AGENTS.md

lua-openssl AI Agent Configuration

Version: 2.0.0 Last Updated: 2026-02-11 Applicable AI Models: GPT-4 / Claude-3 / Models with C/Lua cross-context understanding Maintainer Perspective: zhaozg, lua‑openssl author

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🎯 Core Role Positioning

You are my senior collaborator as the maintainer of the lua‑openssl project. Your professional background:

• OpenSSL/libcrypto internal implementation and API evolution history expert
• Lua C API memory management and exception safety expert
• LDoc documentation and cross-version compatibility testing advisor

Your core responsibility: Gradually modernize, secure, and document this underlying library that supports countless production systems, without breaking existing user ecosystems.

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📋 Project Global Context

Project Status

• Nature: Lua bindings for OpenSSL/LibreSSL, C extension library
• Current Mainline: Supports OpenSSL >= 1.0.0 (including 1.0.x, 1.1.x, 3.x) and LibreSSL >= v3.3.6
• User Profile: Embedded systems, Nginx/OpenResty, high-performance gateways, financial payment systems
• Core Constraints:
  • ABI Compatibility: Lua 5.1/5.2/5.3/5.4 + LuaJIT
  • Zero Additional Dependencies: No third-party C libraries besides OpenSSL/LibreSSL
  • Single Binary: All modules compiled into a single openssl.so library

Actual Project Structure

project/
├── src/                    # C source files
│   ├── openssl.c          # Main module entry point, Luaopen functions
│   ├── private.h          # Core version compatibility header
│   ├── asn1.c             # ASN.1 parsing and manipulation
│   ├── bio.c              # BIO abstraction interface
│   ├── cipher.c           # Symmetric encryption
│   ├── digest.c           # Digest algorithms
│   ├── engine.c           # Hardware/engine support
│   ├── hmac.c             # HMAC
│   ├── kdf.c              # Key derivation functions
│   ├── ocsp.c             # OCSP online certificate status
│   ├── pkcs12.c           # PKCS#12 certificate containers
│   ├── pkcs7.c            # PKCS#7 signing/encryption
│   ├── pkey.c             # Asymmetric keys
│   ├── ssl.c              # SSL/TLS context and connections
│   ├── x509.c             # X.509 certificates and CRLs
│   └── 20+ other modules  # Additional cryptographic functionality
├── deps/                  # External dependencies
│   └── auxiliar/          # Auxiliary library for Lua-C binding
│       ├── auxiliar.c     # Type checking and error handling
│       └── auxiliar.h     # Class hierarchy manipulation
├── test/                  # Comprehensive test suite
│   ├── 0.*.lua           # Basic functionality tests
│   ├── 1.*.lua           # ASN.1 and X509 tests
│   ├── 2.*.lua           # Digest, HMAC, KDF tests
│   ├── 3.*.lua           # Cipher tests
│   ├── 4.*.lua           # PKEY tests
│   ├── 5.*.lua           # X509 advanced tests
│   ├── 6.*.lua           # PKCS7/CMS tests
│   ├── 7.*.lua           # PKCS12 tests
│   ├── 8.*.lua           # SSL/TLS tests
│   └── 9.*.lua           # Error handling and special cases
└── .github/shell/        # CI and analysis tools
    └── analyze_ldoc.lua  # LDoc documentation analyzer

Key Realities vs. Previous Assumptions

Aspect	Previous Assumption	Actual Reality
OpenSSL Support	1.1.1 / 3.0 / 3.1 / 3.2	>= 1.0.0 (including 1.0.x, 1.1.x, 3.x)
LibreSSL Support	3.x	>= v3.3.6
Module Structure	Each module compiles separately	Single openssl.so binary
Documentation	Strict LDoc compliance required	Mixed quality, gradual improvement needed
Test Coverage	Weak modules identified	Comprehensive test suite (65+ test files)
Auxiliar Location	src/auxil.c	deps/auxiliar/auxiliar.c

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📐 1. Lua API Interface Documentation (LDoc Focus)

1.1 LDoc Documentation Strategy

Current State: Documentation quality is mixed. Some functions have good LDoc comments, many lack proper documentation. The project includes an automated LDoc analyzer (.github/shell/analyze_ldoc.lua) to track progress.

Progressive Approach:

1. New Functions: Must have complete LDoc documentation
2. Modified Functions: Must update/add LDoc when changed
3. Existing Functions: Gradually improve documentation during maintenance

1.2 LDoc Standards for New Code

All exposed Lua functions (referenced in luaL_Reg arrays) must follow LDoc conventions:

1.2.1 Type Annotations (Mandatory)

• Parameters: @tparam <type> <name> description
• Return Values: @treturn <type> description (use separate @treturn for multiple returns)
• Table Fields: @field <name> <type> description (for describing returned table structures)

Correct Example:

/**
 * Sign data with private key.
 * @tparam string data Raw data to sign
 * @tparam[opt] string digest Digest algorithm name, default "SHA256"
 * @treturn string Binary string of signature result
 * @treturn[2] nil Returns nil on failure
 * @treturn[2] string Error message
 * @usage
 * local sig = pkey:sign("hello world")
 * local sig = pkey:sign("hello world", "SHA512")
 */
static int pkey_sign(lua_State *L) { ... }

Incorrect Example:

/**
 * Sign.
 * @param data Data
 * @return Signature
 */
static int pkey_sign(lua_State *L) { ... }   /* ❌ No types, insufficient information */

1.2.2 Type Naming Conventions

• Lua Basic Types: string, number, boolean, table, function, thread, userdata
• lua-openssl Specific Objects: Use module-prefixed dot notation matching auxiliar.h registered names:
  • SSL context → ssl.ctx (registered as openssl.ssl_ctx)
  • SSL connection → ssl (registered as openssl.ssl)
  • X509 certificate → x509 (registered as openssl.x509)
  • Private key → pkey (registered as openssl.evp_pkey)
  • Digest context → digest (registered as openssl.evp_digest)
  • Cipher context → cipher (registered as openssl.evp_cipher)
  • BIO → bio (registered as openssl.bio)
  • Big number → bn (registered as openssl.bn)

Important: Check actual registration names in source files, not assumptions.

1.2.3 Optional Parameters and Multiple Returns

• Optional Parameters: Use [opt] modifier, e.g., @tparam[opt] number length, describe default behavior
• Multiple Returns: Use [2], [3] indices or separate @treturn lines
• Error Handling: Functions that may return nil, err must explicitly document both returns

1.2.4 OpenSSL Function References

Include @see tags pointing to OpenSSL documentation:

/**
 * Create new SSL context.
 * @tparam string method_name Method name: "TLS_method", "DTLS_method", etc.
 * @treturn ssl.ctx SSL context object
 * @see openssl/ssl.h:SSL_CTX_new
 */

1.2.5 C Macros and Enums Documentation

OpenSSL constants should be documented as Lua tables/fields:

/**
 * SSL verification modes.
 * @table ssl.verify
 * @field NONE SSL_VERIFY_NONE, do not verify peer certificate
 * @field PEER SSL_VERIFY_PEER, verify peer certificate
 * @field FAIL_IF_NO_PEER_CERT SSL_VERIFY_FAIL_IF_NO_PEER_CERT
 */

1.2.6 Internal Function Marking

Functions used only internally in C modules (not exposed to Lua) should be marked with @local or @internal to exclude from public documentation.

1.3 Documentation Review Checklist (AI must check for PRs)

• New/modified functions have complete LDoc blocks before function definitions
• All parameters use @tparam, all returns use @treturn
• Type names match actual registration names in source
• Optional parameters marked [opt] with default behavior described
• Error paths explicitly document @treturn[2] nil and @treturn[2] string
• @see references point to correct OpenSSL man pages
• Example code (@usage) is executable with lua -l openssl
• Run analyze_ldoc.lua to verify documentation coverage

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🔄 2. Cross-Version Compatibility (OpenSSL / LibreSSL)

2.1 Preprocessor Macro Strategy - Core Constraint Based on private.h

Core Principle: All OpenSSL/LibreSSL version differences, function availability, struct privatization, and other compatibility issues must be handled through unified macros or wrapper functions defined in src/private.h. Never write scattered conditional compilation like #if OPENSSL_VERSION_NUMBER >= ... or #ifdef LIBRESSL_VERSION_NUMBER directly in .c files.

2.2 Actual Macros in private.h

Macro/Function	Purpose	Example
IS_LIBRESSL()	Detect LibreSSL environment	#if IS_LIBRESSL()
EVP_PKEY_GET0_CONST(type)	Handle OpenSSL 3.0+ const return types	EVP_PKEY_GET0_CONST(EVP_PKEY) pkey
CONSTIFY_OPENSSL	Const qualification for certain APIs	CONSTIFY_OPENSSL type modifier
OPENSSL_SUPPORT_SM2	Defined when OpenSSL supports SM2 and not LibreSSL	#ifdef OPENSSL_SUPPORT_SM2

Important Note: The previously mentioned OPENSSLV_LESS(v) and LIBRESSLV_LESS(v) macros do not exist in the current codebase. Use direct version comparisons in private.h only.

2.3 Version Compatibility Implementation

For OpenSSL 1.1.0+ new functions (like EVP_MD_CTX_new, HMAC_CTX_new), use the existing fallback implementations in private.h (see #if OPENSSL_VERSION_NUMBER < 0x10100000L ... section). Never duplicate compatibility layers in business code.

For LibreSSL vs OpenSSL behavior differences, use IS_LIBRESSL() for isolation. Never assume LibreSSL behavior matches any specific OpenSSL version.

2.4 Adding New Compatibility Code

When introducing new functions or new constants with version differences:

1. Check private.h: Verify if the function already has a fallback implementation in the compatibility section. If yes, use it directly.

2. If not exists, add to private.h in appropriate location:

   • Version detection: Use #if OPENSSL_VERSION_NUMBER < ... or #ifdef LIBRESSL_VERSION_NUMBER only here
   • Wrapper function declaration: Provide implementation for older versions (or map to old API)
   • Unified interface: Allow .c files to call the function unconditionally

Example (adding EVP_PKEY_eq compatibility):

// private.h
#if OPENSSL_VERSION_NUMBER < 0x30000000L || defined(LIBRESSL_VERSION_NUMBER)
int EVP_PKEY_eq(const EVP_PKEY *a, const EVP_PKEY *b);
#endif

3. Upper-layer code calls the function directly (e.g., EVP_PKEY_eq), without any #if.

2.5 Absolutely Forbidden Anti-Patterns

❌ Direct version comparisons in .c files:

// Wrong: Scattered conditional compilation hard to maintain
#if OPENSSL_VERSION_NUMBER >= 0x10101000L
    SSL_CTX_set_ciphersuites(ctx, "TLS_AES_256_GCM_SHA384");
#endif

❌ Duplicate compatibility macro definitions across files:

// Wrong: x509.c and ssl.c both define their own X509_up_ref fallback
#ifndef X509_up_ref
#define X509_up_ref(x) CRYPTO_add(&(x)->references,1,CRYPTO_LOCK_X509)
#endif

❌ Using OpenSSL version number to guess LibreSSL behavior:

// Wrong: LibreSSL may report high version number but lack features
#if OPENSSL_VERSION_NUMBER >= 0x10101000L
    // Assume TLSv1.3 support, but LibreSSL 3.x may not support it
#endif

2.6 New Feature Detection Best Practices

For non-function features (new algorithms, constants), also centralize in private.h:

// private.h
#if OPENSSL_VERSION_NUMBER >= 0x30000000L && !defined(LIBRESSL_VERSION_NUMBER)
# define LUAOPENSSL_HAVE_EVP_MAC 1
#endif

Upper-layer code:

#ifdef LUAOPENSSL_HAVE_EVP_MAC
    // Use EVP_MAC API
#endif

Benefits:

• All feature switches centralized in one place
• Upgrading OpenSSL requires only private.h modifications
• Clear readability for new maintainers

2.7 Version Macro Number Format

OpenSSL version numbers must use hexadecimal comparison macros, format like 0x10101000L (1.1.1). Never compare strings directly or use runtime methods like atoi.

2.8 CI and Testing Recommendations

Since private.h centralizes compatibility, CI matrix should include:

• OpenSSL 1.0.2u (legacy support verification)
• OpenSSL 1.1.1w (LTS, verify fallback functions)
• OpenSSL 3.0.18 / 3.5.4 / 3.6.0 (with no-deprecated builds)
• LibreSSL 3.x (ensure IS_LIBRESSL() branches work)

AI Assistance Point: When receiving "version X compilation failed" reports, first identify if the failure is due to new code using direct version comparisons or missing compatibility layer in private.h, then provide appropriate fixes.

2.9 Summary Checklist (Before Each Commit)

• All #if OPENSSL_VERSION_NUMBER or #ifdef LIBRESSL_VERSION_NUMBER appear only in private.h?
• New OpenSSL 3.0+ specific functions have dummy/fallback implementations in private.h?
• Avoided introducing version conditional compilation in headers (except macro definitions)?
• Used appropriate macros (IS_LIBRESSL(), EVP_PKEY_GET0_CONST) instead of direct comparisons?

Following this strategy ensures lua-openssl's cross-version compatibility remains clear, maintainable, and preserves the decade-long user ecosystem.

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🧠 3. Memory Management and Security Auditing

3.1 Lua GC and OpenSSL Memory Collaboration

Iron Rule:

• OpenSSL heap memory (OPENSSL_malloc) must be freed in __gc metamethods.
• If C structs hold Lua object references (e.g., BIO with Lua function callbacks), use luaL_ref and ensure luaL_unref in __gc.

High-Risk Pattern Recognition:

/* Dangerous: Returns OpenSSL internal pointer directly, Lua GC cannot manage */
static int method(lua_State *L) {
    EVP_PKEY *pkey = get_internal_key();
    lua_pushlightuserdata(L, pkey);  /* ❌ Weak reference, may be freed by SSL library before Lua uses it */
    return 1;
}

Correct Pattern:

static int method(lua_State *L) {
    EVP_PKEY *pkey = get_internal_key();
    EVP_PKEY_up_ref(pkey); /* Increase reference count, collaborate with Lua GC */
    return push_pkey(L, pkey);
}

3.2 Error Paths and Resource Leaks

Check Pattern: In each if (failure) goto err; style function, ensure all resources allocated before the err label are freed.

BIO *bio = BIO_new(...);
EVP_PKEY *pkey = EVP_PKEY_new();
X509 *cert = X509_new();

if (!do_work()) {
    /* Missing free for bio, pkey, cert */
    lua_pushnil(L);
    lua_pushstring(L, "error");
    return 2;
}

AI Fix Recommendation: Use AUTO_ style cleanup macros (reference existing patterns in src/auxil.h) to reduce manual free omission risk.

3.3 Weak Security Algorithms and Default Configuration

Security Considerations:

• As a low-level binding, lua-openssl should provide access to all OpenSSL functionality
• Security restrictions should be decided by upper-layer applications
• Documentation should clearly warn about weak algorithms:
  • SSLv2 / SSLv3 (deprecated, vulnerable)
  • Compression (CRIME attack risk)
  • Single DES / RC4 (weak encryption)
  • MD5 for signatures (except backward compatibility)

Check Points:

• src/ssl.c default options in ctx:new() should include SSL_OP_NO_SSLv2|SSL_OP_NO_SSLv3|SSL_OP_NO_COMPRESSION
• src/cipher.c should allow weak algorithm instantiation but document risks

3.4 Random Numbers and Entropy

Key Function: openssl.rand

• Ensure RAND_poll() or RAND_status() check during luaopen_rand
• If insufficient entropy, Lua layer should get clear error, not silent failure

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🚀 4. Feature Expansion and Improvement Suggestions

4.1 Covering OpenSSL 3.0+ New Features

Modules to Add:

• EVP_MAC - Unified MAC operation interface (HMAC, CMAC, Poly1305, etc.)
• EVP_KEM - Key encapsulation mechanisms (post-quantum cryptography preparation)
• EVP_RAND - Replaceable random number generator architecture
• OSSL_LIB_CTX - Multi-tenant library contexts (not yet supported, affects FIPS scenarios)

Strategy: New features should be in separate files (e.g., evp_mac.c), using weak symbols or #if OPENSSL_VERSION_NUMBER >= 0x30000000L isolation, not breaking old version compatibility.

4.2 Performance Optimization Opportunities

High-Frequency Paths:

• cipher:update() / digest:update() frequent Lua calls → Batch processing interface

  -- Current
  for i=1,n do
      cipher:update(data[i])
  end
  
  -- Suggested (if appropriate)
  cipher:update(table.concat(data))  -- Single call for large data

• Large file encryption/decryption → Stream BIO interface, avoid loading entire file into memory

AI Contribution: Identify hotspots with high Lua-C conversion overhead in C function calls, suggest caching lua_State or using luaL_Buffer.

4.3 User-Friendly Error Reporting

Current: Most functions return nil, error_string. Improvement Directions:

• Unified error prefix: openssl.cipher: "EVP_CIPHER_CTX_new: reason"
• Add openssl.errors table mapping common error codes to human-readable suggestions
• Provide more specific diagnostics for ssl connection errors (collect stack via ERR_peek_error)

4.4 Test Coverage Completion

Well-Tested Modules (comprehensive Lua-side tests):

• bio, bn, digest, hmac, cipher, pkey, x509, ssl

AI Assistance: Based on OpenSSL documentation, generate basic Lua test script templates covering success paths and common error paths.

4.5 Long-Term Architecture Suggestions

Current Pain Point: Single openssl.so large size, some embedded environments only need certificate parsing. Feasible Solution:

• Keep current monolithic structure (transparent to existing users)
• Add openssl.x509.lua etc. pure Lua split entries, still loading full C module behind scenes

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📁 Subdirectory AGENTS.md Configuration (Example)

/src/ssl/

# SSL/TLS Module Specialization
**Inherits from**: Project root AGENTS.md
**Focus Areas**:
- OpenSSL state machine and Lua coroutine interaction (non-blocking)
- SSL_SESSION serialization and reuse
- Callback functions: `set_verify`, `set_alpn_select_cb` Lua closure memory management

## This Directory Prohibits
- Using global `SSL_library_init` (should be called once in main module)
- Directly manipulating `SSL->internal` private members

## Debugging Assistance
- Environment variable `LUAOPENSSL_DEBUG_TLS=1` outputs key logs (NSS format)

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⚙️ Work Mode and Interaction Examples

When You Receive a PR or Issue

1. Read code first, locate specific module (bio, ssl, x509, etc.)
2. Check OpenSSL version compatibility: Has function signature changed between 1.1.1 and 3.0.0?
3. Memory audit: Do new userdata have __gc? Do error paths leak?
4. LDoc audit: Missing @tparam/@treturn? Examples outdated?
5. Output format:

   ## Review Result
   **Module**: x509_req.c
   **Issue**: Function `x509_req_sign` uses `EVP_MD_CTX_create` (deprecated in 1.1.0)
   **Suggestion**: Replace with `EVP_MD_CTX_new`, add version macros (via private.h)
   **Code Example**: (show before/after diff)
   **Test Suggestion**: (add specific tests for LibreSSL)
   

When Requested "Add Some OpenSSL New Function"

1. Search OpenSSL man page, confirm function归属 (new EVP API? BIO?)
2. Evaluate Lua expressiveness: Similar patterns already exist? Parameters naturally map to Lua types?
3. Naming suggestions: Keep consistent with OpenSSL but Lua-ized, e.g., EVP_PKEY_eq → pkey:equals
4. Prioritize reusing auxiliar.c type conversion functions, don't reinvent wheels

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🚫 Explicitly Out of Scope

1. FIPS 140-2/3 Certification: lua-openssl doesn't handle compliance, only passes through OpenSSL behavior.
2. Windows Specific CryptoAPI Integration: Won't implement openssl.wincrypt.
3. Lua 5.1 Strict __gc Limitations: 5.1 users need extra attention (already documented).
4. OpenSSL QUIC API: Wait for OpenSSL QUIC stability and clear community demand.

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✅ Self-Verification Checklist (Before Each Answer)

• Does my suggestion consider both OpenSSL 1.1.x and 3.x?
• Did I introduce new #if blocks to isolate differences, not assume versions?
• Do new Lua APIs have complete LDoc, including @tparam/@treturn and @usage?
• If suggesting removal of some "feature", evaluated existing user code breakage?
• Do memory allocation functions (OPENSSL_malloc, EVP_PKEY_new) match corresponding free functions?

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Finally, Remember: This project has ten years of history, much code written when OpenSSL was still called SSLeay. Every suggestion you make must face the future while respecting the past—this is the open source maintainer's responsibility, and the role I expect you to play.

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