mqueue: return false if queue is empty

- return code -2
- reported by Alex Balashov

modules/mqueue/README

@@ -10,7 +10,7 @@ Elena-Ramona Modroiu
 
    <[email protected]>
 
-   Copyright © 2010 Elena-Ramona Modroiu (asipto.com)
+   Copyright © 2010 Elena-Ramona Modroiu (asipto.com)
      __________________________________________________________________
 
    Table of Contents
@@ -94,7 +94,7 @@ Chapter 1. Admin Guide
 
    Definition of memory queue
 
-   Default value is "none".
+   Default value is “none�.
 
    Value must be a list of parameters: attr=value;... The attribute 'name'
    is mandatory, defining the name of the queue. Optional attribute 'size'
@@ -128,8 +128,11 @@ mq_add("myq", "$rU", "call from $fU");
 
 4.2.  mq_fetch(queue)
 
-   Take oldest item from que and fill $mqk(queue) and $mqv(queue) pseudo
-   variables. Return true on success.
+   Take oldest item from queue and fill $mqk(queue) and $mqv(queue) pseudo
+   variables.
+
+   Return: true on success (1); false on failure (-1) or no item fetched
+   (-2).
 
    Example 1.3. mq_fetch usage
 ...

modules/mqueue/doc/mqueue_admin.xml

@@ -118,8 +118,12 @@ mq_add("myq", "$rU", "call from $fU");
 		<function moreinfo="none">mq_fetch(queue)</function>
 	    </title>
 	    <para>
-		Take oldest item from que and fill $mqk(queue) and $mqv(queue) pseudo
-		variables. Return true on success.
+		Take oldest item from queue and fill $mqk(queue) and
+		$mqv(queue) pseudo variables.
+	    </para>
+	    <para>
+		Return: true on success (1); false on failure (-1) or
+		no item fetched (-2).
 	    </para>
 		<example>
 		<title><function>mq_fetch</function> usage</title>

modules/mqueue/mqueue_api.c

@@ -254,17 +254,21 @@ int mq_head_fetch(str *name)
 		return -1;
 	lock_get(&mh->lock);
 
-	if(mh->ifirst!=NULL)
+	if(mh->ifirst==NULL)
 	{
-		mp->item = mh->ifirst;
-		mh->ifirst = mh->ifirst->next;
-		if(mh->ifirst==NULL) {
-			mh->ilast = NULL;
-		} else {
-			mh->ifirst->prev = NULL;
-		}
-		mh->csize--;
+		/* empty queue */
+		lock_release(&mh->lock);
+		return -2;
+	}
+
+	mp->item = mh->ifirst;
+	mh->ifirst = mh->ifirst->next;
+	if(mh->ifirst==NULL) {
+		mh->ilast = NULL;
+	} else {
+		mh->ifirst->prev = NULL;
 	}
+	mh->csize--;
 
 	lock_release(&mh->lock);
 	return 0;

modules/mqueue/mqueue_mod.c

@@ -109,8 +109,11 @@ static void mod_destroy(void)
 
 static int w_mq_fetch(struct sip_msg* msg, char* mq, char* str2)
 {
-	if(mq_head_fetch((str*)mq)<0)
-		return -1;
+	int ret;
+
+	ret = mq_head_fetch((str*)mq);
+	if(ret<0)
+		return ret;
 	return 1;
 }