esp-idf/examples/protocols/http_server/async_handlers/main/main.c

/* Async Request Handlers HTTP Server Example

   This example code is in the Public Domain (or CC0 licensed, at your option.)

   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/
#include "freertos/FreeRTOS.h"
#include "freertos/semphr.h"
#include <esp_wifi.h>
#include <esp_event.h>
#include <esp_log.h>
#include <esp_system.h>
#include <nvs_flash.h>
#include <sys/param.h>
#include "nvs_flash.h"
#include "esp_netif.h"
#include "esp_eth.h"
#include "protocol_examples_common.h"
#include "esp_tls_crypto.h"
#include <esp_http_server.h>

/* An example that demonstrates multiple
   long running http requests running in parallel.

   In this example, multiple long http request can run at
   the same time. (uri: /long)

   While these long requests are running, the server can still
   respond to other incoming synchronous requests. (uri: /quick)
 */

#define ASYNC_WORKER_TASK_PRIORITY      5
#define ASYNC_WORKER_TASK_STACK_SIZE    2048

static const char *TAG = "example";

// Async requests are queued here while they wait to
// be processed by the workers
static QueueHandle_t async_req_queue;

// Track the number of free workers at any given time
static SemaphoreHandle_t worker_ready_count;

// Each worker has its own thread
static TaskHandle_t worker_handles[CONFIG_EXAMPLE_MAX_ASYNC_REQUESTS];

typedef esp_err_t (*httpd_req_handler_t)(httpd_req_t *req);

typedef struct {
    httpd_req_t* req;
    httpd_req_handler_t handler;
} httpd_async_req_t;


static bool is_on_async_worker_thread(void)
{
    // is our handle one of the known async handles?
    TaskHandle_t handle = xTaskGetCurrentTaskHandle();
    for (int i = 0; i < CONFIG_EXAMPLE_MAX_ASYNC_REQUESTS; i++) {
        if (worker_handles[i] == handle) {
            return true;
        }
    }
    return false;
}


// Submit an HTTP req to the async worker queue
static esp_err_t submit_async_req(httpd_req_t *req, httpd_req_handler_t handler)
{
    // must create a copy of the request that we own
    httpd_req_t* copy = NULL;
    esp_err_t err = httpd_req_async_handler_begin(req, &copy);
    if (err != ESP_OK) {
        return err;
    }

    httpd_async_req_t async_req = {
        .req = copy,
        .handler = handler,
    };

    // How should we handle resource exhaustion?
    // In this example, we immediately respond with an
    // http error if no workers are available.
    int ticks = 0;

    // counting semaphore: if success, we know 1 or
    // more asyncReqTaskWorkers are available.
    if (xSemaphoreTake(worker_ready_count, ticks) == false) {
        ESP_LOGE(TAG, "No workers are available");
        httpd_req_async_handler_complete(copy); // cleanup
        return ESP_FAIL;
    }

    // Since worker_ready_count > 0 the queue should already have space.
    // But lets wait up to 100ms just to be safe.
    if (xQueueSend(async_req_queue, &async_req, pdMS_TO_TICKS(100)) == false) {
        ESP_LOGE(TAG, "worker queue is full");
        httpd_req_async_handler_complete(copy); // cleanup
        return ESP_FAIL;
    }

    return ESP_OK;
}


/* A long running HTTP GET handler */
static esp_err_t long_async_handler(httpd_req_t *req)
{
    ESP_LOGI(TAG, "uri: /long");
    // This handler is first invoked on the httpd thread.
    // In order to free the httpd thread to handle other requests,
    // we must resubmit our request to be handled on an async worker thread.
    if (is_on_async_worker_thread() == false) {

        // submit
        if (submit_async_req(req, long_async_handler) == ESP_OK) {
            return ESP_OK;
        } else {
            httpd_resp_set_status(req, "503 Busy");
            httpd_resp_sendstr(req, "<div> no workers available. server busy.</div>");
            return ESP_OK;
        }
    }

    // track the number of long requests
    static uint8_t req_count = 0;
    req_count++;

    // send a request count
    char s[100];
    snprintf(s, sizeof(s), "<div>req: %u</div>\n", req_count);
    httpd_resp_sendstr_chunk(req, s);

    // then every second, send a "tick"
    for (int i = 0; i < 60; i++) {

        // This delay makes this a "long running task".
        // In a real application, this may be a long calculation,
        // or some IO dependent code for instance.
        vTaskDelay(pdMS_TO_TICKS(1000));

        // send a tick
        snprintf(s, sizeof(s), "<div>%u</div>\n", i);
        httpd_resp_sendstr_chunk(req, s);
    }

    // send "complete"
    httpd_resp_sendstr_chunk(req, NULL);

    return ESP_OK;
}

static void async_req_worker_task(void *p)
{
    ESP_LOGI(TAG, "starting async req task worker");

    while (true) {

        // counting semaphore - this signals that a worker
        // is ready to accept work
        xSemaphoreGive(worker_ready_count);

        // wait for a request
        httpd_async_req_t async_req;
        if (xQueueReceive(async_req_queue, &async_req, portMAX_DELAY)) {

            ESP_LOGI(TAG, "invoking %s", async_req.req->uri);

            // call the handler
            async_req.handler(async_req.req);

            // Inform the server that it can purge the socket used for
            // this request, if needed.
            if (httpd_req_async_handler_complete(async_req.req) != ESP_OK) {
                ESP_LOGE(TAG, "failed to complete async req");
            }
        }
    }

    ESP_LOGW(TAG, "worker stopped");
    vTaskDelete(NULL);
}

static void start_async_req_workers(void)
{

    // counting semaphore keeps track of available workers
    worker_ready_count = xSemaphoreCreateCounting(
        CONFIG_EXAMPLE_MAX_ASYNC_REQUESTS,  // Max Count
        0); // Initial Count
    if (worker_ready_count == NULL) {
        ESP_LOGE(TAG, "Failed to create workers counting Semaphore");
        return;
    }

    // create queue
    async_req_queue = xQueueCreate(1, sizeof(httpd_async_req_t));
    if (async_req_queue == NULL){
        ESP_LOGE(TAG, "Failed to create async_req_queue");
        vSemaphoreDelete(worker_ready_count);
        return;
    }

    // start worker tasks
    for (int i = 0; i < CONFIG_EXAMPLE_MAX_ASYNC_REQUESTS; i++) {

        bool success = xTaskCreate(async_req_worker_task, "async_req_worker",
                                    ASYNC_WORKER_TASK_STACK_SIZE, // stack size
                                    (void *)0, // argument
                                    ASYNC_WORKER_TASK_PRIORITY, // priority
                                    &worker_handles[i]);

        if (!success) {
            ESP_LOGE(TAG, "Failed to start asyncReqWorker");
            continue;
        }
    }
}


/* A quick HTTP GET handler, which does not
   use any asynchronous features */
static esp_err_t quick_handler(httpd_req_t *req)
{
    ESP_LOGI(TAG, "uri: /quick");
    char s[100];
    snprintf(s, sizeof(s), "random: %u\n", rand());
    httpd_resp_sendstr(req, s);
    return ESP_OK;
}

static esp_err_t index_handler(httpd_req_t *req)
{
    ESP_LOGI(TAG, "uri: /");
    const char* html = "<div><a href=\"/long\">long</a></div>"
        "<div><a href=\"/quick\">quick</a></div>";
    httpd_resp_sendstr(req, html);
    return ESP_OK;
}

static httpd_handle_t start_webserver(void)
{
    httpd_handle_t server = NULL;
    httpd_config_t config = HTTPD_DEFAULT_CONFIG();
    config.lru_purge_enable = true;

    // It is advisable that httpd_config_t->max_open_sockets > MAX_ASYNC_REQUESTS
    // Why? This leaves at least one socket still available to handle
    // quick synchronous requests. Otherwise, all the sockets will
    // get taken by the long async handlers, and your server will no
    // longer be responsive.
    config.max_open_sockets = CONFIG_EXAMPLE_MAX_ASYNC_REQUESTS + 1;

    // Start the httpd server
    ESP_LOGI(TAG, "Starting server on port: '%d'", config.server_port);
    if (httpd_start(&server, &config) != ESP_OK) {
        ESP_LOGI(TAG, "Error starting server!");
        return NULL;
    }

    const httpd_uri_t index_uri = {
        .uri       = "/",
        .method    = HTTP_GET,
        .handler   = index_handler,
    };

    const httpd_uri_t long_uri = {
        .uri       = "/long",
        .method    = HTTP_GET,
        .handler   = long_async_handler,
    };

    const httpd_uri_t quick_uri = {
        .uri       = "/quick",
        .method    = HTTP_GET,
        .handler   = quick_handler,
    };

    // Set URI handlers
    ESP_LOGI(TAG, "Registering URI handlers");
    httpd_register_uri_handler(server, &index_uri);
    httpd_register_uri_handler(server, &long_uri);
    httpd_register_uri_handler(server, &quick_uri);

    return server;
}

static esp_err_t stop_webserver(httpd_handle_t server)
{
    // Stop the httpd server
    return httpd_stop(server);
}

static void disconnect_handler(void* arg, esp_event_base_t event_base,
                               int32_t event_id, void* event_data)
{
    httpd_handle_t* server = (httpd_handle_t*) arg;
    if (*server) {
        ESP_LOGI(TAG, "Stopping webserver");
        if (stop_webserver(*server) == ESP_OK) {
            *server = NULL;
        } else {
            ESP_LOGE(TAG, "Failed to stop http server");
        }
    }
}

static void connect_handler(void* arg, esp_event_base_t event_base,
                            int32_t event_id, void* event_data)
{
    httpd_handle_t* server = (httpd_handle_t*) arg;
    if (*server == NULL) {
        ESP_LOGI(TAG, "Starting webserver");
        *server = start_webserver();
    }
}

void app_main(void)
{
    static httpd_handle_t server = NULL;

    ESP_ERROR_CHECK(nvs_flash_init());
    ESP_ERROR_CHECK(esp_netif_init());
    ESP_ERROR_CHECK(esp_event_loop_create_default());

    /* This helper function configures Wi-Fi or Ethernet, as selected in menuconfig.
     * Read "Establishing Wi-Fi or Ethernet Connection" section in
     * examples/protocols/README.md for more information about this function.
     */
    ESP_ERROR_CHECK(example_connect());

    /* Register event handlers to stop the server when Wi-Fi or Ethernet is disconnected,
     * and re-start it upon connection.
     */
#ifdef CONFIG_EXAMPLE_CONNECT_WIFI
    ESP_ERROR_CHECK(esp_event_handler_register(IP_EVENT, IP_EVENT_STA_GOT_IP, &connect_handler, &server));
    ESP_ERROR_CHECK(esp_event_handler_register(WIFI_EVENT, WIFI_EVENT_STA_DISCONNECTED, &disconnect_handler, &server));
#endif // CONFIG_EXAMPLE_CONNECT_WIFI
#ifdef CONFIG_EXAMPLE_CONNECT_ETHERNET
    ESP_ERROR_CHECK(esp_event_handler_register(IP_EVENT, IP_EVENT_ETH_GOT_IP, &connect_handler, &server));
    ESP_ERROR_CHECK(esp_event_handler_register(ETH_EVENT, ETHERNET_EVENT_DISCONNECTED, &disconnect_handler, &server));
#endif // CONFIG_EXAMPLE_CONNECT_ETHERNET

    // start workers
    start_async_req_workers();

    /* Start the server for the first time */
    server = start_webserver();
}