BitLogger/docs/api/prefix-message.md

name, group, category, update-time, description, key-word

name	group	category	update-time	description	key-word
prefix-message	api	patching	20260512	Create a reusable record patch that prepends text to the message.	patch message transform public

Prefix-message

Create a RecordPatch that prepends a fixed prefix to rec.message. This helper is useful for tagging records with stable context without changing every call site.

Interface

pub fn prefix_message(prefix : String) -> RecordPatch {}

input

• prefix : String - Text inserted before the original message.

output

• RecordPatch - Patch that returns a record whose message starts with prefix.

Explanation

Detailed rules explaining key parameters and behaviors

• The patch preserves the original message content after the inserted prefix.
• It does not touch target, level, timestamp, or fields.
• This helper is useful for environment tags, subsystem labels, and compatibility shims.
• When combined with other patches, composition order controls whether the prefix is applied before or after other message rewrites.

How to Use

Here are some specific examples provided.

When Add A Stable Channel Marker

When console output should show one visible label:

let logger = Logger::new(console_sink())
  .with_patch(prefix_message("[worker] "))

In this example, every emitted message starts with [worker] .

When Compose With Redaction

When records need both labeling and field protection:

let patch = compose_patches([
  prefix_message("[safe] "),
  redact_field("token"),
])

In this example, message text is rewritten while fields remain independently patchable.

Error Case

e.g.:

• If prefix is empty, the patch behaves like a pass-through message rewrite.

• If several patches prepend text, the final message reflects composition order.

Notes

1. Prefer this helper over concatenating prefixes at every log call site.

2. Keep prefixes short so they do not drown out the original message text.