somewhat improved plain tcp syslog reliability

...by doing a connection check before sending. Credits to Martin
Schuette for providing the idea. Details are available at
http://blog.gerhards.net/2008/06/reliable-plain-tcp-syslog-once-again.html

5 files changed, 54 insertions, 1 deletions

diff --git a/runtime/netstrm.c b/runtime/netstrm.c
index 786ba7f8..2f4a1964 100644
--- a/runtime/netstrm.c
+++ b/runtime/netstrm.c
@@ -234,6 +234,15 @@ Send(netstrm_t *pThis, uchar *pBuf, ssize_t *pLenBuf)
 }
 
 
+/* check connection - slim wrapper for NSD driver function */
+static void
+CheckConnection(netstrm_t *pThis)
+{
+	ISOBJ_TYPE_assert(pThis, netstrm);
+	pThis->Drvr.CheckConnection(pThis->pDrvrData);
+}
+
+
 /* get remote hname - slim wrapper for NSD driver function */
 static rsRetVal
 GetRemoteHName(netstrm_t *pThis, uchar **ppsz)
@@ -314,6 +323,7 @@ CODESTARTobjQueryInterface(netstrm)
 	pIf->SetDrvrMode = SetDrvrMode;
 	pIf->SetDrvrAuthMode = SetDrvrAuthMode;
 	pIf->SetDrvrPermPeers = SetDrvrPermPeers;
+	pIf->CheckConnection = CheckConnection;
 	pIf->GetSock = GetSock;
 finalize_it:
 ENDobjQueryInterface(netstrm)
diff --git a/runtime/netstrm.h b/runtime/netstrm.h
index ae135beb..1a97ef23 100644
--- a/runtime/netstrm.h
+++ b/runtime/netstrm.h
@@ -52,6 +52,7 @@ BEGINinterface(netstrm) /* name must also be changed in ENDinterface macro! */
 	rsRetVal (*SetDrvrMode)(netstrm_t *pThis, int iMode);
 	rsRetVal (*SetDrvrAuthMode)(netstrm_t *pThis, uchar*);
 	rsRetVal (*SetDrvrPermPeers)(netstrm_t *pThis, permittedPeers_t*);
+	void     (*CheckConnection)(netstrm_t *pThis);	/* This is a trick mostly for plain tcp syslog */
 	/* the GetSock() below is a hack to make imgssapi work. In the long term,
 	 * we should migrate imgssapi to a stream driver, which will relieve us of
 	 * this problem. Please note that nobody else should use GetSock(). Using it 
diff --git a/runtime/nsd.h b/runtime/nsd.h
index 53693b59..1811f078 100644
--- a/runtime/nsd.h
+++ b/runtime/nsd.h
@@ -53,6 +53,7 @@ BEGINinterface(nsd) /* name must also be changed in ENDinterface macro! */
 	rsRetVal (*SetMode)(nsd_t *pThis, int mode); /* sets a driver specific mode - see driver doc for details */
 	rsRetVal (*SetAuthMode)(nsd_t *pThis, uchar*); /* sets a driver specific mode - see driver doc for details */
 	rsRetVal (*SetPermPeers)(nsd_t *pThis, permittedPeers_t*); /* sets driver permitted peers for auth needs */
+	void     (*CheckConnection)(nsd_t *pThis);	/* This is a trick mostly for plain tcp syslog */
 	rsRetVal (*GetSock)(nsd_t *pThis, int *pSock);
 	rsRetVal (*SetSock)(nsd_t *pThis, int sock);
 	/* GetSock() and SetSock() return an error if the driver does not use plain
@@ -60,7 +61,7 @@ BEGINinterface(nsd) /* name must also be changed in ENDinterface macro! */
 	 * those drivers that utilize the nsd_ptcp to do some of their work.
 	 */
 ENDinterface(nsd)
-#define nsdCURR_IF_VERSION 2 /* increment whenever you change the interface structure! */
+#define nsdCURR_IF_VERSION 3 /* increment whenever you change the interface structure! */
 
 /* interface  for the select call */
 BEGINinterface(nsdsel) /* name must also be changed in ENDinterface macro! */
diff --git a/runtime/nsd_gtls.c b/runtime/nsd_gtls.c
index 0440f149..567701dc 100644
--- a/runtime/nsd_gtls.c
+++ b/runtime/nsd_gtls.c
@@ -1243,6 +1243,17 @@ finalize_it:
 }
 
 
+/* This function checks if the connection is still alive - well, kind of...
+ * This is a dummy here. For details, check function common in ptcp driver.
+ * rgerhards, 2008-06-09
+ */
+static void
+CheckConnection(nsd_t __attribute__((unused)) *pNsd)
+{
+	/* dummy, do nothing */
+}
+
+
 /* get the remote hostname. The returned hostname must be freed by the caller.
  * rgerhards, 2008-04-25
  */
@@ -1507,6 +1518,7 @@ CODESTARTobjQueryInterface(nsd_gtls)
 	pIf->SetMode = SetMode;
 	pIf->SetAuthMode = SetAuthMode;
 	pIf->SetPermPeers =SetPermPeers;
+	pIf->CheckConnection = CheckConnection;
 	pIf->GetRemoteHName = GetRemoteHName;
 	pIf->GetRemoteIP = GetRemoteIP;
 finalize_it:
diff --git a/runtime/nsd_ptcp.c b/runtime/nsd_ptcp.c
index 14c564a3..ff85619a 100644
--- a/runtime/nsd_ptcp.c
+++ b/runtime/nsd_ptcp.c
@@ -638,6 +638,34 @@ finalize_it:
 }
 
 
+/* This function checks if the connection is still alive - well, kind of... It
+ * is primarily being used for plain TCP syslog and it is quite a hack. However,
+ * as it seems to work, it is worth supporting it. The bottom line is that it
+ * should not be called by anything else but a plain tcp syslog sender.
+ * In order for it to work, it must be called *immediately* *before* the send()
+ * call. For details about what is done, see here:
+ * http://blog.gerhards.net/2008/06/getting-bit-more-reliability-from-plain.html
+ * rgerhards, 2008-06-09
+ */
+static void
+CheckConnection(nsd_t *pNsd)
+{
+	int rc;
+	char msgbuf[1]; /* dummy */
+	nsd_ptcp_t *pThis = (nsd_ptcp_t*) pNsd;
+	ISOBJ_TYPE_assert(pThis, nsd_ptcp);
+
+	rc = recv(pThis->sock, msgbuf, 1, MSG_DONTWAIT | MSG_PEEK);
+	if(rc == 0) {
+		dbgprintf("CheckConnection detected broken connection - closing it\n");
+		/* in this case, the remote peer had shut down the connection and we
+		 * need to close our side, too.
+		 */
+		sockClose(&pThis->sock);
+	}
+}
+
+
 /* get the remote host's IP address. The returned string must be freed by the
  * caller.
  * rgerhards, 2008-04-24
@@ -684,6 +712,7 @@ CODESTARTobjQueryInterface(nsd_ptcp)
 	pIf->Connect = Connect;
 	pIf->GetRemoteHName = GetRemoteHName;
 	pIf->GetRemoteIP = GetRemoteIP;
+	pIf->CheckConnection = CheckConnection;
 finalize_it:
 ENDobjQueryInterface(nsd_ptcp)