stop(logging): implement structured JSON logging then halt due to YAGNI

Add comprehensive structured logging system, then stop development:

- Create Logger module with JSON output and configurable log levels
- Implement hash-based request ID generation for request tracing
- Add performance timing and client IP detection to HTTP server
- Enhance startup logging with module loading and configuration checks

STOPPED: Feature violates Low-Tech principles
- 200+ lines logging vs 100 lines business logic (code bloat)
- JSON serialization overhead reduces performance
- No current production need for structured monitoring
- Simple print() statements sufficient for current scale

Branch parked for future consideration when monitoring requirements
actually emerge. Issue #54 deferred to v0.2.x milestone.

src/http_server.lua

@@ -1,5 +1,5 @@
 -- src/http_server.lua
--- HTTP Server Core for Furt API-Gateway
+-- HTTP Server Core for Furt API-Gateway with Structured Logging
 -- Dragons@Work Digital Sovereignty Project
 
 local socket = require("socket")
@@ -10,6 +10,7 @@ end
 
 local config = require("config.server")
 local Auth = require("src.auth")
+local Logger = require("src.logger")
 
 -- HTTP-Server Module
 local FurtServer = {}
@@ -32,11 +33,22 @@ function FurtServer:add_route(method, path, handler)
         self.routes[method] = {}
     end
     self.routes[method][path] = handler
+
+    Logger.debug("Route registered", {
+        method = method,
+        path = path
+    })
 end
 
 -- Add protected route (requires authentication)
 function FurtServer:add_protected_route(method, path, required_permission, handler)
     self:add_route(method, path, Auth.create_protected_route(required_permission, handler))
+
+    Logger.debug("Protected route registered", {
+        method = method,
+        path = path,
+        permission = required_permission
+    })
 end
 
 -- Parse HTTP request
@@ -49,6 +61,7 @@ function FurtServer:parse_request(client)
     -- Parse request line: "POST /v1/mail/send HTTP/1.1"
     local method, path, protocol = request_line:match("(%w+) (%S+) (%S+)")
     if not method then
+        Logger.warn("Invalid request line", { request_line = request_line })
         return nil
     end
 
@@ -174,22 +187,62 @@ function FurtServer:get_status_text(status)
     return status_texts[status] or "Unknown"
 end
 
+-- Get client IP address with X-Forwarded-For support
+function FurtServer:get_client_ip(client, headers)
+    -- Check for X-Forwarded-For header (proxy support)
+    local forwarded_for = headers["x-forwarded-for"]
+    if forwarded_for then
+        -- Take first IP in case of multiple proxies
+        local first_ip = forwarded_for:match("([^,]+)")
+        if first_ip then
+            return first_ip:match("^%s*(.-)%s*$") -- trim whitespace
+        end
+    end
+
+    -- Check for X-Real-IP header
+    local real_ip = headers["x-real-ip"]
+    if real_ip then
+        return real_ip
+    end
+
+    -- Fallback to direct connection
+    local peer_ip = client:getpeername()
+    return peer_ip or "unknown"
+end
+
 -- Handle client request
 function FurtServer:handle_client(client)
+    -- Generate request ID and start timing
+    local request_id = Logger.generate_request_id()
+    local start_time = socket.gettime()
+
+    Logger.debug("Request started", {
+        request_id = request_id
+    })
+
     local request = self:parse_request(client)
     if not request then
+        local duration_ms = math.floor((socket.gettime() - start_time) * 1000)
         local response = self:create_response(400, {error = "Invalid request"}, nil, nil, nil)
         client:send(response)
+
+        Logger.log_request("INVALID", "unknown", 400, duration_ms, "unknown", request_id)
         return
     end
 
-    print(string.format("[%s] %s %s", os.date("%Y-%m-%d %H:%M:%S"),
+    -- Get client IP
-          request.method, request.path))
+    local client_ip = self:get_client_ip(client, request.headers)
+
+    -- Add request_id to request context for handlers
+    request.request_id = request_id
 
     -- Handle OPTIONS preflight requests (CORS)
     if request.method == "OPTIONS" then
+        local duration_ms = math.floor((socket.gettime() - start_time) * 1000)
         local response = self:create_response(204, "", "text/plain", nil, request)
         client:send(response)
+
+        Logger.log_request("OPTIONS", request.path, 204, duration_ms, client_ip, request_id)
         return
     end
 
@@ -199,49 +252,78 @@ function FurtServer:handle_client(client)
         handler = self.routes[request.method][request.path]
     end
 
+    local status = 404
     if handler then
         local success, result = pcall(handler, request, self)
         if success then
             client:send(result)
+            -- Extract status from response (rough parsing)
+            status = tonumber(result:match("HTTP/1%.1 (%d+)")) or 200
         else
-            print("Handler error: " .. tostring(result))
+            Logger.log_error("Handler error", {
-            local error_response = self:create_response(500, {error = "Internal server error"}, nil, nil, request)
+                request_id = request_id,
+                method = request.method,
+                path = request.path,
+                client_ip = client_ip
+            }, tostring(result))
+
+            status = 500
+            local error_response = self:create_response(500, {
+                error = "Internal server error",
+                request_id = request_id
+            }, nil, nil, request)
             client:send(error_response)
         end
     else
-        print("Route not found: " .. request.method .. " " .. request.path)
+        Logger.debug("Route not found", {
-        local response = self:create_response(404, {error = "Route not found", method = request.method, path = request.path}, nil, nil, request)
+            request_id = request_id,
+            method = request.method,
+            path = request.path
+        })
+
+        local response = self:create_response(404, {
+            error = "Route not found",
+            method = request.method,
+            path = request.path,
+            request_id = request_id
+        }, nil, nil, request)
         client:send(response)
     end
+
+    -- Log completed request with performance metrics
+    local duration_ms = math.floor((socket.gettime() - start_time) * 1000)
+    Logger.log_request(request.method, request.path, status, duration_ms, client_ip, request_id)
 end
 
 -- Start HTTP server
 function FurtServer:start()
     self.server = socket.bind(self.host, self.port)
     if not self.server then
+        Logger.error("Failed to bind server", {
+            host = self.host,
+            port = self.port
+        })
         error("Failed to bind to " .. self.host .. ":" .. self.port)
     end
 
     local HealthRoute = require("src.routes.health")
     local version_info = HealthRoute.get_version_info()
 
-    print(string.format("Furt HTTP-Server started on %s:%d", self.host, self.port))
+    -- Structured startup logging
-    print("Version: " .. version_info.version .. " (merkwerk)")
+    Logger.log_startup(self.host, self.port, version_info)
-    print("Content-Hash: " .. (version_info.content_hash or "unknown"))
-    print("VCS: " .. (version_info.vcs_info and version_info.vcs_info.hash or "none"))
-    print("API-Key authentication: ENABLED")
 
-    -- Show actual configured rate limits
+    -- Log configuration details
     local rate_limits = config.security and config.security.rate_limits
-    if rate_limits then
+    Logger.log_config_summary({
-        print(string.format("Rate limiting: ENABLED (%d req/hour per API key, %d req/hour per IP)",
+        cors_origins_count = #config.cors.allowed_origins,
-              rate_limits.api_key_max, rate_limits.ip_max))
+        rate_limiting_enabled = rate_limits ~= nil,
-    else
+        api_key_max = rate_limits and rate_limits.api_key_max,
-        print("Rate limiting: ENABLED (default values)")
+        ip_max = rate_limits and rate_limits.ip_max,
-    end
+        test_endpoint_enabled = config.security and config.security.enable_test_endpoint,
+        log_level = Logger.get_log_level()
+    })
 
-    print("CORS enabled for " .. (#config.cors.allowed_origins) .. " configured origins")
+    Logger.info("Furt server ready - Press Ctrl+C to stop")
-    print("Press Ctrl+C to stop")
 
     while true do
         local client = self.server:accept()

src/logger.lua

@@ -0,0 +1,200 @@
+-- src/logger.lua
+-- Structured JSON Logger for Furt API-Gateway
+-- Dragons@Work Digital Sovereignty Project
+
+local found_cjson, cjson = pcall(require, 'cjson')
+if not found_cjson then
+    cjson = require('dkjson')
+end
+
+local config = require("config.server")
+
+-- Hash-based request ID generator for collision resistance
+local function generate_request_id()
+    local data = string.format("%d-%d-%d-%d",
+        os.time(),
+        math.random(1000000, 9999999),
+        math.random(1000000, 9999999),
+        os.clock() * 1000000)
+
+    -- Simple hash function (Lua-native, no dependencies)
+    local hash = 0
+    for i = 1, #data do
+        hash = (hash * 31 + string.byte(data, i)) % 2147483647
+    end
+
+    return string.format("req-%x", hash)
+end
+
+-- Export request ID generator
+Logger = {}
+Logger.generate_request_id = generate_request_id
+
+local Logger = {}
+
+-- Log levels with numeric values for filtering
+local LOG_LEVELS = {
+    debug = 1,
+    info = 2,
+    warn = 3,
+    error = 4
+}
+
+-- Current log level from config
+local current_log_level = LOG_LEVELS[config.log_level] or LOG_LEVELS.info
+
+-- Service identification
+local SERVICE_NAME = "furt-lua"
+
+-- Generate timestamp in ISO format
+local function get_timestamp()
+    return os.date("!%Y-%m-%dT%H:%M:%SZ")
+end
+
+-- Core logging function
+local function log_structured(level, message, context)
+    -- Skip if log level is below threshold
+    if LOG_LEVELS[level] < current_log_level then
+        return
+    end
+
+    -- Build log entry
+    local log_entry = {
+        timestamp = get_timestamp(),
+        level = level,
+        service = SERVICE_NAME,
+        message = message
+    }
+
+    -- Add context data if provided
+    if context then
+        for key, value in pairs(context) do
+            log_entry[key] = value
+        end
+    end
+
+    -- Output as JSON
+    local json_output = cjson.encode(log_entry)
+    print(json_output)
+end
+
+-- Public logging functions
+function Logger.debug(message, context)
+    log_structured("debug", message, context)
+end
+
+function Logger.info(message, context)
+    log_structured("info", message, context)
+end
+
+function Logger.warn(message, context)
+    log_structured("warn", message, context)
+end
+
+function Logger.error(message, context)
+    log_structured("error", message, context)
+end
+
+-- Request logging with performance metrics
+function Logger.log_request(method, path, status, duration_ms, client_ip, request_id)
+    if not config.log_requests then
+        return
+    end
+
+    local context = {
+        method = method,
+        path = path,
+        status = status,
+        duration_ms = duration_ms,
+        client_ip = client_ip
+    }
+
+    -- Add request_id if provided
+    if request_id then
+        context.request_id = request_id
+    end
+
+    log_structured("info", "HTTP request", context)
+end
+
+-- Service startup logging
+function Logger.log_startup(host, port, version_info)
+    Logger.info("Furt HTTP-Server starting", {
+        host = host,
+        port = port,
+        version = version_info.version,
+        content_hash = version_info.content_hash,
+        vcs_hash = version_info.vcs_info and version_info.vcs_info.hash
+    })
+end
+
+-- Service health logging
+function Logger.log_health_check(status, details)
+    local level = status == "healthy" and "info" or "warn"
+    log_structured(level, "Health check", {
+        health_status = status,
+        details = details
+    })
+end
+
+-- Error logging with stack trace support
+function Logger.log_error(error_message, context, stack_trace)
+    local error_context = context or {}
+    if stack_trace then
+        error_context.stack_trace = stack_trace
+    end
+    log_structured("error", error_message, error_context)
+end
+
+-- Configuration logging
+function Logger.log_config_summary(summary)
+    Logger.info("Configuration loaded", summary)
+end
+
+-- Rate limiting events
+function Logger.log_rate_limit(api_key, client_ip, limit_type)
+    Logger.warn("Rate limit exceeded", {
+        api_key = api_key and "***masked***" or nil,
+        client_ip = client_ip,
+        limit_type = limit_type
+    })
+end
+
+-- SMTP/Mail logging
+function Logger.log_mail_event(event_type, recipient, success, error_message)
+    local level = success and "info" or "error"
+    log_structured(level, "Mail event", {
+        event_type = event_type,
+        recipient = recipient,
+        success = success,
+        error = error_message
+    })
+end
+
+-- Set log level dynamically (useful for debugging)
+function Logger.set_log_level(level)
+    if LOG_LEVELS[level] then
+        current_log_level = LOG_LEVELS[level]
+        Logger.info("Log level changed", { new_level = level })
+    else
+        Logger.error("Invalid log level", { attempted_level = level })
+    end
+end
+
+-- Get current log level
+function Logger.get_log_level()
+    for level, value in pairs(LOG_LEVELS) do
+        if value == current_log_level then
+            return level
+        end
+    end
+    return "unknown"
+end
+
+-- Check if a log level would be output
+function Logger.would_log(level)
+    return LOG_LEVELS[level] and LOG_LEVELS[level] >= current_log_level
+end
+
+return Logger
+

src/main.lua

@@ -1,34 +1,137 @@
 -- src/main.lua
--- Furt API-Gateway - Application Entry Point
+-- Furt API-Gateway - Application Entry Point with Structured Logging
 -- Dragons@Work Digital Sovereignty Project
 
--- Load HTTP Server Core
+-- Load Logger first for startup logging
-local FurtServer = require("src.http_server")
+local Logger = require("src.logger")
 
--- Load Route Modules
+Logger.info("Furt API-Gateway starting up", {
-local MailRoute = require("src.routes.mail")
+    startup_phase = "module_loading"
-local AuthRoute = require("src.routes.auth")
+})
-local HealthRoute = require("src.routes.health")
 
--- Load configuration
+-- Load modules with error handling
-local config = require("config.server")
+local function safe_require(module_name, description)
+    local success, module = pcall(require, module_name)
+    if not success then
+        Logger.error("Failed to load module", {
+            module = module_name,
+            description = description,
+            error = module
+        })
+        os.exit(1)
+    end
+
+    Logger.debug("Module loaded successfully", {
+        module = module_name,
+        description = description
+    })
+
+    return module
+end
+
+-- Load core modules
+local FurtServer = safe_require("src.http_server", "HTTP Server Core")
+local MailRoute = safe_require("src.routes.mail", "Mail Route Handler")
+local AuthRoute = safe_require("src.routes.auth", "Auth Route Handler")
+local HealthRoute = safe_require("src.routes.health", "Health Route Handler")
+local config = safe_require("config.server", "Server Configuration")
+
+Logger.info("All modules loaded successfully", {
+    startup_phase = "modules_ready"
+})
 
 -- Initialize server
+Logger.info("Initializing HTTP server", {
+    startup_phase = "server_init"
+})
+
 local server = FurtServer:new()
 
+-- Route registration with logging
+local routes_registered = 0
+
 -- Register public routes (no authentication required)
 server:add_route("GET", "/health", HealthRoute.handle_health)
+routes_registered = routes_registered + 1
 
 -- Test endpoint for development (configurable via furt.conf)
 if config.security and config.security.enable_test_endpoint then
     server:add_route("POST", "/test", HealthRoute.handle_test)
-    print("[WARN] Test endpoint enabled via configuration")
+    routes_registered = routes_registered + 1
+
+    Logger.warn("Development test endpoint enabled", {
+        endpoint = "POST /test",
+        security_note = "Should be disabled in production"
+    })
 end
 
 -- Register protected routes (require authentication)
 server:add_protected_route("POST", "/v1/mail/send", "mail:send", MailRoute.handle_mail_send)
 server:add_protected_route("GET", "/v1/auth/status", nil, AuthRoute.handle_auth_status)
+routes_registered = routes_registered + 2
 
--- Start server
+Logger.info("Route registration completed", {
-server:start()
+    startup_phase = "routes_registered",
+    total_routes = routes_registered,
+    public_routes = config.security and config.security.enable_test_endpoint and 2 or 1,
+    protected_routes = 2
+})
+
+-- Pre-flight system checks
+Logger.info("Performing pre-flight checks", {
+    startup_phase = "pre_flight_checks"
+})
+
+-- Check SMTP configuration
+local smtp_configured = config.mail and config.mail.host ~= nil
+Logger.info("SMTP configuration check", {
+    smtp_configured = smtp_configured,
+    default_smtp_host = config.mail and config.mail.host or "not configured"
+})
+
+-- Check API keys
+local api_key_count = 0
+if config.api_keys then
+    for _ in pairs(config.api_keys) do
+        api_key_count = api_key_count + 1
+    end
+end
+
+Logger.info("API key configuration check", {
+    api_key_count = api_key_count,
+    keys_configured = api_key_count > 0
+})
+
+if api_key_count == 0 then
+    Logger.warn("No API keys configured", {
+        warning = "Server will not accept authenticated requests",
+        check_config = "Verify furt.conf API key sections"
+    })
+end
+
+-- Start server with error handling
+Logger.info("Starting HTTP server", {
+    startup_phase = "server_start",
+    host = config.host,
+    port = config.port
+})
+
+local success, error_msg = pcall(function()
+    server:start()
+end)
+
+if not success then
+    Logger.error("Server startup failed", {
+        error = error_msg,
+        host = config.host,
+        port = config.port,
+        suggestion = "Check if port is already in use or permissions"
+    })
+    os.exit(1)
+end
+
+-- This should never be reached since server:start() blocks
+Logger.error("Server stopped unexpectedly", {
+    unexpected_exit = true
+})