diameter_codec(3)

📦
version 29.0.6 · 2 versions
, in nixos 26.05, nixpkgs unstable, ubuntu stonking

🎀 NAME 🎀

okay so bestie, welcome to diameter_codec, a page straight out of the Erlang Module Definition collection ✨ and it does exactly one thing: Decode and encode of Diameter messages. that's it, that's the girl. 💖

🌸 DESCRIPTION 🌸

so here's the tea, fr fr: incoming Diameter messages get decoded from binary() before they're ever communicated to your diameter_app callbacks. and on the flip side, outgoing Diameter messages get encoded into binary() before being passed to the appropriate diameter_transport module for transmission. the functions documented right here are the ones implementing the default encode/decode. slay. ✨

⚠️ WARNING bestie, listen closely: the diameter user does not need to call functions here explicitly when sending and receiving messages using diameter:call/4 and the callback interface documented in diameter_app. diameter itself provides encode/decode as a consequence of configuration passed to diameter:start_service/2, and the results may differ from those returned by the functions documented here, depending on configuration. so don't be out here hand-rolling calls and then acting shocked at the output 🙈

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. no cap. 📚

🦋 DATA TYPES 🦋

  • uint8() = 0..255
  • uint24() = 0..16777215
  • uint32() = 0..4294967295

these three cuties are the 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. bestie, this one has fields, and here's what they're giving:
    • code = uint32()
    • is_mandatory = boolean()
    • need_encryption = boolean()
    • vendor_id = uint32() | undefined — these are the 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, the AVP is unknown, or if the decode format is none. the type of a decoded value is as document in diameter_dict(4). 👑
    • 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. the range is ranging, literally. 🌈
  • 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. iykyk. 💅
  • 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. (chaotic. love that for you. 🙈)

the fields, and their types:

  • version = uint8()
  • length = uint24()
  • cmd_code = uint24()
  • application_id = uint32()
  • hop_by_hop_id = uint32()
  • end_to_end_id = uint32() — these are the 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() | maybe_improper_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(4): 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 either a list of AVP name/values pairs or a map with values keyed on AVP names. the format at decode is determined by diameter:service_opt() decode_format. any of the formats is accepted at encode. 🦋

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 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. main character energy, zero notes. 👑

  • packet() = #diameter_packet{} — a container for incoming and outgoing Diameter messages. the 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 term corresponding to the configured decode format 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 value in the msg field does not imply an absence of decode errors. the errors field should also be examined. don't skip the vibe check on that one bestie 😭
  • 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. 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. 🚀

🌟 SEE ALSO 🌟

go read those too, bestie, they're all linked in the group chat 🫶

💜 DATA TYPES 💜 (the encore)

yes she's back, she's the same girl, she just wanted a second moment 💅

  • 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. ⭐

  • message() :: record() | maybe_improper_list().

the representation of a Diameter message as passed to diameter:call/4 or returned from a handle_request/3 callback. 🌸

  • packet() :: #diameter_packet{}.

a container for incoming and outgoing Diameter messages. 🎁

🔥 FUNCTIONS 🔥

  • decode(Mod, Bin) -> Pkt
decode(Mod, Bin) -> Pkt
                when
                    Mod :: dictionary(),
                    Bin :: binary(),
                    Pkt :: packet().

Decode a Diameter message. that's it, that's the job. decode and thrive. ✨

  • encode(Mod, Msg) -> Pkt
encode(Mod, Msg) -> Pkt
                when
                    Mod :: dictionary(),
                    Msg :: message() | packet(),
                    Pkt :: packet().

Encode a Diameter message. the remix. the return. 🔥

okay that's the whole page bestie, you ate this 💅 this was brought to you by Ericsson AB, rockin' diameter 2.7.2, and it's diameter_codec(3), dated and everything — so go forth, decode, encode, and be iconic. periodt. 👑💖🦋

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