Do not report completion while a 0-RTT client is in early data

Sources/NIOSSL/QUIC/NIOSSLQUICHandshake.swift

@@ -506,6 +506,16 @@ public final class NIOSSLQUICHandshake {
         }
         let rc = CNIOBoringSSL_SSL_do_handshake(self.ssl)
         if rc == 1 {
+            // A client that offered 0-RTT reaches SSL_do_handshake == 1 as soon as
+            // it may send early data, while SSL_in_early_data() is still true and
+            // the handshake is not yet complete: the server confirms or rejects the
+            // 0-RTT in its response (RFC 9001 § 4.6.1). Report completion only once
+            // the client has left the early-data state, so a driver keeps advancing
+            // to consume that response instead of stopping short and never learning
+            // whether its 0-RTT was accepted.
+            if CNIOBoringSSL_SSL_in_early_data(self.ssl) == 1 {
+                return .wantsMoreData
+            }
             return .complete
         }
         let result = CNIOBoringSSL_SSL_get_error(self.ssl, rc)

Tests/NIOSSLTests/NIOSSLQUICHandshakeTests.swift

@@ -1080,4 +1080,27 @@ final class NIOSSLQUICHandshakeTests: XCTestCase {
         XCTAssertTrue(client.handshake.earlyDataAccepted, "the client did not see its 0-RTT accepted")
         XCTAssertTrue(server.handshake.earlyDataAccepted, "the server did not accept the offered 0-RTT")
     }
+
+    func testOfferedEarlyDataStaysInHandshakeUntilConfirmed() throws {
+        // A client that offers 0-RTT reaches SSL_do_handshake == 1 as soon as it
+        // may send early data, while the handshake is still in flight: advance()
+        // must report .wantsMoreData, not .complete, so a driver keeps advancing
+        // to consume the server's confirmation (RFC 9001 § 4.6.1). Reporting
+        // completion here would strand the 0-RTT unconfirmed.
+        let clientContext = try self.makeClientContext()
+        let serverContext = try self.makeServerContext()
+        let earlyDataContext = Array("nioquic".utf8)
+        let session = try self.earlyDataSession(
+            clientContext: clientContext,
+            serverContext: serverContext,
+            earlyDataContext: earlyDataContext
+        )
+        let client = try NIOSSLQUICHandshake(
+            context: clientContext,
+            role: .client,
+            localTransportParameters: Self.clientTransportParameters,
+            resumption: .offerEarlyData(session: session)
+        )
+        XCTAssertEqual(try client.advance(), .wantsMoreData)
+    }
 }