Lookahead & lookbehind

The optional alcatraz/lookaround module handles rules that need (?<=…), (?=…), (?!…) or backreferences, such as regexes supplied in a config file. It is a separate module, so importing it is the only way to pull in the backtracking engine (dlclark/regexp2); the Alcatraz core stays dependency-free and linear-time.

go get github.com/hoophq/alcatraz/lookaround   # regexp2 only for importers of this package

import "github.com/hoophq/alcatraz/lookaround"

// One call turns user-configured regex rules into a recognizer.
rec, err := lookaround.NewRecognizer("Secret", "API_SECRET", "en",
    lookaround.Spec{Name: "bearer", Regex: `(?<=Bearer )[A-Za-z0-9._-]{8,}`, Score: 0.95},
    lookaround.Spec{Name: "domain", Regex: `(?<=@)(\w+)\.com`, Score: 0.6, Group: 1},
)
reg.Add("en", rec)

ReDoS bound

Backtracking has no linear-time guarantee, so every compiled matcher carries a MatchTimeout (default 1s) to bound catastrophic backtracking (ReDoS); set your own with CompileWithTimeout. Matches report byte offsets in the same form as the core, so results feed the same Engine with no conversion.

Before you reach for this

Two pure-Go alternatives cover most cases without a backtracking engine: a context validator and a capture-group span. See Custom recognizers.