Wire Formats

Real hosts exchange bytes, often with a binary bitmap, packed BCD numbers or EBCDIC text. iso8583sim.wire converts between the two.

from iso8583sim.core.builder import ISO8583Builder
from iso8583sim.core.parser import ISO8583Parser
from iso8583sim.core.samples import sample_message
from iso8583sim.wire import WireFormat

data = ISO8583Builder().build_bytes(sample_message(), WireFormat.bcd())   # bytes, 63 long
message = ISO8583Parser().parse_bytes(data, WireFormat.bcd())             # ISO8583Message

Decoded messages have the same field values the string parser gives, so validation, explain, conversion and the rest work on them unchanged. The same functions are available directly as iso8583sim.wire.encode_message and decode_message.

Presets

Preset	MTI	Bitmap	Lengths	Numbers	Text	Binary fields	Typical use
`WireFormat.ascii_hex()`	ASCII	hex text	ASCII	ASCII	ASCII	hex text	Exactly `build()` output as bytes
`WireFormat.ascii_binary()` (default)	ASCII	binary	ASCII	ASCII	ASCII	raw	Many host links
`WireFormat.bcd()`	BCD	binary	BCD	BCD	ASCII	raw	POS terminal links
`WireFormat.ebcdic()`	EBCDIC	binary	EBCDIC	EBCDIC	EBCDIC	raw	IBM mainframe hosts

WireFormat.preset("bcd") looks a preset up by name.

Custom formats

Every part is configurable:

from iso8583sim.wire import Encoding, WireFormat

fmt = WireFormat(
    mti=Encoding.BCD,
    bitmap="binary",               # or "hex"
    length_prefix=Encoding.BINARY, # ASCII, EBCDIC, BCD or BINARY
    numeric=Encoding.BCD,          # ASCII, EBCDIC or BCD
    text=Encoding.ASCII,           # ASCII or EBCDIC
    binary_fields="raw",           # or "hex"
    ebcdic_codec="cp037",          # cp037 (US/Canada) or cp500 (international)
    bcd_odd_padding="right",       # odd-length variable BCD: "left" (leading 0) or "right" (trailing F)
)

Rules worth knowing:

BCD packs two digits per byte. An LLVAR BCD length is one byte, an LLLVAR length two bytes. The length counts digits, not bytes.
Odd digit counts need a filler nibble. Fixed numeric fields always get a leading 0. For variable fields, networks differ, so bcd_odd_padding chooses a leading 0 or a trailing F.
Track 2 (field 35) uses = as a separator, which BCD writes as the nibble D.
Content types. Fields 2, 32, 33, 99 and 100 are numeric, fields 35 and 36 are track data, and field 55 (EMV) is binary. Other variable fields are text.

Accuracy

The encodings are tested against the independent pyiso8583 library configured the same way, and every preset round-trips every field type. Length headers and TPDUs for sending over TCP are covered separately.

Get started

Core

Card networks

Tools and interfaces

LLM features

Architecture

Operations

Presets

Custom formats

Accuracy

​Presets

​Custom formats

​Accuracy

Presets

Custom formats

Accuracy