ESP32/main/dacp_client.c

/**
 * DACP client — sends control commands to AirPlay source device.
 *
 * Works with both AirPlay 1 and AirPlay 2. The client's DACP service
 * is discovered via mDNS using the DACP-ID from the RTSP handshake.
 * Commands are fire-and-forget HTTP GETs dispatched on a dedicated
 * worker task so callers (button task) never block on network I/O.
 *
 * Thread safety: dacp_set_session/clear may be called from the RTSP
 * server task while dacp_send_* are called from the button task.
 * A mutex protects the session state.
 */

#include "dacp_client.h"

#include "esp_http_client.h"
#include "esp_log.h"
#include "mdns.h"

#include "freertos/FreeRTOS.h"
#include "freertos/queue.h"
#include "freertos/semphr.h"

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

static const char *TAG = "dacp";

#define DACP_ID_MAX         32
#define ACTIVE_REMOTE_MAX   32
#define MDNS_TIMEOUT_MS     1500
#define MDNS_RETRY_COUNT    1
#define MDNS_RETRY_DELAY_MS 500
#define CMD_PATH_MAX        80
#define CMD_QUEUE_LEN       4
#define HTTP_TIMEOUT_MS     800
#define WORKER_STACK        4096

static SemaphoreHandle_t s_mutex;
static bool s_initialized;
static char s_dacp_id[DACP_ID_MAX];
static char s_active_remote[ACTIVE_REMOTE_MAX];
static uint32_t s_client_ip;
static uint16_t s_dacp_port; // Discovered via mDNS
static bool s_session_valid;
static bool
    s_discovery_failed; // True if mDNS discovery failed for this session
static QueueHandle_t s_cmd_queue;
static TaskHandle_t s_worker_handle;

// Special sentinel posted to the command queue to trigger mDNS discovery
// on the worker task (avoids spawning a new task per session).
static const char CMD_DISCOVER[] = "\x01";

// Discover the DACP port via mDNS. Called WITHOUT the mutex held since
// mDNS queries can block for several seconds. Copies the DACP-ID under
// the lock, performs discovery lock-free, then stores the result.
static void discover_dacp_port(void) {
  char dacp_id_local[DACP_ID_MAX];

  xSemaphoreTake(s_mutex, portMAX_DELAY);
  // Skip if port is already known or discovery already failed
  if (s_dacp_port != 0 || s_discovery_failed) {
    xSemaphoreGive(s_mutex);
    return;
  }
  strlcpy(dacp_id_local, s_dacp_id, sizeof(dacp_id_local));
  xSemaphoreGive(s_mutex);

  if (dacp_id_local[0] == '\0') {
    return;
  }

  uint16_t found_port = 0;

  for (int attempt = 0; attempt < MDNS_RETRY_COUNT && found_port == 0;
       attempt++) {
    if (attempt > 0) {
      vTaskDelay(pdMS_TO_TICKS(MDNS_RETRY_DELAY_MS));
      ESP_LOGI(TAG, "DACP mDNS retry %d/%d", attempt + 1, MDNS_RETRY_COUNT);
    }

    // Query mDNS for _dacp._tcp services
    mdns_result_t *results = NULL;
    esp_err_t err =
        mdns_query_ptr("_dacp", "_tcp", MDNS_TIMEOUT_MS, 8, &results);
    if (err != ESP_OK || !results) {
      ESP_LOGW(TAG, "mDNS DACP query failed or no results (err=%s)",
               esp_err_to_name(err));
      continue;
    }

    // Find the result matching our DACP-ID.
    // iOS advertises as "iTunes_Ctrl_<DACPID>" or just "<DACPID>".
    for (mdns_result_t *r = results; r; r = r->next) {
      ESP_LOGI(TAG, "mDNS DACP service: instance='%s' port=%u",
               r->instance_name ? r->instance_name : "(null)", r->port);
      if (!r->instance_name || r->port == 0) {
        continue;
      }
      // Match: exact, or instance contains the DACP-ID as a substring
      if (strcasecmp(r->instance_name, dacp_id_local) == 0 ||
          strcasestr(r->instance_name, dacp_id_local) != NULL) {
        found_port = r->port;
        ESP_LOGI(TAG, "Matched DACP service: '%s' port %u", r->instance_name,
                 found_port);
        break;
      }
    }

    mdns_query_results_free(results);
  }

  // Store discovered port under the lock
  xSemaphoreTake(s_mutex, portMAX_DELAY);
  s_dacp_port = found_port;
  if (found_port == 0) {
    s_discovery_failed = true;
  }
  xSemaphoreGive(s_mutex);

  if (found_port == 0) {
    ESP_LOGW(TAG, "DACP service not found for ID '%s' after %d attempts",
             dacp_id_local, MDNS_RETRY_COUNT);
  }
}

// Execute a DACP HTTP request synchronously. Only called from the worker task.
static void execute_dacp_request(const char *path) {
  if (xSemaphoreTake(s_mutex, pdMS_TO_TICKS(100)) != pdTRUE) {
    ESP_LOGW(TAG, "DACP mutex timeout for '%s'", path);
    return;
  }

  if (!s_session_valid || s_active_remote[0] == '\0') {
    xSemaphoreGive(s_mutex);
    ESP_LOGD(TAG, "DACP: no active session, skipping '%s'", path);
    return;
  }

  // Copy session state under the lock, then release before any I/O
  char active_remote_copy[ACTIVE_REMOTE_MAX];
  uint32_t client_ip_copy = s_client_ip;
  uint16_t port_copy = s_dacp_port;
  strlcpy(active_remote_copy, s_active_remote, sizeof(active_remote_copy));

  xSemaphoreGive(s_mutex);

  // If port not yet discovered, skip — the eager discovery task will
  // populate it. Never block the worker on mDNS.
  if (port_copy == 0) {
    ESP_LOGD(TAG, "DACP: port not ready, skipping '%s'", path);
    return;
  }

  // Build URL: http://<ip>:<port>/ctrl-int/1/<path>
  char url[128];
  uint8_t *ip = (uint8_t *)&client_ip_copy;
  snprintf(url, sizeof(url), "http://%u.%u.%u.%u:%u/ctrl-int/1/%s", ip[0],
           ip[1], ip[2], ip[3], port_copy, path);

  // Fire-and-forget HTTP GET
  esp_http_client_config_t config = {
      .url = url,
      .timeout_ms = HTTP_TIMEOUT_MS,
      .disable_auto_redirect = true,
  };

  esp_http_client_handle_t client = esp_http_client_init(&config);
  if (!client) {
    ESP_LOGW(TAG, "Failed to init HTTP client");
    return;
  }

  esp_http_client_set_header(client, "Active-Remote", active_remote_copy);
  esp_http_client_set_method(client, HTTP_METHOD_GET);

  esp_err_t err = esp_http_client_perform(client);
  if (err != ESP_OK) {
    ESP_LOGW(TAG, "DACP request failed: %s (%s)", path, esp_err_to_name(err));
    // Connection failed — invalidate port so next command re-discovers
    xSemaphoreTake(s_mutex, portMAX_DELAY);
    s_dacp_port = 0;
    xSemaphoreGive(s_mutex);
  } else {
    int status = esp_http_client_get_status_code(client);
    ESP_LOGI(TAG, "DACP: %s -> %d", path, status);
    if (status == 403 || status == 401) {
      ESP_LOGW(TAG, "DACP auth rejected — Active-Remote may be wrong");
    }
  }

  esp_http_client_cleanup(client);
}

// Worker task: drains the command queue and executes HTTP requests.
// A sentinel command (CMD_DISCOVER) triggers mDNS discovery inline,
// serialising discovery with HTTP commands and avoiding extra tasks.
static void dacp_worker_task(void *pvParameters) {
  (void)pvParameters;
  char path[CMD_PATH_MAX];
  while (1) {
    if (xQueueReceive(s_cmd_queue, path, portMAX_DELAY) == pdTRUE) {
      if (path[0] == CMD_DISCOVER[0]) {
        discover_dacp_port();
      } else {
        execute_dacp_request(path);
      }
    }
  }
}

// Enqueue a command for the worker task. Returns immediately (non-blocking).
static void send_dacp_request(const char *path) {
  if (!s_cmd_queue) {
    return;
  }
  char buf[CMD_PATH_MAX];
  strlcpy(buf, path, sizeof(buf));
  // Non-blocking: drop if queue is full (better than blocking caller)
  if (xQueueSend(s_cmd_queue, buf, 0) != pdTRUE) {
    ESP_LOGD(TAG, "DACP queue full, dropping '%s'", path);
  }
}

// ============================================================================
// Public API
// ============================================================================

void dacp_init(void) {
  if (s_initialized) {
    return;
  }
  s_mutex = xSemaphoreCreateMutex();
  s_cmd_queue = xQueueCreate(CMD_QUEUE_LEN, CMD_PATH_MAX);
  xTaskCreate(dacp_worker_task, "dacp_wk", WORKER_STACK, NULL, 4,
              &s_worker_handle);
  s_initialized = true;
  ESP_LOGI(TAG, "DACP client initialized");
}

void dacp_set_session(const char *dacp_id, const char *active_remote,
                      uint32_t client_ip) {
  xSemaphoreTake(s_mutex, portMAX_DELAY);

  const char *id = dacp_id ? dacp_id : "";
  const char *remote = active_remote ? active_remote : "";

  // If same DACP-ID, just update the active-remote token and IP in place.
  // No need to re-discover — the port doesn't change within a session.
  bool same_session = (strcmp(s_dacp_id, id) == 0 && s_session_valid);
  if (same_session) {
    strlcpy(s_active_remote, remote, sizeof(s_active_remote));
    s_client_ip = client_ip;
    xSemaphoreGive(s_mutex);
    return;
  }

  // New session — reset everything
  strlcpy(s_dacp_id, id, sizeof(s_dacp_id));
  strlcpy(s_active_remote, remote, sizeof(s_active_remote));
  s_client_ip = client_ip;
  s_dacp_port = 0;
  s_discovery_failed = false;
  s_session_valid = (s_dacp_id[0] != '\0' && s_active_remote[0] != '\0');
  bool valid = s_session_valid;

  xSemaphoreGive(s_mutex);

  if (valid) {
    ESP_LOGI(TAG, "DACP session: id=%s", id);
    // Kick off discovery on the worker task so the port is ready before
    // the user presses a button.  Posting to front so it runs before any
    // queued commands; non-blocking drop is fine if queue is full.
    char sentinel[CMD_PATH_MAX] = {CMD_DISCOVER[0]};
    xQueueSendToFront(s_cmd_queue, sentinel, 0);
  }
}

void dacp_clear_session(void) {
  if (!s_initialized) {
    return;
  }

  xSemaphoreTake(s_mutex, portMAX_DELAY);
  s_dacp_id[0] = '\0';
  s_active_remote[0] = '\0';
  s_dacp_port = 0;
  s_session_valid = false;
  s_discovery_failed = false;
  xSemaphoreGive(s_mutex);

  ESP_LOGD(TAG, "DACP session cleared");
}

void dacp_send_playpause(void) {
  send_dacp_request("playpause");
}

void dacp_send_next(void) {
  send_dacp_request("nextitem");
}

void dacp_send_prev(void) {
  send_dacp_request("previtem");
}

void dacp_send_volume_up(void) {
  send_dacp_request("volumeup");
}

void dacp_send_volume_down(void) {
  send_dacp_request("volumedown");
}

void dacp_send_volume(float volume_percent) {
  if (volume_percent < 0.0f) {
    volume_percent = 0.0f;
  }
  if (volume_percent > 100.0f) {
    volume_percent = 100.0f;
  }

  char path[64];
  snprintf(path, sizeof(path), "setproperty?dmcp.volume=%.0f", volume_percent);
  send_dacp_request(path);
}

bool dacp_is_active(void) {
  if (!s_initialized) {
    return false;
  }
  bool active = false;
  if (xSemaphoreTake(s_mutex, pdMS_TO_TICKS(50)) == pdTRUE) {
    active = s_session_valid;
    xSemaphoreGive(s_mutex);
  }
  return active;
}

bool dacp_probe_service(void) {
  if (!s_initialized) {
    return false;
  }

  char dacp_id_copy[DACP_ID_MAX];
  if (xSemaphoreTake(s_mutex, pdMS_TO_TICKS(100)) != pdTRUE) {
    return false;
  }
  if (s_dacp_id[0] == '\0') {
    xSemaphoreGive(s_mutex);
    return false;
  }
  strlcpy(dacp_id_copy, s_dacp_id, sizeof(dacp_id_copy));
  xSemaphoreGive(s_mutex);

  mdns_result_t *results = NULL;
  esp_err_t err = mdns_query_ptr("_dacp", "_tcp", 2000, 8, &results);
  if (err != ESP_OK || !results) {
    return false;
  }

  bool found = false;
  for (mdns_result_t *r = results; r; r = r->next) {
    if (r->instance_name &&
        (strcasecmp(r->instance_name, dacp_id_copy) == 0 ||
         strcasestr(r->instance_name, dacp_id_copy) != NULL)) {
      found = true;
      break;
    }
  }

  mdns_query_results_free(results);
  return found;
}