Implemented PresetRequestParser

Author: marklagendijk

src/ImageSharp.Web/Commands/PresetRequestParser.cs

@@ -0,0 +1,47 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.WebUtilities;
+using Microsoft.Extensions.Options;
+using Microsoft.Extensions.Primitives;
+
+namespace SixLabors.ImageSharp.Web.Commands
+{
+    /// <summary>
+    /// Parses ImageSharp.Web image processing requests to ImageSharp.Web commands based on statically defined presets.
+    /// The advantages of this are:
+    /// 1. Image processing for certain scenarios can be adjusted in a single place, by adjusting the preset definition.
+    /// 2. Security. Only known presets are applied. Limits DOS opportunities.
+    /// </summary>
+    public class PresetRequestParser : IRequestParser
+    {
+        private readonly IDictionary<string, IDictionary<string, string>> presets;
+
+        public PresetRequestParser(IOptions<PresetRequestParserOptions> options) => this.presets = ParsePresets(options.Value.Presets);
+
+        public IDictionary<string, string> ParseRequestCommands(HttpContext context)
+        {
+            var requestedPreset = context.Request.Query["preset"].ToString();
+            return this.presets.GetValueOrDefault(requestedPreset) ?? new Dictionary<string, string>();
+        }
+
+        private static IDictionary<string, IDictionary<string, string>> ParsePresets(IDictionary<string, string> unparsedPresets) =>
+            unparsedPresets
+                .Select(keyValue => new KeyValuePair<string, IDictionary<string, string>>(keyValue.Key, ParsePreset(keyValue.Value)))
+                .ToDictionary(keyValue => keyValue.Key, keyValue => keyValue.Value);
+
+        private static IDictionary<string, string> ParsePreset(string unparsedPresetValue)
+        {
+            Dictionary<string, StringValues> parsed = QueryHelpers.ParseQuery(unparsedPresetValue);
+            var transformed = new Dictionary<string, string>(parsed.Count);
+            foreach (KeyValuePair<string, StringValues> keyValue in parsed)
+            {
+                transformed[keyValue.Key] = keyValue.Value.ToString();
+            }
+            return transformed;
+        }
+    }
+}

src/ImageSharp.Web/Commands/PresetRequestParserOptions.cs

@@ -0,0 +1,12 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Web.Commands
+{
+    public class PresetRequestParserOptions
+    {
+        public IDictionary<string, string> Presets { get; set; } = new Dictionary<string, string>();
+    }
+}