#35903 contrib: fix crash in message-capture-parser.py on non-printable msgtype

• Prevent message capture parser crashes when encountering unprintable message types
• Ensure developers analyzing network traffic can parse full capture files without losing output

Fixes an unhandled TypeError crash in `contrib/message-capture/message-capture-parser.py` when encountering unprintable message types in capture files. The script previously called `raise UnicodeDecodeError` with no arguments inside a try block expecting 5 constructor arguments. The patch replaces the flawed exception raise with an inline printability check, falling back to labeling the message type as "UNREADABLE".

Problem: When parsing a message capture file containing non-printable message types, `message-capture-parser.py` crashes on a TypeError before writing any output. Developers analyzing p2p traffic lose the entire parse of a capture file if a single message has an unprintable type.

P4 · bug fix

• P4 because message capture parsing is a niche developer script with low overall usage
• Fixes a genuine script crash but only impacts developers inspecting traffic captures

P4 because `message-capture-parser.py` is a niche developer script, and tooling priorities rank single-user and niche contrib scripts lowest. The patch fixes a genuine TypeError bug where `raise UnicodeDecodeError` was called without parameters.

Membership: Modifies `contrib/message-capture/message-capture-parser.py`, a developer helper script under contrib.

Factors: security/stability 0, bug 1, performance 0, user value 1, leverage 0

• Ready to review because the change is tiny and CI passes

The change is tiny, CI is green, and no code changes are pending.

Author status: silent since opening PR on 2026-08-05

Open concerns:

• sedited questioned whether the bug is still reachable after #35958 aligned v2 message validation with v1 range

• No formal reviews or approvals yet
• Questioned whether the crash remains reachable after recent message validation changes (sedited)

No reviews yet; sedited asked whether the crash remains reachable after #35958

No reviewer has reviewed or ACKed the PR. A single clarifying question on applicability was asked without an evaluation of the patch.

• sedited: 'Is this still relevant after #35958?'

Review verdicts (DrahtBot): 0

6 lines under test/bench/ci.

• contrib/message-capture/message-capture-parser.py +2/-4

This PR fixes a crash in `contrib/message-capture/message-capture-parser.py` when handling non-printable message types. The script previously attempted to raise `UnicodeDecodeError` without constructor arguments, triggering an unhandled `TypeError` that aborts the parse and discards all output. The change replaces the raise with a safe inline printability fallback to label the message type as UNREADABLE. It addresses a narrow bug in a niche diagnostic script under contrib and has received no reviews beyond a question regarding whether #35958 makes the condition unreachable.