Architecture

Module Overview

LiteHTTPD is an LSIAPI module (litehttpd_htaccess.so) that hooks into OpenLiteSpeed at two request lifecycle phases. The same .so binary is used in both editions: LiteHTTPD-Thin runs on stock OLS and provides all directives except RewriteRule execution and php_value passthrough. LiteHTTPD-Full runs on patched OLS (via openlitespeed-litehttpd RPM) and adds RewriteRule execution, php_value/php_flag, Options -Indexes 403, and readApacheConf. The module detects patch availability at runtime via NULL pointer checks on the extended LSIAPI function pointers.

Client Request
    |
    v
+-------------------+
| OLS Engine        |
|  PROCESS_NEW_URI  |
|  VHOST_REWRITE    |
|  CONTEXT_MAP      |
+-------------------+
    |
    v
+-------------------+     +------------------+
| URI_MAP Hook      | --> | mod_htaccess.c   |
| (Request Phase)   |     |  on_uri_map()    |
+-------------------+     +------------------+
    |                           |
    |    +----------------------+
    |    | htaccess_dirwalk()
    |    | -> parse .htaccess files
    |    | -> merge directives
    |    | -> AllowOverride filter
    |    +----------------------+
    |                           |
    |    Execute request-phase directives:
    |    - ACL (Order/Allow/Deny)
    |    - Auth (AuthType/Require)
    |    - Redirect/RedirectMatch
    |    - RewriteRule (via OLS engine)
    |    - PHP config (php_value/flag)
    |    - SetEnv/SetEnvIf
    |    - Options
    |    - If/ElseIf/Else chains
    |
    v
+-------------------+
| OLS Engine        |
|  FILE_MAP         |
|  PHP Processing   |
+-------------------+
    |
    v
+-------------------+     +------------------+
| SEND_RESP_HEADER  | --> | mod_htaccess.c   |
| (Response Phase)  |     | on_send_resp()   |
+-------------------+     +------------------+
    |                           |
    |    Execute response-phase directives:
    |    - Header set/unset/append/merge
    |    - If/ElseIf/Else (response children)
    |    - Expires/Cache-Control
    |    - AddType/ForceType/AddCharset
    |    - ErrorDocument
    |
    v
  Response to Client

Source File Organization

Core Module

File	Purpose	LOC
`mod_htaccess.c`	LSIAPI entry point, hooks, directive dispatch	~1900
`htaccess_parser.c`	Apache .htaccess syntax parser	~2500
`htaccess_dirwalker.c`	Directory walk, merge, AllowOverride	~1000
`htaccess_cache.c`	LRU cache for parsed directives	~300
`htaccess_directive.c`	Directive data structures and free	~200
`htaccess_expr.c`	ap_expr expression evaluator	~800
`htaccess_printer.c`	AST to text serialization	~400
`lsiapi_shim.c`	LSIAPI function wrappers	~400

Executor Modules (one per directive category)

File	Handles
`htaccess_exec_acl.c`	Order, Allow, Deny
`htaccess_exec_auth.c`	AuthType, AuthName, AuthUserFile, Require valid-user
`htaccess_exec_header.c`	Header, RequestHeader (all variants)
`htaccess_exec_redirect.c`	Redirect, RedirectMatch, ErrorDocument
`htaccess_exec_rewrite.c`	RewriteEngine, RewriteRule, RewriteCond
`htaccess_exec_expires.c`	ExpiresActive, ExpiresByType, ExpiresDefault
`htaccess_exec_require.c`	Require all/ip/env, RequireAny/All
`htaccess_exec_env.c`	SetEnv, SetEnvIf, BrowserMatch
`htaccess_exec_php.c`	php_value, php_flag
`htaccess_exec_options.c`	Options
`htaccess_exec_limit.c`	Limit, LimitExcept
`htaccess_exec_files_match.c`	FilesMatch
`htaccess_exec_handler.c`	AddHandler, SetHandler (no-op)
`htaccess_exec_forcetype.c`	ForceType
`htaccess_exec_encoding.c`	AddType, AddEncoding, AddCharset
`htaccess_exec_brute_force.c`	LSBruteForce*

Caching Strategy

LiteHTTPD uses a multi-level caching strategy:

File-level cache (htaccess_cache.c) — parsed directive trees cached by file path + mtime + st_blocks
Request-level cache (req_cache) — thread-local cache storing directives between URI_MAP and SEND_RESP_HEADER hooks for the same request
Rewrite handle cache (rw_cache) — thread-local cache for compiled RewriteRule handles, keyed by directive fingerprint
Negative stat cache — thread-local cache of non-existent .htaccess paths to avoid repeated stat() calls

Thread Safety

All caches use __thread (thread-local storage) — no locks needed
OLS uses multi-process, single-thread-per-process architecture
The module is reentrant within a single worker process