--- a/src/endp_create.c	Sat Nov 23 19:08:28 2024 +0000
+++ b/src/endp_create.c	Thu Dec 19 01:10:08 2024 +0000
@@ -12,8 +12,32 @@
 
 #include <themwi/rtp/endp.h>
 #include <themwi/rtp/twjit.h>
+#include <themwi/rtp/rtp_basic_hdr.h>
+#include <themwi/rtp/rtcp_defs.h>
 #include "endp_internal.h"
 
+/* We need to know maximum expected sizes of RTP and RTCP Rx packets
+ * for osmo_io msgb allocation.  For RTP, the largest packet size in
+ * 3GPP and IP-PSTN applications is 176 bytes: 12 bytes of RTP header
+ * plus 160 bytes of payload for 20 ms of uncompressed G.711 audio
+ * or CSData.  Of course there may be other applications that use
+ * larger RTP packets, in which case we may have to add an API function
+ * that overrides our default msgb alloc size setting - but let's
+ * cross that bridge if and when we actually have such users.
+ *
+ * In case of RTCP, we fully process all received packets inside
+ * the present library, hence we can set osmo_io msgb alloc size
+ * based on what our RTCP Rx code can parse and make use of.  Any
+ * additional RTCP Rx data, such as very long SDES strings, will
+ * simply be truncated at osmo_io level - but the subsequent parsing
+ * code will never get to those bits anyway.
+ */
+
+#define	MAX_RTP_RX_PACKET	(sizeof(struct rtp_basic_hdr) + 160)
+#define	MAX_RTCP_RX_PACKET	(sizeof(struct rtcp_sr_rr_hdr) + \
+					sizeof(struct rtcp_sr_block) + \
+					sizeof(struct rtcp_rr_block) * 31)
+
 struct twrtp_endp *twrtp_endp_create(void *ctx,
 				     struct twrtp_jibuf_config *config)
 {
@@ -30,6 +54,7 @@
 		talloc_free(endp);
 		return NULL;
 	}
+	osmo_iofd_set_alloc_info(endp->iofd_rtp, MAX_RTP_RX_PACKET, 0);
 
 	endp->iofd_rtcp = osmo_iofd_setup(endp, -1, NULL,
 					  OSMO_IO_FD_MODE_RECVFROM_SENDTO,
@@ -39,6 +64,7 @@
 		talloc_free(endp);
 		return NULL;
 	}
+	osmo_iofd_set_alloc_info(endp->iofd_rtcp, MAX_RTCP_RX_PACKET, 0);
 
 	endp->twjit = twrtp_jibuf_create(endp, config);
 	if (!endp->twjit) {