initial commit

main.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+var Version = "development"
+
+// this struct used to parse config.yaml
+type Config struct {
+	Calendars   []CalendarConfig `yaml:"calendars"`
+	AllowUnsafe bool             `yaml:"unsafe"`
+}
+
+// This function loads the configuration file and does some basic validation
+// Returns false if the config is not valid or an error occurs
+func (config *Config) LoadConfig(file string) bool {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		slog.Error("Unable to open config file! You can use -config to specify a different file", "file", file)
+		return false
+	}
+	err = yaml.Unmarshal(data, &config)
+	if err != nil {
+		slog.Error("Error while unmarshalling yaml! Check config file is valid", "file", file)
+		return false
+	}
+
+	// ensure calendars exist
+	if len(config.Calendars) == 0 {
+		slog.Error("No calendars found! Configuration should define at least one calendar")
+		return false
+	}
+
+	// validate calendar configs
+	for _, calendarConfig := range config.Calendars {
+
+		// check if url seems valid
+		if !strings.HasPrefix(calendarConfig.FeedURL, "http://") && !strings.HasPrefix(calendarConfig.FeedURL, "https://") {
+			slog.Debug("Calendar URL must begin with http:// or https://", "calendar", calendarConfig.Name, "feed_url", len(calendarConfig.Filters))
+			return false
+		}
+
+		// Check to see if auth is disabled (token not set)
+		// If so print a warning message and make sure unsafe is enabled in config
+		if len(calendarConfig.Token) == 0 {
+			slog.Warn("Calendar has no token set. Authentication will be disabled", "calendar", calendarConfig.Name)
+			if !config.AllowUnsafe {
+				slog.Error("Calendar cannot have authentication disabled without unsafe optionenabled in the configuration", "calendar", calendarConfig.Name)
+				return false
+			}
+		}
+
+		// Print a warning if the calendar has no filters
+		if len(calendarConfig.Filters) == 0 {
+			slog.Warn("Calendar has no filters and will be proxy-only", "calendar", calendarConfig.Name)
+			break
+		}
+
+	}
+
+	return true // config is parsed successfully
+
+}
+
+func main() {
+
+	// command-line args
+	var (
+		configFile     string
+		debugLogging   bool
+		jsonLogging    bool
+		listenPort     int
+		validateConfig bool
+		printVersion   bool
+	)
+	flag.StringVar(&configFile, "config", "config.yaml", "config file")
+	flag.BoolVar(&debugLogging, "debug", false, "enable debug logging")
+	flag.BoolVar(&printVersion, "version", false, "print version and exit")
+	flag.BoolVar(&jsonLogging, "json", false, "output logging in JSON format")
+	flag.IntVar(&listenPort, "port", 8080, "listening port for api")
+	flag.BoolVar(&validateConfig, "validate", false, "validate config and exit")
+	flag.Parse()
+
+	// print version and exit
+	if printVersion {
+		fmt.Println("version:", Version)
+		os.Exit(0)
+	}
+
+	// setup logging options
+	loggingLevel := slog.LevelInfo // default loglevel
+	if debugLogging {
+		loggingLevel = slog.LevelDebug // debug logging enabled
+	}
+	opts := &slog.HandlerOptions{
+		Level: loggingLevel,
+	}
+
+	// create json or text logger based on args
+	var logger *slog.Logger
+	if jsonLogging {
+		logger = slog.New(slog.NewJSONHandler(os.Stdout, opts))
+	} else {
+		logger = slog.New(slog.NewTextHandler(os.Stdout, opts))
+	}
+	slog.SetDefault(logger)
+
+	// load configuration
+	slog.Debug("reading config", "configFile", configFile)
+	var config Config
+	if !config.LoadConfig(configFile) {
+		os.Exit(1) // fail if config is not valid
+	}
+	slog.Debug("loaded config")
+
+	// print a message and exit if validate arg was specified
+	if validateConfig {
+		slog.Info("configuration was validated successfully")
+		os.Exit(0)
+	}
+
+	// iterate through calendars in the config and setup a handler for each
+	// todo: consider refactor to route requests dynamically?
+	for _, calendarConfig := range config.Calendars {
+
+		// configure HTTP endpoint
+		httpPath := "/calendars/" + calendarConfig.Name + "/feed"
+		slog.Debug("Configuring endpoint", "calendar", calendarConfig.Name, "http_path", httpPath)
+		http.HandleFunc(httpPath, func(w http.ResponseWriter, r *http.Request) {
+
+			slog.Debug("Received request for calendar", "http_path", httpPath, "calendar", calendarConfig.Name, "client_ip", r.RemoteAddr)
+
+			// validate token
+			token := r.URL.Query().Get("token")
+			if token != calendarConfig.Token {
+				slog.Warn("Unauthorized access attempt", "client_ip", r.RemoteAddr)
+				http.Error(w, "Unauthorized", http.StatusUnauthorized)
+				return
+			}
+
+			// fetch and filter upstream calendar
+			feed, err := calendarConfig.fetch()
+			if err != nil {
+				slog.Error("Error fetching and filtering feed", "error", err)
+				http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+				return
+			}
+
+			// return calendar
+			w.Header().Set("Content-Type", "text/calendar")
+			_, err = w.Write(feed)
+			if err != nil {
+				slog.Error("Error writing response", "error", err)
+				http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+				return
+			}
+
+			slog.Info("Calendar request processed", "http_path", httpPath, "calendar", calendarConfig.Name, "client_ip", r.RemoteAddr)
+		})
+
+	}
+
+	// add a readiness and liveness check endpoint (return blank 200 OK response)
+	http.HandleFunc("/liveness", func(w http.ResponseWriter, r *http.Request) {})
+	http.HandleFunc("/readiness", func(w http.ResponseWriter, r *http.Request) {})
+
+	// start the webserver
+	slog.Info("Starting web server", "port", listenPort)
+	if err := http.ListenAndServe(":"+strconv.Itoa(listenPort), nil); err != nil {
+		slog.Error("Error starting web server", "error", err)
+	}
+
+}