int lookup(struct sip_msg* _m, char* _t, char* _f, char* _s)
{
	unsigned int flags;
	urecord_t* r;
	str aor, uri;
	ucontact_t* ptr,*it;
	int res;
	int ret;
	str path_dst;
	str flags_s;
	pv_value_t val;
	int_str istr;
	str sip_instance = {0,0},call_id = {0,0};

	flags = 0;
	if (_f && _f[0]!=0) {
		if (fixup_get_svalue( _m, (gparam_p)_f, &flags_s)!=0) {
			LM_ERR("invalid owner uri parameter");
			return -1;
		}
		for( res=0 ; res< flags_s.len ; res++ ) {
			switch (flags_s.s[res]) {
				case 'm': flags |= REG_LOOKUP_METHODFILTER_FLAG; break;
				case 'b': flags |= REG_LOOKUP_NOBRANCH_FLAG; break;
				default: LM_WARN("unsuported flag %c \n",flags_s.s[res]);
			}
		}
	}

	if (_s) {
		if (pv_get_spec_value( _m, (pv_spec_p)_s, &val)!=0) {
			LM_ERR("failed to get PV value\n");
			return -1;
		}
		if ( (val.flags&PV_VAL_STR)==0 ) {
			LM_ERR("PV vals is not string\n");
			return -1;
		}
		uri = val.rs;
	} else {
		if (_m->new_uri.s) uri = _m->new_uri;
		else uri = _m->first_line.u.request.uri;
	}

	if (extract_aor(&uri, &aor,&sip_instance,&call_id) < 0) {
		LM_ERR("failed to extract address of record\n");
		return -3;
	}

	get_act_time();

	ul.lock_udomain((udomain_t*)_t, &aor);
	res = ul.get_urecord((udomain_t*)_t, &aor, &r);
	if (res > 0) {
		LM_DBG("'%.*s' Not found in usrloc\n", aor.len, ZSW(aor.s));
		ul.unlock_udomain((udomain_t*)_t, &aor);
		return -1;
	}

	ptr = r->contacts;
	ret = -1;
	/* look first for an un-expired and suported contact */
search_valid_contact:
	while ( (ptr) &&
	!(VALID_CONTACT(ptr,act_time) && (ret=-2) && allowed_method(_m,ptr,flags)))
		ptr = ptr->next;
	if (ptr==0) {
		/* nothing found */
		LM_DBG("nothing found !\n");
		goto done;
	}

	if (sip_instance.len && sip_instance.s) {
		LM_DBG("ruri has gruu in lookup\n");
		/* uri has GRUU */
		if (ptr->instance.len-2 != sip_instance.len || 
				memcmp(ptr->instance.s+1,sip_instance.s,sip_instance.len)) {
			LM_DBG("no match to sip instace - [%.*s] - [%.*s]\n",ptr->instance.len-2,ptr->instance.s+1,
					sip_instance.len,sip_instance.s);
			/* not the targeted instance, search some more */
			ptr = ptr->next;
			goto search_valid_contact;
		}

		LM_DBG("matched sip instace\n");
	}

	if (call_id.len && call_id.s) {
		/* decide whether GRUU is expired or not
		 *
		 * first - match call-id */
		if (ptr->callid.len != call_id.len ||
				memcmp(ptr->callid.s,call_id.s,call_id.len)) {
			LM_DBG("no match to call id - [%.*s] - [%.*s]\n",ptr->callid.len,ptr->callid.s,
					call_id.len,call_id.s);
			ptr = ptr->next;
			goto search_valid_contact;
		}

		/* matched call-id, check if there are newer contacts with
		 * same sip instace bup newer last_modified */

		it = ptr->next;
		while ( it ) {
			if (VALID_CONTACT(it,act_time)) {
				if (it->instance.len-2 == sip_instance.len &&
						memcmp(it->instance.s+1,sip_instance.s,sip_instance.len) == 0)
					if (it->last_modified > ptr->last_modified) {
						/* same instance id, but newer modified -> expired GRUU, no match at all */
						break;
					}
			}
		}

		if (it != NULL) {
			ret = -1;
			goto done;
		}
	}

	LM_DBG("found a complete match\n");

	ret = 1;
	if (ptr) {
		LM_DBG("setting as ruri <%.*s>\n",ptr->c.len,ptr->c.s);
		if (set_ruri(_m, &ptr->c) < 0) {
			LM_ERR("unable to rewrite Request-URI\n");
			ret = -3;
			goto done;
		}

		/* If a Path is present, use first path-uri in favour of
		 * received-uri because in that case the last hop towards the uac
		 * has to handle NAT. - agranig */
		if (ptr->path.s && ptr->path.len) {
			if (get_path_dst_uri(&ptr->path, &path_dst) < 0) {
				LM_ERR("failed to get dst_uri for Path\n");
				ret = -3;
				goto done;
			}
			if (set_path_vector(_m, &ptr->path) < 0) {
				LM_ERR("failed to set path vector\n");
				ret = -3;
				goto done;
			}
			if (set_dst_uri(_m, &path_dst) < 0) {
				LM_ERR("failed to set dst_uri of Path\n");
				ret = -3;
				goto done;
			}
		} else if (ptr->received.s && ptr->received.len) {
			if (set_dst_uri(_m, &ptr->received) < 0) {
				ret = -3;
				goto done;
			}
		}

		set_ruri_q(ptr->q);

		setbflag( 0, ptr->cflags);

		if (ptr->sock)
			_m->force_send_socket = ptr->sock;

		/* populate the 'attributes' avp */
		if (attr_avp_name != -1) {
			istr.s = ptr->attr;
			if (add_avp_last(AVP_VAL_STR, attr_avp_name, istr) != 0) {
				LM_ERR("Failed to populate attr avp!\n");
			}
		}

		ptr = ptr->next;
	}

	/* Append branches if enabled */
	/* If we got to this point and the URI had a ;gr parameter and it was matched
	 * to a contact. No point in branching */
	if ( flags&REG_LOOKUP_NOBRANCH_FLAG || (sip_instance.len && sip_instance.s) ) goto done;
	LM_DBG("looking for branches\n");

	for( ; ptr ; ptr = ptr->next ) {
		if (VALID_CONTACT(ptr, act_time) && allowed_method(_m,ptr,flags)) {
			path_dst.len = 0;
			if(ptr->path.s && ptr->path.len 
			&& get_path_dst_uri(&ptr->path, &path_dst) < 0) {
				LM_ERR("failed to get dst_uri for Path\n");
				continue;
			}

			/* The same as for the first contact applies for branches 
			 * regarding path vs. received. */
			LM_DBG("setting branch <%.*s>\n",ptr->c.len,ptr->c.s);
			if (append_branch(_m,&ptr->c,path_dst.len?&path_dst:&ptr->received,
			&ptr->path, ptr->q, ptr->cflags, ptr->sock) == -1) {
				LM_ERR("failed to append a branch\n");
				/* Also give a chance to the next branches*/
				continue;
			}

			/* populate the 'attributes' avp */
			if (attr_avp_name != -1) {
				istr.s = ptr->attr;
				if (add_avp_last(AVP_VAL_STR, attr_avp_name, istr) != 0) {
					LM_ERR("Failed to populate attr avp!\n");
				}
			}
		}
	}

done:
	ul.release_urecord(r);
	ul.unlock_udomain((udomain_t*)_t, &aor);
	return ret;
}
The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.