RegexByteOffsetAsCharacterOffset

warning native on by default

Group: Probable bugs

Detect a PREG_OFFSET_CAPTURE byte offset flowing into the start argument of mb_substr or grapheme_substr for the same proven string value.

Example

<?php
preg_match('/x/u','ñx',$m,PREG_OFFSET_CAPTURE); echo mb_substr('ñx',$m[0][1],1);

Reported:

• line 2: Convert byte offsets before using character-based slicing.

Detection

• Report a PREG_OFFSET_CAPTURE byte offset flowing into the start argument of mb_substr or grapheme_substr for the same proven string value.
• Resolve builtin calls and named arguments before checking the contract. Project-local callees are considered only when their bodies or immutable summaries establish the required facts. The default is enabled, with positive proof required.
• For flow-dependent conditions, require a reachable source-to-use path with no intervening invalidation. Unknown calls, ambiguous aliases, recursion or analysis-budget exhaustion cannot establish definite facts.

Exceptions (no report)

• Explicit byte-to-character conversion, ASCII-only strings, byte-based substr and unknown identities are excluded.
• Unresolved targets, incomplete required facts, suppressed findings and PHP versions lacking the referenced API or language feature produce no report. User declarations shadowing builtin names are not builtin contracts.

Fix

No automatic fix: the caller must choose character offset conversion or byte slicing.

PHP versions

Apply only on PHP versions supporting the referenced APIs and syntax (within PHP 5.3–8.5). Builtin behavior and argument contracts follow the configured PHP version. Extension-specific calls require resolved extension API symbols; do not treat same-named application functions as extension calls.

Options

None. Enable or disable this rule through normal rule configuration.

Configure

In custos.json:

{
  "rules": {
    "RegexByteOffsetAsCharacterOffset": {
      "enabled": false
    }
  }
}

Suppress

Before the statement or declaration (or the first statement of the file):

// @custos-ignore RegexByteOffsetAsCharacterOffset