in the WWW Library</TITLE>
2.13 ! timbl 4: <NEXTID N="z13">
2.10 timbl 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
2.11 timbl 18: NAME="z8" HREF="HTFormat.h">HTFormat.h</A> include
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;
2.13 ! timbl 42:
! 43: </PRE>Now we can pick up the HTAccess definitions
! 44: which we need later on but which
! 45: use HTFormat.
! 46: <PRE>#include "HTAccess.h" /* Required for HTRequest definition */
! 47:
2.1 timbl 48:
49: </PRE>These macros (which used to be constants)
50: define some basic internally referenced
2.13 ! timbl 51: representations.
! 52: <H3>Internal ones</H3>The www/xxx ones are of course not
! 53: MIME standard.<P>
2.1 timbl 54: www/source is an output format which
55: leaves the input untouched. It is
56: useful for diagnostics, and for users
57: who want to see the original, whatever
58: it is.
2.13 ! timbl 59: <H3></H3>
! 60: <PRE>#define WWW_SOURCE HTAtom_for("www/source") /* Whatever it was originally*/
2.1 timbl 61:
62: </PRE>www/present represents the user's
63: perception of the document. If you
64: convert to www/present, you present
65: the material to the user.
66: <PRE>#define WWW_PRESENT HTAtom_for("www/present") /* The user's perception */
67:
68: </PRE>The message/rfc822 format means a
69: MIME message or a plain text message
70: with no MIME header. This is what
71: is returned by an HTTP server.
72: <PRE>#define WWW_MIME HTAtom_for("www/mime") /* A MIME message */
2.10 timbl 73:
2.1 timbl 74: </PRE>www/print is like www/present except
75: it represents a printed copy.
76: <PRE>#define WWW_PRINT HTAtom_for("www/print") /* A printed copy */
77:
2.10 timbl 78: </PRE>www/unknown is a really unknown type.
2.11 timbl 79: Some default action is appropriate.
2.10 timbl 80: <PRE>#define WWW_UNKNOWN HTAtom_for("www/unknown")
81:
2.13 ! timbl 82:
! 83:
! 84: </PRE>
! 85: <H3>MIME ones (a few)</H3>These are regular MIME types. HTML
2.11 timbl 86: is assumed to be added by the W3
87: code. application/octet-stream was
88: mistakenly application/binary in
89: earlier libwww versions (pre 2.11).
2.10 timbl 90: <PRE>#define WWW_PLAINTEXT HTAtom_for("text/plain")
2.1 timbl 91: #define WWW_POSTSCRIPT HTAtom_for("application/postscript")
92: #define WWW_RICHTEXT HTAtom_for("application/rtf")
2.10 timbl 93: #define WWW_AUDIO HTAtom_for("audio/basic")
2.1 timbl 94: #define WWW_HTML HTAtom_for("text/html")
2.11 timbl 95: #define WWW_BINARY HTAtom_for("application/octet-stream")
2.7 timbl 96:
2.1 timbl 97: </PRE>We must include the following file
98: after defining HTFormat, to which
2.10 timbl 99: it makes reference.
100: <H2>The HTEncoding type</H2>
101: <PRE>typedef HTAtom* HTEncoding;
102:
103: </PRE>The following are values for the
104: MIME types:
105: <PRE>#define WWW_ENC_7BIT HTAtom_for("7bit")
106: #define WWW_ENC_8BIT HTAtom_for("8bit")
107: #define WWW_ENC_BINARY HTAtom_for("binary")
108:
109: </PRE>We also add
110: <PRE>#define WWW_ENC_COMPRESS HTAtom_for("compress")
111:
112: #include "HTAnchor.h"
2.1 timbl 113:
114: </PRE>
115: <H2>The HTPresentation and HTConverter
116: types</H2>This HTPresentation structure represents
117: a possible conversion algorithm from
118: one format to annother. It includes
119: a pointer to a conversion routine.
120: The conversion routine returns a
121: stream to which data should be fed.
122: See also <A
2.12 timbl 123: NAME="z5" HREF="#z3">HTStreamStack</A> which scans
2.1 timbl 124: the list of registered converters
125: and calls one. See the <A
2.10 timbl 126: NAME="z6" HREF="HTInit.html">initialisation
2.1 timbl 127: module</A> for a list of conversion routines.
128: <PRE>typedef struct _HTPresentation HTPresentation;
129:
2.13 ! timbl 130: typedef HTStream * <A
! 131: NAME="z12">HTConverter</A> PARAMS((
! 132: HTRequest * request,
! 133: void * param,
! 134: HTFormat input_format,
! 135: HTFormat output_format,
! 136: HTStream * output_stream));
2.1 timbl 137:
138: struct _HTPresentation {
2.13 ! timbl 139: HTAtom* rep; /* representation name atomized */
2.1 timbl 140: HTAtom* rep_out; /* resulting representation */
2.2 timbl 141: HTConverter *converter; /* The routine to gen the stream stack */
2.1 timbl 142: char * command; /* MIME-format string */
143: float quality; /* Between 0 (bad) and 1 (good) */
144: float secs;
145: float secs_per_byte;
146: };
147:
148: </PRE>The list of presentations is kept
149: by this module. It is also scanned
150: by modules which want to know the
151: set of formats supported. for example.
2.13 ! timbl 152: <PRE>/* extern HTList * HTPresentations; */
2.1 timbl 153:
2.12 timbl 154: </PRE>The default presentation is used
2.13 ! timbl 155: when no other is approporate
! 156: <PRE>/* extern HTPresentation* default_presentation; */
2.12 timbl 157:
2.1 timbl 158: </PRE>
159: <H2>HTSetPresentation: Register a system
160: command to present a format</H2>
2.8 timbl 161: <H3>On entry,</H3>
2.1 timbl 162: <DL>
163: <DT>rep
164: <DD> is the MIME - style format name
165: <DT>command
166: <DD> is the MAILCAP - style command
167: template
168: <DT>quality
169: <DD> A degradation faction 0..1
170: <DT>maxbytes
171: <DD> A limit on the length acceptable
172: as input (0 infinite)
173: <DT>maxsecs
174: <DD> A limit on the time user
175: will wait (0 for infinity)
176: </DL>
177:
178: <PRE>extern void HTSetPresentation PARAMS((
2.13 ! timbl 179: HTList * conversions,
! 180: CONST char * representation,
! 181: CONST char * command,
! 182: float quality,
! 183: float secs,
! 184: float secs_per_byte
2.1 timbl 185: ));
186:
187:
188: </PRE>
189: <H2>HTSetConversion: Register a converstion
190: routine</H2>
2.8 timbl 191: <H3>On entry,</H3>
2.1 timbl 192: <DL>
193: <DT>rep_in
194: <DD> is the content-type input
195: <DT>rep_out
196: <DD> is the resulting content-type
197: <DT>converter
198: <DD> is the routine to make
199: the stream to do it
200: </DL>
201:
202: <PRE>
203: extern void HTSetConversion PARAMS((
2.13 ! timbl 204: HTList * conversions,
2.1 timbl 205: CONST char * rep_in,
206: CONST char * rep_out,
2.2 timbl 207: HTConverter * converter,
2.1 timbl 208: float quality,
209: float secs,
210: float secs_per_byte
211: ));
212:
213:
214: </PRE>
215: <H2><A
2.10 timbl 216: NAME="z3">HTStreamStack: Create a stack of
2.1 timbl 217: streams</A></H2>This is the routine which actually
218: sets up the conversion. It currently
219: checks only for direct conversions,
2.8 timbl 220: but multi-stage conversions are forseen.
2.2 timbl 221: It takes a stream into which the
2.1 timbl 222: output should be sent in the final
223: format, builds the conversion stack,
224: and returns a stream into which the
225: data in the input format should be
226: fed. The anchor is passed because
227: hypertxet objects load information
228: into the anchor object which represents
229: them.
230: <PRE>extern HTStream * HTStreamStack PARAMS((
231: HTFormat format_in,
2.13 ! timbl 232: HTRequest * request));
2.1 timbl 233:
234: </PRE>
235: <H2>HTStackValue: Find the cost of a
236: filter stack</H2>Must return the cost of the same
237: stack which HTStreamStack would set
238: up.
2.8 timbl 239: <H3>On entry,</H3>
2.1 timbl 240: <DL>
241: <DT>format_in
242: <DD> The fomat of the data to
243: be converted
244: <DT>format_out
245: <DD> The format required
246: <DT>initial_value
247: <DD> The intrinsic "value"
248: of the data before conversion on
249: a scale from 0 to 1
250: <DT>length
251: <DD> The number of bytes expected
252: in the input format
253: </DL>
254:
255: <PRE>extern float HTStackValue PARAMS((
2.13 ! timbl 256: HTList * conversions,
2.1 timbl 257: HTFormat format_in,
2.13 ! timbl 258: HTFormat format_out,
2.1 timbl 259: float initial_value,
260: long int length));
261:
262: #define NO_VALUE_FOUND -1e20 /* returned if none found */
263:
264: </PRE>
265: <H2><A
2.10 timbl 266: NAME="z1">HTCopy: Copy a socket to a stream</A></H2>This is used by the protocol engines
2.6 secret 267: to send data down a stream, typically
2.1 timbl 268: one which has been generated by HTStreamStack.
269: <PRE>extern void HTCopy PARAMS((
270: int file_number,
271: HTStream* sink));
272:
273:
2.6 secret 274: </PRE>
275: <H2><A
2.10 timbl 276: NAME="c6">HTFileCopy: Copy a file to a stream</A></H2>This is used by the protocol engines
2.6 secret 277: to send data down a stream, typically
2.7 timbl 278: one which has been generated by HTStreamStack.
279: It is currently called by <A
2.12 timbl 280: NAME="z9" HREF="#c7">HTParseFile</A>
2.6 secret 281: <PRE>extern void HTFileCopy PARAMS((
282: FILE* fp,
283: HTStream* sink));
284:
285:
2.7 timbl 286: </PRE>
287: <H2><A
2.10 timbl 288: NAME="c2">HTCopyNoCR: Copy a socket to a stream,
2.7 timbl 289: stripping CR characters.</A></H2>It is slower than <A
2.12 timbl 290: NAME="z2" HREF="#z1">HTCopy</A> .
2.1 timbl 291: <PRE>
292: extern void HTCopyNoCR PARAMS((
293: int file_number,
294: HTStream* sink));
295:
296:
297: </PRE>
298: <H2>Clear input buffer and set file number</H2>This routine and the one below provide
299: simple character input from sockets.
300: (They are left over from the older
301: architecure and may not be used very
302: much.) The existence of a common
303: routine and buffer saves memory space
304: in small implementations.
305: <PRE>extern void HTInitInput PARAMS((int file_number));
306:
307: </PRE>
308: <H2>Get next character from buffer</H2>
309: <PRE>extern char HTGetChararcter NOPARAMS;
310:
311:
312: </PRE>
313: <H2>HTParseSocket: Parse a socket given
314: its format</H2>This routine is called by protocol
315: modules to load an object. uses<A
2.12 timbl 316: NAME="z4" HREF="#z3">
2.1 timbl 317: HTStreamStack</A> and the copy routines
318: above. Returns HT_LOADED if succesful,
319: <0 if not.
320: <PRE>extern int HTParseSocket PARAMS((
321: HTFormat format_in,
322: int file_number,
2.13 ! timbl 323: HTRequest * request));
2.6 secret 324:
325: </PRE>
326: <H2><A
2.10 timbl 327: NAME="c1">HTParseFile: Parse a File through
2.7 timbl 328: a file pointer</A></H2>This routine is called by protocols
329: modules to load an object. uses<A
2.12 timbl 330: NAME="z4" HREF="#z3"> HTStreamStack</A>
2.7 timbl 331: and <A
2.12 timbl 332: NAME="c7" HREF="#c6">HTFileCopy</A> . Returns HT_LOADED
2.7 timbl 333: if succesful, <0 if not.
2.6 secret 334: <PRE>extern int HTParseFile PARAMS((
335: HTFormat format_in,
336: FILE *fp,
2.13 ! timbl 337: HTRequest * request));
2.8 timbl 338:
339: </PRE>
2.11 timbl 340: <H2><A
341: NAME="z11">HTNetToText: Convert Net ASCII to
342: local representation</A></H2>This is a filter stream suitable
343: for taking text from a socket and
344: passing it into a stream which expects
345: text in the local C representation.
346: It does ASCII and newline conversion.
347: As usual, pass its output stream
348: to it when creating it.
349: <PRE>extern HTStream * HTNetToText PARAMS ((HTStream * sink));
350:
351: </PRE>
2.8 timbl 352: <H2>HTFormatInit: Set up default presentations
353: and conversions</H2>These are defined in HTInit.c or
354: HTSInit.c if these have been replaced.
355: If you don't call this routine, and
356: you don't define any presentations,
357: then this routine will automatically
358: be called the first time a conversion
359: is needed. However, if you explicitly
360: add some conversions (eg using HTLoadRules)
361: then you may want also to explicitly
362: call this to get the defaults as
363: well.
2.13 ! timbl 364: <PRE>extern void HTFormatInit PARAMS((HTList * conversions));
2.1 timbl 365:
366: </PRE>
367: <H2>Epilogue</H2>
368: <PRE>extern BOOL HTOutputSource; /* Flag: shortcut parser */
369: #endif
370:
2.11 timbl 371: </PRE>end</BODY>
2.10 timbl 372: </HTML>
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