Purpose: Make the server tell the client a recommended Message-ID before POST.

Reasoning: Many clients need to know the Message-IDs of their own
postings for bookkeeping or other purposes, so they generate them
themselves. But the better place for devising Message-IDs is the
server to guarantee unambiguity. This is a simple NNTP protocol
extension: in the 340 response to POST, the server gives a recommended 
Message-ID. It can be recognized by the <...@...> syntax.
To utilize this feature, we need better clients, of course.

Patch against: snapshot 19981013

--- nnrpd/commands.c.orig	Wed Jul 22 07:12:30 1998
+++ nnrpd/commands.c	Sat Oct 24 20:05:40 1998
@@ -660,12 +660,15 @@
 	size = 4096;
 	article = NEW(char, size);
     }
+    idbuff[0] = 0;
+    if ((p = GenerateMessageID()) != NULL)
+        strcpy(idbuff, p);
+    Reply("%d Ok, recommended ID %s\r\n", NNTP_START_POST_VAL, idbuff);
+    (void)fflush(stdout);
+
     p = article;
     end = &article[size];
 
-    Reply("%d Ok\r\n", NNTP_START_POST_VAL);
-    (void)fflush(stdout);
-
     for (l = 0, longline = 0; ; l++) {
 	/* Need more room? */
 	if (end - p < ART_LINE_MALLOC) {
@@ -731,7 +734,7 @@
     response = ARTpost(article, idbuff);
     if (response == NULL) {
 	syslog(L_NOTICE, "%s post ok %s", ClientHost, idbuff);
-	Reply("%s\r\n", NNTP_POSTEDOK);
+	Reply("%s %s\r\n", NNTP_POSTEDOK, idbuff);
 	POSTreceived++;
     }
     else {
--- nnrpd/post.c.orig	Thu Aug 20 07:12:47 1998
+++ nnrpd/post.c	Sat Oct 24 19:38:49 1998
@@ -323,8 +323,9 @@
 **  Return NULL if okay, or an error message.
 */
 STATIC STRING
-ProcessHeaders(linecount)
+ProcessHeaders(linecount, idbuff)
     int			linecount;
+    char                *idbuff;
 {
     static char		MONTHS[] = "JanFebMarAprMayJunJulAugSepOctNovDec";
     static char		datebuff[40];
@@ -414,12 +415,7 @@
 
     /* Set Message-ID */
     if (HDR(_messageid) == NULL) {
-	if ((p = GenerateMessageID()) == NULL) {
-	    (void)sprintf(Error, "Can't generate Message-ID, %s",
-		    strerror(errno));
-	    return Error;
-	}
-	HDR(_messageid) = p;
+	HDR(_messageid) = idbuff;
     }
 
     /* Set Path */
@@ -911,7 +907,7 @@
 	if ((error = CheckIncludedText(article, i)) != NULL)
 		return error;
     }
-    if ((error = ProcessHeaders(i)) != NULL)
+    if ((error = ProcessHeaders(i, idbuff)) != NULL)
 	return error;
     if (i == 0 && HDR(_control) == NULL)
 	return "Article is empty";