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JAMES-4210 Add SMTP SASL bridge scaffold
Add a minimal SMTP bridge for the shared SASL SPI. The bridge keeps SMTP-specific AUTH framing outside the generic SPI: it converts SMTP AUTH initial responses to SaslInitialRequest, handles the "=" empty initial response marker, maps SASL challenges to SMTP 334 responses, decodes client continuation lines, and wires abort/close lifecycle handling around SaslExchange. Add unit tests for initial response decoding, SMTP challenge formatting, client response decoding, and exchange cleanup.
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‎protocols/smtp/src/main/java/org/apache/james/protocols/smtp/core/esmtp/SmtpSaslBridge.java‎

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/****************************************************************
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* Licensed to the Apache Software Foundation (ASF) under one *
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* or more contributor license agreements. See the NOTICE file *
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* distributed with this work for additional information *
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* regarding copyright ownership. The ASF licenses this file *
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* to you under the Apache License, Version 2.0 (the *
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* "License"); you may not use this file except in compliance *
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* with the License. You may obtain a copy of the License at *
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* *
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* http://www.apache.org/licenses/LICENSE-2.0 *
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* *
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* Unless required by applicable law or agreed to in writing, *
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* software distributed under the License is distributed on an *
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY *
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* KIND, either express or implied. See the License for the *
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* specific language governing permissions and limitations *
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* under the License. *
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****************************************************************/
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package org.apache.james.protocols.smtp.core.esmtp;
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import java.nio.charset.StandardCharsets;
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import java.util.Base64;
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import java.util.Objects;
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import java.util.Optional;
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import org.apache.james.protocols.api.sasl.SaslExchange;
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import org.apache.james.protocols.api.sasl.SaslInitialRequest;
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import org.apache.james.protocols.api.sasl.SaslProtocol;
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import org.apache.james.protocols.api.sasl.SaslStep;
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import org.apache.james.protocols.smtp.SMTPResponse;
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import org.apache.james.protocols.smtp.SMTPRetCode;
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public class SmtpSaslBridge {
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/**
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* Converts an SMTP AUTH request into a protocol-neutral SASL initial request.
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*/
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public SaslInitialRequest initialRequest(String mechanismName, Optional<String> initialClientResponse) {
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return new SaslInitialRequest(SaslProtocol.SMTP, mechanismName,
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Objects.requireNonNull(initialClientResponse).map(this::decodeInitialClientResponse));
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}
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/**
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* Encodes a SASL challenge payload as an SMTP AUTH 334 response.
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*/
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public SMTPResponse challenge(SaslStep.Challenge challenge) {
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return new SMTPResponse(SMTPRetCode.AUTH_READY,
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challenge.payload()
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.map(Base64.getEncoder()::encodeToString)
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.orElse(""));
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}
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/**
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* Decodes an SMTP client continuation line and forwards it to the SASL exchange.
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*/
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public SaslStep onClientResponse(SaslExchange exchange, byte[] line) {
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return exchange.onResponse(decodeBase64(stripTrailingCrlf(line)));
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}
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/**
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* Aborts and closes an active SASL exchange.
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*/
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public void abort(SaslExchange exchange) {
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exchange.abort();
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exchange.close();
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}
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/**
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* Closes an active SASL exchange.
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*/
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public void close(SaslExchange exchange) {
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exchange.close();
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}
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private byte[] decodeBase64(String value) {
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return Base64.getDecoder().decode(value);
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}
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private byte[] decodeInitialClientResponse(String value) {
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if (value.equals("=")) {
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return new byte[0];
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}
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return decodeBase64(value);
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}
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private String stripTrailingCrlf(byte[] line) {
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String value = new String(line, StandardCharsets.US_ASCII);
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if (value.endsWith("\r\n")) {
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return value.substring(0, value.length() - 2);
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}
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return value;
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}
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}

‎protocols/smtp/src/test/java/org/apache/james/protocols/smtp/core/esmtp/SmtpSaslBridgeTest.java‎

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/****************************************************************
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* Licensed to the Apache Software Foundation (ASF) under one *
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* or more contributor license agreements. See the NOTICE file *
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* distributed with this work for additional information *
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* regarding copyright ownership. The ASF licenses this file *
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* to you under the Apache License, Version 2.0 (the *
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* "License"); you may not use this file except in compliance *
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* with the License. You may obtain a copy of the License at *
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* *
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* http://www.apache.org/licenses/LICENSE-2.0 *
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* *
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* Unless required by applicable law or agreed to in writing, *
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* software distributed under the License is distributed on an *
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY *
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* KIND, either express or implied. See the License for the *
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* specific language governing permissions and limitations *
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* under the License. *
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****************************************************************/
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package org.apache.james.protocols.smtp.core.esmtp;
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import static org.assertj.core.api.Assertions.assertThat;
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import java.nio.charset.StandardCharsets;
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import java.util.ArrayList;
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import java.util.Base64;
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import java.util.List;
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import java.util.Optional;
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import org.apache.james.core.Username;
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import org.apache.james.protocols.api.sasl.SaslExchange;
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import org.apache.james.protocols.api.sasl.SaslIdentity;
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import org.apache.james.protocols.api.sasl.SaslInitialRequest;
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import org.apache.james.protocols.api.sasl.SaslProtocol;
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import org.apache.james.protocols.api.sasl.SaslStep;
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import org.apache.james.protocols.smtp.SMTPResponse;
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import org.apache.james.protocols.smtp.SMTPRetCode;
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import org.junit.jupiter.api.Test;
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class SmtpSaslBridgeTest {
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private static final Username USER = Username.of("user@example.com");
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private static final SaslIdentity IDENTITY = new SaslIdentity(USER, USER);
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private final SmtpSaslBridge testee = new SmtpSaslBridge();
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private static class RecordingExchange implements SaslExchange {
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private final List<String> lifecycleEvents;
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private byte[] lastClientResponse;
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private RecordingExchange() {
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this.lifecycleEvents = new ArrayList<>();
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}
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@Override
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public SaslStep firstStep() {
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return new SaslStep.Challenge(Optional.of(bytes("challenge")));
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}
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@Override
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public SaslStep onResponse(byte[] clientResponse) {
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lastClientResponse = clientResponse.clone();
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return new SaslStep.Success(IDENTITY, Optional.empty(), "success");
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}
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@Override
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public void abort() {
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lifecycleEvents.add("abort");
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}
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@Override
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public void close() {
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lifecycleEvents.add("close");
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}
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}
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@Test
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void initialRequestShouldDecodeInitialClientResponse() {
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String encodedInitialResponse = Base64.getEncoder().encodeToString(bytes("initial"));
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SaslInitialRequest request = testee.initialRequest("PLAIN", Optional.of(encodedInitialResponse));
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assertThat(request.protocol()).isEqualTo(SaslProtocol.SMTP);
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assertThat(request.mechanismName()).isEqualTo("PLAIN");
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assertThat(request.initialResponse()).hasValueSatisfying(value -> assertThat(value).containsExactly(bytes("initial")));
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}
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@Test
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void initialRequestShouldDecodeEqualSignAsEmptyInitialClientResponse() {
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SaslInitialRequest request = testee.initialRequest("PLAIN", Optional.of("="));
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assertThat(request.initialResponse()).hasValueSatisfying(value -> assertThat(value).isEmpty());
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}
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@Test
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void challengeShouldReturnAuthReadyWithBase64EncodedChallengePayload() {
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SaslStep.Challenge challenge = new SaslStep.Challenge(Optional.of(bytes("challenge")));
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SMTPResponse response = testee.challenge(challenge);
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assertThat(response.getRetCode()).isEqualTo(SMTPRetCode.AUTH_READY);
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assertThat(response.getLines()).containsExactly(SMTPRetCode.AUTH_READY + " " + Base64.getEncoder().encodeToString(bytes("challenge")));
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}
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@Test
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void challengeShouldReturnAuthReadyWithEmptyDescriptionWhenChallengeHasNoPayload() {
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SaslStep.Challenge challenge = new SaslStep.Challenge(Optional.empty());
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SMTPResponse response = testee.challenge(challenge);
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assertThat(response.getRetCode()).isEqualTo(SMTPRetCode.AUTH_READY);
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assertThat(response.getLines()).containsExactly(SMTPRetCode.AUTH_READY + " ");
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}
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@Test
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void onClientResponseShouldDecodeLineAndContinueExchange() {
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RecordingExchange exchange = new RecordingExchange();
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byte[] line = (Base64.getEncoder().encodeToString(bytes("response")) + "\r\n").getBytes(StandardCharsets.US_ASCII);
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SaslStep step = testee.onClientResponse(exchange, line);
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assertThat(((SaslStep.Success) step).identity()).isEqualTo(IDENTITY);
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assertThat(exchange.lastClientResponse).containsExactly(bytes("response"));
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}
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@Test
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void abortShouldAbortThenCloseExchange() {
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RecordingExchange exchange = new RecordingExchange();
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testee.abort(exchange);
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assertThat(exchange.lifecycleEvents).containsExactly("abort", "close");
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}
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@Test
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void closeShouldCloseExchange() {
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RecordingExchange exchange = new RecordingExchange();
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testee.close(exchange);
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assertThat(exchange.lifecycleEvents).containsExactly("close");
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}
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private static byte[] bytes(String value) {
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return value.getBytes(StandardCharsets.UTF_8);
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}
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}

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