Annotation of libwww/Library/src/HTFormat.html, revision 2.76

2.10      timbl       1: <HTML>
                      2: <HEAD>
2.71      frystyk     3:   <!-- Changed by: Henrik Frystyk Nielsen, 15-Jul-1996 -->
2.75      frystyk     4:   <TITLE>W3C Sample Code Library libwww Stream Pipe Manager</TITLE>
2.10      timbl       5: </HEAD>
2.1       timbl       6: <BODY>
2.67      frystyk     7: <H1>
2.68      frystyk     8:   The Stream Pipe Manager
2.67      frystyk     9: </H1>
2.33      frystyk    10: <PRE>
                     11: /*
2.41      frystyk    12: **     (c) COPYRIGHT MIT 1995.
2.33      frystyk    13: **     Please first read the full copyright statement in the file COPYRIGH.
                     14: */
                     15: </PRE>
2.67      frystyk    16: <P>
2.68      frystyk    17: The Stream Pipe Manager is responsible for setting up the stream pipe from
                     18: the <A HREF="HTChannl.html">Channel Object</A> to the
                     19: <A HREF="HTReq.html">Request Object</A> when data is arriving, for example
                     20: as a response to s <A HREF="HTTP.html">HTTP</A> <B>Get</B> request. As data
                     21: arrives, we start to parse it and the more we know the more we can build
                     22: up our stream pipe. For example, in the case of HTTP, we first have a stream
                     23: that can parse the HTTP response line containing "<CODE>200 OK</CODE>". Then
                     24: we have a <A HREF="HTMIME.html">MIME parser</A> for handling the MIME headers.
                     25: When the MIME headers have been parsed, we know the content type and any
                     26: encoding of the MIME body. If we need to decode a chunked encoding then we
                     27: set up a chunked decoder, and if we have to parse a HTML object then we set
                     28: up a HTML parser.
2.67      frystyk    29: <P>
                     30: The Format Manager is also responsible for keeping track of the
                     31: "<I>preferences</I>" of the application and/or user. It is an integral part
                     32: of the Web and HTTP, that the client application can express its preferences
                     33: as a set of "accept" headers in a HTTP request. This task is highly related
                     34: to the task mentioned above as we there use the modules that are registered
                     35: and here tell the remote server what we are capable of doing and what we
                     36: would prefer.
                     37: <P>
                     38: <B>Note</B>: The library <B>core</B> does not define any default decoders
                     39: or parsers - they are all considered part of the application. The library
                     40: comes with a default set of parsers including the ones mentioned above which
                     41: can be initiated using the functions in <A HREF="HTInit.html">HTInit
                     42: module</A>. There are different initialization functions for content type
                     43: parsers and content encodings respectively.
                     44: <P>
                     45: <UL>
                     46:   <LI>
                     47:     <A HREF="#type">Content Type Converters and Presenters</A>
                     48:   <LI>
                     49:     <A HREF="#encoding">Content Encoders and Decoders</A>
                     50:   <LI>
                     51:     <A HREF="#charset">Content Charsets</A>
                     52:   <LI>
                     53:     <A HREF="#language">Natural Languages</A>
                     54: </UL>
                     55: <P>
                     56: The application can assign its preferences in two ways: either <I>locally</I>
                     57: to a single request or <I>globally</I> to all requests. The local assignment
                     58: can either <I>add to </I>or <I>override</I> the global settings depending
                     59: on how they are registered. All local registration is handled by the
                     60: <A HREF="HTReq.html">Request Object</A> and the global registration is handled
2.73      frystyk    61: by the Format Manager.
2.67      frystyk    62: <P>
                     63: This module is implemented by <A HREF="HTFormat.c">HTFormat.c</A>, and it
2.75      frystyk    64: is a part of the <A HREF="http://www.w3.org/pub/WWW/Library/">W3C Sample Code
2.67      frystyk    65: Library</A>.
2.31      frystyk    66: <PRE>
                     67: #ifndef HTFORMAT_H
2.1       timbl      68: #define HTFORMAT_H
                     69: 
2.63      frystyk    70: #include "<A HREF="HTUtils.html">HTUtils.h</A>"
                     71: #include "<A HREF="HTStream.html">HTStream.h</A>"
                     72: #include "<A HREF="HTAtom.html">HTAtom.h</A>"
                     73: #include "<A HREF="HTList.html">HTList.h</A>"
                     74: #include "<A HREF="HTAnchor.html">HTAnchor.h</A>"
                     75: #include "<A HREF="HTReq.html">HTReq.h</A>"
2.31      frystyk    76: </PRE>
2.67      frystyk    77: <H2>
2.73      frystyk    78:   <A NAME="type">Converters and Presenters</A>
2.67      frystyk    79: </H2>
                     80: <P>
                     81: All content type converters are subclassed from the Generic stream objetc.
                     82: That way, we allow the application to do very fast progressive display of
                     83: incoming data. In other words, the stream model of the Library provides data
                     84: as soon as it arrives from the network, the application does not have to
                     85: wait until the whole document has been down loaded before it starts parsing
                     86: it.
                     87: <H3>
                     88:   Predefined Content Types
                     89: </H3>
                     90: <P>
                     91: These macros (which used to be constants) define some basic internally referenced
                     92: representations. The <CODE>www/xxx</CODE> ones are of course not MIME standard.
                     93: They are internal representations used in the Library but they can't be exported
                     94: to other apps!
2.28      frystyk    95: <PRE>
2.57      frystyk    96: #define WWW_RAW                HTAtom_for("www/void")   /* Raw output from Protocol */
2.28      frystyk    97: </PRE>
2.67      frystyk    98: <P>
                     99: <CODE>WWW_RAW</CODE> is an output format which leaves the input untouched
                    100: <EM>exactly</EM> as it is received by the protocol module. For example, in
                    101: the case of FTP, this format returns raw ASCII objects for directory listings;
                    102: for HTTP, everything including the header is returned, for Gopher, a raw
                    103: ASCII object is returned for a menu etc.
                    104: <PRE>
                    105: #define WWW_SOURCE     HTAtom_for("*/*")
                    106: </PRE>
                    107: <P>
                    108: <CODE>WWW_SOURCE</CODE> is an output format which leaves the input untouched
                    109: <EM>exactly</EM> as it is received by the protocol module <B>IF</B> not a
                    110: suitable converter has been registered with a quality factor higher than
                    111: 1 (for example 2). In this case the <EM>SUPER CONVERTER</EM> is preferred
                    112: for the raw output. This can be used as a filter effect that allows conversion
                    113: from, for example raw FTPdirectory listings into HTML but passes a MIME body
                    114: untouched.
                    115: <PRE>
                    116: #define WWW_PRESENT    HTAtom_for("www/present")
                    117: </PRE>
                    118: <P>
                    119: <CODE>WWW_PRESENT</CODE> represents the user's perception of the document.
                    120: If you convert to <CODE>WWW_PRESENT</CODE>, you present the material to the
                    121: user.
2.58      frystyk   122: <PRE>
                    123: #define WWW_DEBUG      HTAtom_for("www/debug")
                    124: </PRE>
2.67      frystyk   125: <P>
                    126: <CODE>WWW_DEBUG</CODE> represents the user's perception of debug information,
                    127: for example sent as a HTML document in a HTTP redirection message.
2.28      frystyk   128: <PRE>
2.52      frystyk   129: #define WWW_UNKNOWN     HTAtom_for("www/unknown")
2.28      frystyk   130: </PRE>
2.67      frystyk   131: <P>
                    132: <CODE>WWW_UNKNOWN</CODE> is a really unknown type. It differs from the real
                    133: MIME type <EM>"application/octet-stream"</EM> in that we haven't even tried
                    134: to figure out the content type at this point.
2.71      frystyk   135: <PRE>
2.72      frystyk   136: #define WWW_CACHE         HTAtom_for("www/cache")
                    137: #define WWW_CACHE_APPEND  HTAtom_for("www/cache-append")
2.71      frystyk   138: </PRE>
                    139: <P>
                    140: <CODE>WWW_CACHE</CODE> is the internal content-type designated for a persistent
2.72      frystyk   141: cache module which can store the object to local storage. The cache append
                    142: format is special in that we append information to an already existing cache
                    143: entry. This can happen if we have issued a <CODE>If-Range </CODE>request
                    144: and got back a "206 Partial response".
2.67      frystyk   145: <P>
2.31      frystyk   146: These are regular MIME types defined. Others can be added!
2.28      frystyk   147: <PRE>
2.52      frystyk   148: #define WWW_HTML       HTAtom_for("text/html")
2.28      frystyk   149: #define WWW_PLAINTEXT  HTAtom_for("text/plain")
2.69      frystyk   150: #define WWW_FORM       HTAtom_for("application/x-www-form-urlencoded")
2.52      frystyk   151: 
                    152: #define WWW_MIME       HTAtom_for("message/rfc822")
2.60      frystyk   153: #define WWW_MIME_HEAD  HTAtom_for("message/x-rfc822-head")
2.65      frystyk   154: #define WWW_MIME_FOOT  HTAtom_for("message/x-rfc822-foot")
2.72      frystyk   155: #define WWW_MIME_PART   HTAtom_for("message/x-rfc822-partial")
2.76    ! frystyk   156: #define WWW_MIME_CONT   HTAtom_for("message/x-rfc822-cont")
2.52      frystyk   157: 
2.10      timbl     158: #define WWW_AUDIO       HTAtom_for("audio/basic")
2.52      frystyk   159: 
2.26      frystyk   160: #define WWW_VIDEO      HTAtom_for("video/mpeg")
2.52      frystyk   161: 
2.70      frystyk   162: #define WWW_GIF        HTAtom_for("image/gif")
2.63      frystyk   163: #define WWW_JPEG       HTAtom_for("image/jpeg")
                    164: #define WWW_TIFF       HTAtom_for("image/tiff")
2.52      frystyk   165: #define WWW_PNG        HTAtom_for("image/png")
                    166: 
                    167: #define WWW_BINARY     HTAtom_for("application/octet-stream")
                    168: #define WWW_POSTSCRIPT         HTAtom_for("application/postscript")
                    169: #define WWW_RICHTEXT   HTAtom_for("application/rtf")
2.48      frystyk   170: </PRE>
2.67      frystyk   171: <P>
                    172: We also have some MIME types that come from the various protocols when we
                    173: convert from ASCII to HTML.
2.48      frystyk   174: <PRE>
                    175: #define WWW_GOPHER_MENU HTAtom_for("text/x-gopher")
2.53      frystyk   176: #define WWW_CSO_SEARCH HTAtom_for("text/x-cso")
2.48      frystyk   177: 
                    178: #define WWW_FTP_LNST   HTAtom_for("text/x-ftp-lnst")
                    179: #define WWW_FTP_LIST   HTAtom_for("text/x-ftp-list")
                    180: 
                    181: #define WWW_NNTP_LIST   HTAtom_for("text/x-nntp-list")
                    182: #define WWW_NNTP_OVER  HTAtom_for("text/x-nntp-over")
                    183: #define WWW_NNTP_HEAD  HTAtom_for("text/x-nntp-head")
2.59      frystyk   184: 
                    185: #define WWW_HTTP       HTAtom_for("text/x-http")
2.55      frystyk   186: </PRE>
2.67      frystyk   187: <P>
                    188: Finally we have defined a special format for our RULE files as they can be
                    189: handled by a special converter.
2.73      frystyk   190: <PRE>#define WWW_RULES HTAtom_for("application/x-www-rules")
                    191: </PRE>
                    192: <H3>
                    193:   The Quality Factor
                    194: </H3>
                    195: <P>
                    196: Characteristic for all preferences is that there is a quality factor associated
                    197: with each member. The quality factor is a real number between 0 and 1 with
                    198: 0 meaning "very bad" and 1 means "perfect". By registering a natural language
                    199: or any or other preference in this group together with a quality factor you
                    200: can specify "how well the preference is handled" either by the application
                    201: or by the user. In the case of the user the quality factor of a natural language
                    202: is how well the user understands the language. In my case, the quality factors
                    203: for, for example Greek would be close to zero and 1 for Danish (nothing bad
                    204: said about Greek!).
                    205: <P>
                    206: It is a bit different for converters where it is often the application's
                    207: ability of handling the data format rather than the user's perception. As
                    208: an example it is often faster to use a converter than a presenter as it takes
                    209: time to launch the external application and libwww can not use progressive
                    210: display mechanisms which is often the case for converters. Therefore, as
                    211: an example, if we capable of handling an image in <EM>png</EM> format inline
                    212: but rely on an external viewer for presenting postscript, we might set up
                    213: the following list:
                    214: <P>
                    215: <SAMP>HTConversion_add (converters, "image", "www/present", GifPresenter,
                    216: <B>1.0</B>, 0.0, 0.0);<BR>
                    217: HTPresentation_add (presenters, "application/postscript", "ghostview %s",
                    218: NULL, <B>0.5</B>, 0.0, 0.0);&gt;</SAMP>
                    219: <P>
                    220: where the gif converter is registered with a quality factor of <B>1.0</B>
                    221: and the postscript presenter with a quality factor of <B>0.5</B>.Register
                    222: Presenters
                    223: <H3>
                    224:   The Converter Class
                    225: </H3>
                    226: <P>
                    227: A <CODE>converter</CODE> is a stream with a special set of parameters and
                    228: which is registered as capable of converting from a MIME type to something
                    229: else (maybe another MIME-type). A converter is defined to be a function returning
                    230: a stream and accepting the following parameters. The content type elements
                    231: are atoms for which we have defined a prototype.
2.55      frystyk   232: <PRE>
2.73      frystyk   233: typedef HTStream * HTConverter (HTRequest *    request,
                    234:                                 void *         param,
                    235:                                 HTFormat       input_format,
                    236:                                 HTFormat       output_format,
                    237:                                 HTStream *     output_stream);
                    238: 
                    239: extern void HTConversion_add   (HTList *       conversions,
                    240:                                const char *    rep_in,
                    241:                                const char *    rep_out,
                    242:                                HTConverter *   converter,
                    243:                                double          quality,
                    244:                                double          secs, 
                    245:                                double          secs_per_byte);
                    246: 
                    247: extern void HTConversion_deleteAll     (HTList * list);
2.28      frystyk   248: </PRE>
2.67      frystyk   249: <H3>
2.73      frystyk   250:   The Presenter Class
2.67      frystyk   251: </H3>
                    252: <P>
2.73      frystyk   253: A <CODE>presenter</CODE> is a module (possibly an external program) which
                    254: can present a graphic object of a certain MIME type to the user. That is,
                    255: <CODE>presenters</CODE> are normally used to present objects that the
                    256: <CODE>converters</CODE> are not able to handle. Data is transferred to the
                    257: external program using for example the
                    258: <A HREF="HTFWrite.html">HTSaveAndExecute</A> stream which writes to a local
                    259: file. Both presenters and converters are of the type
                    260: <A HREF="#converter">HTConverter</A>.
2.31      frystyk   261: <PRE>
2.49      frystyk   262: extern void HTPresentation_add (HTList *       conversions,
2.73      frystyk   263: </PRE>
                    264: <PRE>                          const char *    representation,
2.61      frystyk   265:                                const char *    command,
                    266:                                const char *    test_command,
2.49      frystyk   267:                                double          quality,
                    268:                                double          secs, 
                    269:                                double          secs_per_byte);
2.1       timbl     270: 
2.50      frystyk   271: extern void HTPresentation_deleteAll   (HTList * list);
                    272: </PRE>
2.67      frystyk   273: <H3>
2.73      frystyk   274:   Basic Converters
2.67      frystyk   275: </H3>
                    276: <P>
2.73      frystyk   277: We have a small set of basic converters that can be hooked in anywhere. They
                    278: don't "convert" anything but are nice to have.
                    279: <PRE>extern HTConverter HTThroughLine;
                    280: extern HTConverter HTBlackHoleConverter;
2.42      frystyk   281: </PRE>
2.67      frystyk   282: <H2>
                    283:   <A NAME="encoding">Content and Transfer Encoders and Decoders</A>
                    284: </H2>
                    285: <P>
                    286: Content codins are transformations applied to an entity object after it was
                    287: created in its original form. The Library handles two types of codings:
2.64      frystyk   288: <DL>
2.67      frystyk   289:   <DT>
                    290:     <B>Content Codings</B>
                    291:   <DD>
                    292:     Content codings values indicate an encoding transformation that has been
                    293:     applied to a resource. Content cosings are primarily used to allow a document
                    294:     to be compressed or encrypted without loosing the identity of its underlying
                    295:     media type.
                    296:   <DT>
                    297:     <B>Content Transfer Codings</B>
                    298:   <DD>
                    299:     Content transfer codings values are used to indicate an encoding transformation
                    300:     that has been, can be, or may be need to be applied to an enity body in order
                    301:     to ensure safe transport through the network. This differs from a content
                    302:     coding in that the transfer coding is a property of the message, not the
                    303:     original message.
2.64      frystyk   304: </DL>
2.67      frystyk   305: <P>
                    306: Both types of encodings use the same registration mechanism in the Library
                    307: which we describe below:
                    308: <H3>
                    309:   Encoders and Decoders
                    310: </H3>
                    311: <P>
                    312: <EM>Encoders</EM> and <EM>decoders</EM> are subclassed from the
                    313: <A HREF="HTStream.html">generic stream class</A>. <EM>Encoders</EM> are capable
                    314: of adding a content coding to a data object and <EM>decoders</EM> can remove
                    315: a content coding.
2.50      frystyk   316: <PRE>
2.64      frystyk   317: typedef HTStream * HTCoder     (HTRequest *    request,
                    318:                                 void *         param,
                    319:                                 HTEncoding     coding,
                    320:                                 HTStream *     target);
2.50      frystyk   321: </PRE>
2.67      frystyk   322: <P>
                    323: The <EM>encoding</EM> is the name of the encoding mechanism reporesented
                    324: as an <A HREF="HTAtom.html">atom</A>, for example "zip", "chunked", etc.
                    325: Encodings are registered in lists and content encodings are separated from
                    326: transfer encodings by registering them in different lists.
                    327: <H3>
                    328:   The HTCoding Object
                    329: </H3>
                    330: <P>
                    331: The <EM>HTCoding</EM> object represents a registered encoding together with
                    332: a encoder and a decoder.
2.63      frystyk   333: <PRE>
2.64      frystyk   334: typedef struct _HTCoding HTCoding;
2.63      frystyk   335: </PRE>
2.67      frystyk   336: <P>
                    337: Predefined Coding Types We have a set of pre defined atoms for various types
                    338: of content encodings and transfer encodings. "chunked" is not exactly in
                    339: the same group as the other encodings such as "binary" but it really doesn't
                    340: make any difference as it is just a matter of how the words are chosen. The
                    341: first three transfer encodings are actually not encodings - they are just
                    342: left overs from brain dead mail systems.
2.42      frystyk   343: <PRE>
2.63      frystyk   344: #define WWW_CTE_7BIT           HTAtom_for("7bit")
                    345: #define WWW_CTE_8BIT           HTAtom_for("8bit")
                    346: #define WWW_CTE_BINARY         HTAtom_for("binary")
2.64      frystyk   347: 
2.63      frystyk   348: #define WWW_CTE_BASE64         HTAtom_for("base64")
                    349: #define WWW_CTE_MACBINHEX      HTAtom_for("macbinhex")
2.64      frystyk   350: #define WWW_CTE_CHUNKED                HTAtom_for("chunked")
2.63      frystyk   351: 
                    352: #define WWW_CE_COMPRESS                HTAtom_for("compress")
                    353: #define WWW_CE_GZIP            HTAtom_for("gzip")
2.42      frystyk   354: </PRE>
2.67      frystyk   355: <H3>
                    356:   Register Content Coders
                    357: </H3>
                    358: <P>
2.73      frystyk   359: Some documents are not send in their original data obejct but is encoded
                    360: in some way. On the Web this is mostly some kind of compression but other
                    361: encodings for example base 64 can be encountered when talking to NNTP servers
                    362: etc. Just as for the other preferences, an application can register a supported
                    363: encoders or decodes as a list. Encoders and decoders are registered in the
                    364: same way with no differentiation whether it is a encoder or a decoder:
2.42      frystyk   365: <PRE>
2.64      frystyk   366: extern BOOL HTCoding_add (HTList *     list,
                    367:                         const char *   encoding,
                    368:                         HTCoder *      encoder,
                    369:                         HTCoder *      decoder,
                    370:                         double         quality);
2.63      frystyk   371: 
2.64      frystyk   372: extern void HTCoding_deleteAll (HTList * list);
2.42      frystyk   373: 
2.64      frystyk   374: extern const char * HTCoding_name (HTCoding * me);
2.42      frystyk   375: </PRE>
2.67      frystyk   376: <H2>
                    377:   <A NAME="charset">Content Charsets</A>
                    378: </H2>
2.73      frystyk   379: <P>
                    380: As the Web reaches all parts of the Internet there are more and more documents
                    381: written in languages which contains characters not included in the ISO-8859-1
                    382: character set. A consequence of this the set of characters sets is often
                    383: tightly connected with the natural language. libwww does not directly support
                    384: other character sets but in case an application is capable of handling
                    385: alternative sets it can register these as preferred character sets along
                    386: with a quality factor just as all the other preferences in this section.
                    387: <PRE>extern void HTCharset_add (HTList * list, const char * charset, double quality);
2.42      frystyk   388: </PRE>
2.73      frystyk   389: <PRE>typedef struct _HTAcceptNode {
2.63      frystyk   390:     HTAtom *   atom;
                    391:     double     quality;
                    392: } HTAcceptNode;
                    393: </PRE>
                    394: <PRE>
2.50      frystyk   395: extern void HTCharset_deleteAll        (HTList * list);
                    396: </PRE>
2.67      frystyk   397: <H2>
                    398:   <A NAME="language">Content Languages</A>
                    399: </H2>
2.73      frystyk   400: <P>
                    401: The preferred natural language or languages is in almost all situations dependent
                    402: on the individual user and an application should therefore give the user
                    403: the opportunity to change the setup. When specifying a natural language
                    404: preference, libwww will send this preference along with all HTTP requests.
                    405: The remote server will then (it if supports this feature) look for a version
                    406: in the language or languages mentioned. If it finds a matching document then
                    407: it returns this one, otherwise it uses the best alternative. If no language
                    408: is specified the remote server may whatever version it finds.
                    409: <PRE>extern void HTLanguage_add (HTList * list, const char * lang, double quality);
2.51      frystyk   410: extern void HTLanguage_deleteAll (HTList * list);
2.50      frystyk   411: </PRE>
2.67      frystyk   412: <H2>
                    413:   <A NAME="global">Global Preferences</A>
                    414: </H2>
                    415: <P>
2.50      frystyk   416: There are two places where these preferences can be registered: in a
2.67      frystyk   417: <EM>global</EM> list valid for <B>all</B> requests and a <EM>local</EM> list
                    418: valid for a particular request only. These are valid for <EM>all</EM> requests.
                    419: See the <A HREF="HTReq.html">Request Manager</A> fro local sets.
                    420: <H3>
2.73      frystyk   421:   Global Converters and Presenters
2.67      frystyk   422: </H3>
                    423: <P>
                    424: The <EM>global</EM> list of specific conversions which the format manager
                    425: can do in order to fulfill the request. There is also a
                    426: <A HREF="HTReq.html"><EM>local</EM></A> list of conversions which contains
                    427: a generic set of possible conversions.
2.73      frystyk   428: <PRE>extern void HTFormat_setConversion        (HTList * list);
2.50      frystyk   429: extern HTList * HTFormat_conversion    (void);
2.69      frystyk   430: 
                    431: extern void HTFormat_addConversion (const char *       input_format,
                    432:                                    const char *        output_format,
                    433:                                    HTConverter *       converter,
                    434:                                    double              quality,
                    435:                                    double              secs, 
                    436:                                    double              secs_per_byte);
2.31      frystyk   437: </PRE>
2.67      frystyk   438: <H3>
2.73      frystyk   439:   Global Content Codings
2.67      frystyk   440: </H3>
2.73      frystyk   441: <PRE>extern void HTFormat_setContentCoding     (HTList * list);
2.64      frystyk   442: extern HTList * HTFormat_contentCoding (void);
2.69      frystyk   443: 
                    444: extern BOOL HTFormat_addCoding ( char *                encoding,
                    445:                                 HTCoder *      encoder,
                    446:                                 HTCoder *      decoder,
                    447:                                 double         quality);
2.50      frystyk   448: </PRE>
2.74      frystyk   449: <P>
                    450: We also define a macro to find out whether a content encoding is really
                    451: an encoding or whether it is a unity encoder.
                    452: <PRE>
                    453: #define HTFormat_isUnityContent(me) \
                    454:        ((me)==NULL)
                    455: </PRE>
2.67      frystyk   456: <H3>
2.73      frystyk   457:   Global Content Transfer Codings
2.67      frystyk   458: </H3>
2.73      frystyk   459: <PRE>extern void HTFormat_setTransferCoding    (HTList * list);
2.64      frystyk   460: extern HTList * HTFormat_transferCoding        (void);
2.69      frystyk   461: 
                    462: extern BOOL HTFormat_addTransferCoding ( char *                encoding,
                    463:                                         HTCoder *      encoder,
                    464:                                         HTCoder *      decoder,
                    465:                                         double         quality);
2.64      frystyk   466: </PRE>
2.67      frystyk   467: <P>
                    468: We also define a macro to find out whether a transfer encoding is really
                    469: an encoding or whether it is just a "dummy" as for example 7bit, 8bit, and
                    470: binary.
2.64      frystyk   471: <PRE>
                    472: #define HTFormat_isUnityTransfer(me) \
                    473:        ((me)==NULL \
                    474:        || (me)==WWW_CTE_BINARY ||  (me)==WWW_CTE_7BIT || (me)==WWW_CTE_8BIT)
                    475: </PRE>
2.67      frystyk   476: <H3>
2.73      frystyk   477:   Global Content Languages
2.67      frystyk   478: </H3>
2.73      frystyk   479: <PRE>extern void HTFormat_setLanguage  (HTList * list);
2.50      frystyk   480: extern HTList * HTFormat_language      (void);
                    481: </PRE>
2.67      frystyk   482: <H3>
2.73      frystyk   483:   Global Content Charsets
2.67      frystyk   484: </H3>
2.73      frystyk   485: <PRE>extern void HTFormat_setCharset           (HTList * list);
2.50      frystyk   486: extern HTList * HTFormat_charset       (void);
2.31      frystyk   487: </PRE>
2.67      frystyk   488: <H3>
                    489:   Delete All Global Lists
                    490: </H3>
                    491: <P>
2.50      frystyk   492: This is a convenience function that might make life easier.
2.73      frystyk   493: <PRE>extern void HTFormat_deleteAll (void);
2.34      frystyk   494: </PRE>
2.67      frystyk   495: <H2>
                    496:   <A NAME="CTStack">The Content Type Stream Stack</A>
                    497: </H2>
                    498: <P>
                    499: This is the routine which actually sets up the content type conversion. It
                    500: currently checks only for direct conversions, but multi-stage conversions
                    501: are forseen. It takes a stream into which the output should be sent in the
                    502: final format, builds the conversion stack, and returns a stream into which
                    503: the data in the input format should be fed. If <CODE>guess</CODE> is true
                    504: and input format is <CODE>www/unknown</CODE>, try to guess the format by
                    505: looking at the first few bytes of the stream.
2.31      frystyk   506: <PRE>
2.52      frystyk   507: extern HTStream * HTStreamStack (HTFormat      rep_in,
                    508:                                 HTFormat       rep_out,
                    509:                                 HTStream *     output_stream,
                    510:                                 HTRequest *    request,
                    511:                                 BOOL           guess);
2.1       timbl     512: </PRE>
2.67      frystyk   513: <H3>
                    514:   Cost of a Stream Stack
                    515: </H3>
                    516: <P>
                    517: Must return the cost of the same stack which HTStreamStack would set up.
2.31      frystyk   518: <PRE>
2.52      frystyk   519: extern double HTStackValue     (HTList *       conversions,
                    520:                                 HTFormat       format_in,
                    521:                                 HTFormat       format_out,
                    522:                                 double         initial_value,
                    523:                                 long int       length);
2.64      frystyk   524: </PRE>
2.67      frystyk   525: <H2>
                    526:   <A NAME="CEStack">Content Encoding Stream Stack</A>
                    527: </H2>
                    528: <P>
                    529: When creating a coding stream stack, it is important that we keep the right
                    530: order of encoders and decoders. As an example, the HTTP spec specifies that
                    531: the list in the <EM>Content-Encoding</EM> header follows the order in which
                    532: the encodings have been applied to the object. Internally, we represent the
                    533: content encodings as <A HREF="HTAtom.html">atoms</A> in a linked
                    534: <A HREF="HTList.html">list object</A>.
                    535: <P>
                    536: The creation of the content coding stack is not based on quality factors
                    537: as we don't have the freedom as with content types. When using content codings
                    538: we <EM>must</EM> apply the codings specified or fail.
2.64      frystyk   539: <PRE>
                    540: extern HTStream * HTContentCodingStack (HTEncoding     coding,
                    541:                                        HTStream *      target,
                    542:                                        HTRequest *     request,
                    543:                                        void *          param,
                    544:                                        BOOL            encoding);
                    545: </PRE>
2.67      frystyk   546: <P>
                    547: Here you can provide a complete list instead of a single token. The list
                    548: has to be filled up in the order the _encodings_ are to be applied
2.64      frystyk   549: <PRE>
                    550: extern HTStream * HTContentEncodingStack (HTList *     encodings,
                    551:                                          HTStream *    target,
                    552:                                          HTRequest *   request,
                    553:                                          void *        param);
                    554: </PRE>
2.67      frystyk   555: <P>
                    556: Here you can provide a complete list instead of a single token. The list
                    557: has to be in the order the _encodings_ were applied - that is, the same way
                    558: that _encodings_ are to be applied. This is all consistent with the order
                    559: of the Content-Encoding header.
2.64      frystyk   560: <PRE>
                    561: extern HTStream * HTContentDecodingStack (HTList *     encodings,
                    562:                                          HTStream *    target,
                    563:                                          HTRequest *   request,
                    564:                                          void *        param);
                    565: </PRE>
2.67      frystyk   566: <H2>
                    567:   <A NAME="CTEStack">Content Transfer Encoding Stream Stack</A>
                    568: </H2>
                    569: <P>
                    570: Creating the transfer content encoding stream stack is not based on quality
                    571: factors as we don't have the freedom as with content types. Specify whether
                    572: you you want encoding or decoding using the BOOL "encode" flag.
2.64      frystyk   573: <PRE>
                    574: extern HTStream * HTTransferCodingStack (HTEncoding    encoding,
                    575:                                         HTStream *     target,
                    576:                                         HTRequest *    request,
                    577:                                         void *         param,
                    578:                                         BOOL           encode);
                    579: </PRE>
2.73      frystyk   580: <H3>
                    581:   Presentation Object
                    582: </H3>
                    583: <P>
                    584: This object is not to be used - it should have been hidden&nbsp;
                    585: <PRE>typedef struct _HTPresentation {
                    586:     HTFormat   rep;                         /* representation name atomized */
                    587:     HTFormat   rep_out;                         /* resulting representation */
                    588:     HTConverter *converter;          /* The routine to gen the stream stack */
                    589:     char *     command;                               /* MIME-format string */
                    590:     char *     test_command;                          /* MIME-format string */
                    591:     double     quality;                     /* Between 0 (bad) and 1 (good) */
                    592:     double     secs;
                    593:     double     secs_per_byte;
                    594: } HTPresentation;
                    595: </PRE>
2.64      frystyk   596: <PRE>
2.42      frystyk   597: #endif /* HTFORMAT */
2.38      frystyk   598: </PRE>
2.67      frystyk   599: <P>
                    600:   <HR>
2.63      frystyk   601: <ADDRESS>
2.76    ! frystyk   602:   @(#) $Id: HTFormat.html,v 2.75 1997/02/16 18:42:17 frystyk Exp $
2.63      frystyk   603: </ADDRESS>
2.67      frystyk   604: </BODY></HTML>

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