gsm0808: allow decoding of zero length speech codec lists.

3GPP_TS_48.008, 3.2.2.103 Speech Codec List states the following:

"The length indicator (octet 2) is a binary number indicating the
absolute length of the contents after the length indicator.
The length depends on the number and type of Speech Codec Elements
to be included. The minimum length of one Speech Codec Element is 1
octet and the maximum length is 3 octets. The maximum number of
Speech Codec Elements within the Speech Codec List is not defined."

This clearly refers only to the length of a single speech codec
element but not on the overall list. So speech codec lists with
length 0 are indeed permitted by the spec.

- Remove the assertion that checks on zero length speech codec
  lists.

Change-Id: I1eb1f4466b98bdd26d765b0e4cc690b5e89e9dd6
Related: OS#3657

2 files changed, 23 insertions, 10 deletions

diff --git a/src/gsm/gsm0808_utils.c b/src/gsm/gsm0808_utils.c
index 886f546a..2348105d 100644
--- a/src/gsm/gsm0808_utils.c
+++ b/src/gsm/gsm0808_utils.c
@@ -349,9 +349,6 @@ uint8_t gsm0808_enc_speech_codec_list(struct msgb *msg,
 	OSMO_ASSERT(msg);
 	OSMO_ASSERT(scl);
 
-	/* Empty list */
-	OSMO_ASSERT(scl->len >= 1);
-
 	msgb_put_u8(msg, GSM0808_IE_SPEECH_CODEC_LIST);
 	tlv_len = msgb_put(msg, 1);
 	old_tail = msg->tail;
@@ -384,8 +381,6 @@ int gsm0808_dec_speech_codec_list(struct gsm0808_speech_codec_list *scl,
 	OSMO_ASSERT(scl);
 	if (!elem)
 		return -EINVAL;
-	if (len == 0)
-		return -EINVAL;
 
 	memset(scl, 0, sizeof(*scl));
 
@@ -404,11 +399,6 @@ int gsm0808_dec_speech_codec_list(struct gsm0808_speech_codec_list *scl,
 
 	scl->len = decoded;
 
-	/* Empty list */
-	if (decoded < 1) {
-		return -EINVAL;
-	}
-
 	return (int)(elem - old_elem);
 }
 
diff --git a/tests/gsm0808/gsm0808_test.c b/tests/gsm0808/gsm0808_test.c
index 8cf1cf4c..0b2794f1 100644
--- a/tests/gsm0808/gsm0808_test.c
+++ b/tests/gsm0808/gsm0808_test.c
@@ -695,6 +695,28 @@ static void test_gsm0808_enc_dec_speech_codec_list()
 	msgb_free(msg);
 }
 
+static void test_gsm0808_enc_dec_empty_speech_codec_list()
+{
+	struct gsm0808_speech_codec_list enc_scl = {
+		.len = 0,
+	};
+	struct gsm0808_speech_codec_list dec_scl = {};
+	struct msgb *msg;
+	uint8_t rc_enc;
+	int rc_dec;
+
+	msg = msgb_alloc(1024, "output buffer");
+	rc_enc = gsm0808_enc_speech_codec_list(msg, &enc_scl);
+	OSMO_ASSERT(rc_enc == 2);
+
+	rc_dec = gsm0808_dec_speech_codec_list(&dec_scl, msg->data + 2, msg->len - 2);
+	OSMO_ASSERT(rc_dec == 0);
+
+	OSMO_ASSERT(memcmp(&enc_scl, &dec_scl, sizeof(enc_scl)) == 0);
+
+	msgb_free(msg);
+}
+
 static void test_gsm0808_enc_dec_channel_type()
 {
 	struct gsm0808_channel_type enc_ct = {
@@ -1725,6 +1747,7 @@ int main(int argc, char **argv)
 	test_gsm0808_enc_dec_speech_codec_ext_with_cfg();
 	test_gsm0808_enc_dec_speech_codec_with_cfg();
 	test_gsm0808_enc_dec_speech_codec_list();
+	test_gsm0808_enc_dec_empty_speech_codec_list();
 	test_gsm0808_enc_dec_channel_type();
 	test_gsm0808_enc_dec_encrypt_info();