trim

The trim transform strips characters from one end (or both ends) of a token. It is a literal, single-pass operation — not a character-class match — and runs against whichever end (or both) the configured mode targets.

• Transform type name (config/API): trim
• Shorthand format: trim(type=...,value=...)

Quick Start

Strip a fixed prefix:

"type": "trim",
"config": {
    "type": "left",
    "value": "REQID_"
}

Strip surrounding whitespace:

"type": "trim",
"config": {
    "type": "spaces"
}

How It Works

trim does all of its work in the first phase. The second phase is a no-op — the trimmed value is passed through to whatever the next transform produces, and the chain does not re-attach the stripped portion.

type	Behavior
left	If the token starts with value, remove that exact prefix once. Otherwise return the token unchanged.
right	If the token ends with value, remove that exact suffix once. Otherwise return the token unchanged.
spaces	Remove all leading and trailing Unicode whitespace characters. value is ignored.

The trimmed output replaces the value in the chain. Because nothing puts the stripped portion back, what gets trimmed off is lost — there is no automatic round-trip to the original token. If you need the surrounding text preserved, use regex instead.

Configuration

"type": "trim",
"config": {
    "type": "<left|right|spaces>",
    "value": "<prefix or suffix>"
}

Parameter	Required	Default	Description
type	No	spaces	Trim mode: left (prefix), right (suffix), or spaces (whitespace). An unrecognized value fails chain initialization.
value	No	" " (single space)	The literal string to strip. Ignored when type=spaces.

Examples

Example 1 — Strip an ID prefix

req_body() → json_path(path="requestId") → trim(type=left, value="REQID_")

• REQID_abc123 → abc123
• abc123 → abc123 (no prefix; unchanged)

Example 2 — Strip a token suffix before re-issuing

http_req_header(header="X-Custom-Token") → trim(type=right, value="_TOKEN")

• user_session_12345_TOKEN → user_session_12345

Example 3 — Normalise a message field's whitespace

res_body() → json_path(path="message") → trim(type=spaces)

• " Welcome to our API service " → "Welcome to our API service"

Example 4 — Combine with smart_replace

smart_replace() → http_req_header(header="Authorization") → trim(type=left, value="Bearer ") → jwt_resign(...)

Strip Bearer so jwt_resign receives the raw JWT. Use this only when jwt_resign's own prefix handling isn't sufficient — jwt_resign strips and re-prepends Bearer natively (see jwt_resign).

Common Misconceptions

1. "value is a character class." No. trim(type=left, value="abc") strips the literal three-character prefix abc, not any of a, b, or c. Use regex for character-class trimming.

2. "It strips repeated occurrences of the prefix/suffix." No. The prefix or suffix is removed only once per run. Bearer Bearer foo with value="Bearer " becomes Bearer foo, not foo.

3. "spaces strips ASCII spaces only." It strips all Unicode whitespace characters — tabs, newlines, non-breaking space, etc.

4. "The original prefix/suffix is restored downstream." No. Insert is a no-op. Whatever the chain produces gets written back to the extracted field without the trimmed portion. If you need the surrounding text preserved, use regex with a capture group on the inner portion.

Troubleshooting

Symptom	Likely cause	Fix
Chain init: unknown trim type ...	type is set to something other than left, right, or spaces	Use one of the three valid values
Field unchanged after the transform	The prefix/suffix didn't match exactly	Check for extra whitespace, case mismatch, or a different surrounding character
Only one occurrence stripped from a repeated prefix	This is the documented behavior	Add another trim in the chain, or switch to regex
Bearer prefix appears in re-signed token	jwt_resign already handles Bearer ; a manual trim may be unnecessary	Remove the trim and let jwt_resign's prefixes config handle it

Related Transforms

• regex — for character-class or pattern-based stripping, or when the surrounding context must be re-inserted.
• replace — for general literal-to-literal substitution rather than edge stripping.
• jwt_resign — already handles Bearer / JWTBearer prefixes internally.