Add Redirect Policy to Azure core

sdk/core/azure-core/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Features Added
 
 - Added `HttpAuthorization` which supports configuring a generic `Authorization` header on a request.
+- Added `RedirectPolicy` to standardize the ability to redirect HTTP requests.
 
 ## 1.19.0 (2021-08-06)
 

sdk/core/azure-core/src/main/java/com/azure/core/http/policy/BearerTokenAuthenticationPolicy.java

@@ -92,7 +92,7 @@ public Mono<HttpResponse> process(HttpPipelineCallContext context, HttpPipelineN
      * Authorizes the request with the bearer token acquired using the specified {@code tokenRequestContext}
      *
      * @param context the HTTP pipeline context.
-     * @param tokenRequestContext the token request conext to be used for token acquisition.
+     * @param tokenRequestContext the token request context to be used for token acquisition.
      * @return a {@link Mono} containing {@link Void}
      */
     public Mono<Void> setAuthorizationHeader(HttpPipelineCallContext context, TokenRequestContext tokenRequestContext) {

sdk/core/azure-core/src/main/java/com/azure/core/http/policy/DefaultRedirectStrategy.java

@@ -0,0 +1,198 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.core.http.policy;
+
+import com.azure.core.http.HttpHeaders;
+import com.azure.core.http.HttpMethod;
+import com.azure.core.http.HttpPipelineCallContext;
+import com.azure.core.http.HttpRequest;
+import com.azure.core.http.HttpResponse;
+import com.azure.core.util.CoreUtils;
+import com.azure.core.util.logging.ClientLogger;
+
+import java.net.HttpURLConnection;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * A default implementation of {@link RedirectStrategy} that uses the provided maximum retry attempts,
+ * header name to look up redirect url value for, http methods and a known set of
+ * redirect status response code (301, 302, 307, 308) to determine if request should be redirected.
+ */
+public final class DefaultRedirectStrategy implements RedirectStrategy {
+    private final ClientLogger logger = new ClientLogger(DefaultRedirectStrategy.class);
+
+    private static final int DEFAULT_MAX_REDIRECT_ATTEMPTS = 3;
+    private static final String DEFAULT_REDIRECT_LOCATION_HEADER_NAME = "Location";
+    private static final int PERMANENT_REDIRECT_STATUS_CODE = 308;
+    private static final int TEMPORARY_REDIRECT_STATUS_CODE = 307;
+    private static final Set<HttpMethod> DEFAULT_REDIRECT_ALLOWED_METHODS = new HashSet<HttpMethod>() {
+        {
+            add(HttpMethod.GET);
+            add(HttpMethod.HEAD);
+        }
+    };
+
+    private final int maxAttempts;
+    private final String locationHeader;
+    private final Set<HttpMethod> redirectMethods;
+
+    /**
+     * Creates an instance of {@link DefaultRedirectStrategy} with a maximum number of redirect attempts 3,
+     * header name "Location" to locate the redirect url in the response headers and {@link HttpMethod#GET}
+     * and {@link HttpMethod#HEAD} as allowed methods for performing the redirect.
+     *
+     * @throws IllegalArgumentException if {@code maxAttempts} is less than 0.
+     */
+    public DefaultRedirectStrategy() {
+        this(DEFAULT_MAX_REDIRECT_ATTEMPTS, DEFAULT_REDIRECT_LOCATION_HEADER_NAME, DEFAULT_REDIRECT_ALLOWED_METHODS);
+    }
+
+    /**
+     * Creates an instance of {@link DefaultRedirectStrategy} with the provided number of redirect attempts and
+     * default header name "Location" to locate the redirect url in the response headers and {@link HttpMethod#GET}
+     * and {@link HttpMethod#HEAD} as allowed methods for performing the redirect.
+     *
+     * @param maxAttempts The max number of redirect attempts that can be made.
+     * @throws IllegalArgumentException if {@code maxAttempts} is less than 0.
+     */
+    public DefaultRedirectStrategy(int maxAttempts) {
+        this(maxAttempts, DEFAULT_REDIRECT_LOCATION_HEADER_NAME, DEFAULT_REDIRECT_ALLOWED_METHODS);
+    }
+
+    /**
+     * Creates an instance of {@link DefaultRedirectStrategy}.
+     *
+     * @param maxAttempts The max number of redirect attempts that can be made.
+     * @param locationHeader The header name containing the redirect URL.
+     * @param allowedMethods The set of {@link HttpMethod} that are allowed to be redirected.
+     * @throws IllegalArgumentException if {@code maxAttempts} is less than 0.
+     */
+    public DefaultRedirectStrategy(int maxAttempts, String locationHeader, Set<HttpMethod> allowedMethods) {
+        if (maxAttempts < 0) {
+            throw logger.logExceptionAsError(new IllegalArgumentException("Max attempts cannot be less than 0."));
+        }
+        this.maxAttempts = maxAttempts;
+        this.locationHeader = locationHeader == null ? DEFAULT_REDIRECT_LOCATION_HEADER_NAME : locationHeader;
+        this.redirectMethods = allowedMethods == null ? DEFAULT_REDIRECT_ALLOWED_METHODS : allowedMethods;
+    }
+
+    @Override
+    public boolean shouldAttemptRedirect(HttpPipelineCallContext context,
+                                         HttpResponse httpResponse, int tryCount,
+                                         Set<String> attemptedRedirectUrls) {
+        String redirectUrl =
+            tryGetRedirectHeader(httpResponse.getHeaders(), this.getLocationHeader());
+
+        if (isValidRedirectCount(tryCount)
+            && !alreadyAttemptedRedirectUrl(redirectUrl, attemptedRedirectUrls)
+            && isValidRedirectStatusCode(httpResponse.getStatusCode())
+            && isAllowedRedirectMethod(httpResponse.getRequest().getHttpMethod())) {
+            logger.verbose("[Redirecting] Try count: {}, Attempted Redirect URLs: {}", tryCount,
+                attemptedRedirectUrls.toString());
+            attemptedRedirectUrls.add(redirectUrl);
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    @Override
+    public HttpRequest createRedirect(HttpResponse httpResponse) {
+        String responseLocation =
+            tryGetRedirectHeader(httpResponse.getHeaders(), this.getLocationHeader());
+        if (responseLocation != null) {
+            return httpResponse.getRequest().setUrl(responseLocation);
+        } else {
+            return httpResponse.getRequest();
+        }
+    }
+
+    @Override
+    public int getMaxAttempts() {
+        return maxAttempts;
+    }
+
+    @Override
+    public String getLocationHeader() {
+        return locationHeader;
+    }
+
+    @Override
+    public Set<HttpMethod> getAllowedMethods() {
+        return redirectMethods;
+    }
+
+    /**
+     * Check if the redirect url provided in the response headers is already attempted.
+     *
+     * @param redirectUrl the redirect url provided in the response header.
+     * @param attemptedRedirectUrls the set containing a list of attempted redirect locations.
+     * @return {@code true} if the redirectUrl provided in the response header is already being attempted for redirect
+     * , {@code false} otherwise.
+     */
+    private boolean alreadyAttemptedRedirectUrl(String redirectUrl,
+                                                Set<String> attemptedRedirectUrls) {
+        if (attemptedRedirectUrls.contains(redirectUrl)) {
+            logger.error(String.format("Request was redirected more than once to: %s", redirectUrl));
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * Check if the attempt count of the redirect is less than the {@code maxAttempts}
+     *
+     * @param tryCount the try count for the HTTP request associated to the HTTP response.
+     * @return {@code true} if the {@code tryCount} is greater than the {@code maxAttempts}, {@code false} otherwise.
+     */
+    private boolean isValidRedirectCount(int tryCount) {
+        if (tryCount >= getMaxAttempts()) {
+            logger.error(String.format("Request has been redirected more than %d times.", getMaxAttempts()));
+            return false;
+        }
+        return true;
+    }
+
+    /**
+     * Check if the request http method is a valid redirect method.
+     *
+     * @param httpMethod the http method of the request.
+     * @return {@code true} if the request {@code httpMethod} is a valid http redirect method, {@code false} otherwise.
+     */
+    private boolean isAllowedRedirectMethod(HttpMethod httpMethod) {
+        if (getAllowedMethods().contains(httpMethod)) {
+            return true;
+        } else {
+            logger.error(
+                String.format("Request was redirected from a non redirect-able method: %s", httpMethod));
+            return false;
+        }
+    }
+
+    /**
+     * Checks if the incoming request status code is a valid redirect status code.
+     *
+     * @param statusCode the status code of the incoming request.
+     * @return {@code true} if the request {@code statusCode} is a valid http redirect method, {@code false} otherwise.
+     */
+    private boolean isValidRedirectStatusCode(int statusCode) {
+        return statusCode == HttpURLConnection.HTTP_MOVED_TEMP
+            || statusCode == HttpURLConnection.HTTP_MOVED_PERM
+            || statusCode == PERMANENT_REDIRECT_STATUS_CODE
+            || statusCode == TEMPORARY_REDIRECT_STATUS_CODE;
+    }
+
+    /**
+     * Gets the redirect url from the response headers.
+     *
+     * @param headers the http response headers.
+     * @param headerName the header name to look up value for.
+     * @return the header value for the provided header name, {@code null} otherwise.
+     */
+    private static String tryGetRedirectHeader(HttpHeaders headers, String headerName) {
+        String headerValue = headers.getValue(headerName);
+        return CoreUtils.isNullOrEmpty(headerValue) ? null : headerValue;
+    }
+}

sdk/core/azure-core/src/main/java/com/azure/core/http/policy/RedirectPolicy.java

@@ -0,0 +1,70 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.core.http.policy;
+
+import com.azure.core.http.HttpPipelineCallContext;
+import com.azure.core.http.HttpPipelineNextPolicy;
+import com.azure.core.http.HttpRequest;
+import com.azure.core.http.HttpResponse;
+import reactor.core.publisher.Mono;
+
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * A {@link HttpPipelinePolicy} that redirects a {@link HttpRequest} when an HTTP Redirect is received as response.
+ */
+public final class RedirectPolicy implements HttpPipelinePolicy {
+    private final RedirectStrategy redirectStrategy;
+    private final Set<String> attemptedRedirectUrls = new HashSet<>();
+
+    /**
+     * Creates {@link RedirectPolicy} with default {@link DefaultRedirectStrategy} as {@link RedirectStrategy} and
+     * uses the redirect status response code (301, 302, 307, 308) to determine if this request should be redirected.
+     */
+    public RedirectPolicy() {
+        this(new DefaultRedirectStrategy());
+    }
+
+    /**
+     * Creates {@link RedirectPolicy} with the provided {@code redirectStrategy} as {@link RedirectStrategy} and
+     * uses the redirect status response code (301, 302, 307, 308) to determine if this request should be redirected.
+     *
+     * @param redirectStrategy The {@link RedirectStrategy} used for redirection.
+     * @throws NullPointerException When {@code redirectStrategy} is null.
+     */
+    public RedirectPolicy(RedirectStrategy redirectStrategy) {
+        this.redirectStrategy = Objects.requireNonNull(redirectStrategy, "'redirectStrategy' cannot be null.");
+    }
+
+    @Override
+    public Mono<HttpResponse> process(HttpPipelineCallContext context, HttpPipelineNextPolicy next) {
+        return attemptRedirect(context, next, context.getHttpRequest(), 1);
+    }
+
+    /**
+     * Function to process through the HTTP Response received in the pipeline
+     * and redirect sending the request with new redirect url.
+     */
+    private Mono<HttpResponse> attemptRedirect(final HttpPipelineCallContext context,
+                                               final HttpPipelineNextPolicy next,
+                                               final HttpRequest originalHttpRequest,
+                                               final int redirectAttempt) {
+        context.setHttpRequest(originalHttpRequest.copy());
+
+        return next.clone().process()
+            .flatMap(httpResponse -> {
+                if (redirectStrategy.shouldAttemptRedirect(context, httpResponse, redirectAttempt, attemptedRedirectUrls)) {
+                    HttpRequest redirectRequestCopy = redirectStrategy.createRedirect(httpResponse);
+                    return httpResponse.getBody()
+                        .ignoreElements()
+                        .then(attemptRedirect(context, next, redirectRequestCopy, redirectAttempt + 1));
+                } else {
+                    return Mono.just(httpResponse);
+                }
+            });
+    }
+
+}

sdk/core/azure-core/src/main/java/com/azure/core/http/policy/RedirectStrategy.java

@@ -0,0 +1,57 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.core.http.policy;
+
+import com.azure.core.http.HttpMethod;
+import com.azure.core.http.HttpPipelineCallContext;
+import com.azure.core.http.HttpRequest;
+import com.azure.core.http.HttpResponse;
+
+import java.util.Set;
+
+/**
+ * The interface for determining the {@link RedirectStrategy redirect strategy} used in {@link RedirectPolicy}.
+ */
+public interface RedirectStrategy {
+    /**
+     * Max number of redirect attempts to be made.
+     *
+     * @return The max number of redirect attempts.
+     */
+    int getMaxAttempts();
+
+    /**
+     * The header name to look up the value for the redirect url in response headers.
+     *
+     * @return the value of the header, or null if the header doesn't exist in the response.
+     */
+    String getLocationHeader();
+
+    /**
+     * The {@link HttpMethod http methods} that are allowed to be redirected.
+     *
+     * @return the set of redirect allowed methods.
+     */
+    Set<HttpMethod> getAllowedMethods();
+
+    /**
+     * Determines if the url should be redirected between each try.
+     *
+     * @param context the {@link HttpPipelineCallContext HTTP pipeline context}.
+     * @param httpResponse the {@link HttpRequest} containing the redirect url present in the response headers
+     * @param tryCount redirect attempts so far
+     * @param attemptedRedirectUrls attempted redirect locations used so far.
+     * @return {@code true} if the request should be redirected, {@code false} otherwise
+     */
+    boolean shouldAttemptRedirect(HttpPipelineCallContext context, HttpResponse httpResponse, int tryCount,
+                                  Set<String> attemptedRedirectUrls);
+
+    /**
+     * Creates the {@link HttpRequest request} for the redirect attempt.
+     *
+     * @param httpResponse the {@link HttpRequest} containing the redirect url present in the response headers
+     * @return the modified {@link HttpRequest} to redirect the incoming request.
+     */
+    HttpRequest createRedirect(HttpResponse httpResponse);
+}