JAL-1705 check Retry-After response header

diff --git a/src/jalview/ext/ensembl/EnsemblRestClient.java b/src/jalview/ext/ensembl/EnsemblRestClient.java
index 1c47373..34f8816 100644 (file)
--- a/src/jalview/ext/ensembl/EnsemblRestClient.java
+++ b/src/jalview/ext/ensembl/EnsemblRestClient.java
@@ -44,6 +44,11 @@ abstract class EnsemblRestClient extends EnsemblSequenceFetcher
 
   private static long lastCheck = -1;
 
+  /*
+   * absolute time to wait till if we overloaded the REST service
+   */
+  private static long retryAfter;
+
   protected volatile boolean inProgress = false;
 
   /**
@@ -228,6 +233,8 @@ abstract class EnsemblRestClient extends EnsemblSequenceFetcher
     }
     // System.out.println(getClass().getName() + " took "
     // + (System.currentTimeMillis() - now) + "ms to fetch");
+
+    checkRateLimits(connection);
   
     BufferedReader reader = null;
     reader = new BufferedReader(new InputStreamReader(response, "UTF-8"));
@@ -235,6 +242,52 @@ abstract class EnsemblRestClient extends EnsemblSequenceFetcher
   }
 
   /**
+   * Inspect response headers for any sign of server overload and respect any
+   * 'retry-after' directive
+   * 
+   * @see https://github.com/Ensembl/ensembl-rest/wiki/Rate-Limits
+   * @param connection
+   */
+  void checkRateLimits(HttpURLConnection connection)
+  {
+    // number of requests allowed per time interval:
+    String limit = connection.getHeaderField("X-RateLimit-Limit");
+    // length of quota time interval in seconds:
+    // String period = connection.getHeaderField("X-RateLimit-Period");
+    // seconds remaining until usage quota is reset:
+    String reset = connection.getHeaderField("X-RateLimit-Reset");
+    // number of requests remaining from quota for current period:
+    String remaining = connection.getHeaderField("X-RateLimit-Remaining");
+    // number of seconds to wait before retrying (if remaining == 0)
+    String retryDelay = connection.getHeaderField("Retry-After");
+
+    // to test:
+    // retryDelay = "5";
+
+    if (retryDelay != null)
+    {
+      System.err.println("Ensembl REST service rate limit exceeded, wait "
+              + retryDelay + " seconds before retrying");
+      try
+      {
+        retryAfter = System.currentTimeMillis()
+                + (1000 * Integer.valueOf(retryDelay));
+      } catch (NumberFormatException e)
+      {
+        System.err.println("Unexpected value for Retry-After: "
+                + retryDelay);
+      }
+    }
+    else
+    {
+      retryAfter = 0;
+      // debug:
+      // System.out.println(String.format(
+      // "%s Ensembl requests remaining of %s (reset in %ss)",
+      // remaining, limit, reset));
+    }
+  }
+  /**
    * Rechecks if Ensembl is responding, unless the last check was successful and
    * the retest interval has not yet elapsed. Returns true if Ensembl is up,
    * else false.
@@ -244,6 +297,21 @@ abstract class EnsemblRestClient extends EnsemblSequenceFetcher
   protected boolean isEnsemblAvailable()
   {
     long now = System.currentTimeMillis();
+
+    /*
+     * check if we are waiting for 'Retry-After' to expire
+     */
+    if (retryAfter > now)
+    {
+      System.err.println("Still " + (1 + (retryAfter - now) / 1000)
+              + " secs to wait before retrying Ensembl");
+      return false;
+    }
+    else
+    {
+      retryAfter = 0;
+    }
+
     boolean retest = now - lastCheck > RETEST_INTERVAL;
     if (ensemblRestAvailable && !retest)
     {