ESP HTTP Client

Overview

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

esp_http_client_init(): Creates an esp_http_client_config_t instance i.e. a HTTP client handle based on the given esp_http_client_config_t configuration. This function must be the first to be called; default values will be assumed for the configuration values that are not explicitly defined by the user.

esp_http_client_perform(): Performs all operations of the esp_http_client - opening the connection, exchanging data and closing the connection (as required), while blocking the current task until its completion. All related events will be invoked through the event handler (as specified in esp_http_client_config_t).

esp_http_client_cleanup(): Closes the connection (if any) and frees up all the memory allocated to the HTTP client instance. This must be the last function to be called after the completion of operations.

Application Example

Simple example that uses ESP HTTP Client to make HTTP/S requests at protocols/esp_http_client.

Basic HTTP request

Check out the example functions http_rest_with_url and http_rest_with_hostname_path in the application example for implementation details.

Persistent Connections

Persistent connection means that the HTTP client can re-use the same connection for several exchanges. If the server does not request to close the connection with the Connection: close header, the connection is not dropped but is instead kept open and used for further requests.

To allow ESP HTTP client to take full advantage of persistent connections, one should make as many requests as possible using the same handle instance.

Check out the example functions http_rest_with_url and http_rest_with_hostname_path in the application example. Here, once the connection is created, multiple requests (GET, POST, PUT, etc.) are made before the connection is closed.

HTTPS Request

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

Note

While making HTTPS requests, if server verification is needed, additional root certificate (in PEM format) needs to be provided to the cert_pem member in esp_http_client_config_t configuration. Users can also use the ESP x509 Certificate Bundle for server verification using the crt_bundle_attach member of the esp_http_client_config_t configuration.

Check out the example functions https_with_url and https_with_hostname_path in the application example. (Implementation details of the above note are found here)

HTTP Stream

Some applications need to open the connection and control the exchange of data actively (data streaming). In such cases, the application flow is different from regular requests. Example flow is given below:

esp_http_client_init(): Create a HTTP client handle

esp_http_client_set_* or esp_http_client_delete_*: Modify the HTTP connection parameters (optional)

esp_http_client_open(): Open the HTTP connection with write_len parameter (content length that needs to be written to server), set write_len=0 for read-only connection

esp_http_client_write(): Write data to server with a maximum length equal to write_len of esp_http_client_open() function; no need to call this function for write_len=0

esp_http_client_fetch_headers(): Read the HTTP Server response headers, after sending the request headers and server data (if any). Returns the content-length from the server and can be succeeded by esp_http_client_get_status_code() for getting the HTTP status of the connection.

esp_http_client_read(): Read the HTTP stream

esp_http_client_close(): Close the connection

esp_http_client_cleanup(): Release allocated resources

Check out the example function http_perform_as_stream_reader in the application example for implementation details.

HTTP Authentication

ESP HTTP client supports both Basic and Digest Authentication.

Users can provide the username and password in the url or the username and password members of the esp_http_client_config_t configuration. For auth_type = HTTP_AUTH_TYPE_BASIC, the HTTP client takes only 1 perform operation to pass the authentication process.
If auth_type = HTTP_AUTH_TYPE_NONE, but the username and password fields are present in the configuration, the HTTP client takes 2 perform operations. The client will receive the 401 Unauthorized header in its first attempt to connect to the server. Based on this information, it decides which authentication method to choose and performs it in the second operation.
Check out the example functions http_auth_basic, http_auth_basic_redirect (for Basic authentication) and http_auth_digest (for Digest authentication) in the application example for implementation details.

Examples of Authentication Configuration

Authentication with URI

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

Authentication with username and 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,
};

API Reference

Header File

components/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.

Parameters

config – [in] The configurations, see http_client_config_t

Returns

esp_http_client_handle_t
NULL if any errors

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.

Parameters

client – The esp_http_client handle

Returns

ESP_OK on successful
ESP_FAIL on error

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.

Parameters

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

Returns

ESP_OK
ESP_FAIL

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.

Parameters

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

Returns

ESP_OK
ESP_FAIL

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

Get current post field information.

Parameters

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

Returns

Size of post data

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.

Parameters

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

Returns

ESP_OK
ESP_FAIL

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.

Parameters

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

Returns

ESP_OK
ESP_FAIL

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.

Parameters

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

Returns

ESP_OK
ESP_ERR_INVALID_ARG

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.

Parameters

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

Returns

ESP_OK
ESP_ERR_INVALID_ARG

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.

Parameters

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

Returns

ESP_OK
ESP_ERR_INVALID_ARG

esp_err_t esp_http_client_set_password(esp_http_client_handle_t client, const 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.

Parameters

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

Returns

ESP_OK
ESP_ERR_INVALID_ARG

esp_err_t esp_http_client_set_authtype(esp_http_client_handle_t client, esp_http_client_auth_type_t auth_type)

Set http request auth_type.

Parameters

client – [in] The esp_http_client handle
auth_type – [in] The esp_http_client auth type

Returns

ESP_OK
ESP_ERR_INVALID_ARG

int esp_http_client_get_errno(esp_http_client_handle_t client)

Get HTTP client session errno.

Parameters

client – [in] The esp_http_client handle

Returns

(-1) if invalid argument
errno

esp_err_t esp_http_client_set_method(esp_http_client_handle_t client, esp_http_client_method_t method)

Set http request method.

Parameters

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

Returns

ESP_OK
ESP_ERR_INVALID_ARG

esp_err_t esp_http_client_set_timeout_ms(esp_http_client_handle_t client, int timeout_ms)

Set http request timeout.

Parameters

client – [in] The esp_http_client handle
timeout_ms – [in] The timeout value

Returns

ESP_OK
ESP_ERR_INVALID_ARG

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

Delete http request header.

Parameters

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

Returns

ESP_OK
ESP_FAIL

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.

Parameters

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

Returns

ESP_OK
ESP_FAIL

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()

Parameters

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

Returns

(-1) if any errors
Length of data written

int64_t 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.

Parameters

client – [in] The esp_http_client handle

Returns

(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
(-ESP_ERR_HTTP_EAGAIN = -0x7007) if call is timed-out before any data was ready
Download data length defined by content-length header

bool esp_http_client_is_chunked_response(esp_http_client_handle_t client)

Check response data is chunked.

Parameters: client – [in] The esp_http_client handle
Returns: true or false

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

Read data from http stream.

Note

(-ESP_ERR_HTTP_EAGAIN = -0x7007) is returned when call is timed-out before any data was ready

Parameters

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

Returns

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

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

Parameters: client – [in] The esp_http_client handle
Returns: Status code

int64_t 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

Parameters

client – [in] The esp_http_client handle

Returns

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

esp_err_t esp_http_client_close(esp_http_client_handle_t client)

Close http connection, still kept all http request resources.

Parameters

client – [in] The esp_http_client handle

Returns

ESP_OK
ESP_FAIL

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.

Parameters

client – [in] The esp_http_client handle

Returns

ESP_OK
ESP_FAIL

esp_http_client_transport_t esp_http_client_get_transport_type(esp_http_client_handle_t client)

Get transport type.

Parameters

client – [in] The esp_http_client handle

Returns

HTTP_TRANSPORT_UNKNOWN
HTTP_TRANSPORT_OVER_TCP
HTTP_TRANSPORT_OVER_SSL

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. When disable_auto_redirect is set, the client will not call this function but the event HTTP_EVENT_REDIRECT will be dispatched giving the user contol over the redirection event.

Parameters

client – [in] The esp_http_client handle

Returns

ESP_OK
ESP_FAIL

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: client – [in] 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.

Parameters

client – [in] The esp_http_client handle

Returns

true
false

int esp_http_client_read_response(esp_http_client_handle_t client, char *buffer, int len)

Helper API to read larger data chunks This is a helper API which internally calls esp_http_client_read multiple times till the end of data is reached or till the buffer gets full.

Parameters

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

Returns

Length of data was read

esp_err_t esp_http_client_flush_response(esp_http_client_handle_t client, int *len)

Process all remaining response data This uses an internal buffer to repeatedly receive, parse, and discard response data until complete data is processed. As no additional user-supplied buffer is required, this may be preferrable to esp_http_client_read_response in situations where the content of the response may be ignored.

Parameters

client – [in] The esp_http_client handle
len – Length of data discarded

Returns

ESP_OK If successful, len will have discarded length
ESP_FAIL If failed to read response
ESP_ERR_INVALID_ARG If the client is NULL

esp_err_t esp_http_client_get_url(esp_http_client_handle_t client, char *url, const int len)

Get URL from client.

Parameters

client – [in] The esp_http_client handle
url – [inout] The buffer to store URL
len – [in] The buffer length

Returns

ESP_OK
ESP_FAIL

esp_err_t esp_http_client_get_chunk_length(esp_http_client_handle_t client, int *len)

Get Chunk-Length from client.

Parameters

client – [in] The esp_http_client handle
len – [out] Variable to store length

Returns

ESP_OK If successful, len will have length of current chunk
ESP_FAIL If the server is not a chunked server
ESP_ERR_INVALID_ARG If the client or len are NULL

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

size_t cert_len: Length of the buffer pointed to by cert_pem. May be 0 for null-terminated pem

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

size_t client_cert_len: Length of the buffer pointed to by client_cert_pem. May be 0 for null-terminated pem

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

size_t client_key_len: Length of the buffer pointed to by client_key_pem. May be 0 for null-terminated pem

const char *client_key_password: Client key decryption password string

size_t client_key_password_len: String length of the password pointed to by client_key_password

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 number of redirections on receiving HTTP redirect status code, using default value if zero

int max_authorization_retries: Max connection retries on receiving HTTP unauthorized status code, using default value if zero. Disables authorization retry if -1

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

esp_err_t (*crt_bundle_attach)(void *conf): Function pointer to esp_crt_bundle_attach. Enables the use of certification bundle for server verification, must be enabled in menuconfig

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

struct ifreq *if_name: The name of interface for data to go through. Use the default interface without setting

void *ds_data: Pointer for digital signature peripheral context, see ESP-TLS Documentation for more details

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

ESP_ERR_HTTP_CONNECTION_CLOSED: Read FIN from peer and the connection closed

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:

enumerator HTTP_EVENT_ERROR: This event occurs when there are any errors during execution

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

enumerator HTTP_EVENT_HEADERS_SENT: After sending all the headers to the server

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

enumerator HTTP_EVENT_ON_HEADER: Occurs when receiving each header sent from the server

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

enumerator HTTP_EVENT_ON_FINISH: Occurs when finish a HTTP session

enumerator HTTP_EVENT_DISCONNECTED: The connection has been disconnected

enumerator HTTP_EVENT_REDIRECT: Intercepting HTTP redirects to handle them manually

enum esp_http_client_transport_t

HTTP Client transport.

Values:

enumerator HTTP_TRANSPORT_UNKNOWN: Unknown

enumerator HTTP_TRANSPORT_OVER_TCP: Transport over tcp

enumerator HTTP_TRANSPORT_OVER_SSL: Transport over ssl

enum esp_http_client_method_t

HTTP method.

Values:

enumerator HTTP_METHOD_GET: HTTP GET Method

enumerator HTTP_METHOD_POST: HTTP POST Method

enumerator HTTP_METHOD_PUT: HTTP PUT Method

enumerator HTTP_METHOD_PATCH: HTTP PATCH Method

enumerator HTTP_METHOD_DELETE: HTTP DELETE Method

enumerator HTTP_METHOD_HEAD: HTTP HEAD Method

enumerator HTTP_METHOD_NOTIFY: HTTP NOTIFY Method

enumerator HTTP_METHOD_SUBSCRIBE: HTTP SUBSCRIBE Method

enumerator HTTP_METHOD_UNSUBSCRIBE: HTTP UNSUBSCRIBE Method

enumerator HTTP_METHOD_OPTIONS: HTTP OPTIONS Method

enumerator HTTP_METHOD_COPY: HTTP COPY Method

enumerator HTTP_METHOD_MOVE: HTTP MOVE Method

enumerator HTTP_METHOD_LOCK: HTTP LOCK Method

enumerator HTTP_METHOD_UNLOCK: HTTP UNLOCK Method

enumerator HTTP_METHOD_PROPFIND: HTTP PROPFIND Method

enumerator HTTP_METHOD_PROPPATCH: HTTP PROPPATCH Method

enumerator HTTP_METHOD_MKCOL: HTTP MKCOL Method

enumerator HTTP_METHOD_MAX

enum esp_http_client_auth_type_t

HTTP Authentication type.

Values:

enumerator HTTP_AUTH_TYPE_NONE: No authention

enumerator HTTP_AUTH_TYPE_BASIC: HTTP Basic authentication

enumerator HTTP_AUTH_TYPE_DIGEST: HTTP Disgest authentication

enum HttpStatus_Code

Enum for the HTTP status codes.

Values:

enumerator HttpStatus_Ok

enumerator HttpStatus_MultipleChoices

enumerator HttpStatus_MovedPermanently

enumerator HttpStatus_Found

enumerator HttpStatus_SeeOther

enumerator HttpStatus_TemporaryRedirect

enumerator HttpStatus_PermanentRedirect

enumerator HttpStatus_BadRequest

enumerator HttpStatus_Unauthorized

enumerator HttpStatus_Forbidden

enumerator HttpStatus_NotFound

enumerator HttpStatus_InternalError

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