Add option 'n' and 'S' to groups REST API to limit group results.

List groups endpoint now has an option to limit the number of results
returned and a start to define nonzero offset in order to support
groups pagination.

Add and document 'n' and 'S' function to allow query group list from
a specified limit and start.

Both options will then be used to render group list with pagination
in web UI.

Change-Id: Ibf244b1cfe83c56dc1c23aabf70a55697b52c835

2 files changed, 40 insertions, 0 deletions

diff --git a/Documentation/rest-api-groups.txt b/Documentation/rest-api-groups.txt
index 6289e5a419..2f73fc7deb 100644
--- a/Documentation/rest-api-groups.txt
+++ b/Documentation/rest-api-groups.txt
@@ -165,6 +165,24 @@ returned.
   }
 ----
 
+[[group-limit]]
+==== Group Limit
+The `/groups/` URL also accepts a limit integer in the `n` parameter.
+This limits the results to show `n` groups.
+
+Query the first 25 groups in group list.
+----
+  GET /groups/?n=25 HTTP/1.0
+----
+
+The `/groups/` URL also accepts a start integer in the `S` parameter.
+The results will skip `S` groups from group list.
+
+Query 25 groups starting from index 50.
+----
+  GET /groups/?n=25&S=50 HTTP/1.0
+----
+
 [[get-group]]
 Get Group
 ~~~~~~~~~
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/group/ListGroups.java b/gerrit-server/src/main/java/com/google/gerrit/server/group/ListGroups.java
index 03ec06722a..4764e41831 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/group/ListGroups.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/group/ListGroups.java
@@ -93,6 +93,12 @@ public class ListGroups implements RestReadView<TopLevelResource> {
     groupsToInspect.add(id);
   }
 
+  @Option(name = "--limit", aliases = {"-n"}, metaVar = "CNT", usage = "maximum number of groups to list")
+  private int limit;
+
+  @Option(name = "-S", metaVar = "CNT", usage = "number of groups to skip")
+  private int start;
+
   @Option(name = "-m", metaVar = "MATCH", usage = "match group substring")
   private String matchSubstring;
 
@@ -175,7 +181,15 @@ public class ListGroups implements RestReadView<TopLevelResource> {
           groupList = filterGroups(groupCache.all());
         }
         groupInfos = Lists.newArrayListWithCapacity(groupList.size());
+        int found = 0;
+        int foundIndex = 0;
         for (AccountGroup group : groupList) {
+          if (foundIndex++ < start) {
+            continue;
+          }
+          if (limit > 0 && ++found > limit) {
+            break;
+          }
           groupInfos.add(json.addOptions(options).format(
               GroupDescriptions.forAccountGroup(group)));
         }
@@ -187,11 +201,19 @@ public class ListGroups implements RestReadView<TopLevelResource> {
   private List<GroupInfo> getGroupsOwnedBy(IdentifiedUser user)
       throws OrmException {
     List<GroupInfo> groups = Lists.newArrayList();
+    int found = 0;
+    int foundIndex = 0;
     for (AccountGroup g : filterGroups(groupCache.all())) {
       GroupControl ctl = groupControlFactory.controlFor(g);
       try {
         if (genericGroupControlFactory.controlFor(user, g.getGroupUUID())
             .isOwner()) {
+          if (foundIndex++ < start) {
+            continue;
+          }
+          if (limit > 0 && ++found > limit) {
+            break;
+          }
           groups.add(json.addOptions(options).format(ctl.getGroup()));
         }
       } catch (NoSuchGroupException e) {