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:

esp_http_client_init(): To use the HTTP client, the first thing we must do is create an esp_http_client by pass into this function with the esp_http_client_config_t configurations. Which configuration values we do not define, the library will use default.

esp_http_client_perform(): The esp_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 esp_http_client_config_t). This function performs its job and blocks the current task until it’s done

esp_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¶

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¶

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 :ref:CONFIG_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¶

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 esp_http_client_perform() function with that handle, and esp_http_client_init() alway to called first to get the handle. Perform that functions in the order below:

esp_http_client_init(): to create and handle

esp_http_client_set_* or esp_http_client_delete_*: to modify the http connection information (optional)

esp_http_client_open(): Open the http connection with write_len parameter, write_len=0 if we only need read

esp_http_client_write(): Upload data, max length equal to write_len of esp_http_client_open() function. We may not need to call it if write_len=0

esp_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 esp_http_client_get_status_code() for the HTTP status of the connection.

esp_http_client_read(): Now, we can read the HTTP stream by this function.

esp_http_client_close(): We should the connection after finish

esp_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¶

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¶

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¶

Header File¶

esp_http_client/include/esp_http_client.h

Functions¶

esp_http_client_handle_t esp_http_client_init(const esp_http_client_config_t *config)¶

Start a HTTP session This function must be the first function to call, and it returns a esp_http_client_handle_t that you must use as input to other functions in the interface. This call MUST have a corresponding call to esp_http_client_cleanup when the operation is complete.

Return

esp_http_client_handle_t
NULL if any errors

Parameters

[in] config: The configurations, see http_client_config_t

esp_err_t esp_http_client_perform(esp_http_client_handle_t client)¶

Invoke this function after esp_http_client_init and all the options calls are made, and will perform the transfer as described in the options. It must be called with the same esp_http_client_handle_t as input as the esp_http_client_init call returned. esp_http_client_perform performs the entire request in either blocking or non-blocking manner. By default, the API performs request in a blocking manner and returns when done, or if it failed, and in non-blocking manner, it returns if EAGAIN/EWOULDBLOCK or EINPROGRESS is encountered, or if it failed. And in case of non-blocking request, the user may call this API multiple times unless request & response is complete or there is a failure. To enable non-blocking esp_http_client_perform(), is_async member of esp_http_client_config_t must be set while making a call to esp_http_client_init() API. You can do any amount of calls to esp_http_client_perform while using the same esp_http_client_handle_t. The underlying connection may be kept open if the server allows it. If you intend to transfer more than one file, you are even encouraged to do so. esp_http_client will then attempt to re-use the same connection for the following transfers, thus making the operations faster, less CPU intense and using less network resources. Just note that you will have to use esp_http_client_set_** between the invokes to set options for the following esp_http_client_perform.

Note

You must never call this function simultaneously from two places using the same client handle. Let the function return first before invoking it another time. If you want parallel transfers, you must use several esp_http_client_handle_t. This function include esp_http_client_open -> esp_http_client_write -> esp_http_client_fetch_headers -> esp_http_client_read (and option) esp_http_client_close.

Return

ESP_OK on successful
ESP_FAIL on error

Parameters

client: The esp_http_client handle

esp_err_t esp_http_client_set_url(esp_http_client_handle_t client, const char *url)¶

Set URL for client, when performing this behavior, the options in the URL will replace the old ones.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle
[in] url: The url

esp_err_t esp_http_client_set_post_field(esp_http_client_handle_t client, const char *data, int len)¶

Set post data, this function must be called before esp_http_client_perform. Note: The data parameter passed to this function is a pointer and this function will not copy the data.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle
[in] data: post data pointer
[in] len: post length

int esp_http_client_get_post_field(esp_http_client_handle_t client, char **data)¶

Get current post field information.

Return

Size of post data

Parameters

[in] client: The client
[out] data: Point to post data pointer

esp_err_t esp_http_client_set_header(esp_http_client_handle_t client, const char *key, const char *value)¶

Set http request header, this function must be called after esp_http_client_init and before any perform function.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle
[in] key: The header key
[in] value: The header value

esp_err_t esp_http_client_get_header(esp_http_client_handle_t client, const char *key, char **value)¶

Get http request header. The value parameter will be set to NULL if there is no header which is same as the key specified, otherwise the address of header value will be assigned to value parameter. This function must be called after esp_http_client_init.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle
[in] key: The header key
[out] value: The header value

esp_err_t esp_http_client_get_username(esp_http_client_handle_t client, char **value)¶

Get http request username. The address of username buffer will be assigned to value parameter. This function must be called after esp_http_client_init.

Return

ESP_OK
ESP_ERR_INVALID_ARG

Parameters

[in] client: The esp_http_client handle
[out] value: The username value

esp_err_t esp_http_client_set_username(esp_http_client_handle_t client, const char *username)¶

Set http request username. The value of username parameter will be assigned to username buffer. If the username parameter is NULL then username buffer will be freed.

Return

ESP_OK
ESP_ERR_INVALID_ARG

Parameters

[in] client: The esp_http_client handle
[in] username: The username value

esp_err_t esp_http_client_get_password(esp_http_client_handle_t client, char **value)¶

Get http request password. The address of password buffer will be assigned to value parameter. This function must be called after esp_http_client_init.

Return

ESP_OK
ESP_ERR_INVALID_ARG

Parameters

[in] client: The esp_http_client handle
[out] value: The password value

esp_err_t esp_http_client_set_password(esp_http_client_handle_t client, char *password)¶

Set http request password. The value of password parameter will be assigned to password buffer. If the password parameter is NULL then password buffer will be freed.

Return

ESP_OK
ESP_ERR_INVALID_ARG

Parameters

[in] client: The esp_http_client handle
[in] password: The password value

esp_err_t esp_http_client_set_method(esp_http_client_handle_t client, esp_http_client_method_t method)¶

Set http request method.

Return

ESP_OK
ESP_ERR_INVALID_ARG

Parameters

[in] client: The esp_http_client handle
[in] method: The method

esp_err_t esp_http_client_delete_header(esp_http_client_handle_t client, const char *key)¶

Delete http request header.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle
[in] key: The key

esp_err_t esp_http_client_open(esp_http_client_handle_t client, int write_len)¶

This function will be open the connection, write all header strings and return.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle
[in] write_len: HTTP Content length need to write to the server

int esp_http_client_write(esp_http_client_handle_t client, const char *buffer, int len)¶

This function will write data to the HTTP connection previously opened by esp_http_client_open()

Return

(-1) if any errors
Length of data written

Parameters

[in] client: The esp_http_client handle
buffer: The buffer
[in] len: This value must not be larger than the write_len parameter provided to esp_http_client_open()

int esp_http_client_fetch_headers(esp_http_client_handle_t client)¶

This function need to call after esp_http_client_open, it will read from http stream, process all receive headers.

Return

(0) if stream doesn’t contain content-length header, or chunked encoding (checked by esp_http_client_is_chunked response)
(-1: ESP_FAIL) if any errors
Download data length defined by content-length header

Parameters

[in] client: The esp_http_client handle

bool esp_http_client_is_chunked_response(esp_http_client_handle_t client)¶

Check response data is chunked.

Return

true or false

Parameters

[in] client: The esp_http_client handle

int esp_http_client_read(esp_http_client_handle_t client, char *buffer, int len)¶

Read data from http stream.

Return

(-1) if any errors
Length of data was read

Parameters

[in] client: The esp_http_client handle
buffer: The buffer
[in] len: The length

int esp_http_client_get_status_code(esp_http_client_handle_t client)¶

Get http response status code, the valid value if this function invoke after esp_http_client_perform

Return

Status code

Parameters

[in] client: The esp_http_client handle

int esp_http_client_get_content_length(esp_http_client_handle_t client)¶

Get http response content length (from header Content-Length) the valid value if this function invoke after esp_http_client_perform

Return

(-1) Chunked transfer
Content-Length value as bytes

Parameters

[in] client: The esp_http_client handle

esp_err_t esp_http_client_close(esp_http_client_handle_t client)¶

Close http connection, still kept all http request resources.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle

esp_err_t esp_http_client_cleanup(esp_http_client_handle_t client)¶

This function must be the last function to call for an session. It is the opposite of the esp_http_client_init function and must be called with the same handle as input that a esp_http_client_init call returned. This might close all connections this handle has used and possibly has kept open until now. Don’t call this function if you intend to transfer more files, re-using handles is a key to good performance with esp_http_client.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle

esp_http_client_transport_t esp_http_client_get_transport_type(esp_http_client_handle_t client)¶

Get transport type.

Return

HTTP_TRANSPORT_UNKNOWN
HTTP_TRANSPORT_OVER_TCP
HTTP_TRANSPORT_OVER_SSL

Parameters

[in] client: The esp_http_client handle

esp_err_t esp_http_client_set_redirection(esp_http_client_handle_t client)¶

Set redirection URL. When received the 30x code from the server, the client stores the redirect URL provided by the server. This function will set the current URL to redirect to enable client to execute the redirection request.

Return

ESP_OK
ESP_FAIL

Parameters

[in] client: The esp_http_client handle

void esp_http_client_add_auth(esp_http_client_handle_t client)¶

On receiving HTTP Status code 401, this API can be invoked to add authorization information.

Note

There is a possibility of receiving body message with redirection status codes, thus make sure to flush off body data after calling this API.

Parameters

[in] client: The esp_http_client handle

bool esp_http_client_is_complete_data_received(esp_http_client_handle_t client)¶

Checks if entire data in the response has been read without any error.

Return

true
false

Parameters

[in] client: The esp_http_client handle

Structures¶

struct esp_http_client_event¶

HTTP Client events data.

Public Members

esp_http_client_event_id_t event_id¶: event_id, to know the cause of the event

esp_http_client_handle_t client¶: esp_http_client_handle_t context

void *data¶: data of the event

int data_len¶: data length of data

void *user_data¶: user_data context, from esp_http_client_config_t user_data

char *header_key¶: For HTTP_EVENT_ON_HEADER event_id, it’s store current http header key

char *header_value¶: For HTTP_EVENT_ON_HEADER event_id, it’s store current http header value

struct esp_http_client_config_t¶

HTTP configuration.

Public Members

const char *url¶: HTTP URL, the information on the URL is most important, it overrides the other fields below, if any

const char *host¶: Domain or IP as string

int port¶: Port to connect, default depend on esp_http_client_transport_t (80 or 443)

const char *username¶: Using for Http authentication

const char *password¶: Using for Http authentication

esp_http_client_auth_type_t auth_type¶: Http authentication type, see esp_http_client_auth_type_t

const char *path¶: HTTP Path, if not set, default is /

const char *query¶: HTTP query

const char *cert_pem¶: SSL server certification, PEM format as string, if the client requires to verify server

const char *client_cert_pem¶: SSL client certification, PEM format as string, if the server requires to verify client

const char *client_key_pem¶: SSL client key, PEM format as string, if the server requires to verify client

const char *user_agent¶: The User Agent string to send with HTTP requests

esp_http_client_method_t method¶: HTTP Method

int timeout_ms¶: Network timeout in milliseconds

bool disable_auto_redirect¶: Disable HTTP automatic redirects

int max_redirection_count¶: Max redirection number, using default value if zero

http_event_handle_cb event_handler¶: HTTP Event Handle

esp_http_client_transport_t transport_type¶: HTTP transport type, see esp_http_client_transport_t

int buffer_size¶: HTTP receive buffer size

int buffer_size_tx¶: HTTP transmit buffer size

void *user_data¶: HTTP user_data context

bool is_async¶: Set asynchronous mode, only supported with HTTPS for now

bool use_global_ca_store¶: Use a global ca_store for all the connections in which this bool is set.

bool skip_cert_common_name_check¶: Skip any validation of server certificate CN field

bool keep_alive_enable¶: Enable keep-alive timeout

int keep_alive_idle¶: Keep-alive idle time. Default is 5 (second)

int keep_alive_interval¶: Keep-alive interval time. Default is 5 (second)

int keep_alive_count¶: Keep-alive packet retry send count. Default is 3 counts

Macros¶

DEFAULT_HTTP_BUF_SIZE¶

ESP_ERR_HTTP_BASE¶: Starting number of HTTP error codes

ESP_ERR_HTTP_MAX_REDIRECT¶: The error exceeds the number of HTTP redirects

ESP_ERR_HTTP_CONNECT¶: Error open the HTTP connection

ESP_ERR_HTTP_WRITE_DATA¶: Error write HTTP data

ESP_ERR_HTTP_FETCH_HEADER¶: Error read HTTP header from server

ESP_ERR_HTTP_INVALID_TRANSPORT¶: There are no transport support for the input scheme

ESP_ERR_HTTP_CONNECTING¶: HTTP connection hasn’t been established yet

ESP_ERR_HTTP_EAGAIN¶: Mapping of errno EAGAIN to esp_err_t

Type Definitions¶

typedef struct esp_http_client *esp_http_client_handle_t¶

typedef struct esp_http_client_event *esp_http_client_event_handle_t¶

typedef struct esp_http_client_event esp_http_client_event_t¶: HTTP Client events data.

typedef esp_err_t (*http_event_handle_cb)(esp_http_client_event_t *evt)¶

Enumerations¶

enum esp_http_client_event_id_t¶

HTTP Client events id.

Values:

HTTP_EVENT_ERROR = 0¶: This event occurs when there are any errors during execution

HTTP_EVENT_ON_CONNECTED¶: Once the HTTP has been connected to the server, no data exchange has been performed

HTTP_EVENT_HEADERS_SENT¶: After sending all the headers to the server

HTTP_EVENT_HEADER_SENT = HTTP_EVENT_HEADERS_SENT ¶: This header has been kept for backward compatability and will be deprecated in future versions esp-idf

HTTP_EVENT_ON_HEADER¶: Occurs when receiving each header sent from the server

HTTP_EVENT_ON_DATA¶: Occurs when receiving data from the server, possibly multiple portions of the packet

HTTP_EVENT_ON_FINISH¶: Occurs when finish a HTTP session

HTTP_EVENT_DISCONNECTED¶: The connection has been disconnected

enum esp_http_client_transport_t¶

HTTP Client transport.

Values:

HTTP_TRANSPORT_UNKNOWN = 0x0¶: Unknown

HTTP_TRANSPORT_OVER_TCP¶: Transport over tcp

HTTP_TRANSPORT_OVER_SSL¶: Transport over ssl

enum esp_http_client_method_t¶

HTTP method.

Values:

HTTP_METHOD_GET = 0¶: HTTP GET Method

HTTP_METHOD_POST¶: HTTP POST Method

HTTP_METHOD_PUT¶: HTTP PUT Method

HTTP_METHOD_PATCH¶: HTTP PATCH Method

HTTP_METHOD_DELETE¶: HTTP DELETE Method

HTTP_METHOD_HEAD¶: HTTP HEAD Method

HTTP_METHOD_NOTIFY¶: HTTP NOTIFY Method

HTTP_METHOD_SUBSCRIBE¶: HTTP SUBSCRIBE Method

HTTP_METHOD_UNSUBSCRIBE¶: HTTP UNSUBSCRIBE Method

HTTP_METHOD_OPTIONS¶: HTTP OPTIONS Method

HTTP_METHOD_MAX¶

enum esp_http_client_auth_type_t¶

HTTP Authentication type.

Values:

HTTP_AUTH_TYPE_NONE = 0¶: No authention

HTTP_AUTH_TYPE_BASIC¶: HTTP Basic authentication

HTTP_AUTH_TYPE_DIGEST¶: HTTP Disgest authentication

enum HttpStatus_Code¶

Enum for the HTTP status codes.

Values:

HttpStatus_Ok = 200¶

HttpStatus_MultipleChoices = 300¶

HttpStatus_MovedPermanently = 301¶

HttpStatus_Found = 302¶

HttpStatus_Unauthorized = 401¶

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