Add placeholders

LinkRouter/App/Configuration/Config.cs

@@ -1,4 +1,7 @@
-using LinkRouter.App.Models;
+using System.Text;
+using System.Text.Json.Serialization;
+using System.Text.RegularExpressions;
+using LinkRouter.App.Models;
 
 namespace LinkRouter.App.Configuration;
 
@@ -8,7 +11,8 @@ public class Config
 
     public NotFoundBehaviorConfig NotFoundBehavior { get; set; } = new();
 
-    public RedirectRoute[] Routes { get; set; } = [
+    public RedirectRoute[] Routes { get; set; } =
+    [
         new RedirectRoute()
         {
             Route = "/instagram",
@@ -20,10 +24,85 @@ public class Config
             RedirectUrl = "https://example.com"
         },
     ];
-    
+
     public class NotFoundBehaviorConfig
     {
         public bool RedirectOn404 { get; set; } = false;
         public string RedirectUrl { get; set; } = "https://example.com/404";
     }
+
+    [JsonIgnore] public CompiledRoute[]? CompiledRoutes { get; set; }
+
+    public void CompileRoutes()
+    {
+        var compiledRoutes = new List<CompiledRoute>();
+
+        foreach (var route in Routes)
+        {
+            if (!route.Route.StartsWith("/"))
+                route.Route = "/" + route.Route;
+
+            if (!route.Route.EndsWith("/"))
+                route.Route += "/";
+
+            var compiled = new CompiledRoute
+            {
+                Route = route.Route,
+                RedirectUrl = route.RedirectUrl
+            };
+
+            var replacements = new List<(int Index, int Length, string NewText)>();
+
+            var escaped = Regex.Escape(route.Route);
+
+            var pattern = new Regex(@"\\\{(\d|\w+)\}", RegexOptions.CultureInvariant);
+
+            var matches = pattern.Matches(escaped);
+
+            foreach (var match in matches.Select(x => x))
+            {
+                // Check if the placeholder is immediately followed by another placeholder
+                if (escaped.Length >= match.Index + match.Length + 2
+                    && escaped.Substring(match.Index + match.Length, 2) == "\\{")
+                    throw new InvalidOperationException(
+                        $"Placeholder {match.Groups[1].Value} cannot be immediately followed by another placeholder. " +
+                        $"Please add any separator.");
+
+                replacements.Add((match.Index, match.Length, "(.+)"));
+            }
+
+            var compiledRouteBuilder = new StringBuilder(escaped);
+
+            foreach (var replacement in replacements.OrderByDescending(r => r.Index))
+            {
+                compiledRouteBuilder.Remove(replacement.Index, replacement.Length);
+                compiledRouteBuilder.Insert(replacement.Index, replacement.NewText);
+            }
+
+            compiled.CompiledPattern = new Regex(compiledRouteBuilder.ToString(),
+                RegexOptions.Compiled | RegexOptions.CultureInvariant);
+
+            var duplicate = matches
+                .Select((m, i) => m.Groups[1].Value)
+                .GroupBy(x => x)
+                .FirstOrDefault(x => x.Count() > 1);
+
+            if (duplicate != null)
+                throw new InvalidOperationException("Cannot use a placeholder twice in the route: " + duplicate.Key);
+
+            compiled.Placeholders = matches
+                .Select((m, i) => m.Groups[1].Value)
+                .Distinct()
+                .Select((name, i) => (name, i))
+                .ToDictionary(x => x.name, x => x.i + 1);
+
+            compiledRoutes.Add(compiled);
+        }
+
+        CompiledRoutes = compiledRoutes
+            .ToArray();
+    }
+
+    [JsonIgnore] public static Regex ErrorCodePattern = new(@"\s*\-\>\s*(\d+)\s*$", RegexOptions.Compiled | RegexOptions.CultureInvariant);
+
 }

LinkRouter/App/Http/Controllers/RedirectController.cs

@@ -10,7 +10,6 @@ public class RedirectController : Controller
 {
 
     private readonly Config Config;
-
 
     private readonly Counter RouteCounter = Metrics.CreateCounter(
         "linkrouter_requests",
@@ -37,38 +36,71 @@ public RedirectController(Config config)
     }
 
     [HttpGet("/{*path}")]
-    public IActionResult RedirectToExternalUrl(string path)
+    public async Task<ActionResult> RedirectToExternalUrl(string path)
     {
-        var redirectRoute = Config.Routes.FirstOrDefault(x => x.Route == path || x.Route == path + "/" || x.Route == "/" + path);
-
-        if (redirectRoute != null)
+        if (!path.EndsWith("/"))
+            path += "/";
+
+        path = "/" + path;
+
+        Console.WriteLine(path);
+
+        var redirectRoute = Config.CompiledRoutes?.FirstOrDefault(x => x.CompiledPattern.IsMatch(path));
+
+        if (redirectRoute == null)
         {
-            RouteCounter
-                .WithLabels(redirectRoute.Route)
+            NotFoundCounter
+                .WithLabels(path)
                 .Inc();
 
-            return Redirect(redirectRoute.RedirectUrl);
-        }
+            if (Config.NotFoundBehavior.RedirectOn404)
+                if (Config.ErrorCodePattern.IsMatch(Config.NotFoundBehavior.RedirectUrl))
+                {
+                    var errorCodeMatch = Config.ErrorCodePattern.Match(Config.NotFoundBehavior.RedirectUrl);
+                    var errorCode = int.Parse(errorCodeMatch.Groups[1].Value);
+                    return StatusCode(errorCode);
+                } else
+                    return Redirect(Config.NotFoundBehavior.RedirectUrl);
 
-        NotFoundCounter
-            .WithLabels("/" + path)
-            .Inc();
+            return NotFound();
+        }
 
-        if (Config.NotFoundBehavior.RedirectOn404)
-            return Redirect(Config.NotFoundBehavior.RedirectUrl);
+        var match = redirectRoute.CompiledPattern.Match(path);
 
-        return NotFound();
+        string redirectUrl = redirectRoute.RedirectUrl;
+
+        if (Config.ErrorCodePattern.IsMatch(redirectUrl))
+        {
+            var errorCodeMatch = Config.ErrorCodePattern.Match(redirectUrl);
+            var errorCode = int.Parse(errorCodeMatch.Groups[1].Value);
+            return StatusCode(errorCode);
+        }
+
+        foreach (var placeholder in redirectRoute.Placeholders)
+        {
+            var value = match.Groups[placeholder.Value].Value;
+            redirectUrl = redirectUrl.Replace("{" + placeholder.Key + "}", value);
+        }
+
+        return Redirect(redirectUrl);
     }
-    
+
     [HttpGet("/")]
     public IActionResult GetRootRoute()
     {
         RouteCounter
             .WithLabels("/")
             .Inc();
-        
+
         string url = Config.RootRoute;
 
+        if (Config.ErrorCodePattern.IsMatch(url))
+        {
+            var errorCodeMatch = Config.ErrorCodePattern.Match(url);
+            var errorCode = int.Parse(errorCodeMatch.Groups[1].Value);
+            return StatusCode(errorCode);
+        }
+
         return Redirect(url);
     }
 }

LinkRouter/App/Models/CompiledRoute.cs

@@ -0,0 +1,10 @@
+using System.Text.RegularExpressions;
+
+namespace LinkRouter.App.Models;
+
+public class CompiledRoute : RedirectRoute
+{
+    public Regex CompiledPattern { get; set; }
+
+    public Dictionary<string, int> Placeholders { get; set; } = new();
+}

LinkRouter/App/Models/RedirectRoute.cs

@@ -3,6 +3,6 @@
 public class RedirectRoute
 {
     public string Route { get; set; }
-    
+
     public string RedirectUrl { get; set; }
 }

LinkRouter/App/Services/ConfigWatcher.cs

@@ -22,32 +22,44 @@ protected override Task ExecuteAsync(CancellationToken stoppingToken)
         {
             Logger.LogWarning("Watched file does not exist: {FilePath}", ConfigPath);
         }
-        
+
         Watcher = new FileSystemWatcher(Path.GetDirectoryName(ConfigPath) ?? throw new InvalidOperationException())
         {
             Filter = Path.GetFileName(ConfigPath),
             NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.Size | NotifyFilters.CreationTime
         };
-
+
+        OnChanged(Watcher, new FileSystemEventArgs(WatcherChangeTypes.Created, string.Empty, string.Empty));
+
         Watcher.Changed += OnChanged;
-        
+
         Watcher.EnableRaisingEvents = true;
-        
+
         return Task.CompletedTask;
     }
-    
+
     private void OnChanged(object sender, FileSystemEventArgs e)
     {
         try
         {
             var content = File.ReadAllText(ConfigPath);
-            
+
             var config = JsonSerializer.Deserialize<Config>(content);
-            
+
             Config.Routes = config?.Routes ?? [];
             Config.RootRoute = config?.RootRoute ?? "https://example.com";
-            
+
             Logger.LogInformation("Config file changed.");
+
+            try
+            {
+                Config.CompileRoutes();
+            }
+            catch (InvalidOperationException ex)
+            {
+                Logger.LogError("Failed to compile routes: " + ex.Message);
+                Environment.Exit(1);
+            }
         }
         catch (IOException ex)
         {

LinkRouter/Program.cs

@@ -12,46 +12,44 @@ public abstract class Program
     public static void Main(string[] args)
     {
         var builder = WebApplication.CreateBuilder(args);
-        
+
         Directory.CreateDirectory(PathBuilder.Dir("data"));
-        
+
         builder.Services.AddControllers();
-        
+
         var loggerProviders = LoggerBuildHelper.BuildFromConfiguration(configuration =>
         {
             configuration.Console.Enable = true;
             configuration.Console.EnableAnsiMode = true;
         });
-        
+
         builder.Logging.ClearProviders();
         builder.Logging.AddProviders(loggerProviders);
 
         builder.Services.AddHostedService<ConfigWatcher>();
-        
+
         var configPath = Path.Combine("data", "config.json");
-        
+
         if (!File.Exists(configPath))
             File.WriteAllText(
-                configPath, 
-                JsonSerializer.Serialize(new Config(), new JsonSerializerOptions {WriteIndented = true}
+                configPath,
+                JsonSerializer.Serialize(new Config(), new JsonSerializerOptions { WriteIndented = true }
                 ));
-        
+
         Config config = JsonSerializer.Deserialize<Config>(File.ReadAllText(configPath)) ?? new Config();
 
-        File.WriteAllText(configPath, JsonSerializer.Serialize(config, new JsonSerializerOptions {WriteIndented = true}));
-
+        File.WriteAllText(configPath,
+            JsonSerializer.Serialize(config, new JsonSerializerOptions { WriteIndented = true }));
+
         builder.Services.AddSingleton(config);
-
-        builder.Services.AddMetricServer(options =>
-        {
-            options.Port = 5000;
-        });
-
+
+        builder.Services.AddMetricServer(options => { options.Port = 5000; });
+
         var app = builder.Build();
 
         app.UseMetricServer();
         app.MapControllers();
 
         app.Run();
     }
-}
+}

README.md

@@ -4,11 +4,13 @@
 [⬇️How to install⬇️](#installation)
 
 ## Features
- -   **Path-based Redirection:** Reads a config file that maps paths to redirect URLs. When a request hits a registered path, the router issues an HTTP redirect to the corresponding target.
+-   **Path-based Redirection:** Reads a config file that maps paths to redirect URLs. When a request hits a registered path, the router issues an HTTP redirect to the corresponding target.
 -   **Hot Reloading:** The config is cached at startup and automatically reloaded when the file changes — no restart required. [Example config](#example-config)
 -   **Low Resource Usage:** Uses less than 50MB of RAM, making it ideal for constrained environments. 
 -   **Metrics Endpoint:** Exposes Prometheus-compatible metrics at `:5000/metrics` for easy observability and monitoring. [How to use](#metrics)
- -   **Docker-Deployable:** Comes with a minimal Dockerfile for easy containerized deployment.
+-   **Docker-Deployable:** Comes with a minimal Dockerfile for easy containerized deployment.
+-   **Placeholders:** Supports placeholders in redirect URLs, allowing dynamic URL generation based on the requested path. For example, a route defined as `/user/{username}` can redirect to `https://example.com/profile/{username}`, where `{username}` is replaced with the actual value from the request.
+-   **Status Code:** You are able to configure if the redirect should redirect to an url or just return a custom status code of your choice. Example `"RedirectUrl": "-> 418"` will return the status code 418 (I'm a teapot :) )
 
 ## Configuration
 Routes are managed via a configuration file, `/data/config.json`. You can define paths and their corresponding URLs in this file. The application automatically normalizes routes to handle both trailing and non-trailing slashes.
@@ -24,11 +26,15 @@ Routes are managed via a configuration file, `/data/config.json`. You can define
   "Routes": [
     {
       "Route": "/instagram", // has to start with a slash
-      "RedirectUrl": "https://instagram.com/{yourname}"
+      "RedirectUrl": "https://instagram.com/maxmustermann"
     },
     {
-      "Route": "/example", // has to start with a slash
-      "RedirectUrl": "https://example.com"
+      "Route": "/article/{id}", // {id} is a placeholder
+      "RedirectUrl": "https://example.com/article/{id}", // {id} will be replaced with the actual value from the request
+    },
+    {
+      "Route": "/teapot",
+      "RedirectUrl": "-> 418" // will return a 418 status code (I'm a teapot :) )
     }
   ]
 }