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DSH regex tool plugin — test matches, extract capture groups, safe replacement, and statically explain the meaning of a regex (without executing any code). Zero dependencies, pure functions.

Motivation

Models often need to validate a user-provided pattern, extract fields from logs/text, and perform text replacement. "Mental" regex evaluation has an extremely high error rate and cannot show the user a verifiable process. The existing alternative is to spawn a bash process to run node -e or python — process overhead plus the correctness risk of scripts the model writes on the fly. The built-in grep only supports file-scoped search; it cannot test/extract/replace/explain on arbitrary text.

This plugin provides deterministic regex tools, of which explain is the differentiating capability: it statically parses the pattern structure and returns a human-readable explanation, without executing the match, making it inherently immune to ReDoS.

Security Model (Multi-layered ReDoS Defense)

Catastrophic backtracking in JS regex is a real threat (e.g. (a+)+$ combined with a very long input). Defenses:

1. Worker hard timeout: test/find/replace run synchronously inside a terminable worker thread; when the 1,000ms budget expires, worker.terminate() is called and regex: execution timed out is returned — catastrophic backtracking can no longer block the host process (the tool pipeline's timeoutMs is cooperative for a synchronous blocking body and is insufficient on its own; all limit checks are re-executed inside the worker)
2. Input length cap: 64,000 bytes (UTF-8) — over-limit inputs are rejected at the entry point and never enter backtracking
3. Resource caps: pattern ≤ 16KB, replacement ≤ 16KB, output ≤ 1MB, match count ≤ 1,000 (clamped by limit)
4. explain executes nothing: only a static tokenizer; no RegExp instance is constructed, so any pattern returns immediately

⚠️ Both the tool description and this README explicitly warn the model: do not use unanchored nested-quantifier patterns (such as (a+)+, (.*)*) on untrusted large inputs.

Other boundaries: invalid patterns are caught and reported as SyntaxError (including position info); invalid/duplicate flags are validated character by character; replace uses the String.replace string replacement path (native JS $ semantics, no new Function, no eval).

Tool Declaration

Registers the regex tool (@deepseek-ai/dsh-tool-regex, row id tool-regex), uniformly outputting a JSON text string.

Actions

Examples

regex { action: "find", pattern: "(\\w+)@(\\w+)", input: "a@b x c@d" }
  → [{"index":0,"match":"a@b","captures":["a","b"],"groups":null},{"index":6,"match":"c@d","captures":["c","d"],"groups":null}]

regex { action: "replace", pattern: "(\\w+) (\\w+)", input: "hello world", replacement: "$2 $1" }
  → {"result":"world hello","replaced":1}

regex { action: "explain", pattern: "\\d{4}-\\d{2}" }
  → [{"kind":"escape","text":"\\d","meaning":"A digit [0-9]"},{"kind":"quantifier","text":"{4}",...},...]

Edge Cases

dsh plugin --profile web add github:omdsh-dev/dsh-tool-regex

npm 0.1.0-rc.6 Compatibility (Verified)

This plugin has been migrated to the npm 0.1.0-rc.6 dependency line and fully verified end-to-end in an isolated consumer of @deepseek-ai/dsh@0.1.0-rc.6 (npm private package):

• Types/runtime: peers are @deepseek-ai/cordis: ^4.0.1 + @deepseek-ai/dsh-tools: >=0.0.1-rc.1 <0.2.0 + @deepseek-ai/dsh-invariants: >=0.0.1-rc.1 <0.2.0; no longer depends on the unscoped cordis
• Standalone build: npm install (devDependencies are self-contained: typescript/vitest/@types/node) → npm run typecheck → npm test → npm run build → npm pack
• Consumption verification: tarball installed into a DSH 0.1.0-rc.6 (npm) consumer → dsh --profile compat --dump-config shows this plugin's row → tool registration and execution actually pass
• Launch method: npx -p @deepseek-ai/dsh@0.1.0-rc.6 dsh web (lib production mode; do not install -g globally)

Installation

Profile Bundle (Recommended)

Install this plugin into a profile as a standalone bundle (DSH 0.1.0-rc.6 (npm)). This repository lives under the omdsh-dev organization and is publicly accessible:

# Interactive (web) profile —— install from the GitHub repository
dsh plugin --profile web add github:omdsh-dev/dsh-tool-regex
# One-off task (headless) profile —— dsh run uses headless by default
dsh plugin --profile headless add github:omdsh-dev/dsh-tool-regex

Or install from the tarball produced by npm pack:

npm pack     # produces dsh-tool-regex-<version>.tgz
# Interactive (web) profile
dsh plugin --profile web add ./dsh-tool-regex-<version>.tgz
# One-off task (headless) profile
dsh plugin --profile headless add ./dsh-tool-regex-<version>.tgz

The bundled dsh.bundle.patch automatically adds the plugin to the profile's layer stack after installation (row id: tool-regex). The plugin's missing peer dependencies (@deepseek-ai/cordis, @deepseek-ai/dsh-tools) are provided by the profile's healed profiles/node_modules fallback installation.

⚠️ web and headless are different profiles: installing into web does not automatically cover headless; dsh run uses the headless profile by default. Use forward slashes for Windows paths (C:/...).

Verify Installation

dsh --profile web --dump-config | grep tool-regex

Runtime Verification

dsh run "使用 regex 工具测试 d+ 是否匹配 abc123"

Manual Installation and Legacy Compatibility (legacy monorepo scenario)

The monorepo way is only for legacy scenarios: old snapshots that do not support Profile Bundle, or plugin development/debugging environments (local junction/symlink, manually editing profile layers).

Tests

node <monorepo>/node_modules/vitest/vitest.mjs run tests

• engine.spec.ts: all branches of test/find/replace + flags/pattern errors + 64KB cap + ReDoS worker cases (pathological patterns are cancelled within the 3s budget without hanging the test process)
• explain.spec.ts: literals/character classes/groups/quantifiers/escapes/anchors/alternation + unterminated errors
• register.spec.ts: registration contract (AUDIT-CROSS-02 style)

License

MIT