Retrieving News groups and articles

	The [[ag-nntp]] agent has a single argument: a URL of the form
	[[news:*]], [[news:group]], [[news:articleID]] or
	[[news:group/articlenumber]]. Instead of `news', the name
	`nntp' may also be used. Which NNTP server to contact is
	determined by the [[NNTPSERVER]] environment variable, or by
	the compiled-in default. The default is defined in
	[["../config.h"]].

	If the argument is of the first form, [[news:*]], the agent
	contacts the NNTP server and asks for a list of all available
	newsgroups. The program prefixes the list with a status code
	and a MIME header and prints it on standard output. The MIME
	Content-Type of such a list is [[text/x-newsgroup-list]]. The
	status code will be 200 if all goes well.

	If the argument is of the form [[news:group]], where group is
	any newsgroup name, then the agent sends a series of commands
	to the NNTP server to retrieve a list of all articles in that
	group. For each article, the agent sends the [[HEAD]] command
	to get the header information, of which the subject and author
	are retained and the rest is thrown away. The list is then
	prefixed with a status code and a MIME header and printed to
	stdout. The MIME type is [[text/x-article-list]]

	If the argument is of the form [[news:group/number]], the
	agent retrieves the indicated article from the group. If the
	header of that article does not include a MIME type, a header
	line for [[Content-Type: text/plain]] is added. The complete
	article, header plus body, is then printed on standard output,
	prefixed with a status code.

	Instead of a number, the message ID can also be used. In that
	case the [[group]] is redundant.

	When the URL is of the form [[news:articleID]], then the
	indicated article will be retrieved. The ID must be given
	without [[<]] and [[>]] brackets. The agent distinguishes
	between [[news:group]] and [[news:articleID]] by looking for a
	[[@]] character. Such a character occurs iff it is an ID.

	NOTE: In this version, the second and third command line
	argument (method, resp. title) are ignored. This nees to be
	changed. Especially the second argument (method) should be
	taken into account, since it may be a [[POST]] method.

<<*>>=
#include <config.h>
#include <str.h>
#include <url.h>
#include <tcp.h>
#include <mime.h>
#include "get-all.e"
#include "get-group.e"
#include "get-article.e"
#include "get-artID.e"

void main(int argc, char *argv[])
{
    int s;
    FILE *f;
    char *server, *p, line[MAXLINELEN], *method = NULL, *title = "no title";
    char *url;

    switch (argc) {
    case 4: title = argv[3]; /* fall through */
    case 3: method = argv[2]; /* fall through */
    case 2: url = argv[1]; break;
    default: errexit("400 Incorrect number of arguments\r\n");
    }

    if (strncmp(url, "news:", 5) != 0
	&& strncmp(url, "nntp:", 5) != 0)
	errexit("400 Bad URL syntax\r\n");

    if (! (server = getenv("NNTPSERVER")))
	server = NNTPSERVER;

    debug("Connecting to %s\n", server);

    if ((s = connectTCP(server, "nntp")) == -1)
	errexit("500 Could not connect\r\n");

    if (! (f = fdopen(s, "r+")))
	errexit("500 I/O error\r\n");

    if (! fgets(line, sizeof(line), f))
	errexit("500 No response from server\r\n");
    if (line[0] != '2')
	errexit(line);

    debug("Sending commands\n");

    if (strcmp(url + 5, "*") == 0) {
	get_all_groups(f);			/* news:* */
    } else if (strchr(url + 5, '@')) {
	get_article_by_ID(f, url + 5);		/* news:articleID */
    } else if (! (p = strchr(url + 5, '/'))) {
	get_group(f, url + 5);			/* news:group */
    } else {
	*p = '\0';
	get_article(f, url + 5, p + 1);		/* news:group/number */
    }

    exit(0);
}