lgtv_audio_cap/native/src/sinks/sink_http.c

// HTTP audio stream served by the TV.
//
// The friendliest sink to test with, because everything already speaks HTTP:
//
//   vlc http://<tv-ip>:4012/audio.wav
//   ffplay http://<tv-ip>:4012/audio.wav
//   mpv    http://<tv-ip>:4012/audio.wav
//
// The WAV header declares an unknown length (0xFFFFFFFF sizes), which is the
// usual convention for endless streams and what every player above expects.
// Request /audio.raw instead to get headerless S16LE, for the odd consumer
// that would rather be told the format out of band.

#include "sink.h"
#include "../common/log.h"
#include "../net/streamserv.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define WAV_HEADER_BYTES 44
#define WAV_UNKNOWN_SIZE 0xFFFFFFFFu

typedef struct {
    streamserv_t* server;
    int port;
    audio_format_t fmt;
} http_priv_t;

static void put_u32le(uint8_t* p, uint32_t v)
{
    p[0] = (uint8_t)(v & 0xFF);
    p[1] = (uint8_t)((v >> 8) & 0xFF);
    p[2] = (uint8_t)((v >> 16) & 0xFF);
    p[3] = (uint8_t)((v >> 24) & 0xFF);
}

static void put_u16le(uint8_t* p, uint16_t v)
{
    p[0] = (uint8_t)(v & 0xFF);
    p[1] = (uint8_t)((v >> 8) & 0xFF);
}

static void write_wav_header(uint8_t* h, const audio_format_t* fmt)
{
    const uint16_t bits = 16;
    const uint16_t channels = (uint16_t)fmt->channels;
    const uint32_t rate = (uint32_t)fmt->rate;
    const uint16_t block_align = (uint16_t)(channels * (bits / 8));

    memcpy(h + 0, "RIFF", 4);
    put_u32le(h + 4, WAV_UNKNOWN_SIZE);
    memcpy(h + 8, "WAVE", 4);

    memcpy(h + 12, "fmt ", 4);
    put_u32le(h + 16, 16); // PCM fmt chunk length
    put_u16le(h + 20, 1); // WAVE_FORMAT_PCM
    put_u16le(h + 22, channels);
    put_u32le(h + 24, rate);
    put_u32le(h + 28, rate * block_align); // byte rate
    put_u16le(h + 32, block_align);
    put_u16le(h + 34, bits);

    memcpy(h + 36, "data", 4);
    put_u32le(h + 40, WAV_UNKNOWN_SIZE);
}

// Extracts the path from "GET /audio.wav HTTP/1.1". Returns false for anything
// that is not a GET, so the server drops the connection.
static bool parse_request(const char* request, char* path, size_t pathlen)
{
    if (!request)
        return false;
    if (strncmp(request, "GET ", 4) != 0)
        return false;

    const char* p = request + 4;
    while (*p == ' ')
        p++;

    size_t n = 0;
    while (p[n] && p[n] != ' ' && p[n] != '\r' && p[n] != '\n' && n < pathlen - 1)
        n++;
    memcpy(path, p, n);
    path[n] = '\0';
    return n > 0;
}

static bool http_hello(void* user, const char* request, char** out, size_t* out_len)
{
    http_priv_t* p = user;

    char path[256];
    if (!parse_request(request, path, sizeof(path))) {
        DBG("HTTP sink: rejecting non-GET request");
        return false;
    }

    // Browsers probe for these; answering them with an audio stream is worse
    // than refusing outright.
    if (strcmp(path, "/favicon.ico") == 0 || strcmp(path, "/robots.txt") == 0)
        return false;

    bool raw = strstr(path, ".raw") != NULL || strstr(path, ".pcm") != NULL;

    char headers[512];
    int hlen = snprintf(headers, sizeof(headers),
        "HTTP/1.0 200 OK\r\n"
        "Content-Type: %s\r\n"
        "Cache-Control: no-cache, no-store\r\n"
        "Pragma: no-cache\r\n"
        "Access-Control-Allow-Origin: *\r\n"
        "Connection: close\r\n"
        "\r\n",
        raw ? "application/octet-stream" : "audio/wav");
    if (hlen < 0 || hlen >= (int)sizeof(headers))
        return false;

    size_t total = (size_t)hlen + (raw ? 0 : WAV_HEADER_BYTES);
    uint8_t* buf = malloc(total);
    if (!buf)
        return false;

    memcpy(buf, headers, (size_t)hlen);
    if (!raw)
        write_wav_header(buf + hlen, &p->fmt);

    INFO("HTTP sink: client requested %s (%s)", path, raw ? "raw S16LE" : "WAV");
    *out = (char*)buf;
    *out_len = total;
    return true;
}

static void http_write(sink_t* s, const int16_t* pcm, int frames, const dsp_levels_t* levels)
{
    (void)levels;
    http_priv_t* p = s->priv;
    streamserv_broadcast(p->server, pcm, (size_t)frames * (size_t)audio_frame_bytes(&s->fmt));
}

static void http_status(sink_t* s, json_writer_t* w)
{
    http_priv_t* p = s->priv;
    jw_int(w, "port", p->port);
    jw_int(w, "clients", streamserv_client_count(p->server));
    jw_int(w, "droppedBytes", (long long)streamserv_dropped_bytes(p->server));
    jw_str(w, "wavPath", "/audio.wav");
    jw_str(w, "rawPath", "/audio.raw");
}

static void http_close(sink_t* s)
{
    http_priv_t* p = s->priv;
    if (p) {
        streamserv_stop(p->server);
        free(p);
    }
    free(s);
}

static sink_t* http_open(const json_value_t* cfg, const audio_format_t* fmt, char* err, size_t errlen)
{
    const json_value_t* sc = json_get(cfg, "http");
    int port = json_int(sc, "port", 4012);
    if (port <= 0 || port > 65535) {
        snprintf(err, errlen, "invalid HTTP port %d", port);
        return NULL;
    }

    http_priv_t* p = calloc(1, sizeof(*p));
    sink_t* s = calloc(1, sizeof(*s));
    if (!p || !s) {
        free(p);
        free(s);
        snprintf(err, errlen, "out of memory");
        return NULL;
    }

    p->port = port;
    p->fmt = *fmt;

    // Players buffer ahead; give them a couple of seconds of slack before we
    // start dropping.
    size_t buffer = (size_t)fmt->rate * (size_t)audio_frame_bytes(fmt) * 2;

    streamserv_config_t scfg = {
        .port = port,
        .client_buffer = buffer,
        .max_clients = json_int(sc, "maxClients", 4),
        .http_mode = true,
        .user = p,
        .hello = http_hello,
    };

    p->server = streamserv_start(&scfg, err, errlen);
    if (!p->server) {
        free(p);
        free(s);
        return NULL;
    }

    s->driver = &sink_driver_http;
    s->priv = p;
    s->fmt = *fmt;
    s->write = http_write;
    s->status = http_status;
    s->close = http_close;

    INFO("HTTP sink: http://<tv-ip>:%d/audio.wav (%d Hz, %d ch)", port, fmt->rate, fmt->channels);
    return s;
}

const sink_driver_t sink_driver_http = {
    .id = "http",
    .name = "HTTP WAV stream",
    .description = "Open http://<tv-ip>:4012/audio.wav in VLC, ffplay or mpv. Easiest way to confirm capture works.",
    .open = http_open,
};