esp_http_client.rst

ESP HTTP Client

Overview

esp_http_client provides an API for making HTTP/S requests from ESP-IDF programs. The steps to use this API for an HTTP request are:

• :cppesp_http_client_init: To use the HTTP client, the first thing we must do is create an :cppesp_http_client by pass into this function with the :cppesp_http_client_config_t configurations. Which configuration values we do not define, the library will use default.
• :cppesp_http_client_perform: The :cppesp_http_client argument created from the init function is needed. This function performs all operations of the esp_http_client, from opening the connection, sending data, downloading data and closing the connection if necessary. All related events will be invoked in the event_handle (defined by :cppesp_http_client_config_t). This function performs its job and blocks the current task until it's done
• :cppesp_http_client_cleanup: After completing our esp_http_client's task, this is the last function to be called. It will close the connection (if any) and free up all the memory allocated to the HTTP client

Application Example

c

esp_err_t _http_event_handle(esp_http_client_event_t *evt)
{
    switch(evt->event_id) {
        case HTTP_EVENT_ERROR:
            ESP_LOGI(TAG, "HTTP_EVENT_ERROR");
            break;
        case HTTP_EVENT_ON_CONNECTED:
            ESP_LOGI(TAG, "HTTP_EVENT_ON_CONNECTED");
            break;
        case HTTP_EVENT_HEADER_SENT:
            ESP_LOGI(TAG, "HTTP_EVENT_HEADER_SENT");
            break;
        case HTTP_EVENT_ON_HEADER:
            ESP_LOGI(TAG, "HTTP_EVENT_ON_HEADER");
            printf("%.*s", evt->data_len, (char*)evt->data);
            break;
        case HTTP_EVENT_ON_DATA:
            ESP_LOGI(TAG, "HTTP_EVENT_ON_DATA, len=%d", evt->data_len);
            if (!esp_http_client_is_chunked_response(evt->client)) {
                printf("%.*s", evt->data_len, (char*)evt->data);
            }

            break;
        case HTTP_EVENT_ON_FINISH:
            ESP_LOGI(TAG, "HTTP_EVENT_ON_FINISH");
            break;
        case HTTP_EVENT_DISCONNECTED:
            ESP_LOGI(TAG, "HTTP_EVENT_DISCONNECTED");
            break;
    }
    return ESP_OK;
}

esp_http_client_config_t config = {
   .url = "http://httpbin.org/redirect/2",
   .event_handler = _http_event_handle,
};
esp_http_client_handle_t client = esp_http_client_init(&config);
esp_err_t err = esp_http_client_perform(client);

if (err == ESP_OK) {
   ESP_LOGI(TAG, "Status = %d, content_length = %d",
           esp_http_client_get_status_code(client),
           esp_http_client_get_content_length(client));
}
esp_http_client_cleanup(client);

Persistent Connections

Persistent connections means that the HTTP client can re-use the same connection for several transfers. If the server does not request to close the connection with the Connection: close header, the new transfer with sample ip address, port, and protocol.

To allow the HTTP client to take full advantage of persistent connections, you should do as many of your file transfers as possible using the same handle.

Persistent Connections example

c

esp_err_t err;
esp_http_client_config_t config = {
    .url = "http://httpbin.org/get",
};
esp_http_client_handle_t client = esp_http_client_init(&config);
// first request
err = esp_http_client_perform(client);

// second request
esp_http_client_set_url(client, "http://httpbin.org/anything")
esp_http_client_set_method(client, HTTP_METHOD_DELETE);
esp_http_client_set_header(client, "HeaderKey", "HeaderValue");
err = esp_http_client_perform(client);

esp_http_client_cleanup(client);

HTTPS

The HTTP client supports SSL connections using mbedtls, with the url configuration starting with https scheme (or transport_type = HTTP_TRANSPORT_OVER_SSL). HTTPS support can be configured via CONFIG_ESP_HTTP_CLIENT_ENABLE_HTTPS (enabled by default).

Note

By providing information using HTTPS, the library will use the SSL transport type to connect to the server. If you want to verify server, then need to provide additional certificate in PEM format, and provide to cert_pem in esp_http_client_config_t

HTTPS example

c

static void https()
{
    esp_http_client_config_t config = {
        .url = "https://www.howsmyssl.com",
        .cert_pem = howsmyssl_com_root_cert_pem_start,
    };
    esp_http_client_handle_t client = esp_http_client_init(&config);
    esp_err_t err = esp_http_client_perform(client);

    if (err == ESP_OK) {
        ESP_LOGI(TAG, "Status = %d, content_length = %d",
                esp_http_client_get_status_code(client),
                esp_http_client_get_content_length(client));
    }
    esp_http_client_cleanup(client);
}

HTTP Stream

Some applications need to open the connection and control the reading of the data in an active manner. the HTTP client supports some functions to make this easier, of course, once you use these functions you should not use the :cppesp_http_client_perform function with that handle, and :cppesp_http_client_init alway to called first to get the handle. Perform that functions in the order below:

• :cppesp_http_client_init: to create and handle
• esp_http_client_set_* or esp_http_client_delete_*: to modify the http connection information (optional)
• :cppesp_http_client_open: Open the http connection with write_len parameter, write_len=0 if we only need read
• :cppesp_http_client_write: Upload data, max length equal to write_len of :cppesp_http_client_open function. We may not need to call it if write_len=0
• :cppesp_http_client_fetch_headers: After sending the headers and write data (if any) to the server, this function will read the HTTP Server response headers. Calling this function will return the content-length from the Server, and we can call :cppesp_http_client_get_status_code for the HTTP status of the connection.
• :cppesp_http_client_read: Now, we can read the HTTP stream by this function.
• :cppesp_http_client_close: We should the connection after finish
• :cppesp_http_client_cleanup: And release the resources

Perform HTTP request as Stream reader

Check the example function http_perform_as_stream_reader at protocols/esp_http_client.

HTTP Authentication

The HTTP client supports both Basic and Digest Authentication. By providing usernames and passwords in url or in the username, password of config entry. And with auth_type = HTTP_AUTH_TYPE_BASIC, the HTTP client takes only 1 perform to pass the authentication process. If auth_type = HTTP_AUTH_TYPE_NONE, but there are username and password in the configuration, the HTTP client takes 2 performs. The first time it connects to the server and receives the UNAUTHORIZED header. Based on this information, it will know which authentication method to choose, and perform it on the second.

Config authentication example with URI

c

esp_http_client_config_t config = {
    .url = "http://user:passwd@httpbin.org/basic-auth/user/passwd",
    .auth_type = HTTP_AUTH_TYPE_BASIC,
};

Config authentication example with username, password entry

c

esp_http_client_config_t config = {
    .url = "http://httpbin.org/basic-auth/user/passwd",
    .username = "user",
    .password = "passwd",
    .auth_type = HTTP_AUTH_TYPE_BASIC,
};

HTTP Client example: protocols/esp_http_client.

API Reference

inc/esp_http_client.inc