Do dump announced groups to font-end's `/groups.txt`.

As plain text, one per line, undefined ordering.

src/cache/client.cpp

@@ -514,6 +514,10 @@ struct Client::Impl {
         return *_newest_proto_seen;
     }
 
+    std::set<std::string> get_announced_groups() const {
+        return _dht_groups->groups();
+    }
+
     void set_log_level(log_level_t l) {
         cerr << "Setting cache/client Cache log level to " << l << "\n";
         _log_level = l;
@@ -608,6 +612,11 @@ unsigned Client::get_newest_proto_version() const
     return _impl->get_newest_proto_version();
 }
 
+std::set<std::string> Client::get_announced_groups() const
+{
+    return _impl->get_announced_groups();
+}
+
 void Client::set_log_level(log_level_t l)
 {
     _impl->set_log_level(l);

src/cache/client.h

@@ -7,6 +7,7 @@
 #include "cache_entry.h"
 #include <boost/date_time/posix_time/posix_time.hpp>
 #include <boost/filesystem.hpp>
+#include <set>
 
 namespace ouinet {
 
@@ -59,6 +60,10 @@ public:
     // (e.g. to warn about potential upgrades).
     unsigned get_newest_proto_version() const;
 
+    // Get all groups being announced to the distributed cache index
+    // by this client.
+    std::set<std::string> get_announced_groups() const;
+  
     ~Client();
 
     void        set_log_level(log_level_t);

src/client_front_end.cpp

@@ -182,11 +182,15 @@ static void load_log_file(stringstream& out_ss) {
 
 void ClientFrontEnd::handle_group_list( const Request&
                                       , Response& res
-                                      , std::stringstream& ss)
+                                      , std::stringstream& ss
+                                      , cache::Client* cache_client)
 {
     res.set(http::field::content_type, "text/plain");
 
-    ss << "TODO\n";
+    if (!cache_client) return;
+
+    for (const auto& g : cache_client->get_announced_groups())
+        ss << g << std::endl;
 }
 
 void ClientFrontEnd::handle_portal( ClientConfig& config
@@ -463,7 +467,7 @@ Response ClientFrontEnd::serve( ClientConfig& config
         res.set(http::field::content_type, "text/plain");
         load_log_file(ss);
     } else if (path == group_list_apath) {
-        handle_group_list(req, res, ss);
+        handle_group_list(req, res, ss, cache_client);
     } else if (path == "/api/status") {
         sys::error_code e;
         handle_status( config, udp_port, upnps, reachability

src/client_front_end.h

@@ -102,7 +102,8 @@ private:
 
     void handle_group_list( const Request&
                           , Response&
-                          , std::stringstream&);
+                          , std::stringstream&
+                          , cache::Client*);
 
     void handle_portal( ClientConfig&
                       , const Request&