Provided by: erlang-manpages_16.b.3-dfsg-1ubuntu2.2_all 
NAME
diameter_codec - Decode and encode of Diameter messages.
DESCRIPTION
Incoming Diameter messages are decoded from binary() before being communicated to
diameter_app(3erl) callbacks. Similarly, outgoing Diameter messages are encoded into
binary() before being passed to the appropriate diameter_transport(3erl) module for
transmission. The functions in this module implement this encode/decode.
Note:
Calls to this module are made by diameter itself as a consequence of configuration passed
to diameter:start_service/2. The encode/decode functions may also be useful for other
purposes (eg. test) but the diameter user does not need to call them explicitly when
sending and receiving messages using diameter:call/4 and the callback interface documented
in diameter_app(3erl).
The header() and packet() records below are defined in diameter.hrl, which can be included
as follows.
-include_lib("diameter/include/diameter.hrl").
Application-specific records are defined in the hrl files resulting from dictionary file
compilation.
DATA TYPES
uint8() = 0..255:
uint24() = 0..16777215:
uint32() = 0..4294967295:
8-bit, 24-bit and 32-bit integers occurring in Diameter and AVP headers.
avp() = #diameter_avp{}:
The application-neutral representation of an AVP. Primarily intended for use by relay
applications that need to handle arbitrary Diameter applications. A service
implementing a specific Diameter application (for which it configures a dictionary)
can manipulate values of type message() instead.
Fields have the following types.
code = uint32():
is_mandatory = boolean():
need_encryption = boolean():
vendor_id = uint32() | undefined:
Values in the AVP header, corresponding to AVP Code, the M flag, P flags and Vendor-
ID respectively. A Vendor-ID other than undefined implies a set V flag.
data = iolist():
The data bytes of the AVP.
name = atom():
The name of the AVP as defined in the dictionary file in question, or undefined if
the AVP is unknown to the dictionary file in question.
value = term():
The decoded value of an AVP. Will be undefined on decode if the data bytes could not
be decoded or the AVP is unknown. The type of a decoded value is as document in
diameter_dict(5).
type = atom():
The type of the AVP as specified in the dictionary file in question (or one it
inherits). Possible types are undefined and the Diameter types: OctetString,
Integer32, Integer64, Unsigned32, Unsigned64, Float32, Float64, Grouped, Enumerated,
Address, Time, UTF8String, DiameterIdentity, DiameterURI, IPFilterRule and
QoSFilterRule.
dictionary() = module():
The name of a generated dictionary module as generated by diameterc(1) or
diameter_make:codec/2. The interface provided by a dictionary module is an
implementation detail that may change.
header() = #diameter_header{}:
The record representation of the Diameter header. Values in a packet() returned by
decode/2 are as extracted from the incoming message. Values set in an packet() passed
to encode/2 are preserved in the encoded binary(), with the exception of length,
cmd_code and application_id, all of which are determined by the dictionary() in
question.
Note:
It is not necessary to set header fields explicitly in outgoing messages as diameter
itself will set appropriate values. Setting inappropriate values can be useful for test
purposes.
Fields have the following types.
version = uint8():
length = uint24():
cmd_code = uint24():
application_id = uint32():
hop_by_hop_id = uint32():
end_to_end_id = uint32():
Values of the Version, Message Length, Command-Code, Application-ID, Hop-by-Hop
Identifier and End-to-End Identifier fields of the Diameter header.
is_request = boolean():
is_proxiable = boolean():
is_error = boolean():
is_retransmitted = boolean():
Values corresponding to the R(equest), P(roxiable), E(rror) and T(Potentially re-
transmitted message) flags of the Diameter header.
message() = record() | list():
The representation of a Diameter message as passed to diameter:call/4 or returned from
a handle_request/3 callback. The record representation is as outlined in
diameter_dict(5): a message as defined in a dictionary file is encoded as a record
with one field for each component AVP. Equivalently, a message can also be encoded as
a list whose head is the atom-valued message name (as specified in the relevant
dictionary file) and whose tail is a list of {AvpName, AvpValue} pairs.
Another list-valued representation allows a message to be specified as a list whose
head is a header() and whose tail is an avp() list. This representation is used by
diameter itself when relaying requests as directed by the return value of a
handle_request/3 callback. It differs from the other other two in that it bypasses the
checks for messages that do not agree with their definitions in the dictionary in
question: messages are sent exactly as specified.
packet() = #diameter_packet{}:
A container for incoming and outgoing Diameter messages. Fields have the following
types.
header = header() | undefined:
The Diameter header of the message. Can be (and typically should be) undefined for
an outgoing message in a non-relay application, in which case diameter provides
appropriate values.
avps = [avp()] | undefined:
The AVPs of the message. Ignored for an outgoing message if the msg field is set to
a value other than undefined.
msg = message() | undefined:
The incoming/outgoing message. For an incoming message, a record if the message can
be decoded in a non-relay application, undefined otherwise. For an outgoing message,
setting a [header() | avp()] list is equivalent to setting the header and avps
fields to the corresponding values.
Warning:
A record-valued msg field does not imply an absence of decode errors. The errors
field should also be examined.
bin = binary():
The incoming message prior to encode or the outgoing message after encode.
errors = [5000..5999 | {5000..5999, avp()}]:
Errors detected at decode of an incoming message, as identified by a corresponding
5xxx series Result-Code (Permanent Failures). For an incoming request, these should
be used to formulate an appropriate answer as documented for the handle_request/3
callback in diameter_app(3erl). For an incoming answer, the
diameter:application_opt() answer_errors determines the behaviour.
transport_data = term():
An arbitrary term of meaning only to the transport process in question, as
documented in diameter_transport(3erl).
EXPORTS
decode(Mod, Bin) -> Pkt
Types:
Mod = dictionary()
Bin = binary()
Pkt = packet()
Decode a Diameter message.
encode(Mod, Msg) -> Pkt
Types:
Mod = dictionary()
Msg = message() | packet()
Pkt = packet()
Encode a Diameter message.
SEE ALSO
diameterc(1), diameter_app(3erl), diameter_dict(5), diameter_make(3erl)