Limit 20 authorization attempts.

We use one count for both redirects and authorization attempts. This
seems like good enough policy.

Closes https://github.com/square/okhttp/issues/960

okhttp-tests/src/test/java/com/squareup/okhttp/CallTest.java

@@ -328,6 +328,37 @@ public final class CallTest {
     assertEquals(credential, recordedRequest2.getHeader("Authorization"));
   }
 
+  @Test public void attemptAuthorization20Times() throws Exception {
+    for (int i = 0; i < 20; i++) {
+      server.enqueue(new MockResponse().setResponseCode(401));
+    }
+    server.enqueue(new MockResponse().setBody("Success!"));
+
+    String credential = Credentials.basic("jesse", "secret");
+    client.setAuthenticator(new RecordingOkAuthenticator(credential));
+
+    Request request = new Request.Builder().url(server.getUrl("/")).build();
+    executeSynchronously(request)
+        .assertCode(200)
+        .assertBody("Success!");
+  }
+
+  @Test public void doesNotAttemptAuthorization21Times() throws Exception {
+    for (int i = 0; i < 21; i++) {
+      server.enqueue(new MockResponse().setResponseCode(401));
+    }
+
+    String credential = Credentials.basic("jesse", "secret");
+    client.setAuthenticator(new RecordingOkAuthenticator(credential));
+
+    try {
+      client.newCall(new Request.Builder().url(server.getUrl("/0")).build()).execute();
+      fail();
+    } catch (IOException expected) {
+      assertEquals("Too many follow-up requests: 21", expected.getMessage());
+    }
+  }
+
   @Test public void delete() throws Exception {
     server.enqueue(new MockResponse().setBody("abc"));
 
@@ -1249,7 +1280,7 @@ public final class CallTest {
       client.newCall(new Request.Builder().url(server.getUrl("/0")).build()).execute();
       fail();
     } catch (IOException expected) {
-      assertEquals("Too many redirects: 21", expected.getMessage());
+      assertEquals("Too many follow-up requests: 21", expected.getMessage());
     }
   }
 
@@ -1263,7 +1294,7 @@ public final class CallTest {
 
     Request request = new Request.Builder().url(server.getUrl("/0")).build();
     client.newCall(request).enqueue(callback);
-    callback.await(server.getUrl("/20")).assertFailure("Too many redirects: 21");
+    callback.await(server.getUrl("/20")).assertFailure("Too many follow-up requests: 21");
   }
 
   @Test public void canceledBeforeExecute() throws Exception {

okhttp-tests/src/test/java/com/squareup/okhttp/internal/http/URLConnectionTest.java

@@ -2111,7 +2111,7 @@ public final class URLConnectionTest {
       fail();
     } catch (ProtocolException expected) {
       assertEquals(HttpURLConnection.HTTP_MOVED_TEMP, connection.getResponseCode());
-      assertEquals("Too many redirects: 21", expected.getMessage());
+      assertEquals("Too many follow-up requests: 21", expected.getMessage());
       assertContent("Redirecting to /21", connection);
       assertEquals(server.getUrl("/20"), connection.getURL());
     }
@@ -2786,6 +2786,37 @@ public final class URLConnectionTest {
     assertEquals("/a", redirectedBy.request().url().getPath());
   }
 
+  @Test public void attemptAuthorization20Times() throws Exception {
+    for (int i = 0; i < 20; i++) {
+      server.enqueue(new MockResponse().setResponseCode(401));
+    }
+    server.enqueue(new MockResponse().setBody("Success!"));
+
+    String credential = Credentials.basic("jesse", "peanutbutter");
+    client.client().setAuthenticator(new RecordingOkAuthenticator(credential));
+
+    connection = client.open(server.getUrl("/0"));
+    assertContent("Success!", connection);
+  }
+
+  @Test public void doesNotAttemptAuthorization21Times() throws Exception {
+    for (int i = 0; i < 21; i++) {
+      server.enqueue(new MockResponse().setResponseCode(401));
+    }
+
+    String credential = Credentials.basic("jesse", "peanutbutter");
+    client.client().setAuthenticator(new RecordingOkAuthenticator(credential));
+
+    connection = client.open(server.getUrl("/"));
+    try {
+      connection.getInputStream();
+      fail();
+    } catch (ProtocolException expected) {
+      assertEquals(401, connection.getResponseCode());
+      assertEquals("Too many follow-up requests: 21", expected.getMessage());
+    }
+  }
+
   @Test public void setsNegotiatedProtocolHeader_SPDY_3() throws Exception {
     setsNegotiatedProtocolHeader(Protocol.SPDY_3);
   }

okhttp-urlconnection/src/main/java/com/squareup/okhttp/internal/huc/HttpURLConnectionImpl.java

@@ -80,7 +80,7 @@ public class HttpURLConnectionImpl extends HttpURLConnection {
 
   /** Like the superclass field of the same name, but a long and available on all platforms. */
   private long fixedContentLength = -1;
-  private int redirectionCount;
+  private int followUpCount;
   protected IOException httpEngineFailure;
   protected HttpEngine httpEngine;
   /** Lazily created (with synthetic headers) on first call to getHeaders(). */
@@ -385,8 +385,8 @@ public class HttpURLConnectionImpl extends HttpURLConnection {
         return httpEngine;
       }
 
-      if (response.isRedirect() && ++redirectionCount > HttpEngine.MAX_REDIRECTS) {
-        throw new ProtocolException("Too many redirects: " + redirectionCount);
+      if (++followUpCount > HttpEngine.MAX_FOLLOW_UPS) {
+        throw new ProtocolException("Too many follow-up requests: " + followUpCount);
       }
 
       // The first request was insufficient. Prepare for another...

okhttp/src/main/java/com/squareup/okhttp/Call.java

@@ -24,7 +24,7 @@ import java.net.URL;
 import java.util.logging.Level;
 
 import static com.squareup.okhttp.internal.Internal.logger;
-import static com.squareup.okhttp.internal.http.HttpEngine.MAX_REDIRECTS;
+import static com.squareup.okhttp.internal.http.HttpEngine.MAX_FOLLOW_UPS;
 
 /**
  * A call is a request that has been prepared for execution. A call can be
@@ -251,7 +251,7 @@ public class Call {
     // Create the initial HTTP engine. Retries and redirects need new engine for each attempt.
     engine = new HttpEngine(client, request, false, false, forWebSocket, null, null, null, null);
 
-    int redirectionCount = 0;
+    int followUpCount = 0;
     while (true) {
       if (canceled) {
         engine.releaseConnection();
@@ -282,8 +282,8 @@ public class Call {
         return response;
       }
 
-      if (engine.getResponse().isRedirect() && ++redirectionCount > MAX_REDIRECTS) {
-        throw new ProtocolException("Too many redirects: " + redirectionCount);
+      if (++followUpCount > MAX_FOLLOW_UPS) {
+        throw new ProtocolException("Too many follow-up requests: " + followUpCount);
       }
 
       if (!engine.sameConnection(followUp.url())) {

okhttp/src/main/java/com/squareup/okhttp/internal/http/HttpEngine.java

@@ -88,10 +88,10 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS;
  */
 public final class HttpEngine {
   /**
-   * How many redirects should we follow? Chrome follows 21; Firefox, curl,
-   * and wget follow 20; Safari follows 16; and HTTP/1.0 recommends 5.
+   * How many redirects and auth challenges should we attempt? Chrome follows 21 redirects; Firefox,
+   * curl, and wget follow 20; Safari follows 16; and HTTP/1.0 recommends 5.
    */
-  public static final int MAX_REDIRECTS = 20;
+  public static final int MAX_FOLLOW_UPS = 20;
 
   private static final ResponseBody EMPTY_BODY = new ResponseBody() {
     @Override public MediaType contentType() {