Crack the standard header
Every FIX message on the wire starts the same way. Before business logic, train your eyes on the standard header.
8=FIX.4.4|9=128|35=A|49=ALICE|56=BOB|34=1|52=20260629-08:00:00|98=0|108=30|10=142|
| Piece | Tag | Here |
|---|---|---|
| Version | 8 | FIX.4.4 |
| Body length | 9 | 128 |
| Type | 35 | A (Logon) |
| Who sent | 49 | ALICE |
| Who receives | 56 | BOB |
| Sequence | 34 | 1 |
| Time | 52 | sending time |
Detective note — If
49and56are swapped, the message is for the wrong party. Session may still parse; business will not match your books.