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WHIP: Support ICE handshake by binding.
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1. Create UDP URLContext for ICE, DTLS and RTP.
2. Connect to ice-lite server as UDP client.
3. Create, build and send ICE binding request.
4. Read and verify ICE binding response.
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@winlinvip
winlinvip committed May 1, 2023
1 parent 58821db commit 7be0de7
Showing 1 changed file with 132 additions and 12 deletions.
144 changes: 132 additions & 12 deletions libavformat/rtcenc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -32,8 +32,12 @@
#include "libavutil/avstring.h"
#include "url.h"
#include "libavutil/random_seed.h"
#include "avio_internal.h"
#include "libavutil/hmac.h"
#include "libavutil/crc.h"

#define MAX_SDP_SIZE 8192
#define MAX_UDP_SIZE 1500

typedef struct RTCContext {
AVClass *av_class;
Expand Down Expand Up @@ -70,6 +74,9 @@ typedef struct RTCContext {
int ice_port;
/* The SDP answer received from the WebRTC server. */
char *sdp_answer;

/* The UDP transport is used for delivering ICE, DTLS and SRTP packets. */
URLContext *udp_uc;
} RTCContext;

/**
Expand Down Expand Up @@ -97,12 +104,12 @@ static int check_codec(AVFormatContext *s)
if (par->codec_id != AV_CODEC_ID_H264) {
av_log(s, AV_LOG_ERROR, "Unsupported video codec %s by RTC, choose h264\n",
desc ? desc->name : "unknown");
return AVERROR(EINVAL);
return AVERROR_PATCHWELCOME;
}
if ((par->profile & ~FF_PROFILE_H264_CONSTRAINED) != FF_PROFILE_H264_BASELINE) {
av_log(s, AV_LOG_ERROR, "Profile %d of stream %d is not baseline, currently unsupported by RTC\n",
par->profile, i);
return AVERROR(EINVAL);
return AVERROR_PATCHWELCOME;
}
break;
case AVMEDIA_TYPE_AUDIO:
Expand All @@ -115,24 +122,24 @@ static int check_codec(AVFormatContext *s)
if (par->codec_id != AV_CODEC_ID_OPUS) {
av_log(s, AV_LOG_ERROR, "Unsupported audio codec %s by RTC, choose opus\n",
desc ? desc->name : "unknown");
return AVERROR(EINVAL);
return AVERROR_PATCHWELCOME;
}

if (par->ch_layout.nb_channels != 2) {
av_log(s, AV_LOG_ERROR, "Unsupported audio channels %d by RTC, choose stereo\n",
par->ch_layout.nb_channels);
return AVERROR(EINVAL);
return AVERROR_PATCHWELCOME;
}

if (par->sample_rate != 48000) {
av_log(s, AV_LOG_ERROR, "Unsupported audio sample rate %d by RTC, choose 48000\n", par->sample_rate);
return AVERROR(EINVAL);
return AVERROR_PATCHWELCOME;
}
break;
default:
av_log(s, AV_LOG_ERROR, "Codec type '%s' for stream %d is not supported by RTC\n",
av_get_media_type_string(par->codec_type), i);
return AVERROR(EINVAL);
return AVERROR_PATCHWELCOME;
}
}

Expand Down Expand Up @@ -194,7 +201,7 @@ static int generate_sdp_offer(AVFormatContext *s)
char *tmp = av_mallocz(MAX_SDP_SIZE);
if (!tmp) {
av_log(s, AV_LOG_ERROR, "Failed to alloc answer: %s", s->url);
return AVERROR(EINVAL);
return AVERROR(ENOMEM);
}

if (rtc->sdp_offer) {
Expand Down Expand Up @@ -274,7 +281,7 @@ static int generate_sdp_offer(AVFormatContext *s)
rtc->video_ssrc);
if (ret >= MAX_SDP_SIZE) {
av_log(s, AV_LOG_ERROR, "Offer %d exceed max %d, %s", ret, MAX_SDP_SIZE, tmp);
ret = AVERROR(EINVAL);
ret = AVERROR(EIO);
goto end;
}

Expand Down Expand Up @@ -338,7 +345,7 @@ static int exchange_sdp(AVFormatContext *s)
char *tmp = av_mallocz(MAX_SDP_SIZE);
if (!tmp) {
av_log(s, AV_LOG_ERROR, "Failed to alloc answer: %s", s->url);
return AVERROR(EINVAL);
return AVERROR(ENOMEM);
}

ret = ffurl_alloc(&whip_uc, s->url, AVIO_FLAG_READ_WRITE, &s->interrupt_callback);
Expand Down Expand Up @@ -376,7 +383,7 @@ static int exchange_sdp(AVFormatContext *s)
ret = av_strlcatf(tmp, MAX_SDP_SIZE, "%.*s", ret, buf);
if (ret >= MAX_SDP_SIZE) {
av_log(s, AV_LOG_ERROR, "Answer %d exceed max size %d, %s", ret, MAX_SDP_SIZE, tmp);
ret = AVERROR(EINVAL);
ret = AVERROR(EIO);
goto end;
}
}
Expand Down Expand Up @@ -426,14 +433,14 @@ static int parse_answer(AVFormatContext *s)
if (ret != 4) {
av_log(s, AV_LOG_ERROR, "Failed %d to parse line %d %s from %s",
ret, i, line, rtc->sdp_answer);
ret = AVERROR(EINVAL);
ret = AVERROR(EIO);
goto end;
}

if (av_strcasecmp(protocol, "udp")) {
av_log(s, AV_LOG_ERROR, "Protocol %s is not supported by RTC, choose udp, line %d %s of %s",
protocol, i, line, rtc->sdp_answer);
ret = AVERROR(EINVAL);
ret = AVERROR(EIO);
goto end;
}

Expand All @@ -453,6 +460,115 @@ static int parse_answer(AVFormatContext *s)
return ret;
}

/**
* Open the UDP transport and complete the ICE handshake.
*
* @return 0 if OK, AVERROR_xxx on error
*/
static int ice_handshake(AVFormatContext *s)
{
int ret, len, crc32;
char url[256], buf[MAX_UDP_SIZE];
AVIOContext *pb = NULL;
AVHMAC *hmac = NULL;
RTCContext *rtc = s->priv_data;

pb = avio_alloc_context(buf, sizeof(buf), AVIO_FLAG_WRITE, NULL, NULL, NULL, NULL);
if (!pb) {
av_log(s, AV_LOG_ERROR, "Failed to alloc AVIOContext for ICE");
ret = AVERROR(ENOMEM);
goto end;
}

hmac = av_hmac_alloc(AV_HMAC_SHA1);
if (!hmac) {
av_log(s, AV_LOG_ERROR, "Failed to alloc AVHMAC for ICE");
ret = AVERROR(ENOMEM);
goto end;
}

/* Build UDP URL and create the UDP context as transport. */
ff_url_join(url, sizeof(url), "udp", NULL, rtc->ice_host, rtc->ice_port, NULL);
ret = ffurl_alloc(&rtc->udp_uc, url, AVIO_FLAG_WRITE | AVIO_FLAG_NONBLOCK, &s->interrupt_callback);
if (ret < 0) {
av_log(s, AV_LOG_ERROR, "Failed to open udp://%s:%d", rtc->ice_host, rtc->ice_port);
goto end;
}

av_opt_set(rtc->udp_uc->priv_data, "connect", "1", 0);
av_opt_set(rtc->udp_uc->priv_data, "fifo_size", "0", 0);

ret = ffurl_connect(rtc->udp_uc, NULL);
if (ret < 0) {
av_log(s, AV_LOG_ERROR, "Failed to connect udp://%s:%d", rtc->ice_host, rtc->ice_port);
goto end;
}

/* Set the transport as READ and WRITE after connected. */
rtc->udp_uc->flags |= AVIO_FLAG_READ;

/* Build and send the STUN binding request. */
/* Write 20 bytes header */
avio_wb16(pb, 0x0001); /* STUN binding request */
avio_wb16(pb, 0); /* length */
avio_wb32(pb, 0x2112A442); /* magic cookie */
avio_wb32(pb, av_get_random_seed()); /* transaction ID */
avio_wb32(pb, av_get_random_seed()); /* transaction ID */
avio_wb32(pb, av_get_random_seed()); /* transaction ID */
/* Write the username attribute */
ret = snprintf(url, sizeof(url), "%s:%s", rtc->ice_ufrag_remote, rtc->ice_ufrag_local);
avio_wb16(pb, 0x0006); /* attribute type username */
avio_wb16(pb, ret); /* size of username */
avio_write(pb, url, ret); /* bytes of username */
ffio_fill(pb, 0, (4 - (ret % 4)) % 4); /* padding */
/* Build and update message integrity */
avio_wb16(pb, 0x0008); /* attribute type message integrity */
avio_wb16(pb, 20); /* size of message integrity */
ffio_fill(pb, 0, 20); /* fill with zero to directly write and skip it */
len = avio_tell(pb);
buf[2] = (len - 20) >> 8;
buf[3] = (len - 20) & 0xFF;
av_hmac_init(hmac, rtc->ice_pwd_local, strlen(rtc->ice_pwd_local));
av_hmac_update(hmac, buf, len - 24);
av_hmac_final(hmac, buf + len - 20, 20);
/* Write the fingerprint attribute */
avio_wb16(pb, 0x8028); /* attribute type fingerprint */
avio_wb16(pb, 4); /* size of fingerprint */
ffio_fill(pb, 0, 4); /* fill with zero to directly write and skip it */
len = avio_tell(pb);
buf[2] = (len - 20) >> 8;
buf[3] = (len - 20) & 0xFF;
crc32 = av_crc(av_crc_get_table(AV_CRC_32_IEEE_LE), 0xFFFFFFFF, buf, len - 8) ^ 0xFFFFFFFF;
avio_skip(pb, -4);
avio_wb32(pb, crc32 ^ 0x5354554E); /* hash message by CRC32 */

ret = ffurl_write(rtc->udp_uc, buf, len);
if (ret < 0) {
av_log(s, AV_LOG_ERROR, "Failed to send STUN binding request, size=%d", len);
goto end;
}

/* Read the STUN binding response. */
ret = ffurl_read(rtc->udp_uc, buf, sizeof(buf));
if (ret < 0) {
av_log(s, AV_LOG_ERROR, "Failed to read STUN binding response");
goto end;
}

if (ret < 2 || buf[0] != 0x01 || buf[1] != 0x01) {
av_log(s, AV_LOG_ERROR, "Invalid STUN binding response, size=%d, type=%02X%02X", ret, buf[0], buf[1]);
ret = AVERROR(EIO);
goto end;
}
av_log(s, AV_LOG_VERBOSE, "ICE STUN ok, url=udp://%s:%d, username=%s:%s, request=%dB, response=%dB\n",
rtc->ice_host, rtc->ice_port, rtc->ice_ufrag_remote, rtc->ice_ufrag_local, len, ret);

end:
avio_context_free(&pb);
av_hmac_free(hmac);
return ret;
}

static av_cold int rtc_init(AVFormatContext *s)
{
int ret;
Expand All @@ -469,6 +585,9 @@ static av_cold int rtc_init(AVFormatContext *s)
if ((ret = parse_answer(s)) < 0)
return ret;

if ((ret = ice_handshake(s)) < 0)
return ret;

return 0;
}

Expand Down Expand Up @@ -496,6 +615,7 @@ static av_cold void rtc_deinit(AVFormatContext *s)
av_freep(&rtc->ice_pwd_remote);
av_freep(&rtc->ice_protocol);
av_freep(&rtc->ice_host);
ffurl_closep(&rtc->udp_uc);
}

static const AVOption options[] = {
Expand Down

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