fetchmail workaround for a bug in Microsoft Exchange

treat missing header in response to a FETCH command as a transient error
(Reported by John Connett)

if there are too many transient errors, log it.

4 files changed, 31 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index 1e297d6f..11155c9b 100644
--- a/NEWS
+++ b/NEWS
@@ -95,6 +95,11 @@ fetchmail-6.3.22 (not yet released):
   a header request, in the face of message corruption.  fetchmail now treats
   these as temporary errors. Report and Patch by Mikulas Patocka, Red Hat.
 
+* Some servers, notably Microsoft Exchange, return "A0009 OK FETCH completed."
+  without any header in response to a header request for meeting reminder
+  messages (with a "meeting.ics" attachment). fetchmail now treats these as
+  transient errors.  Report by John Connett, Patch by Sunil Shetye.
+
 
 fetchmail-6.3.21 (released 2011-08-21, 26011 LoC):
 
diff --git a/driver.c b/driver.c
index 25fed3bd..c2917268 100644
--- a/driver.c
+++ b/driver.c
@@ -438,7 +438,8 @@ static int eat_trailer(int sock, struct query *ctl)
 
 static int fetch_messages(int mailserver_socket, struct query *ctl, 
 			  int count, int **msgsizes, int maxfetch,
-			  int *fetches, int *dispatches, int *deletions)
+			  int *fetches, int *dispatches, int *deletions,
+			  int *transient_errors)
 /* fetch messages in lockstep mode */
 {
     flag force_retrieval;
@@ -612,6 +613,7 @@ static int fetch_messages(int mailserver_socket, struct query *ctl,
 			     GT_("couldn't fetch headers, message %s@%s:%d (%d octets)\n"),
 			     ctl->remotename, ctl->server.truename, num,
 			     msgsize);
+		(*transient_errors)++;
 		continue;
 	    }
 	    else if (err != 0)
@@ -653,7 +655,10 @@ static int fetch_messages(int mailserver_socket, struct query *ctl,
 	    if (err == PS_RETAINED)
 		suppress_forward = suppress_delete = retained = TRUE;
 	    else if (err == PS_TRANSIENT)
+	    {
 		suppress_delete = suppress_forward = TRUE;
+		(*transient_errors)++;
+	    }
 	    else if (err == PS_REFUSED)
 		suppress_forward = TRUE;
 	    else if (err)
@@ -714,7 +719,10 @@ static int fetch_messages(int mailserver_socket, struct query *ctl,
 			      len);
 
 		if (err == PS_TRANSIENT)
+		{
 		    suppress_delete = suppress_forward = TRUE;
+		    (*transient_errors)++;
+		}
 		else if (err)
 		    return(err);
 
@@ -940,7 +948,7 @@ static int do_session(
 	/* sigsetjmp returned zero -> normal operation */
 	char buf[MSGBUFSIZE+1], *realhost;
 	int count, newm, bytes;
-	int fetches, dispatches, oldphase;
+	int fetches, dispatches, transient_errors, oldphase;
 	struct idlist *idp;
 
 	/* execute pre-initialization command, if any */
@@ -1297,6 +1305,7 @@ is restored."));
 	    pass = 0;
 	    do {
 		dispatches = 0;
+		transient_errors = 0;
 		++pass;
 
 		/* reset timeout, in case we did an IDLE */
@@ -1426,10 +1435,20 @@ is restored."));
 		    err = fetch_messages(mailserver_socket, ctl, 
 					 count, &msgsizes,
 					 maxfetch,
-					 &fetches, &dispatches, &deletions);
+					 &fetches, &dispatches, &deletions,
+					 &transient_errors);
 		    if (err != PS_SUCCESS && err != PS_MAXFETCH)
 			goto cleanUp;
 
+		    if (transient_errors > MAX_TRANSIENT_ERRORS)
+		    {
+			if (outlevel > O_SILENT)
+			{
+			    report(stderr, GT_("Too many mails skipped (%d > %d) due to transient errors for %s\n"),
+				    transient_errors, MAX_TRANSIENT_ERRORS, buf);
+			}
+		    }
+
 		    if (!check_only && ctl->skipped
 			&& run.poll_interval > 0 && !nodetach)
 		    {
diff --git a/imap.c b/imap.c
index 93f05f2c..cb87eda5 100644
--- a/imap.c
+++ b/imap.c
@@ -1182,7 +1182,7 @@ static int imap_fetch_headers(int sock, struct query *ctl,int number,int *lenp)
 	/* an unexpected tagged response */
 	if (outlevel > O_SILENT)
 	    report(stderr, GT_("Incorrect FETCH response: %s.\n"), buf);
-	return(PS_ERROR);
+	return(PS_TRANSIENT);
     }
     return(ok);
 }
diff --git a/tunable.h b/tunable.h
index 6202e7bd..fddeaf9b 100644
--- a/tunable.h
+++ b/tunable.h
@@ -21,3 +21,6 @@
 
 /* default skipped message warning interval in seconds */
 #define WARNING_INTERVAL	3600
+
+/* maximum transient errors to accept */
+#define MAX_TRANSIENT_ERRORS	20