Merge pull request #5 from sornerol/1-429_retry

Retry when receiving a 429 response code

Author: sornerol

src/main/java/io/github/sornerol/chess/pubapi/client/PubApiClientBase.java

@@ -2,11 +2,11 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import io.github.sornerol.chess.pubapi.client.enums.ResponseCode;
+import io.github.sornerol.chess.pubapi.client.enums.RetryStrategy;
 import io.github.sornerol.chess.pubapi.exception.ChessComPubApiException;
 import lombok.Getter;
 import lombok.Setter;
 import org.apache.commons.io.IOUtils;
-import org.apache.http.Header;
 import org.apache.http.client.methods.CloseableHttpResponse;
 import org.apache.http.client.methods.HttpGet;
 import org.apache.http.impl.client.CloseableHttpClient;
@@ -22,20 +22,68 @@
  */
 abstract class PubApiClientBase {
 
+    /**
+     * Default value for retryInterval.
+     */
+    public static final Integer DEFAULT_RETRY_INTERVAL = 3;
+
+    /**
+     * Default value for maxRetries.
+     */
+    public static final Integer DEFAULT_MAX_RETRIES = 2;
+
+    /**
+     * Default value for retryStrategy.
+     */
+    public static final RetryStrategy DEFAULT_RETRY_STRATEGY = RetryStrategy.RETRY_N_TIMES;
+
     /**
      * If supplied, the userAgent value will be passed in the User-Agent header when making requests to Chess.com.
      * By specifying this value with your contact information, Chess.com can contact you in the event they need to
      * block access for your application.
+     *
      * @see <a href="https://www.chess.com/news/view/published-data-api#pubapi-general-rate-limits">Rate Limiting</a>
      */
     @Getter
     @Setter
     private String userAgent;
 
+    /**
+     * Number of seconds to wait before retrying if a request fails due to a 429 response code. If retryStrategy is set
+     * to NEVER, this field does nothing.
+     *
+     * @see <a href="https://www.chess.com/news/view/published-data-api#pubapi-general-rate-limits">Rate Limiting</a>
+     */
+    @Getter
+    @Setter
+    private Integer retryInterval;
+
+    /**
+     * Maximum number of retries when retryStrategy is RETRY_N_TIMES. This does not include the initial attempt
+     * (e.g. if maxRetries is 2, the client will make three total attempts before giving up).
+     *
+     * @see <a href="https://www.chess.com/news/view/published-data-api#pubapi-general-rate-limits">Rate Limiting</a>
+     */
+    @Getter
+    @Setter
+    private Integer maxRetries;
+
+    /**
+     * Defines the behavior to use when receiving a 429 response from the Chess.com API.
+     *
+     * @see <a href="https://www.chess.com/news/view/published-data-api#pubapi-general-rate-limits">Rate Limiting</a>
+     */
+    @Getter
+    @Setter
+    private RetryStrategy retryStrategy;
+
     private final CloseableHttpClient httpClient;
 
     protected PubApiClientBase() {
         httpClient = HttpClients.createDefault();
+        retryInterval = DEFAULT_RETRY_INTERVAL;
+        maxRetries = DEFAULT_MAX_RETRIES;
+        retryStrategy = DEFAULT_RETRY_STRATEGY;
     }
 
     /**
@@ -70,15 +118,34 @@ protected String getRequest(String endpoint) throws IOException, ChessComPubApiE
         }
 
         String responseBody;
-        try (CloseableHttpResponse response = httpClient.execute(request)) {
-            int statusCode = response.getStatusLine().getStatusCode();
-            //TODO: Handle rate throttling more gracefully
-            if (statusCode != ResponseCode.OK.getValue()) {
-                throw new ChessComPubApiException("Error executing GET request: API returned status code " + statusCode);
+        Integer attempts = 1;
+
+        boolean keepTrying = false;
+        do {
+            try (CloseableHttpResponse response = httpClient.execute(request)) {
+                int statusCode = response.getStatusLine().getStatusCode();
+                if (statusCode == ResponseCode.RATE_LIMIT_EXCEEDED.getValue() && shouldTryRequestAgain(attempts)) {
+                    keepTrying = true;
+                    attempts++;
+                    Thread.sleep(retryInterval * 1000);
+                } else if (statusCode != ResponseCode.OK.getValue()) {
+                    throw new ChessComPubApiException("Error executing GET request: API returned status code " + statusCode);
+                }
+                InputStream inputStream = response.getEntity().getContent();
+                responseBody = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
+            } catch (InterruptedException e) {
+                throw new ChessComPubApiException("Error while executing request: " + e.getMessage());
             }
-            InputStream inputStream = response.getEntity().getContent();
-            responseBody = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
-        }
+        } while (keepTrying);
+
         return responseBody;
     }
+
+    private boolean shouldTryRequestAgain(Integer attemptsSoFar) {
+        if (retryStrategy == RetryStrategy.RETRY_FOREVER) {
+            return true;
+        }
+
+        return retryStrategy == RetryStrategy.RETRY_N_TIMES && attemptsSoFar <= maxRetries;
+    }
 }

src/main/java/io/github/sornerol/chess/pubapi/client/enums/RetryStrategy.java

@@ -0,0 +1,24 @@
+package io.github.sornerol.chess.pubapi.client.enums;
+
+/**
+ * Specifies a retry strategy for the base client. When the Chess.com API returns a 429 response code, the base client
+ * will attempt to retry the request according to the specified retry strategy.
+ */
+public enum RetryStrategy {
+
+    /**
+     * Don't retry the request. In this case, the client will throw an exception if the request fails due to a 429 response.
+     */
+    NEVER,
+
+    /**
+     * Retry a specified number of times. The number of times to retry is specified in the client's maxRetries property. This is the default behavior
+     */
+    RETRY_N_TIMES,
+
+    /**
+     * If a request fails due to a 429 response, keep retrying indefinitely. This behavior is not recommended, since it could theoretically
+     * lead to an infinite loop.
+     */
+    RETRY_FOREVER
+}