suggested libWWW architecture
Dan Connolly <connolly@pixel.convex.com>
Message-id: <9301140111.AA21994@pixel.convex.com>
To: www-talk@nxoc01.cern.ch
Subject: suggested libWWW architecture
Date: Wed, 13 Jan 93 19:11:15 CST
From: Dan Connolly <connolly@pixel.convex.com>
I sent this to tim a while ago, but I don't think
he's had time to look at it.
Meanwhile, libWWW is becomming reentrant, but I still
think the architecture is kinda clumsy: you have to
have a big data structure describing the DTD, and
a routine for each element, etc.
This doesn't mesh well with the MidasWWW architecture, which
can read the DTD from the X resource database at
runtime.
I have an idea for an architecture that the linemode and
MidasWWW could share (along with other new implementations).
It's not radically different from the current libWWW, but
there's a lot of grunt-work between the current libWWW
and what I've got here. But I think the end result would
be much more usable.
We start with the HText class. In stead of the various
style and append methods, we have four methods in a
virtual function table:
typedef struct{
int (*start_tag) PARAMS((SGML_Object this, CONST char* gi,
CONST char** attributes, int nattrs));
VOID (*end_tag) PARAMS((SGML_Object this, CONST char* gi));
VOID (*entity) PARAMS((SGML_Object this, CONST char* name));
VOID (*data) PARAMS((SGML_Object this, CONST char* data, int char_qty));
}SGML_DocClass;
The linemode would declare something like:
SGML_DocClass griddoc = {HText_start_tag, HText_end_tag,
HText_entity, HText_data};
The HText implementation is responsible for keeping track of
the stack of open elements, if it needs to.
On top of these we build some format parsing routines:
SGML_parse(void* dest, void* closure, void* stream, int (getc)(void*));
/* psuedocode:
int read, content;
char buffer[1000];
SGML_DocClass *docclass = (SGML_DocClass*)closure;
while( (read = SGML_read(buffer, content, stream, getc)) != EOF){
switch(read){
case SGML_start_tag:
... parse name, attributes ...
content = (docclass->startTag)(dest, name, attrs);
if(content = empty){
(docclass->endTag)(name);
content = MIXED; /*@@ could be ELEMENT */
}
break;
case SGML_end_tag:
... parse name ...
(docclass->endTag)(name);
content = MIXED; /*@@ could be ELEMENT */
break;
case SGML_entity:
(docclass->entity)(data, name);
break;
default:
(docclass->data)(dest, buffer);
}
*/
PlainText_parse(HText* dest, void* docclass, void* stream, int (getc)(void*));
/* psuedocode:
(docclass->startTag)(dest, "HTML");
(docclass->startTag)(dest, "BODY");
(docclass->startTag)(dest, "PRE");
keep a local buffer of about 1000 chars.
Call (getc)(stream) until EOF.
Call HText_data(dest, buffer) whenever buffer is full.
(docclass->endTag)(dest, "PRE");
(docclass->endTag)(dest, "BODY");
(docclass->endTag)(dest, "HTML");
*/
GopherListing_parse(HText* dest, void* dummy, void* stream, int (getc)(void*));
/* psuedocode:
(docclass->startTag)(dest, "HTML");
(docclass->startTag)(dest, "BODY");
(docclass->startTag)(dest, "MENU");
while(Gopher_parse_line(stream, getc, type, name, host, port, path)){
char addr[BIG];
sprintf(addr, "gopher://%s:%d/%c%s", host, port, type, path);
(docclass->startTag)(dest, "A",
"HREF", addr,
0);
(docclass->data)(dest, name);
(docclass->endTag)(dest, "A");
}
(docclass->endTag)(dest, "MENU");
(docclass->endTag)(dest, "BODY");
(docclass->endTag)(dest, "HTML");
*/
We register each of these with the following routine:
int
ContentType_register(CONST char* type, CONST char* subtype,
HTParseProc parse, void* closure);
For example:
main()
{
ContentType_register("TEXT", "X-HTML", HTML_parse, griddoc);
ContentType_register("TEXT", "PLAIN", PlainText_parse, griddoc);
ContentType_register("APPLICATION", "X-GOPHER",
GopherListing_parse, griddoc);
}
The following routine can be used for any MIME entity. It will dispatch
the appropriate parsing routine based on the content type header:
int
ContentType_parse(const char* ct, HText* dest, void* stream, int (getc)(void*));
Then we build some load routines, one per access scheme:
(note that this design separates format from the access scheme, which
allows us to, for example, load a gopher menu
from a local file, or load HTML text from a Gopher server)
/* I don't have error handling worked out yet. We need to have a coherent
design for this. It's a mess in the current WWWlib. */
/* I think the WWW file: should be split into ftp: and local-file:.
It's cleaner to implement; there are precedents in the MidasWWW local:
scheme and the MIME ftp and local-file access-types. */
int
LocalFile_load(HText* dest, CONST char* path, CONST char* search)
{
FILE* stream;
if(stream = fopen(path)){
const char* content_type = WWW_zen_content_type_from_extension(path);
ContentType_parse(content_type, dest, (void*)stream, (int ()(void*))getc);
fclose(stream);
return 1;
}else{
/* log an error */
return 0;
}
}
int
FTP_load(HText* dest, CONST char* path, CONST char* search);
int
HTTP_load(HText* dest, CONST char* path, CONST char* search);
int
Gopher_load(HText* dest, CONST char* path, CONST char* search);
{
const char* content_type = Gopher_zen_content_type_from_gtype_char(*path);
char* host = HTParse(path, PARSE_HOST);
char* portnum = HTParse(path, PARSE_PORT);
int port = atoi(portnum);
static char* tab = "\007";
static char* crlf = "\015\012";
void* stream = TCPOpen(host, port);
if(stream){
TCPwrite(stream, path, strlen(path);
if(search){
TCPwrite(stream, tab, 1);
TCPwrite(stream, search, strlen(search);
}
TCPwrite(stream, crlf, 2);
ContentType_parse(content_type, dest, stream, TCPgetc);
TCPclose(stream);
return 1;
}else{
/* log an error */
return 0;
}
}
Then we register these just like formats:
HTAccess_register(const char* name, HTLoadProc load, void* closure);
And the HTLoadDocument routine in HTAccess.c becomes this:
int
HTAccess_load(HText* dest, HTParentAnchor* p, CONST char* address)
{
char* scheme = HTParse(address, PARSE_SCHEME);
/* path is everything after the colon, except the anchor */
char* path = HTParse(address, PARSE_HOST|PARSE_PORT|PARSE_PATH);
char* anchor = HTParse(address, PARSE_ANCHOR);
char* search = HTParse(address, PARSE_SEARCH_TERMS);
HText dest = HText_new(p); /* check for doc already loaded in p @@ */
void* closure;
HTLoadProc load;
if(load = /* load routine registered for scheme. find closure too */){
(load)(dest, path, search, closure);
}
HTSelect(dest, anchor);
}
What do you think?
Dan