// -*- mode:doc; -*-
// vim: set syntax=asciidoc,tw=0:

coap_session(3)
=================
:doctype: manpage
:man source:   coap_session
:man version:  @PACKAGE_VERSION@
:man manual:   libcoap Manual

NAME
----
coap_session,
coap_new_client_session,
coap_new_client_session_psk,
coap_new_client_session_pki,
coap_session_reference,
coap_session_release,
coap_session_set_mtu,
coap_session_max_pdu_size,
coap_session_str - Work with CoAP sessions

SYNOPSIS
--------
*#include <coap@LIBCOAP_API_VERSION@/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_psk(coap_context_t *_context_,
const coap_address_t *_local_if_, const coap_address_t *_server_, coap_proto_t
_proto_, const char *_identity_, const uint8_t *_key_, unsigned _key_len_);*

*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_);*

*coap_session_t *coap_session_reference(coap_session_t *_session_);*

*void coap_session_release(coap_session_t *_session_);*

*void coap_session_set_mtu(coap_session_t *_session_, unsigned _mtu_);*

*size_t coap_session_max_pdu_size(coap_session_t *_session_);*

*void coap_session_set_app_data(coap_session_t *_session_, void *_data_);*

*void *coap_session_get_app_data(const coap_session_t *_session_);*

*const char *coap_session_str(const coap_session_t *_session_);*

Link with *-lcoap-@LIBCOAP_API_VERSION@*, *-lcoap-@LIBCOAP_API_VERSION@-gnutls*,
*-lcoap-@LIBCOAP_API_VERSION@-openssl* or
*-lcoap-@LIBCOAP_API_VERSION@-tinydtls* depending on your (D)TLS library
type.

DESCRIPTION
-----------
This man page focuses on the CoAP Session.

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.

The Session network traffic can be encrypted or un-encrypted if there is an
underlying TLS library.

If TLS is going to be used for encrypting the network traffic, then the TLS
information for Pre-Shared Keys (PSK) or Public Key Infrastructure (PKI) needs
to be configured before any network traffic starts to flow. For Servers, this
has to be done before the Endpoint is created, for Clients, this is done
during the Client Session set up.

For Servers, all the encryption information is held internally by the TLS
Context level and the CoAP Context level as the Server is listening for new
incoming traffic based on the Endpoint definition.  The TLS and CoAP session
will not get built until the new traffic starts, which is done by the libcoap
library, with the session having a reference count of 1.

For Clients, all the encryption information can be held at the TLS Context and
CoAP Context levels, or at the TLS Session and CoAP Session levels.  If
defined at the Context level, then when Sessions are created, they 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 Servers looks like
(see coap_context(3) for further information on the functions)
----
coap_new_context()
coap_context_set_pki_root_cas() - if the root CAs need to be updated and PKI
coap_context_set_pki() and/or coap_context_set_psk() - if encryption is required
coap_new_endpoint()
----

Multiple endpoints can be set up per Context, each listening for a new traffic
flow with different TCP/UDP protocols, TLS protocols, port numbers etc. When a
new traffic flow is started, then the CoAP library will create and start a new
server session.

In principle the set-up sequence for CoAP Clients looks like
----
coap_new_context()
coap_context_set_pki_root_cas() if the root CAs need to be updated and PKI
coap_new_client_session(), coap_new_client_session_pki() or coap_new_client_session_psk()
----

Multiple client sessions are supported per Context.

Different CoAP protocols can be defined for _proto_ - the current supported
list is:

[source, c]
----
COAP_PROTO_UDP
COAP_PROTO_DTLS
COAP_PROTO_TCP
COAP_PROTO_TLS
----

The *coap_new_client_session*() function initiates a new client session
associated with _context_ to the specified _server_ using the CoAP protocol
_proto_.  If the port is not specified in _server_, 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.  The session will initially have a reference count of 1.

The *coap_new_client_session_pki*() function, for a specific _context_, is
used to configure the TLS context using the _setup_data_ variables as defined
in the coap_dtls_pki_t structure - see *coap_encrytion*(3).
The session will initially have a reference count of 1.

The *coap_new_client_session_psk*() function, for a specific _context_, is
used to configure the TLS context using the client _identity_, Pre-Shared Key
_key_ with length _key_len_.  All 3 parameters must be defined, NULL is not
valid.  An empty string is not valid for _identity_.  _key_len_ must be greater
than 0.  This function also includes the _server_ to connect to,
optionally the local interface _local_if_ to bind to and the CoAP protocol
_proto_ to use.  The session will initially have a reference count of 1.

The *coap_session_reference*() is used to increment the reference count of
the _session_.  Incrementing the reference count by an application means that
the library will not inadvertently remove the session when it has finished
processing the session.

The *coap_session_release*() function must be used to decrement the _session_
reference count, which when it gets to 0, will free off the session if this is
a Client, which then clears all entries from the receive queue and send
queue.  If the reference count goes to 0 for a Server, then the _session_ is
added to a free pool ready for subsequent re-use. If the Server _session_ is
not used for 5 minutes, then it will get completely freed off.

The *coap_sesson_set_default_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 _session_.

The *coap_session_max_pdu_size*() funcition is used to get the maximum MTU
size of the data for the _session_.

The *coap_session_set_app_data*() funstion is used to define a _data_ pointer
for the _session_ which can then be retieved at a later date.

The *coap_session_get_app_data*() function is used to retrieve the data
pointer previously defined by *coap_session_set_app_data*().

The *coap_session_str*() function is used to get a string containing the
information about the _session_.

RETURN VALUES
-------------
*coap_new_client_session*(), *coap_new_client_session_psk*(),
*coap_new_client_session_pki*() functions returns a newly created client
session or NULL if there is a creation failure.

*coap_session_reference*() function returns a pointer to the session.

*coap_session_get_app_data*() function return a previously defined pointer.

*coap_session_max_pdu_size*() function returns the MTU size.

*coap_session_str*() function returns a description string of the
session.

EXAMPLES
--------
*CoAP Client Non-Encrypted Setup*
[source, c]
----
#include <coap@LIBCOAP_API_VERSION@/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;

  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 PKI Setup*
[source, c]
----
#include <coap@LIBCOAP_API_VERSION@/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 *session,
                   unsigned depth,
                   int 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;

  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.require_peer_cert       = 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.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.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*
[source, c]
----
#include <coap@LIBCOAP_API_VERSION@/coap.h>

#include <netinet/in.h>

static coap_session_t *
setup_client_session_psk (struct in_addr ip_address,
                          const char *identity,
                          const uint8_t *key,
                          unsigned 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;

  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);

  session = coap_new_client_session_psk(context, NULL, &server,
                                        COAP_PROTO_DTLS, identity, key, key_len);
  if (!session) {
    coap_free_context(context);
    return NULL;
  }
  /* The context is in session->context */
  return session;
}
----

*CoAP Client Setup*
[source, c]
----
#include <coap@LIBCOAP_API_VERSION@/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;

  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_context*(3), *coap_resource*(3), *coap_encryption*(3) and *coap_tls_library*(3)

FURTHER INFORMATION
-------------------
See "RFC7252: The Constrained Application Protocol (CoAP)" for further
information.

BUGS
----
Please report bugs on the mailing list for libcoap:
libcoap-developers@lists.sourceforge.net

AUTHORS
-------
The libcoap project <libcoap-developers@lists.sourceforge.net>
