HTTP

[中文]

Does ESP8266 support HTTP hosting?

Yes, it does. ESP8266 can run as a server in both SoftAP and Station modes.

  • When running as a server in SoftAP mode, clients can directly access the ESP8266 host or server at 192.168.4.1 (default) IP address.

  • When the server is accessed via a router, the IP address should be the one allocated to the ESP8266 by the router.

  • When using SDK to write native code, please refer to relevant examples.

  • When using AT commands, start a server using AT+CIPSERVER command.

How to use esp_http_client to send chunked data?

  • Please use HTTP Stream by setting the write_len parameter of esp_http_client_open() to -1. Then the “Transfer-Encoding” will be set to “chunked” automatically，please see http_client_prepare_first_line() in　esp_http_client.c.

  • The code snippet is listed below for your reference：

    static void http_post_chunked_data()
{
    esp_http_client_config_t config = {
    .url = "http://httpbin.org/post",
    .method = HTTP_METHOD_POST, // This is NOT required. write_len < 0 will force POST anyway
  };
  char buffer[MAX_HTTP_OUTPUT_BUFFER] = {0};
  esp_http_client_handle_t client = esp_http_client_init(&config);

  esp_err_t err = esp_http_client_open(client, -1); // write_len=-1 sets header "Transfer-Encoding: chunked" and method to POST
  if (err != ESP_OK) {
    ESP_LOGE(TAG, "Failed to open HTTP connection: %s", esp_err_to_name(err));
    return;
  }

  // Post some data
  esp_http_client_write(client, "5", 1); // length
  esp_http_client_write(client, "\r\n", 2);
  esp_http_client_write(client, "Hello", 5); // data
  esp_http_client_write(client, "\r\n", 2);
  esp_http_client_write(client, "7", 1); // length
  esp_http_client_write(client, "\r\n", 2);
  esp_http_client_write(client, " World!", 7);  // data
  esp_http_client_write(client, "\r\n", 2);
  esp_http_client_write(client, "0", 1);  // end
  esp_http_client_write(client, "\r\n", 2);
  esp_http_client_write(client, "\r\n", 2);


  // After the POST is complete, you can examine the response as required using:
  int content_length = esp_http_client_fetch_headers(client);
  ESP_LOGI(TAG, "content_length: %d, status_code: %d", content_length, esp_http_client_get_status_code(client));

  int read_len = esp_http_client_read(client, buffer, 1024);
  ESP_LOGI(TAG, "receive %d data from server: %s", read_len, buffer);
  esp_http_client_close(client);
  esp_http_client_cleanup(client);
}

Is there a way to set cookies when ESP32 operates as an HTTP client?

ESP32 itself does not have an API for setting cookies directly, but you can use esp_http_client_set_header to add cookies to the HTTP header.

How do I set the maximum number of clients that are allowed for connection when ESP32 serves as an HTTP server? What will happen if the number exceeds the limit?

  • The maximum number of client connections can be set by configuring max_open_sockets in the httpd_config_t structure.

  • If the number of clients exceeds the limit, you can set the lru_purge_enable parameter in the httpd_config_t structure to true. In doing so, if there is no socket available (which is determined by max_open_sockets), the least used socket will be cleared to accept the coming one.

Does ESP32 have an example of implementing a gRPC client over HTTP/2 and above versions?

Not yet.

How to download a specific segment of a file over HTTP in ESP-IDF (i.e., add Range:bytes information to the header)?

Please refer to the http_partial_download function in the esp http client example.

When the ESP module acts as a local HTTP/HTTPS Server, it returns the Header fields are too long for server to interpret error if it is accessed by the browser. Why?

  • The reason for this problem is that the URL is too long for the browser, and the underlying buffer is not big enough. You can increase the HTTP header length by modifying the menuconfig configuration. You can change the default value, which is 512 bytes, to a larger size, for example, 1024 bytes. The specific steps are as follows:

    • idf.py menuconfig > Component config > HTTP Server > (1024)Max HTTP Request Header Length

    • idf.py menuconfig > Component config > HTTP Server > (1024)Max HTTP URI Length

How can I resolve the error of HTTP_HEADER: Buffer length is small to fit all the headers returned by HTTP request?

  • Please change the member buffer_size_tx of the structure esp_http_client_config_t in the file esp-idf/components/esp_http_client/include/esp_http_client.h to 1024 bytes or larger.

Why is the data length always 0 when calling esp_http_client_read_response after executing the esp_http_client_perform function?

The esp_http_client_perform function already handles data reading internally, so calling esp_http_client_read_response afterward is not necessary and will not yield the expected data length. To obtain the data, please handle the HTTP_EVENT_ON_DATA event in the event handler.


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