Add an endpoint for getting the current state of feature flags.

service/src/main/java/org/whispersystems/textsecuregcm/controllers/FeatureFlagsController.java

@@ -6,15 +6,19 @@ import org.whispersystems.textsecuregcm.storage.FeatureFlagsManager;
 
 import javax.ws.rs.DELETE;
 import javax.ws.rs.FormParam;
+import javax.ws.rs.GET;
 import javax.ws.rs.HeaderParam;
 import javax.ws.rs.PUT;
 import javax.ws.rs.Path;
 import javax.ws.rs.PathParam;
+import javax.ws.rs.Produces;
 import javax.ws.rs.WebApplicationException;
+import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.Response;
 import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.util.List;
+import java.util.Map;
 import java.util.stream.Collectors;
 
 @Path("/v1/featureflag")
@@ -28,6 +32,17 @@ public class FeatureFlagsController {
         this.authorizedTokens    = authorizedTokens.stream().map(token -> token.getBytes(StandardCharsets.UTF_8)).collect(Collectors.toList());
     }
 
+    @Timed
+    @GET
+    @Produces(MediaType.APPLICATION_JSON)
+    public Map<String, Boolean> get(@HeaderParam("Token") final String token) {
+        if (!isAuthorized(token)) {
+            throw new WebApplicationException(Response.Status.UNAUTHORIZED);
+        }
+
+        return featureFlagsManager.getAllFlags();
+    }
+
     @Timed
     @PUT
     @Path("/{featureFlag}")

service/src/main/java/org/whispersystems/textsecuregcm/storage/FeatureFlagsManager.java

@@ -67,11 +67,15 @@ public class FeatureFlagsManager implements Managed {
         refreshFeatureFlags();
     }
 
+    public Map<String, Boolean> getAllFlags() {
+        return featureFlags.get();
+    }
+
     @VisibleForTesting
     void refreshFeatureFlags() {
         final Map<String, Boolean> refreshedFeatureFlags = featureFlagDatabase.getFeatureFlags();
 
-        featureFlags.set(refreshedFeatureFlags);
+        featureFlags.set(Collections.unmodifiableMap(refreshedFeatureFlags));
 
         for (final Map.Entry<String, Boolean> entry : refreshedFeatureFlags.entrySet()) {
             final String  featureFlag = entry.getKey();

service/src/test/java/org/whispersystems/textsecuregcm/controllers/FeatureFlagsControllerTest.java

@@ -20,12 +20,15 @@ import javax.ws.rs.client.Entity;
 import javax.ws.rs.core.Form;
 import javax.ws.rs.core.Response;
 import java.util.List;
+import java.util.Map;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.reset;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.when;
 
 @RunWith(JUnitParamsRunner.class)
 public class FeatureFlagsControllerTest {
@@ -83,6 +86,35 @@ public class FeatureFlagsControllerTest {
         }
     }
 
+    @SuppressWarnings("rawtypes")
+    @Test
+    public void testGet() {
+        final Map<String, Boolean> managedFlags = Map.of("activeFlag", true, "inactiveFlag", false);
+        when(FEATURE_FLAG_MANAGER.getAllFlags()).thenReturn(managedFlags);
+
+        {
+            final Map returnedFlags = resources.getJerseyTest()
+                    .target("/v1/featureflag")
+                    .request()
+                    .header("Token", "first")
+                    .get(Map.class);
+
+            verify(FEATURE_FLAG_MANAGER).getAllFlags();
+            assertEquals(managedFlags, returnedFlags);
+        }
+
+        {
+            final Response response = resources.getJerseyTest()
+                    .target("/v1/featureflag")
+                    .request()
+                    .header("Token", "bogus-token")
+                    .get();
+
+            assertEquals(401, response.getStatus());
+            verifyNoMoreInteractions(FEATURE_FLAG_MANAGER);
+        }
+    }
+
     @Test
     public void testDelete() {
         {