Fix concurrency issues with GHIssue addLabels and removeLabels

Fixes hub4j#1049

src/main/java/org/kohsuke/github/GHIssue.java

@@ -360,17 +360,11 @@ public void addLabels(Collection<GHLabel> labels) throws IOException {
     }
 
     private void _addLabels(Collection<String> names) throws IOException {
-        List<String> newLabels = new ArrayList<String>();
-
-        for (GHLabel label : getLabels()) {
-            newLabels.add(label.getName());
-        }
-        for (String name : names) {
-            if (!newLabels.contains(name)) {
-                newLabels.add(name);
-            }
-        }
-        setLabels(newLabels.toArray(new String[0]));
+        root.createRequest()
+                .with("labels", names.toArray(new String[0]))
+                .method("POST")
+                .withUrlPath(getIssuesApiRoute() + "/labels")
+                .send();
     }
 
     /**
@@ -411,15 +405,12 @@ public void removeLabels(Collection<GHLabel> labels) throws IOException {
     }
 
     private void _removeLabels(Collection<String> names) throws IOException {
-        List<String> newLabels = new ArrayList<String>();
-
-        for (GHLabel l : getLabels()) {
-            if (!names.contains(l.getName())) {
-                newLabels.add(l.getName());
-            }
+        for (String name : names) {
+            root.createRequest()
+                    .method("DELETE")
+                    .withUrlPath(getIssuesApiRoute() + "/labels", name)
+                    .send();
         }
-
-        setLabels(newLabels.toArray(new String[0]));
     }
 
     /**

src/test/java/org/kohsuke/github/GHIssueEventTest.java

@@ -18,7 +18,7 @@ public void testEventsForSingleIssue() throws Exception {
         GHIssue issue = builder.create();
 
         // Generate some events.
-        issue.addLabels("test-label");
+        issue.setLabels("test-label");
 
         // Test that the events are present.
         List<GHIssueEvent> list = issue.listEvents().toList();

src/test/java/org/kohsuke/github/GHPullRequestTest.java

@@ -9,7 +9,7 @@
 import java.util.Collections;
 import java.util.List;
 
-import static org.hamcrest.CoreMatchers.*;
+import static org.hamcrest.Matchers.*;
 
 /**
  * @author Kohsuke Kawaguchi
@@ -421,6 +421,40 @@ public void setLabels() throws Exception {
         assertEquals(label, labels.iterator().next().getName());
     }
 
+    @Test
+    // Requires push access to the test repo to pass
+    public void addLabels() throws Exception {
+        GHPullRequest p = getRepository().createPullRequest("addLabels", "test/stable", "master", "## test");
+        String initialLabel = "setLabels_label_name";
+        p.setLabels(initialLabel);
+
+        String addedLabel = "addLabels_label_name";
+        p.addLabels(addedLabel);
+
+        Collection<GHLabel> labels = getRepository().getPullRequest(p.getNumber()).getLabels();
+        assertEquals(2, labels.size());
+        assertThat(labels, containsInAnyOrder(initialLabel, addedLabel));
+    }
+
+    @Test
+    // Requires push access to the test repo to pass
+    public void removeLabels() throws Exception {
+        GHPullRequest p = getRepository().createPullRequest("removeLabels", "test/stable", "master", "## test");
+        String label1 = "removeLabels_label_name_1";
+        String label2 = "removeLabels_label_name_2";
+        String label3 = "removeLabels_label_name_3";
+        p.setLabels(label1, label2, label3);
+
+        Collection<GHLabel> labels = getRepository().getPullRequest(p.getNumber()).getLabels();
+        assertEquals(3, labels.size());
+
+        p.removeLabels(label2, label3);
+
+        labels = getRepository().getPullRequest(p.getNumber()).getLabels();
+        assertEquals(1, labels.size());
+        assertEquals(label1, labels.iterator().next().getName());
+    }
+
     @Test
     // Requires push access to the test repo to pass
     public void setAssignee() throws Exception {