-- This schema specifies binary encoding of EMQX's internal
-- representation of a message.
--
-- Note: MQTT standard specifies that certain properties like topic
-- should be UTF8 strings. Here we represent them as OCTET STRING to
-- avoid extra checks.

DurableMessage DEFINITIONS AUTOMATIC TAGS ::=
BEGIN
  -- Non-standard flag:
  MiscFlag ::= SEQUENCE {
    key UTF8String,
    value BOOLEAN
  }

  -- Non-standard header or property.
  -- Both key and value are interpreted as erlang terms:
  MiscProperty ::= SEQUENCE {
    key OCTET STRING,
    value OCTET STRING
  }

  ClientAttr ::= SEQUENCE {
    key OCTET STRING,
    value OCTET STRING
  }

  -- Wrapper for any data that doesn't comply with the strict schema:
  Misc ::= CHOICE {
    flag MiscFlag,
    header MiscProperty,
    property MiscProperty,
    -- Currently these are unused:
    clientAttr ClientAttr,
    extra MiscProperty
  }

  -- Both key and value are interpreted as binaries:
  UserProperty ::= SEQUENCE {
    key OCTET STRING,
    value OCTET STRING
  }

  -- Common properties that are present in almost any message:
  StdProperties ::= SEQUENCE {
    payloadFormatIndicator INTEGER (0..255) OPTIONAL,
    messageExpiryInterval INTEGER (0..4294967295) OPTIONAL,
    responseTopic OCTET STRING OPTIONAL,
    correlationData  OCTET STRING OPTIONAL,
    contentType OCTET STRING OPTIONAL,
    userProperty SEQUENCE OF UserProperty
  }

  ProtoVer ::= CHOICE {
    mqtt INTEGER(0..255),
    mqtt-sn INTEGER(0..255),
    coap INTEGER(0..255)
  }

  -- Common headers that are present in almost any message:
  StdHeaders ::= SEQUENCE {
    protoVer ProtoVer OPTIONAL,
    peerhost OCTET STRING (SIZE(4..16)) OPTIONAL, -- IPv4 (4 octets) .. IPv6 (16 octets)
    peername OCTET STRING (SIZE(6..18)) OPTIONAL, -- IPv4 (4 octets) .. IPv6 (16 octets) + 2 octets for (TCP/UDP) port
    username OCTET STRING OPTIONAL
  }

  From ::= CHOICE {
    atom UTF8String,
    binary OCTET STRING
  }

  DurableMessage ::= SEQUENCE {
    id OCTET STRING,
    from From,
    topic OCTET STRING,
    payload OCTET STRING,
    timestamp INTEGER,
    qos INTEGER (0..2),
    -- MQTT PUBLISH flags:
    sys BOOLEAN,
    dup BOOLEAN,
    retain BOOLEAN,
    -- Headers:
    headers StdHeaders,
    properties StdProperties,
    -- Miscellaneous, highly EMQX-specific internal data:
    misc SEQUENCE OF Misc OPTIONAL
  }
END