individual messages should get an etag and be cached forever

Author: thefringeninja

src/SqlStreamStore.HAL/CacheControl.cs

@@ -0,0 +1,44 @@
+namespace SqlStreamStore.HAL
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using Microsoft.Extensions.Primitives;
+
+    internal struct CacheControl : IEquatable<CacheControl>
+    {
+        private readonly string[] _values;
+
+        public static readonly CacheControl NoCache = new CacheControl(
+            "max-age=0",
+            "no-cache",
+            "must-revalidate");
+
+        public static readonly CacheControl OneYear = new CacheControl("max-age=31536000");
+
+        private CacheControl(params string[] values)
+        {
+            if(values == null)
+                throw new ArgumentNullException(nameof(values));
+            _values = values;
+        }
+
+        public bool Equals(CacheControl other) => _values
+            .OrderBy(value => value)
+            .SequenceEqual(other._values.OrderBy(value => value), StringComparer.OrdinalIgnoreCase);
+
+        public override bool Equals(object obj) => obj is CacheControl other && Equals(other);
+
+        public override int GetHashCode() => _values
+            .Aggregate(397, (previous, value) => previous ^ (value.GetHashCode() * 397));
+
+        public static bool operator ==(CacheControl left, CacheControl right) => left.Equals(right);
+        public static bool operator !=(CacheControl left, CacheControl right) => !left.Equals(right);
+        public static implicit operator string[](CacheControl cacheControl) => cacheControl._values;
+        public static implicit operator StringValues(CacheControl cacheControl) =>
+            new StringValues(cacheControl._values);
+        public static implicit operator KeyValuePair<string, string[]>(CacheControl cacheControl)
+            => new KeyValuePair<string, string[]>(Constants.Headers.CacheControl, cacheControl._values);
+
+    }
+}

src/SqlStreamStore.HAL/ETag.cs

@@ -1,21 +1,24 @@
 namespace SqlStreamStore.HAL
 {
     using System;
+    using System.Collections.Generic;
+    using Microsoft.Extensions.Primitives;
 
     internal struct ETag : IEquatable<ETag>
     {
         private readonly string _value;
-        
+
         public static ETag FromPosition(long position) => new ETag($@"""{position}""");
         public static ETag FromStreamVersion(int streamVersion) => new ETag($@"""{streamVersion}""");
         public static readonly ETag None = default;
-        
+
         private ETag(string value)
         {
             if(value == null)
             {
                 throw new ArgumentNullException(nameof(value));
             }
+
             if(value[0] != '"' || value[value.Length - 1] != '"')
             {
                 throw new ArgumentException("ETags bust be enclosed in double quotes.", nameof(value));
@@ -31,5 +34,9 @@ private ETag(string value)
         public static bool operator !=(ETag left, ETag right) => !left.Equals(right);
         public static implicit operator string(ETag etag) => etag._value;
         public static implicit operator string[](ETag etag) => new[] { etag._value };
+        public static implicit operator StringValues(ETag etag) => new StringValues(etag._value);
+
+        public static implicit operator KeyValuePair<string, string[]>(ETag etag)
+            => new KeyValuePair<string, string[]>(Constants.Headers.ETag, new[] { etag._value });
     }
 }

src/SqlStreamStore.HAL/Resources/AllStreamResource.cs

@@ -91,7 +91,12 @@ public async Task<Response> Get(
 
             if(page.TryGetETag(operation.FromPositionInclusive, out var eTag))
             {
-                response.Headers[Constants.Headers.ETag] = eTag;
+                response.Headers.Add(eTag);
+                response.Headers.Add(CacheControl.NoCache);
+            }
+            else
+            {
+                response.Headers.Add(CacheControl.OneYear);
             }
 
             return response;

src/SqlStreamStore.HAL/Resources/StreamMessageResource.cs

@@ -85,7 +85,8 @@ public async Task<Response> Get(
             {
                 Headers =
                 {
-                    [Constants.Headers.ETag] = eTag
+                    eTag,
+                    CacheControl.OneYear
                 }
             };
         }

src/SqlStreamStore.HAL/Resources/StreamMetadataResource.cs

@@ -50,7 +50,7 @@ public async Task<Response> Get(
             {
                 Headers =
                 {
-                    [Constants.Headers.ETag] = ETag.FromStreamVersion(result.MetadataStreamVersion)
+                    ETag.FromStreamVersion(result.MetadataStreamVersion)
                 }
             };
 

src/SqlStreamStore.HAL/Resources/StreamResource.cs

@@ -115,7 +115,7 @@ public async Task<Response> Get(ReadStreamOperation operation, CancellationToken
 
             if (page.TryGetETag(out var eTag))
             {
-                response.Headers[Constants.Headers.ETag] = eTag;
+                response.Headers.Add(eTag);
             }
 
             return response;

src/SqlStreamStore.HAL/SqlStreamStoreHalMiddleware.cs

@@ -79,23 +79,6 @@ private static MidFunc MethodsNotAllowed(params string[] methods) => (context, n
             }
         };
 
-        private static MidFunc CacheControl => (context, next) =>
-        {
-            Task AddCacheControlHeaders()
-            {
-                context.Response.Headers[Constants.Headers.CacheControl] =
-                    context.Response.Headers.ContainsKey(Constants.Headers.ETag)
-                        ? s_NoCache
-                        : s_CacheForOneYear;
-
-                return Task.CompletedTask;
-            }
-
-            context.Response.OnStarting(AddCacheControlHeaders);
-
-            return next();
-        };
-
         public static IApplicationBuilder UseSqlStreamStoreHal(
             this IApplicationBuilder builder,
             IStreamStore streamStore)
@@ -110,7 +93,6 @@ public static IApplicationBuilder UseSqlStreamStoreHal(
                 .Use(CaseSensitiveQueryStrings)
                 .Use(AcceptHalJson)
                 .Use(HeadRequests)
-                .Use(CacheControl)
                 .UseIndex()
                 .Map("/stream", UseAllStream(streamStore))
                 .Map("/streams", UseStream(streamStore));