net: pkt: Add function net_pkt_get_contiguous_len()

This returns the available contingous space in the packet starting from
the current cursor position.

Signed-off-by: Christian Taedcke <[email protected]>

include/net/net_pkt.h

@@ -1904,6 +1904,16 @@ uint16_t net_pkt_get_current_offset(struct net_pkt *pkt);
  */
 bool net_pkt_is_contiguous(struct net_pkt *pkt, size_t size);
 
+/**
+ * Get the contiguous buffer space
+ *
+ * @param pkt Network packet
+ *
+ * @return The available contiguous buffer space in bytes starting from the
+ *         current cursor position. 0 in case of an error.
+ */
+size_t net_pkt_get_contiguous_len(struct net_pkt *pkt);
+
 struct net_pkt_data_access {
 #if !defined(CONFIG_NET_HEADERS_ALWAYS_CONTIGUOUS)
 	void *data;

subsys/net/ip/net_pkt.c

@@ -1958,6 +1958,13 @@ uint16_t net_pkt_get_current_offset(struct net_pkt *pkt)
 }
 
 bool net_pkt_is_contiguous(struct net_pkt *pkt, size_t size)
+{
+	size_t len = net_pkt_get_contiguous_len(pkt);
+
+	return len >= size;
+}
+
+size_t net_pkt_get_contiguous_len(struct net_pkt *pkt)
 {
 	pkt_cursor_advance(pkt, !net_pkt_is_being_overwritten(pkt));
 
@@ -1967,12 +1974,10 @@ bool net_pkt_is_contiguous(struct net_pkt *pkt, size_t size)
 		len = net_pkt_is_being_overwritten(pkt) ?
 			pkt->cursor.buf->len : pkt->cursor.buf->size;
 		len -= pkt->cursor.pos - pkt->cursor.buf->data;
-		if (len >= size) {
-			return true;
-		}
+		return len;
 	}
 
-	return false;
+	return 0;
 }
 
 void *net_pkt_get_data(struct net_pkt *pkt,

tests/net/net_pkt/src/main.c

@@ -912,6 +912,68 @@ void test_net_pkt_headroom_copy(void)
 	net_pkt_unref(pkt_src);
 }
 
+static void test_net_pkt_get_contiguous_len(void)
+{
+	size_t cont_len;
+	int res;
+	/* Allocate pkt with 2 fragments */
+	struct net_pkt *pkt = net_pkt_rx_alloc_with_buffer(
+					   NULL, CONFIG_NET_BUF_DATA_SIZE * 2,
+					   AF_UNSPEC, 0, K_NO_WAIT);
+
+	zassert_not_null(pkt, "Pkt not allocated");
+
+	net_pkt_cursor_init(pkt);
+
+	cont_len = net_pkt_get_contiguous_len(pkt);
+	zassert_equal(CONFIG_NET_BUF_DATA_SIZE, cont_len,
+		      "Expected one complete available net_buf");
+
+	net_pkt_set_overwrite(pkt, false);
+
+	/* now write 3 byte into the pkt */
+	for (int i = 0; i < 3; ++i) {
+		res = net_pkt_write_u8(pkt, 0xAA);
+		zassert_equal(0, res, "Write packet failed");
+	}
+
+	cont_len = net_pkt_get_contiguous_len(pkt);
+	zassert_equal(CONFIG_NET_BUF_DATA_SIZE - 3, cont_len,
+		      "Expected a three byte reduction");
+
+	/* Fill the first fragment up until only 3 bytes are free */
+	for (int i = 0; i < CONFIG_NET_BUF_DATA_SIZE - 6; ++i) {
+		res = net_pkt_write_u8(pkt, 0xAA);
+		zassert_equal(0, res, "Write packet failed");
+	}
+
+	cont_len = net_pkt_get_contiguous_len(pkt);
+	zassert_equal(3, cont_len, "Expected only three bytes are available");
+
+	/* Fill the complete first fragment, so the cursor points to the second
+	 * fragment.
+	 */
+	for (int i = 0; i < 3; ++i) {
+		res = net_pkt_write_u8(pkt, 0xAA);
+		zassert_equal(0, res, "Write packet failed");
+	}
+
+	cont_len = net_pkt_get_contiguous_len(pkt);
+	zassert_equal(CONFIG_NET_BUF_DATA_SIZE, cont_len,
+		      "Expected next full net_buf is available");
+
+	/* Fill the last fragment */
+	for (int i = 0; i < CONFIG_NET_BUF_DATA_SIZE; ++i) {
+		res = net_pkt_write_u8(pkt, 0xAA);
+		zassert_equal(0, res, "Write packet failed");
+	}
+
+	cont_len = net_pkt_get_contiguous_len(pkt);
+	zassert_equal(0, cont_len, "Expected no available space");
+
+	net_pkt_unref(pkt);
+}
+
 void test_main(void)
 {
 	eth_if = net_if_get_default();
@@ -926,7 +988,8 @@ void test_main(void)
 			 ztest_unit_test(test_net_pkt_pull),
 			 ztest_unit_test(test_net_pkt_clone),
 			 ztest_unit_test(test_net_pkt_headroom),
-			 ztest_unit_test(test_net_pkt_headroom_copy)
+			 ztest_unit_test(test_net_pkt_headroom_copy),
+			 ztest_unit_test(test_net_pkt_get_contiguous_len)
 		);
 
 	ztest_run_test_suite(net_pkt_tests);