HTTP Server

Overview 

Zephyr provides an HTTP server library, which allows to register HTTP services and HTTP resources associated with those services. The server creates a listening socket for every registered service, and handles incoming client connections. It’s possible to communicate over a plain TCP socket (HTTP) or a TLS socket (HTTPS). Both, HTTP/1.1 (RFC 2616) and HTTP/2 (RFC 9113) protocol versions are supported.

The server operation is generally transparent for the application, running in a background thread. The application can control the server activity with respective API functions.

Certain resource types (for example dynamic resource) provide resource-specific application callbacks, allowing the server to interact with the application (for instance provide resource content, or process request payload).

Currently, the following resource types are supported:

Static resources - content defined compile-time, cannot be modified at runtime (HTTP_RESOURCE_TYPE_STATIC).
Dynamic resources - content provided at runtime by respective application callback (HTTP_RESOURCE_TYPE_DYNAMIC).
Websocket resources - allowing to establish Websocket connections with the server (HTTP_RESOURCE_TYPE_WEBSOCKET).

Zephyr provides a sample demonstrating HTTP(s) server operation and various resource types usage. See HTTP Server for more information.

Server Setup 

A few prerequisites are needed in order to enable HTTP server functionality in the application.

First of all, the HTTP server has to be enabled in applications configuration file with CONFIG_HTTP_SERVER Kconfig option:

prj.conf

CONFIG_HTTP_SERVER=y

All HTTP services and HTTP resources are placed in a dedicated linker section. The linker section for services is predefined locally, however the application is responsible for defining linker sections for resources associated with respective services. Linker section names for resources should be prefixed with http_resource_desc_, appended with the service name.

Linker sections for resources should be defined in a linker file. For example, for a service named my_service, the linker section shall be defined as follows:

sections-rom.ld

#include <zephyr/linker/iterable_sections.h>

ITERABLE_SECTION_ROM(http_resource_desc_my_service, Z_LINK_ITERABLE_SUBALIGN)

Finally, the linker file and linker section have to be added to your application using CMake:

CMakeLists.txt

zephyr_linker_sources(SECTIONS sections-rom.ld)
zephyr_linker_section(NAME http_resource_desc_my_service
                      KVMA RAM_REGION GROUP RODATA_REGION
                      SUBALIGN Z_LINK_ITERABLE_SUBALIGN)

Note

You need to define a separate linker section for each HTTP service registered in the system.

Sample Usage 

Services 

The application needs to define an HTTP service (or multiple services), with the same name as used for the linker section with HTTP_SERVICE_DEFINE macro:

#include <zephyr/net/http/service.h>

static uint16_t http_service_port = 80;

HTTP_SERVICE_DEFINE(my_service, "0.0.0.0", &http_service_port, 1, 10, NULL);

Alternatively, an HTTPS service can be defined with HTTPS_SERVICE_DEFINE:

#include <zephyr/net/http/service.h>
#include <zephyr/net/tls_credentials.h>

#define HTTP_SERVER_CERTIFICATE_TAG 1

static uint16_t https_service_port = 443;
static const sec_tag_t sec_tag_list[] = {
    HTTP_SERVER_CERTIFICATE_TAG,
};

HTTPS_SERVICE_DEFINE(my_service, "0.0.0.0", &https_service_port, 1, 10,
                     NULL, sec_tag_list, sizeof(sec_tag_list));

Note

HTTPS services rely on TLS credentials being registered in the system. See TLS credentials subsystem for information on how to configure TLS credentials in the system.

Once HTTP(s) service is defined, resources can be registered for it with HTTP_RESOURCE_DEFINE macro.

Application can enable resource wildcard support by enabling CONFIG_HTTP_SERVER_RESOURCE_WILDCARD option. When this option is set, then it is possible to match several incoming HTTP requests with just one resource handler. The fnmatch() POSIX API function is used to match the pattern in the URL paths.

Example:

HTTP_RESOURCE_DEFINE(my_resource, my_service, "/foo*", &resource_detail);

This would match all URLs that start with a string foo. See POSIX.2 chapter 2.13 for pattern matching syntax description.

Static resources 

Static resource content is defined build-time and is immutable. The following example shows how gzip compressed webpage can be defined as a static resource in the application:

static const uint8_t index_html_gz[] = {
    #include "index.html.gz.inc"
};

struct http_resource_detail_static index_html_gz_resource_detail = {
    .common = {
        .type = HTTP_RESOURCE_TYPE_STATIC,
        .bitmask_of_supported_http_methods = BIT(HTTP_GET),
        .content_encoding = "gzip",
    },
    .static_data = index_html_gz,
    .static_data_len = sizeof(index_html_gz),
};

HTTP_RESOURCE_DEFINE(index_html_gz_resource, my_service, "/",
                     &index_html_gz_resource_detail);

The resource content and content encoding is application specific. For the above example, a gzip compressed webpage can be generated during build, by adding the following code to the application’s CMakeLists.txt file:

CMakeLists.txt

set(gen_dir ${ZEPHYR_BINARY_DIR}/include/generated/)
set(source_file_index src/index.html)
generate_inc_file_for_target(app ${source_file_index} ${gen_dir}/index.html.gz.inc --gzip)

where src/index.html is the location of the webpage to be compressed.

Dynamic resources 

For dynamic resource, a resource callback is registered to exchange data between the server and the application. The application defines a resource buffer used to pass the request payload data from the server, and to provide response payload to the server. The following example code shows how to register a dynamic resource with a simple resource handler, which echoes received data back to the client:

static uint8_t recv_buffer[1024];

static int dyn_handler(struct http_client_ctx *client,
                       enum http_data_status status, uint8_t *buffer,
                       size_t len, void *user_data)
{
#define MAX_TEMP_PRINT_LEN 32
    static char print_str[MAX_TEMP_PRINT_LEN];
    enum http_method method = client->method;
    static size_t processed;

    __ASSERT_NO_MSG(buffer != NULL);

    if (status == HTTP_SERVER_DATA_ABORTED) {
        LOG_DBG("Transaction aborted after %zd bytes.", processed);
        processed = 0;
        return 0;
    }

    processed += len;

    snprintf(print_str, sizeof(print_str), "%s received (%zd bytes)",
             http_method_str(method), len);
    LOG_HEXDUMP_DBG(buffer, len, print_str);

    if (status == HTTP_SERVER_DATA_FINAL) {
        LOG_DBG("All data received (%zd bytes).", processed);
        processed = 0;
    }

    /* This will echo data back to client as the buffer and recv_buffer
     * point to same area.
     */
    return len;
}

struct http_resource_detail_dynamic dyn_resource_detail = {
    .common = {
        .type = HTTP_RESOURCE_TYPE_DYNAMIC,
        .bitmask_of_supported_http_methods =
            BIT(HTTP_GET) | BIT(HTTP_POST),
    },
    .cb = dyn_handler,
    .data_buffer = recv_buffer,
    .data_buffer_len = sizeof(recv_buffer),
    .user_data = NULL,
};

HTTP_RESOURCE_DEFINE(dyn_resource, my_service, "/dynamic",
                     &dyn_resource_detail);

The resource callback may be called multiple times for a single request, hence the application should be able to keep track of the received data progress.

The status field informs the application about the progress in passing request payload from the server to the application. As long as the status reports HTTP_SERVER_DATA_MORE, the application should expect more data to be provided in a consecutive callback calls. Once all request payload has been passed to the application, the server reports HTTP_SERVER_DATA_FINAL status. In case of communication errors during request processing (for example client closed the connection before complete payload has been received), the server reports HTTP_SERVER_DATA_ABORTED. Either of the two events indicate that the application shall reset any progress recorded for the resource, and await a new request to come. The server guarantees that the resource can only be accessed by single client at a time.

The resource callback returns the number of bytes to be replied in the response payload to the server (provided in the resource data buffer). In case there is no more data to be included in the response, the callback should return 0.

The server will call the resource callback until it provided all request data to the application, and the application reports there is no more data to include in the reply.

Websocket resources 

Websocket resources register an application callback, which is called when a Websocket connection upgrade takes place. The callback is provided with a socket descriptor corresponding to the underlying TCP/TLS connection. Once called, the application takes full control over the socket, i. e. is responsible to release it when done.

static int ws_socket;
static uint8_t ws_recv_buffer[1024];

int ws_setup(int sock, void *user_data)
{
    ws_socket = sock;
    return 0;
}

struct http_resource_detail_websocket ws_resource_detail = {
    .common = {
        .type = HTTP_RESOURCE_TYPE_WEBSOCKET,
        /* We need HTTP/1.1 Get method for upgrading */
        .bitmask_of_supported_http_methods = BIT(HTTP_GET),
    },
    .cb = ws_setup,
    .data_buffer = ws_recv_buffer,
    .data_buffer_len = sizeof(ws_recv_buffer),
    .user_data = NULL, /* Fill this for any user specific data */
};

HTTP_RESOURCE_DEFINE(ws_resource, my_service, "/", &ws_resource_detail);

The above minimalistic example shows how to register a Websocket resource with a simple callback, used only to store the socket descriptor provided. Further processing of the Websocket connection is application-specific, hence outside of scope of this guide. See HTTP Server for an example Websocket-based echo service implementation.

API Reference 

Related code samples

HTTP Server: Implement an HTTP(s) Server demonstrating various resource types.

group http_service

Defines

HTTP_RESOURCE_DEFINE(_name, _service, _resource, _detail)

Define a static HTTP resource.

A static HTTP resource is one that is known prior to system initialization. In contrast, dynamic resources may be discovered upon system initialization. Dynamic resources may also be inserted, or removed by events originating internally or externally to the system at runtime.

Note

The _resource is the URL without the associated protocol, host, or URL parameters. E.g. the resource for #param1=value1 would be /bar/baz.html. It is often referred to as the “path” of the URL. Every (service, resource) pair should be unique. The _resource must be non-NULL.

Parameters:

_name – Name of the resource.
_service – Name of the associated service.
_resource – Pathname-like string identifying the resource.
_detail – Implementation-specific detail associated with the resource.

HTTP_SERVICE_DEFINE_EMPTY(_name, _host, _port, _concurrent, _backlog, _detail)

Define an HTTP service without static resources.

Note

The _host parameter must be non-NULL. It is used to specify an IP address either in IPv4 or IPv6 format a fully-qualified hostname or a virtual host.

Note

The _port parameter must be non-NULL. It points to a location that specifies the port number to use for the service. If the specified port number is zero, then an ephemeral port number will be used and the actual port number assigned will be written back to memory. For ephemeral port numbers, the memory pointed to by _port must be writeable.

Parameters:

_name – Name of the service.
_host – IP address or hostname associated with the service.
_port – [inout] Pointer to port associated with the service.
_concurrent – Maximum number of concurrent clients.
_backlog – Maximum number queued connections.
_detail – Implementation-specific detail associated with the service.

HTTPS_SERVICE_DEFINE_EMPTY(_name, _host, _port, _concurrent, _backlog, _detail, _sec_tag_list, _sec_tag_list_size)

Define an HTTPS service without static resources.

Note

The _host parameter must be non-NULL. It is used to specify an IP address either in IPv4 or IPv6 format a fully-qualified hostname or a virtual host.

Note

The _port parameter must be non-NULL. It points to a location that specifies the port number to use for the service. If the specified port number is zero, then an ephemeral port number will be used and the actual port number assigned will be written back to memory. For ephemeral port numbers, the memory pointed to by _port must be writeable.

Parameters:

_name – Name of the service.
_host – IP address or hostname associated with the service.
_port – [inout] Pointer to port associated with the service.
_concurrent – Maximum number of concurrent clients.
_backlog – Maximum number queued connections.
_detail – Implementation-specific detail associated with the service.
_sec_tag_list – TLS security tag list used to setup a HTTPS socket.
_sec_tag_list_size – TLS security tag list size used to setup a HTTPS socket.

HTTP_SERVICE_DEFINE(_name, _host, _port, _concurrent, _backlog, _detail)

Define an HTTP service with static resources.

Note

The _host parameter must be non-NULL. It is used to specify an IP address either in IPv4 or IPv6 format a fully-qualified hostname or a virtual host.

Note

The _port parameter must be non-NULL. It points to a location that specifies the port number to use for the service. If the specified port number is zero, then an ephemeral port number will be used and the actual port number assigned will be written back to memory. For ephemeral port numbers, the memory pointed to by _port must be writeable.

Parameters:

_name – Name of the service.
_host – IP address or hostname associated with the service.
_port – [inout] Pointer to port associated with the service.
_concurrent – Maximum number of concurrent clients.
_backlog – Maximum number queued connections.
_detail – Implementation-specific detail associated with the service.

HTTPS_SERVICE_DEFINE(_name, _host, _port, _concurrent, _backlog, _detail, _sec_tag_list, _sec_tag_list_size)

Define an HTTPS service with static resources.

Note

The _host parameter must be non-NULL. It is used to specify an IP address either in IPv4 or IPv6 format a fully-qualified hostname or a virtual host.

Note

The _port parameter must be non-NULL. It points to a location that specifies the port number to use for the service. If the specified port number is zero, then an ephemeral port number will be used and the actual port number assigned will be written back to memory. For ephemeral port numbers, the memory pointed to by _port must be writeable.

Parameters:

_name – Name of the service.
_host – IP address or hostname associated with the service.
_port – [inout] Pointer to port associated with the service.
_concurrent – Maximum number of concurrent clients.
_backlog – Maximum number queued connections.
_detail – Implementation-specific detail associated with the service.
_sec_tag_list – TLS security tag list used to setup a HTTPS socket.
_sec_tag_list_size – TLS security tag list size used to setup a HTTPS socket.

HTTP_SERVICE_COUNT(_dst)

Count the number of HTTP services.

Parameters:

_dst – [out] Pointer to location where result is written.

HTTP_SERVICE_RESOURCE_COUNT(_service)

Count HTTP service static resources.

Parameters:

_service – Pointer to a service.

HTTP_SERVICE_FOREACH(_it)

Iterate over all HTTP services.

Parameters:

_it – Name of http_service_desc iterator

HTTP_RESOURCE_FOREACH(_service, _it)

Iterate over static HTTP resources associated with a given _service.

Note

This macro requires that _service is defined with HTTP_SERVICE_DEFINE.

Parameters:

_service – Name of HTTP service
_it – Name of iterator (of type http_resource_desc)

HTTP_SERVICE_FOREACH_RESOURCE(_service, _it)

Iterate over all static resources associated with _service .

Note

This macro is suitable for a _service defined with either HTTP_SERVICE_DEFINE or HTTP_SERVICE_DEFINE_EMPTY.

Parameters:

_service – Pointer to HTTP service
_it – Name of iterator (of type http_resource_desc)

struct http_resource_desc

#include <service.h>

HTTP resource description.

Public Members

const char *resource: Resource name.

void *detail: Detail associated with this resource.

Related code samples

HTTP Server: Implement an HTTP(s) Server demonstrating various resource types.

group http_server

Typedefs

typedef int (*http_resource_dynamic_cb_t)(struct http_client_ctx *client, enum http_data_status status, uint8_t *data_buffer, size_t data_len, void *user_data)

Callback used when data is received.

Data to be sent to client can be specified.

Param client:: HTTP context information for this client connection.
Param status:: HTTP data status, indicate whether more data is expected or not.
Param data_buffer:: Data received.
Param data_len:: Amount of data received.
Param user_data:: User specified data.
Return:: >0 amount of data to be sent to client, let server to call this function again when new data is received. 0 nothing to sent to client, close the connection <0 error, close the connection.

typedef int (*http_resource_websocket_cb_t)(int ws_socket, void *user_data)

Callback used when a Websocket connection is setup.

The application will need to handle all functionality related to the connection like reading and writing websocket data, and closing the connection.

Param ws_socket:: A socket for the Websocket data.
Param user_data:: User specified data.
Return:: 0 Accepting the connection, HTTP server library will no longer handle data to/from the socket and it is application responsibility to send and receive data to/from the supplied socket. <0 error, close the connection.

Enums

enum http_resource_type

HTTP server resource type.

Values:

enumerator HTTP_RESOURCE_TYPE_STATIC: Static resource, cannot be modified on runtime.

enumerator HTTP_RESOURCE_TYPE_DYNAMIC: Dynamic resource, server interacts with the application via registered http_resource_dynamic_cb_t.

enumerator HTTP_RESOURCE_TYPE_WEBSOCKET: Websocket resource, application takes control over Websocket connection after and upgrade.

enum http_data_status

Indicates the status of the currently processed piece of data.

Values:

enumerator HTTP_SERVER_DATA_ABORTED = -1: Transaction aborted, data incomplete.

enumerator HTTP_SERVER_DATA_MORE = 0: Transaction incomplete, more data expected.

enumerator HTTP_SERVER_DATA_FINAL = 1: Final data fragment in current transaction.

Functions

int http_server_start(void)

Start the HTTP2 server.

The server runs in a background thread. Once started, the server will create a server socket for all HTTP services registered in the system and accept connections from clients (see HTTP_SERVICE_DEFINE).

int http_server_stop(void)

Stop the HTTP2 server.

All server sockets are closed and the server thread is suspended.

struct http_resource_detail

#include <server.h>

Representation of a server resource, common for all resource types.

Public Members

uint32_t bitmask_of_supported_http_methods: Bitmask of supported HTTP methods (http_method).

enum http_resource_type type: Resource type.

int path_len: Length of the URL path.

const char *content_encoding: Content encoding of the resource.

const char *content_type: Content type of the resource.

struct http_resource_detail_static

#include <server.h>

Representation of a static server resource.

Public Members

struct http_resource_detail common: Common resource details.

const void *static_data: Content of the static resource.

size_t static_data_len: Size of the static resource.

struct http_resource_detail_dynamic

#include <server.h>

Representation of a dynamic server resource.

Public Members

struct http_resource_detail common: Common resource details.

http_resource_dynamic_cb_t cb: Resource callback used by the server to interact with the application.

uint8_t *data_buffer: Data buffer used to exchanged data between server and the, application.

size_t data_buffer_len: Length of the data in the data buffer.

struct http_client_ctx *holder: A pointer to the client currently processing resource, used to prevent concurrent access to the resource from multiple clients.

void *user_data: A pointer to the user data registered by the application.

struct http_resource_detail_websocket

#include <server.h>

Representation of a websocket server resource.

Public Members

struct http_resource_detail common: Common resource details.

int ws_sock: Websocket socket value.

http_resource_websocket_cb_t cb: Resource callback used by the server to interact with the application.

uint8_t *data_buffer: Data buffer used to exchanged data between server and the, application.

size_t data_buffer_len: Length of the data in the data buffer.

void *user_data: A pointer to the user data registered by the application.

struct http2_stream_ctx

#include <server.h>

HTTP/2 stream representation.

Public Members

int stream_id: Stream identifier.

enum http2_stream_state stream_state: Stream state.

int window_size: Stream-level window size.

bool headers_sent: Flag indicating that headers were sent in the reply.

bool end_stream_sent: Flag indicating that END_STREAM flag was sent.

struct http2_frame

#include <server.h>

HTTP/2 frame representation.

Public Members

uint32_t length: Frame payload length.

uint32_t stream_identifier: Stream ID the frame belongs to.

uint8_t type: Frame type.

uint8_t flags: Frame flags.

uint8_t padding_len: Frame padding length.

struct http_client_ctx

#include <server.h>

Representation of an HTTP client connected to the server.

Public Members

int fd: Socket descriptor associated with the server.

unsigned char buffer[HTTP_SERVER_CLIENT_BUFFER_SIZE]: Client data buffer.

unsigned char *cursor: Cursor indicating currently processed byte.

size_t data_len: Data left to process in the buffer.

int window_size: Connection-level window size.

enum http_server_state server_state: Server state for the associated client.

struct http2_frame current_frame: Currently processed HTTP/2 frame.

struct http_resource_detail *current_detail: Currently processed resource detail.

struct http2_stream_ctx *current_stream: Currently processed stream.

struct http_hpack_header_buf header_field: HTTP/2 header parser context.

struct http2_stream_ctx streams[HTTP_SERVER_MAX_STREAMS]: HTTP/2 streams context.

struct http_parser_settings parser_settings: HTTP/1 parser configuration.

struct http_parser parser: HTTP/1 parser context.

unsigned char url_buffer[HTTP_SERVER_MAX_URL_LENGTH]: Request URL.

unsigned char content_type[HTTP_SERVER_MAX_CONTENT_TYPE_LEN]: Request content type.

unsigned char header_buffer[HTTP_SERVER_MAX_HEADER_LEN]: Temp buffer for currently processed header (HTTP/1 only).

size_t content_len: Request content length.

enum http_method method: Request method.

enum http1_parser_state parser_state: HTTP/1 parser state.

int http1_frag_data_len: Length of the payload length in the currently processed request fragment (HTTP/1 only).

struct k_work_delayable inactivity_timer

Client inactivity timer.

The client connection is closed by the server when it expires.

bool preface_sent: Flag indicating that HTTP2 preface was sent.

bool http1_headers_sent: Flag indicating that HTTP1 headers were sent.

bool has_upgrade_header: Flag indicating that upgrade header was present in the request.

bool http2_upgrade: Flag indicating HTTP/2 upgrade takes place.

bool websocket_upgrade: Flag indicating Websocket upgrade takes place.

bool websocket_sec_key_next: Flag indicating Websocket key is being processed.

bool expect_continuation: The next frame on the stream is expectd to be a continuation frame.