client: Exponential backoff resend intervals

[tattlekey] / client / tattlekey.c

#include "pico/cyw43_arch.h"
#include "pico/stdlib.h"
#include "pico/util/pheap.h"
#include "pico/util/queue.h"

#include "blink.h"
#include "button.h"
#include "config.h"
#include "net.h"

typedef struct {
  uint32_t timestamp;
  u16_t seq;
  u8_t send_count;
} send_t;

uint32_t next_send(send_t *s) {
  return s->timestamp + (1 << s->send_count) - 1;
}

bool next_send_less_than(void *user_data, pheap_node_id_t a,
                         pheap_node_id_t b) {
  send_t *sends = (send_t *)user_data;
  return next_send(&sends[a]) < next_send(&sends[b]);
}

enum event_type { BUTTONPRESS, SEND };
typedef struct {
  enum event_type type;
  union {
    struct {
      uint32_t timestamp;
    } buttonpress;
  };
} event_t;

queue_t queue;

uint32_t time_s() { return time_us_64() / 1000000ul; }

/* Often we don't bother checking for failure (full queue) because
 *   1. The best thing to do in this unfortunate situation is to blithely
 *      continue, dropping some events; continuing is better than stopping.
 *   2. Neither interrupt context nor queue-processing context can block
 *      until space is available, or even sit around & blink the LED to
 *      signal a problem.
 * (We also get a bit of type safety by taking event_t* rather than void*.) */
static void queue_try_add_ignoring_errors(queue_t *q, event_t *e) {
  queue_try_add(q, e);
}

static void button_pressed() {
  /* This runs in interrupt context; don't linger.  */
  static uint64_t last_button_press_time = 0;
  uint32_t now = time_s();
  uint32_t time_since_last_press = now - last_button_press_time;
  if (time_since_last_press >= config_minimum_seconds_between_button_presses) {
    last_button_press_time = now;
    event_t e;
    e.type = BUTTONPRESS;
    e.buttonpress.timestamp = now;
    queue_try_add_ignoring_errors(&queue, &e);
  }
}

static void time_to_send(uint _) {
  /* This runs in interrupt context; don't linger.  */
  event_t e;
  e.type = SEND;
  queue_try_add_ignoring_errors(&queue, &e);
}

void service_sleeps(int alarm, send_t *sleeping_sends, pheap_t *sleeps_heap) {
  hardware_alarm_cancel(alarm);

  while (1) {
    uint32_t now = time_s();
    pheap_node_id_t i = ph_peek_head(sleeps_heap);
    if (i == 0)
      return;
    send_t *send = &sleeping_sends[i];
    if (next_send(send) > now) {
      uint32_t sleep_duration = next_send(send) - now;
      if (hardware_alarm_set_target(
              alarm, make_timeout_time_ms(sleep_duration * 1000)))
        signal_error_by_blinking();
      return;
    }
    if (ph_remove_head(sleeps_heap, false) != i)
      signal_error_by_blinking();
    uint32_t ago = now - send->timestamp;
    send_report(send->seq, ago);
    send->send_count++;
    if (send->send_count < config_resend_count)
      ph_insert_node(sleeps_heap, i);
    else
      ph_free_node(sleeps_heap, i);
  }
}

void service_queue() {
  int alarm = hardware_alarm_claim_unused(true);
  if (alarm == -1)
    signal_error_by_blinking();
  hardware_alarm_set_callback(alarm, time_to_send);

  send_t sleeping_sends[PICO_PHEAP_MAX_ENTRIES];
  pheap_t *sleeps_heap =
      ph_create(PICO_PHEAP_MAX_ENTRIES, next_send_less_than, sleeping_sends);
  u16_t seq = 0;
  while (1) {
    service_sleeps(alarm, sleeping_sends, sleeps_heap);

    event_t e;
    queue_remove_blocking(&queue, &e);
    switch (e.type) {
    case BUTTONPRESS: {
      pheap_node_id_t i = ph_new_node(sleeps_heap);
      if (i == 0) {
        /* TODO: Don't drop new presses just because sleeps_heap is full of old
         * presses. */
        break;
      }
      sleeping_sends[i].timestamp = e.buttonpress.timestamp;
      sleeping_sends[i].seq = seq++;
      sleeping_sends[i].send_count = 0;
      ph_insert_node(sleeps_heap, i);
    } break;
    case SEND: {
      /* OK, we're awake. Cool. Thanks! (We actually do the sends in the
       * service_sleeps() call at the top of the loop.)  */
    } break;
    default:
      signal_error_by_blinking();
    }
  }
}

int main() {
  stdio_init_all();
  if (cyw43_arch_init_with_country(CYW43_COUNTRY_USA))
    signal_error_by_blinking();
  cyw43_arch_enable_sta_mode();
  signal(3, 100);
  if (cyw43_arch_wifi_connect_timeout_ms(config_wifi_ssid, config_wifi_pass,
                                         CYW43_AUTH_WPA2_AES_PSK, 90000))
    signal_error_by_blinking();
  signal(2, 300);

  queue_init(&queue, sizeof(event_t), 99);

  begin_listening_for_button_press(button_pressed);

  service_queue();
}