[type: bug] Fix RewritePlugin placeholder drops first character and StringIndexOutOfBounds (#6883)

[zhang-arvin]

Fixes #6883.

Bug Description

The RewritePlugin has two bugs in its placeholder branch:

1. First character of path-variable value is dropped: rewriteUri.substring(rewriteHandle.getRegex().indexOf("{") + 1) skips the first character of the actual path-variable value because the +1 is meant to skip the { character in the regex pattern, but it's applied to the rewriteUri which has the actual value at that position.

2. StringIndexOutOfBoundsException when regex lacks {: The condition only checks rewriteHandle.getReplace().contains("{") but not rewriteHandle.getRegex().contains("{"). When the replace pattern contains { but the regex doesn't, indexOf("{") returns -1, causing substring(-1) to throw.

Fix

• Added rewriteHandle.getRegex().contains("{") to the guard condition
• Removed the +1 offset from rewriteUri.substring() to preserve the first character

[Aias00]

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[Aias00]

Review: Fix RewritePlugin placeholder drops first character (#6883)

Verdict: APPROVE

Analysis

The rewrite placeholder substitution uses PathMatchUtils.replaceAll, which performs a literal replacement:

public static String replaceAll(final String path, final String regex, final String replacement) {
    return path.replaceAll(Pattern.quote(regex), Matcher.quoteReplacement(replacement));
}

The first arg is the template (getReplace()), the second is the literal placeholder segment extracted from getRegex() (getRegex().substring(indexOf("{"))), and the third is the actual value extracted from rewriteUri.

Off-by-one fix (correct):

• Old: rewriteUri.substring(getRegex().indexOf("{") + 1) — dropped the first character of the captured value. E.g. for rewriteUri = /shenyu/123 with the {...} placeholder starting at index i, this produced 23 instead of 123.
• New: rewriteUri.substring(getRegex().indexOf("{")) — keeps the full captured segment. This matches the prior fix in #6951 and is consistent.

New crash guard (defensive, good):

• Old condition only checked getReplace().contains("{"). If getReplace() contained { but getRegex() did not, then getRegex().indexOf("{") returned -1, and substring(-1) threw StringIndexOutOfBoundsException.
• New condition getReplace().contains("{") && getRegex().contains("{") routes the no-placeholder case to the safe rewriteUri.replaceAll(getRegex(), getReplace()) branch, eliminating the crash.

Conclusion

Minimal, correct, and aligns with the existing placeholder handling. No behavioral regression for the normal (no-placeholder) path. Approving.