Add continuation token support for SyncPoller ARM LROs

- Add PollingState.toContinuationToken() and fromContinuationToken() methods
- Add SyncPoller.serializeContinuationToken() interface method
- Implement ArmLroSyncPoller wrapper with continuation token support
- Add SyncPollerFactory.resumeFromToken() to reconstruct pollers from tokens
- Add comprehensive unit and integration tests (12 tests, all passing)
- Update CHANGELOGs for azure-core and azure-core-management

This enables ARM Long-Running Operations to be resumed across process
restarts by serializing the poller state to a Base64-encoded token.

Author: markli-db

sdk/core/azure-core-management/CHANGELOG.md

@@ -4,6 +4,12 @@
 
 ### Features Added
 
+- Added continuation token support for ARM Long-Running Operations (LROs):
+  - `PollingState.toContinuationToken()` - Serialize polling state to a Base64-encoded token
+  - `PollingState.fromContinuationToken()` - Deserialize token back to polling state
+  - `SyncPollerFactory.resumeFromToken()` - Resume a SyncPoller from a continuation token
+  - `ArmLroSyncPoller` - New implementation that supports continuation tokens for ARM LROs
+
 ### Breaking Changes
 
 ### Bugs Fixed

sdk/core/azure-core-management/src/main/java/com/azure/core/management/implementation/polling/PollingState.java

@@ -169,6 +169,81 @@ public <T> void store(PollingContext<T> context) {
         }
     }
 
+    /**
+     * Serializes the current PollingState into a continuation token string that can be used to resume
+     * the long-running operation at a later time or in a different process.
+     * <p>
+     * The continuation token is a Base64-encoded JSON representation of the polling state. It contains
+     * all necessary information to reconstruct the poller and continue polling the operation, including:
+     * <ul>
+     * <li>Operation URL and HTTP method</li>
+     * <li>Current provisioning state</li>
+     * <li>Polling URLs (Azure-AsyncOperation, Location headers, etc.)</li>
+     * <li>Last known response data</li>
+     * </ul>
+     * <p>
+     * <strong>Security Note:</strong> The continuation token contains the operation URL. Ensure tokens
+     * are stored securely and transmitted over secure channels.
+     * <p>
+     * <strong>Compatibility Note:</strong> The token format is internal and may change between SDK versions.
+     * Tokens should only be used with the same version of the SDK that generated them.
+     *
+     * @return A Base64-encoded continuation token string representing the current polling state.
+     * @throws RuntimeException if the state cannot be serialized into a token.
+     */
+    public String toContinuationToken() {
+        try {
+            String jsonState = this.serializerAdapter.serialize(this, SerializerEncoding.JSON);
+            return java.util.Base64.getEncoder()
+                .encodeToString(jsonState.getBytes(java.nio.charset.StandardCharsets.UTF_8));
+        } catch (IOException ioe) {
+            throw LOGGER.logExceptionAsError(
+                new RuntimeException("Failed to serialize PollingState to continuation token.", ioe));
+        }
+    }
+
+    /**
+     * Deserializes a continuation token string into a PollingState object that can be used to resume
+     * a long-running operation.
+     * <p>
+     * This method is the counterpart to {@link #toContinuationToken()} and reconstructs a PollingState
+     * from a previously serialized token. The reconstructed state can then be used to create a new
+     * SyncPoller that continues polling from where the previous poller left off.
+     *
+     * @param continuationToken The Base64-encoded continuation token string, previously obtained from
+     *                          {@link #toContinuationToken()}.
+     * @param serializerAdapter The serializer for decoding the token. This should be the same serializer
+     *                          type used by the service client.
+     * @return A PollingState object reconstructed from the continuation token.
+     * @throws IllegalArgumentException if the {@code continuationToken} or {@code serializerAdapter} is null or empty.
+     * @throws RuntimeException if the token cannot be decoded or deserialized. This may occur if:
+     *         <ul>
+     *         <li>The token is malformed or corrupted</li>
+     *         <li>The token was created with a different SDK version</li>
+     *         <li>The token format has changed</li>
+     *         </ul>
+     */
+    public static PollingState fromContinuationToken(String continuationToken, SerializerAdapter serializerAdapter) {
+        Objects.requireNonNull(continuationToken, "'continuationToken' cannot be null.");
+        Objects.requireNonNull(serializerAdapter, "'serializerAdapter' cannot be null.");
+
+        if (continuationToken.isEmpty()) {
+            throw LOGGER.logExceptionAsError(new IllegalArgumentException("'continuationToken' cannot be empty."));
+        }
+
+        try {
+            byte[] decodedBytes = java.util.Base64.getDecoder().decode(continuationToken);
+            String jsonState = new String(decodedBytes, java.nio.charset.StandardCharsets.UTF_8);
+            return PollingState.from(serializerAdapter, jsonState);
+        } catch (IllegalArgumentException iae) {
+            throw LOGGER.logExceptionAsError(new RuntimeException(
+                "Failed to decode continuation token. The token may be malformed or corrupted.", iae));
+        } catch (RuntimeException re) {
+            throw LOGGER.logExceptionAsError(new RuntimeException("Failed to deserialize continuation token. "
+                + "The token may have been created with a different SDK version.", re));
+        }
+    }
+
     /**
      * @return the current status of the long-running-operation.
      */
@@ -277,7 +352,7 @@ FinalResult getFinalResult() {
     /**
      * @return the last response body this PollingState received
      */
-    String getLastResponseBody() {
+    public String getLastResponseBody() {
         return this.lastResponseBody;
     }
 

sdk/core/azure-core-management/src/main/java/com/azure/core/management/polling/ArmLroSyncPoller.java

@@ -0,0 +1,119 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.core.management.polling;
+
+import com.azure.core.management.implementation.polling.PollingState;
+import com.azure.core.util.logging.ClientLogger;
+import com.azure.core.util.polling.PollResponse;
+import com.azure.core.util.polling.PollingContext;
+import com.azure.core.util.polling.SyncPoller;
+import com.azure.core.util.serializer.SerializerAdapter;
+
+import java.time.Duration;
+import java.util.Objects;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+
+/**
+ * Azure Resource Manager (ARM) Long-Running Operation SyncPoller implementation with continuation token support.
+ * <p>
+ * This implementation wraps a standard {@link SyncPoller} and adds ARM-specific functionality including
+ * the ability to serialize the poller state to a continuation token and resume from such a token.
+ * <p>
+ * This class is package-private and should only be created through {@link SyncPollerFactory}.
+ *
+ * @param <T> The type of poll response value.
+ * @param <U> The type of the final result of long-running operation.
+ */
+final class ArmLroSyncPoller<T, U> implements SyncPoller<PollResult<T>, U> {
+    private static final ClientLogger LOGGER = new ClientLogger(ArmLroSyncPoller.class);
+
+    private final SyncPoller<PollResult<T>, U> innerPoller;
+    private final SerializerAdapter serializerAdapter;
+    // We'll need a way to access the PollingContext from the inner poller
+    // Since SimpleSyncPoller doesn't expose it, we'll need to track it ourselves
+    private final PollingContextAccessor<PollResult<T>> contextAccessor;
+
+    /**
+     * Functional interface to access the PollingContext from a poller.
+     */
+    @FunctionalInterface
+    interface PollingContextAccessor<T> {
+        PollingContext<T> getContext();
+    }
+
+    /**
+     * Creates an ArmLroSyncPoller.
+     *
+     * @param innerPoller The underlying SyncPoller implementation.
+     * @param serializerAdapter The serializer for encoding/decoding.
+     * @param contextAccessor Accessor to get the current PollingContext.
+     */
+    ArmLroSyncPoller(SyncPoller<PollResult<T>, U> innerPoller, SerializerAdapter serializerAdapter,
+        PollingContextAccessor<PollResult<T>> contextAccessor) {
+        this.innerPoller = Objects.requireNonNull(innerPoller, "'innerPoller' cannot be null.");
+        this.serializerAdapter = Objects.requireNonNull(serializerAdapter, "'serializerAdapter' cannot be null.");
+        this.contextAccessor = Objects.requireNonNull(contextAccessor, "'contextAccessor' cannot be null.");
+    }
+
+    @Override
+    public PollResponse<PollResult<T>> poll() {
+        return innerPoller.poll();
+    }
+
+    @Override
+    public PollResponse<PollResult<T>> waitForCompletion() {
+        return innerPoller.waitForCompletion();
+    }
+
+    @Override
+    public PollResponse<PollResult<T>> waitForCompletion(Duration timeout) {
+        return innerPoller.waitForCompletion(timeout);
+    }
+
+    @Override
+    public PollResponse<PollResult<T>>
+        waitUntil(com.azure.core.util.polling.LongRunningOperationStatus statusToWaitFor) {
+        return innerPoller.waitUntil(statusToWaitFor);
+    }
+
+    @Override
+    public PollResponse<PollResult<T>> waitUntil(Duration timeout,
+        com.azure.core.util.polling.LongRunningOperationStatus statusToWaitFor) {
+        return innerPoller.waitUntil(timeout, statusToWaitFor);
+    }
+
+    @Override
+    public U getFinalResult() {
+        return innerPoller.getFinalResult();
+    }
+
+    @Override
+    public U getFinalResult(Duration timeout) {
+        return innerPoller.getFinalResult(timeout);
+    }
+
+    @Override
+    public void cancelOperation() {
+        innerPoller.cancelOperation();
+    }
+
+    @Override
+    public SyncPoller<PollResult<T>, U> setPollInterval(Duration pollInterval) {
+        innerPoller.setPollInterval(pollInterval);
+        return this;
+    }
+
+    @Override
+    public String serializeContinuationToken() {
+        try {
+            PollingContext<PollResult<T>> context = contextAccessor.getContext();
+            PollingState pollingState = PollingState.from(serializerAdapter, context);
+            return pollingState.toContinuationToken();
+        } catch (Exception e) {
+            throw LOGGER.logExceptionAsError(new RuntimeException("Failed to serialize continuation token. "
+                + "The poller may not have been started or the polling state may be unavailable.", e));
+        }
+    }
+}

sdk/core/azure-core-management/src/main/java/com/azure/core/management/polling/SyncPollerFactory.java

@@ -5,14 +5,19 @@
 
 import com.azure.core.http.HttpPipeline;
 import com.azure.core.http.rest.Response;
+import com.azure.core.management.implementation.polling.PollOperation;
+import com.azure.core.management.implementation.polling.PollingState;
 import com.azure.core.management.implementation.polling.SyncPollOperation;
 import com.azure.core.util.BinaryData;
 import com.azure.core.util.Context;
+import com.azure.core.util.polling.PollResponse;
+import com.azure.core.util.polling.PollingContext;
 import com.azure.core.util.polling.SyncPoller;
 import com.azure.core.util.serializer.SerializerAdapter;
 
 import java.lang.reflect.Type;
 import java.time.Duration;
+import java.util.function.Function;
 import java.util.function.Supplier;
 
 /**
@@ -62,10 +67,132 @@ public static <T, U> SyncPoller<PollResult<T>, U> create(SerializerAdapter seria
     public static <T, U> SyncPoller<PollResult<T>, U> create(SerializerAdapter serializerAdapter,
         HttpPipeline httpPipeline, Type pollResultType, Type finalResultType, Duration defaultPollDuration,
         Supplier<Response<BinaryData>> lroInitialResponseSupplier, Context context) {
-        return SyncPoller.createPoller(defaultPollDuration,
-            SyncPollOperation.activationFunction(serializerAdapter, pollResultType, lroInitialResponseSupplier),
+
+        // Create a holder for the PollingContext that we can access later
+        @SuppressWarnings({ "unchecked", "rawtypes" })
+        final PollingContext<PollResult<T>>[] contextHolder = (PollingContext<PollResult<T>>[]) new PollingContext[1];
+
+        // Wrap the activation function to capture the context
+        Function<PollingContext<PollResult<T>>, PollResponse<PollResult<T>>> wrappedActivation = pollingContext -> {
+            contextHolder[0] = pollingContext;
+            return SyncPollOperation
+                .<T>activationFunction(serializerAdapter, pollResultType, lroInitialResponseSupplier)
+                .apply(pollingContext);
+        };
+
+        SyncPoller<PollResult<T>, U> innerPoller = SyncPoller.createPoller(defaultPollDuration, wrappedActivation,
+            SyncPollOperation.pollFunction(serializerAdapter, httpPipeline, pollResultType, context),
+            SyncPollOperation.cancelFunction(context),
+            SyncPollOperation.fetchResultFunction(serializerAdapter, httpPipeline, finalResultType, context));
+
+        // Wrap in ArmLroSyncPoller to add continuation token support
+        return new ArmLroSyncPoller<>(innerPoller, serializerAdapter, () -> contextHolder[0]);
+    }
+
+    /**
+     * Resumes a SyncPoller for an Azure Resource Manager (ARM) long-running-operation (LRO) from a continuation token.
+     * <p>
+     * This method recreates a SyncPoller from a previously serialized continuation token, allowing the polling
+     * operation to be resumed from its last known state. This is useful for scenarios where a process needs to
+     * survive restarts or where polling needs to be transferred between different processes or instances.
+     * <p>
+     * The continuation token must have been obtained from a previous poller via
+     * {@link SyncPoller#serializeContinuationToken()}.
+     * <p>
+     * <strong>Example: Resuming a server creation operation</strong>
+     * <pre>{@code
+     * // Original process - start operation and get token
+     * SyncPoller<PollResult<ServerInner>, ServerInner> poller = 
+     *     client.beginCreate(resourceGroup, serverName, parameters);
+     * String token = poller.serializeContinuationToken();
+     * // Store token...
+     * 
+     * // Later, in a different process - resume from token
+     * SyncPoller<PollResult<ServerInner>, ServerInner> resumedPoller = 
+     *     SyncPollerFactory.resumeFromToken(
+     *         token,
+     *         client.getSerializerAdapter(),
+     *         client.getHttpPipeline(),
+     *         new TypeReference<PollResult<ServerInner>>() {}.getJavaType(),
+     *         ServerInner.class,
+     *         Duration.ofSeconds(30),
+     *         Context.NONE);
+     * 
+     * // Continue polling until completion
+     * ServerInner result = resumedPoller.getFinalResult();
+     * }</pre>
+     *
+     * @param continuationToken The Base64-encoded continuation token string obtained from a previous poller.
+     * @param serializerAdapter The serializer for any encoding and decoding. This should be the same type
+     *                          as used by the original poller.
+     * @param httpPipeline The HttpPipeline for making HTTP requests (e.g., poll requests). This should be
+     *                     configured with the same authentication and policies as the original poller.
+     * @param pollResultType The type of the poll result. If no result is expected, this should be Void.class.
+     * @param finalResultType The type of the final result. If no result is expected, this should be Void.class.
+     * @param defaultPollDuration The default poll interval to use if the service does not return a retry-after value.
+     * @param context The context shared by all requests.
+     * @param <T> The type of poll result.
+     * @param <U> The type of final result.
+     * @return A SyncPoller that resumes polling from the state captured in the continuation token.
+     * @throws IllegalArgumentException if {@code continuationToken} or {@code serializerAdapter} is null or empty.
+     * @throws RuntimeException if the token cannot be decoded or deserialized, which may occur if:
+     *         <ul>
+     *         <li>The token is malformed or corrupted</li>
+     *         <li>The token was created with a different SDK version</li>
+     *         <li>The token format has changed</li>
+     *         </ul>
+     */
+    public static <T, U> SyncPoller<PollResult<T>, U> resumeFromToken(String continuationToken,
+        SerializerAdapter serializerAdapter, HttpPipeline httpPipeline, Type pollResultType, Type finalResultType,
+        Duration defaultPollDuration, Context context) {
+
+        // Deserialize the continuation token to get the PollingState
+        PollingState pollingState = PollingState.fromContinuationToken(continuationToken, serializerAdapter);
+
+        // Create a holder for the PollingContext
+        @SuppressWarnings({ "unchecked", "rawtypes" })
+        final PollingContext<PollResult<T>>[] contextHolder = (PollingContext<PollResult<T>>[]) new PollingContext[1];
+
+        // Create an activation function that returns the current state as the activation response
+        Function<PollingContext<PollResult<T>>, PollResponse<PollResult<T>>> activationFunction = pollingContext -> {
+            contextHolder[0] = pollingContext;
+            pollingState.store(pollingContext);
+            T result = PollOperation.deserialize(serializerAdapter, pollingState.getLastResponseBody(), pollResultType);
+            return new PollResponse<>(pollingState.getOperationStatus(), new PollResult<>(result),
+                pollingState.getPollDelay());
+        };
+
+        // Create the poller with the standard poll, cancel, and fetch result functions
+        SyncPoller<PollResult<T>, U> innerPoller = SyncPoller.createPoller(defaultPollDuration, activationFunction,
             SyncPollOperation.pollFunction(serializerAdapter, httpPipeline, pollResultType, context),
             SyncPollOperation.cancelFunction(context),
             SyncPollOperation.fetchResultFunction(serializerAdapter, httpPipeline, finalResultType, context));
+
+        // Wrap in ArmLroSyncPoller to add continuation token support
+        return new ArmLroSyncPoller<>(innerPoller, serializerAdapter, () -> contextHolder[0]);
+    }
+
+    /**
+     * Resumes a SyncPoller for an Azure Resource Manager (ARM) long-running-operation (LRO) from a continuation token.
+     * <p>
+     * This is a convenience overload that uses {@link Context#NONE} for the context parameter.
+     *
+     * @param continuationToken The Base64-encoded continuation token string obtained from a previous poller.
+     * @param serializerAdapter The serializer for any encoding and decoding.
+     * @param httpPipeline The HttpPipeline for making HTTP requests.
+     * @param pollResultType The type of the poll result.
+     * @param finalResultType The type of the final result.
+     * @param defaultPollDuration The default poll interval to use.
+     * @param <T> The type of poll result.
+     * @param <U> The type of final result.
+     * @return A SyncPoller that resumes polling from the state captured in the continuation token.
+     * @throws IllegalArgumentException if {@code continuationToken} or {@code serializerAdapter} is null or empty.
+     * @throws RuntimeException if the token cannot be decoded or deserialized.
+     */
+    public static <T, U> SyncPoller<PollResult<T>, U> resumeFromToken(String continuationToken,
+        SerializerAdapter serializerAdapter, HttpPipeline httpPipeline, Type pollResultType, Type finalResultType,
+        Duration defaultPollDuration) {
+        return resumeFromToken(continuationToken, serializerAdapter, httpPipeline, pollResultType, finalResultType,
+            defaultPollDuration, Context.NONE);
     }
 }

sdk/core/azure-core-management/src/test/java/com/azure/core/management/implementation/polling/FooWithProvisioningState.java

@@ -12,12 +12,12 @@ public class FooWithProvisioningState {
     public FooWithProvisioningState() {
     }
 
-    FooWithProvisioningState(String state) {
+    public FooWithProvisioningState(String state) {
         this.properties = new Properties();
         this.properties.provisioningState = state;
     }
 
-    FooWithProvisioningState(String state, String resourceId) {
+    public FooWithProvisioningState(String state, String resourceId) {
         this.properties = new Properties();
         this.properties.provisioningState = state;
         this.properties.resourceId = resourceId;