Provided by: libcoap3t64_4.3.4-1.1build4_amd64 
NAME
coap_endpoint_client, coap_new_client_session, coap_new_client_session_psk2, coap_new_client_session_pki,
coap_session_set_mtu, coap_session_max_pdu_size - Work with CoAP client endpoints
SYNOPSIS
#include <coap3/coap.h>
coap_session_t *coap_new_client_session(coap_context_t *context, const coap_address_t *local_if, const
coap_address_t *server, coap_proto_t proto);
coap_session_t *coap_new_client_session_psk2(coap_context_t *context, const coap_address_t *local_if,
const coap_address_t *server, coap_proto_t proto, coap_dtls_cpsk_t *setup_data);
coap_session_t *coap_new_client_session_pki(coap_context_t *context, const coap_address_t *local_if,
const coap_address_t *server, coap_proto_t proto, coap_dtls_pki_t *setup_data);
void coap_session_set_mtu(coap_session_t *session, unsigned mtu);
size_t coap_session_max_pdu_size(const coap_session_t *session);
For specific (D)TLS library support, link with -lcoap-3-notls, -lcoap-3-gnutls, -lcoap-3-openssl,
-lcoap-3-mbedtls or -lcoap-3-tinydtls. Otherwise, link with -lcoap-3 to get the default (D)TLS library
support.
DESCRIPTION
This man page focuses on the setting up of a CoAP client endpoint and hence creation of a CoAP session
used to connect to a server. For a CoAP server endpoint, see coap_endpoint_server(3). There is no need to
call coap_new_endpoint(3) for a client as well as one of the coap_new_client_server*() functions.
The CoAP stack’s global state is stored in a coap_context_t context object. Resources, Endpoints and
Sessions are associated with this context object. There can be more than one coap_context_t object per
application, it is up to the application to manage each one accordingly.
A CoAP session maintains the state of an ongoing connection between a Client and Server which is stored
in a coap_session_t session object. A CoAP session is tracked by local port, CoAP protocol, remote IP
address and remote port, or in the case of Unix Domain sockets, the local path and the remote path.
The session network traffic can be encrypted or un-encrypted if there is an underlying TLS library.
If (D)TLS is going to be used for encrypting the network traffic, then the (D)TLS information for
Pre-Shared Keys (PSK) or Public Key Infrastructure (PKI) needs to be configured before any network
traffic starts to flow. For Clients, this is done during the Client session set up.
For Clients, all the encryption information can be held at the (D)TLS context and CoAP context levels, or
at the (D)TLS session and CoAP session levels. If defined at the context level, then when a session is
created, it will inherit the context definitions, unless they have separately been defined for the
session level, in which case the session version will get used. Typically the information will be
configured at the session level for Clients.
In principle the set-up sequence for CoAP client endpoints looks like
coap_new_context()
coap_context_set_pki_root_cas() - if the root CAs need to be updated and using PKI
coap_new_client_session(), coap_new_client_session_pki() or coap_new_client_session_psk2()
Multiple client endpoints and hence sessions are supported per context.
Different CoAP protocols can be defined for proto - the current supported list is:
COAP_PROTO_UDP
COAP_PROTO_DTLS
COAP_PROTO_TCP
COAP_PROTO_TLS
COAP_PROTO_WS
COAP_PROTO_WSS
coap_tcp_is_supported(3), coap_dtls_is_supported(3), coap_tls_is_supported(3), coap_ws_is_supported(3)
and coap_wss_is_supported(3) can be used for checking whether the underlying TCP, (D)TLS or WebSocket
protocol support is available. See coap_tls_library(3) for further information on the types of (D)TLS
sessions supported.
Libcoap supports 3 different socket types:
AF_INET IPv4 IP addresses and ports
AF_INET6 IPv6 IP addresses and ports and can be dual IPv4/IPv6 stacked
AF_UNIX Unix Domain using file path names
For AF_INET and AF_INET6, the client does not need to specify a local IP address and/or port as default
values will get filled in. However for AF_UNIX, the local pathname must be provided and must be unique
per client session. This unique local pathname will get deleted on the session being properly closed at
application exit.
The client must specify IP and port when defining the coap_address_t (see coap_address_t(3)) for the
remote end of the session if AF_INET or AF_INET6. If port is 0, then the default CoAP port is used
instead. If AF_UNIX, the unix domain path to connect to must be specified.
FUNCTIONS
Function: coap_new_client_session()
The coap_new_client_session() function creates a client endpoint for a specific context and initiates a
new client session to the specified server using the CoAP protocol proto as defined above. If the port is
set to 0 in server (for AF_INET or AF_INET6), then the default CoAP port is used.
Normally local_if would be set to NULL, but by specifying local_if the source of the network session can
be bound to a specific IP address or port. For AF_UNIX, local_if must be specified pointing to an
appropriate coap_address_t. If local_if is defined, the address families for local_if and server must be
identical. The session will initially have a reference count of 1.
To stop using a client session, the reference count must be decremented to 0 by calling
coap_session_release(3). See coap_session(3). This will remove the client endpoint’s session and all its
associated information.
Function: coap_new_client_session_pki()
The coap_new_client_session_pki() function, for a specific context, is used to configure the (D)TLS
context using the setup_data variables as defined in the coap_dtls_pki_t structure in the newly created
endpoint session - see coap_encryption(3). The connection is to the specified server using the CoAP
protocol proto as defined above. If the port is set to 0 in server (for AF_INET or AF_INET6), then the
default CoAP port is used.
Normally local_if would be set to NULL, but by specifying local_if the source of the network session can
be bound to a specific IP address or port. For AF_UNIX, local_if must be specified pointing to an
appropriate coap_address_t. If local_if is defined, the address families for local_if and server must be
identical. The session will initially have a reference count of 1.
To stop using a client session, the reference count must be decremented to 0 by calling
coap_session_release(3). See coap_session(3). This will remove the client endpoint’s session and all its
associated information.
Function: coap_new_client_session_psk2()
The coap_new_client_session_psk2() function, for a specific context, is used to configure the (D)TLS
context using the setup_data variables as defined in the coap_dtls_cpsk_t structure in the newly created
endpoint session - see coap_encryption(3). The connection is to the specified server using the CoAP
protocol proto as defined above. If the port is set to 0 in server (for AF_INET or AF_INET6), then the
default CoAP port is used.
Normally local_if would be set to NULL, but by specifying local_if the source of the network session can
be bound to a specific IP address or port. For AF_UNIX, local_if must be specified pointing to an
appropriate coap_address_t. If local_if is defined, the address families for local_if and server must be
identical. The session will initially have a reference count of 1.
To stop using a client session, the reference count must be decremented to 0 by calling
coap_session_release(3). See coap_session(3). This will remove the client endpoint’s session and all its
associated information.
Function: coap_session_set_mtu()
The coap_session_set_mtu() function is used to set the MTU size (the maximum message size) of the data in
a packet, excluding any IP or TCP/UDP overhead to mtu for the client endpoint’s session. The default MTU
is 1152.
Function: coap_session_max_pdu_size()
The coap_session_max_pdu_size() function is used to get the maximum MTU size of the data for the client
endpoint’s session.
RETURN VALUES
coap_new_client_session(), coap_new_client_session_psk2(), coap_new_client_session_pki() return a newly
created client. session or NULL if there is a creation failure.
coap_session_max_pdu_size() returns the MTU size.
EXAMPLES
CoAP Client Non-Encrypted Setup
#include <coap3/coap.h>
#include <netinet/in.h>
static coap_session_t *
setup_client_session (struct in_addr ip_address) {
coap_session_t *session;
coap_address_t server;
/* See coap_context(3) */
coap_context_t *context = coap_new_context(NULL);
if (!context)
return NULL;
/* See coap_block(3) */
coap_context_set_block_mode(context,
COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);
/* See coap_address(3) */
coap_address_init(&server);
server.addr.sa.sa_family = AF_INET;
server.addr.sin.sin_addr = ip_address;
server.addr.sin.sin_port = htons (5683);
session = coap_new_client_session(context, NULL, &server, COAP_PROTO_UDP);
if (!session) {
coap_free_context(context);
return NULL;
}
/* The context is in session->context */
return session;
}
CoAP Client Non-Encrypted Unix Domain Setup
#include <coap3/coap.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
static coap_session_t *
setup_client_session (const char *server_ud) {
coap_session_t *session;
coap_address_t server;
coap_address_t local;
/* See coap_context(3) */
coap_context_t *context = coap_new_context(NULL);
if (!context)
return NULL;
/* See coap_block(3) */
coap_context_set_block_mode(context,
COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);
/* See coap_address(3) */
coap_address_init(&server);
server.addr.sa.sa_family = AF_UNIX;
snprintf(server.addr.cun.sun_path, sizeof(server.addr.cun.sun_path),
"%s", server_ud);
/* Need to have a uniquely named local address */
coap_address_init(&local);
local.addr.sa.sa_family = AF_UNIX;
snprintf(local.addr.cun.sun_path, sizeof(server.addr.cun.sun_path),
"/tmp/client.%d", getpid());
/* Only do this if you know it is safe to do so */
unlink(local.addr.cun.sun_path);
session = coap_new_client_session(context, &local, &server, COAP_PROTO_UDP);
if (!session) {
coap_free_context(context);
return NULL;
}
/* The context is in session->context */
return session;
}
CoAP Client PKI Setup
#include <coap3/coap.h>
#include <netinet/in.h>
static int
verify_cn_callback(const char *cn,
const uint8_t *asn1_public_cert,
size_t asn1_length,
coap_session_t *c_session,
unsigned int depth,
int validated,
void *arg
) {
/* Remove (void) definition if variable is used */
(void)cn;
(void)asn1_public_cert;
(void)asn1_length;
(void)c_session;
(void)depth;
(void)validated;
(void)arg;
/* Check that the CN is valid */
/* ... */
return 1;
}
static coap_session_t *
setup_client_session_pki (struct in_addr ip_address,
const char *public_cert_file,
const char *private_key_file,
const char *ca_file
) {
coap_session_t *session;
coap_address_t server;
coap_dtls_pki_t dtls_pki;
/* See coap_context(3) */
coap_context_t *context = coap_new_context(NULL);
if (!context)
return NULL;
/* See coap_block(3) */
coap_context_set_block_mode(context,
COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);
/* See coap_address(3) */
coap_address_init(&server);
server.addr.sa.sa_family = AF_INET;
server.addr.sin.sin_addr = ip_address;
server.addr.sin.sin_port = htons (5684);
memset (&dtls_pki, 0, sizeof (dtls_pki));
/* See coap_encryption(3) */
dtls_pki.version = COAP_DTLS_PKI_SETUP_VERSION;
dtls_pki.verify_peer_cert = 1;
dtls_pki.check_common_ca = 1;
dtls_pki.allow_self_signed = 1;
dtls_pki.allow_expired_certs = 1;
dtls_pki.cert_chain_validation = 1;
dtls_pki.cert_chain_verify_depth = 1;
dtls_pki.check_cert_revocation = 1;
dtls_pki.allow_no_crl = 1;
dtls_pki.allow_expired_crl = 1;
dtls_pki.allow_bad_md_hash = 0;
dtls_pki.allow_short_rsa_length = 0;
dtls_pki.is_rpk_not_cert = 0; /* Set to 1 if RPK */
dtls_pki.validate_cn_call_back = verify_cn_callback;
dtls_pki.cn_call_back_arg = NULL;
dtls_pki.validate_sni_call_back = NULL;
dtls_pki.sni_call_back_arg = NULL;
dtls_pki.additional_tls_setup_call_back = NULL;
dtls_pki.client_sni = NULL;
dtls_pki.pki_key.key_type = COAP_PKI_KEY_PEM;
dtls_pki.pki_key.key.pem.ca_file = ca_file;
dtls_pki.pki_key.key.pem.public_cert = public_cert_file;
dtls_pki.pki_key.key.pem.private_key = private_key_file;
session = coap_new_client_session_pki(context, NULL, &server,
COAP_PROTO_DTLS, &dtls_pki);
if (!session) {
coap_free_context(context);
return NULL;
}
/* The context is in session->context */
return session;
}
CoAP Client PSK Setup
#include <coap3/coap.h>
#include <stdio.h>
#include <netinet/in.h>
#ifndef min
#define min(a,b) ((a) < (b) ? (a) : (b))
#endif
static const coap_dtls_cpsk_info_t *
verify_ih_callback(coap_str_const_t *hint,
coap_session_t *c_session,
void *arg
) {
coap_dtls_cpsk_info_t *psk_info = (coap_dtls_cpsk_info_t *)arg;
/* Remove (void) definition if variable is used */
(void)c_session;
coap_log_info("Identity Hint '%.*s' provided\n", (int)hint->length, hint->s);
/* Just use the defined information for now as passed in by arg */
return psk_info;
}
static coap_dtls_cpsk_t dtls_psk;
static char client_sni[256];
static coap_session_t *
setup_client_session_psk (const char *uri,
struct in_addr ip_address,
const uint8_t *identity,
unsigned int identity_len,
const uint8_t *key,
unsigned int key_len
) {
coap_session_t *session;
coap_address_t server;
/* See coap_context(3) */
coap_context_t *context = coap_new_context(NULL);
if (!context)
return NULL;
/* See coap_block(3) */
coap_context_set_block_mode(context,
COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);
/* See coap_address(3) */
coap_address_init(&server);
server.addr.sa.sa_family = AF_INET;
server.addr.sin.sin_addr = ip_address;
server.addr.sin.sin_port = htons (5684);
/* See coap_encryption(3) */
memset (&dtls_psk, 0, sizeof(dtls_psk));
dtls_psk.version = COAP_DTLS_CPSK_SETUP_VERSION;
dtls_psk.validate_ih_call_back = verify_ih_callback;
dtls_psk.ih_call_back_arg = &dtls_psk.psk_info;
if (uri)
memcpy(client_sni, uri, min(strlen(uri), sizeof(client_sni)-1));
else
memcpy(client_sni, "localhost", 9);
dtls_psk.client_sni = client_sni;
dtls_psk.psk_info.identity.s = identity;
dtls_psk.psk_info.identity.length = identity_len;
dtls_psk.psk_info.key.s = key;
dtls_psk.psk_info.key.length = key_len;
session = coap_new_client_session_psk2(context, NULL, &server,
COAP_PROTO_DTLS, &dtls_psk);
if (!session) {
coap_free_context(context);
return NULL;
}
/* The context is in session->context */
return session;
}
CoAP Client Anonymous PKI Setup
#include <coap3/coap.h>
#include <netinet/in.h>
static coap_session_t *
setup_client_session_dtls (struct in_addr ip_address) {
coap_session_t *session;
coap_address_t server;
/* See coap_context(3) */
coap_context_t *context = coap_new_context(NULL);
if (!context)
return NULL;
/* See coap_block(3) */
coap_context_set_block_mode(context,
COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);
/* See coap_address(3) */
coap_address_init(&server);
server.addr.sa.sa_family = AF_INET;
server.addr.sin.sin_addr = ip_address;
server.addr.sin.sin_port = htons (5683);
session = coap_new_client_session(context, NULL, &server,
COAP_PROTO_DTLS);
if (!session) {
coap_free_context(context);
return NULL;
}
/* The context is in session->context */
return session;
}
SEE ALSO
coap_address(3), coap_block(3), coap_context(3), coap_encryption(3), coap_endpoint_server(3),
coap_resource(3), coap_session(3) and coap_tls_library(3)
FURTHER INFORMATION
See
"RFC7252: The Constrained Application Protocol (CoAP)"
"RFC8323: CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets"
for further information.
BUGS
Please report bugs on the mailing list for libcoap: libcoap-developers@lists.sourceforge.net or raise an
issue on GitHub at https://github.com/obgm/libcoap/issues
AUTHORS
The libcoap project <libcoap-developers@lists.sourceforge.net>