SwiftQUIC: Expose remote datagram frame size through connection metadata

Sources/SwiftNetwork/Protocols/QUICConnectionProtocol.swift

@@ -753,6 +753,7 @@ public struct QUICConnectionProtocol: NetworkProtocol {
         public var applicationErrorReason: String?
 
         public var activeConnectionIDLimit: Int = 0
+        public var remoteMaxDatagramFrameSize: UInt16 = 0
         #if NETWORK_PRIVATE
         var privateStorage = QUICConnectionMetadataPrivateStorage()
         #endif

Sources/SwiftNetwork/QUIC/QUICConnection.swift

@@ -4246,13 +4246,15 @@ public final class QUICConnection: ManyToManyApplicationStreamProtocol,
         }
         guard let remoteTPMaxDatagramFrameSize else {
             self.remoteMaxDatagramFrameSize = 0
+            self.connectionMetadata.remoteMaxDatagramFrameSize = 0
             return
         }
         if remoteTPMaxDatagramFrameSize > TransportParameters.maxDatagramFrameSize {
             self.remoteMaxDatagramFrameSize = Int(TransportParameters.maxDatagramFrameSize)
         } else {
             self.remoteMaxDatagramFrameSize = remoteTPMaxDatagramFrameSize
         }
+        self.connectionMetadata.remoteMaxDatagramFrameSize = UInt16(truncatingIfNeeded: remoteMaxDatagramFrameSize)
     }
 
     private func discardKeys(keyState: PacketKeyState, discardRecoveryState: Bool = true) {

Tests/SwiftNetworkTests/SwiftNetworkQUICHarnessTests.swift

@@ -653,6 +653,36 @@ final class SwiftNetworkQUICHarnessTests: NetTestCase {
         QUICTestHarness().runQUICTest(datagram: true, blockSize: 1000, blockCount: 10)
     }
 
+    func testQUICDatagramRemoteMaxDatagramFrameSize() {
+        QUICTestHarness().runQUICTest(
+            datagram: true,
+            blockSize: 1000,
+            blockCount: 1,
+            afterData: { harness in
+                let expectation = XCTestExpectation(description: "Wait for remote datagram frame size to be fetched")
+                harness.context.async {
+                    let clientMetadata: ProtocolMetadata<QUICProtocol>? = harness.state?.clientHarness.getMetadata()
+                    XCTAssertNotNil(clientMetadata)
+                    if let clientMetadata {
+                        let clientRemoteSize = clientMetadata.connectionMetadata?.remoteMaxDatagramFrameSize
+                        XCTAssertNotNil(clientRemoteSize)
+                        XCTAssertEqual(clientRemoteSize, 65535)
+                    }
+                    let serverMetadata: ProtocolMetadata<QUICProtocol>? = harness.state?.serverHarness.getMetadata()
+                    XCTAssertNotNil(serverMetadata)
+                    if let serverMetadata {
+                        let serverRemoteSize = serverMetadata.connectionMetadata?.remoteMaxDatagramFrameSize
+                        XCTAssertNotNil(serverRemoteSize)
+                        XCTAssertEqual(serverRemoteSize, 65535)
+                    }
+                    expectation.fulfill()
+                }
+                let waitResult = XCTWaiter.wait(for: [expectation], timeout: 2.0)
+                XCTAssertEqual(waitResult, .completed, "Remote datagram frame size fetch should complete")
+            }
+        )
+    }
+
     // MARK: Unidirectional tests
 
     func testQUICHelloWorldUnidirectional() {