cleanup defaults

src/libraries/Common/src/System/Net/Http/HttpHandlerDefaults.cs

@@ -28,7 +28,11 @@ internal static partial class HttpHandlerDefaults
         public static readonly TimeSpan DefaultPooledConnectionIdleTimeout = TimeSpan.FromMinutes(1);
         public static readonly TimeSpan DefaultExpect100ContinueTimeout = TimeSpan.FromSeconds(1);
         public static readonly TimeSpan DefaultConnectTimeout = Timeout.InfiniteTimeSpan;
-        public const int DefaultHttp2MaxStreamWindowSize = 16 * 1024 * 1024;
-        public const double DefaultHttp2StreamWindowScaleThresholdMultiplier = 1.0;
+
+        // This is the default value for SocketsHttpHandler.InitialHttp2StreamWindowSize,
+        // which defines the value we communicate in stream SETTINGS frames.
+        // Should not be confused with Http2Connection.DefaultInitialWindowSize, which defines the RFC default.
+        // Unlike that value, DefaultInitialHttp2StreamWindowSize might be changed in the future.
+        public const int DefaultInitialHttp2StreamWindowSize = 65535;
     }
 }

src/libraries/System.Net.Http/src/System/Net/Http/GlobalHttpSettings.cs

@@ -45,16 +45,19 @@ internal static class SocketsHttpHandler
             // Defaults to 1.0. Higher values result in shorter window, but slower downloads.
             public static double Http2StreamWindowScaleThresholdMultiplier { get; } = GetHttp2StreamWindowScaleThresholdMultiplier();
 
+            public const int DefaultHttp2MaxStreamWindowSize = 16 * 1024 * 1024;
+            public const double DefaultHttp2StreamWindowScaleThresholdMultiplier = 1.0;
+
             private static int GetMaxHttp2StreamWindowSize()
             {
                 int value = RuntimeSettingParser.ParseInt32EnvironmentVariableValue(
                     "DOTNET_SYSTEM_NET_HTTP_SOCKETSHTTPHANDLER_FLOWCONTROL_MAXSTREAMWINDOWSIZE",
-                    HttpHandlerDefaults.DefaultHttp2MaxStreamWindowSize);
+                    DefaultHttp2MaxStreamWindowSize);
 
                 // Disallow small values:
-                if (value < Http2Connection.DefaultInitialWindowSize)
+                if (value < HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize)
                 {
-                    value = Http2Connection.DefaultInitialWindowSize;
+                    value = HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize;
                 }
                 return value;
             }
@@ -63,12 +66,12 @@ private static double GetHttp2StreamWindowScaleThresholdMultiplier()
             {
                 double value = RuntimeSettingParser.ParseDoubleEnvironmentVariableValue(
                     "DOTNET_SYSTEM_NET_HTTP_SOCKETSHTTPHANDLER_FLOWCONTROL_STREAMWINDOWSCALETHRESHOLDMULTIPLIER",
-                    HttpHandlerDefaults.DefaultHttp2StreamWindowScaleThresholdMultiplier);
+                    DefaultHttp2StreamWindowScaleThresholdMultiplier);
 
                 // Disallow negative values:
                 if (value < 0)
                 {
-                    value = HttpHandlerDefaults.DefaultHttp2StreamWindowScaleThresholdMultiplier;
+                    value = DefaultHttp2StreamWindowScaleThresholdMultiplier;
                 }
                 return value;
             }

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs

@@ -82,6 +82,7 @@ internal sealed partial class Http2Connection : HttpConnectionBase, IDisposable
 #endif
         // The default initial window size for streams and connections according to the RFC:
         // https://datatracker.ietf.org/doc/html/rfc7540#section-5.2.1
+        // Unlike HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize, this value should never be changed.
         internal const int DefaultInitialWindowSize = 65535;
 
         // We don't really care about limiting control flow at the connection level.
@@ -198,7 +199,7 @@ public async ValueTask SetupAsync()
                 // The connection-level window size can not be initialized by SETTINGS frames:
                 // https://datatracker.ietf.org/doc/html/rfc7540#section-6.9.2
                 // Send an initial connection-level WINDOW_UPDATE to setup the desired ConnectionWindowSize:
-                uint windowUpdateAmount = (ConnectionWindowSize - DefaultInitialWindowSize);
+                uint windowUpdateAmount = ConnectionWindowSize - DefaultInitialWindowSize;
                 if (NetEventSource.Log.IsEnabled()) Trace($"Initial connection-level WINDOW_UPDATE, windowUpdateAmount={windowUpdateAmount}");
                 FrameHeader.WriteTo(_outgoingBuffer.AvailableSpan, FrameHeader.WindowUpdateLength, FrameType.WindowUpdate, FrameFlags.None, streamId: 0);
                 _outgoingBuffer.Commit(FrameHeader.Size);

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionSettings.cs

@@ -62,7 +62,7 @@ internal sealed class HttpConnectionSettings
         internal IDictionary<string, object?>? _properties;
 
         // Http2 flow control settings:
-        internal int _initialHttp2StreamWindowSize = Http2Connection.DefaultInitialWindowSize;
+        internal int _initialHttp2StreamWindowSize = HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize;
 
         public HttpConnectionSettings()
         {

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpHandler.cs

@@ -67,12 +67,14 @@ public int InitialHttp2StreamWindowSize
             get => _settings._initialHttp2StreamWindowSize;
             set
             {
-                if (value < Http2Connection.DefaultInitialWindowSize || value > GlobalHttpSettings.SocketsHttpHandler.MaxHttp2StreamWindowSize)
+                if (value < HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize || value > GlobalHttpSettings.SocketsHttpHandler.MaxHttp2StreamWindowSize)
                 {
-                    throw new ArgumentOutOfRangeException(
-                        nameof(InitialHttp2StreamWindowSize),
-                        SR.Format(SR.net_http_http2_invalidinitialstreamwindowsize, Http2Connection.DefaultInitialWindowSize,
-                            GlobalHttpSettings.SocketsHttpHandler.MaxHttp2StreamWindowSize));
+                    string message = SR.Format(
+                        SR.net_http_http2_invalidinitialstreamwindowsize,
+                        HttpHandlerDefaults.DefaultInitialHttp2StreamWindowSize,
+                        GlobalHttpSettings.SocketsHttpHandler.MaxHttp2StreamWindowSize);
+
+                    throw new ArgumentOutOfRangeException(nameof(InitialHttp2StreamWindowSize), message);
                 }
                 CheckDisposedOrStarted();
                 _settings._initialHttp2StreamWindowSize = value;