diff --git a/httpserver/service_node.cpp b/httpserver/service_node.cpp
index 03c6b9b..73f105f 100644
--- a/httpserver/service_node.cpp
+++ b/httpserver/service_node.cpp
@@ -404,6 +404,8 @@ void ServiceNode::update_swarms() {
     // const char* ip = "149.56.148.124";
     // const uint16_t port = 22023;
 
+    // TODO: this should be changed to lokid
+
     const uint16_t port = 7777;
     const char* ip = "0.0.0.0";
 
@@ -417,11 +419,16 @@ void ServiceNode::update_swarms() {
             }
         })#";
 
-    make_http_request(
-        ioc_, ip, port, "/json_rpc", req_body,
-        std::bind(&ServiceNode::on_swarm_update, this, std::placeholders::_1));
-
-    /// TODO: make an rpc request to lokid
+    make_http_request(ioc_, ip, port, "/json_rpc", req_body,
+                      [this](std::shared_ptr<std::string> res_body) {
+                          try {
+                              this->on_swarm_update(res_body);
+                          } catch (const std::exception& e) {
+                              BOOST_LOG_TRIVIAL(error)
+                                  << "Exception caught on swarm update: "
+                                  << e.what();
+                          }
+                      });
 
     update_timer_.expires_after(std::chrono::seconds(2));
 
diff --git a/httpserver/swarm.cpp b/httpserver/swarm.cpp
index 1300156..11428a6 100644
--- a/httpserver/swarm.cpp
+++ b/httpserver/swarm.cpp
@@ -4,6 +4,7 @@
 #include "service_node.h"
 
 #include <boost/log/trivial.hpp>
+#include <stdlib.h>
 
 namespace loki {
 
@@ -123,23 +124,40 @@ SwarmEvents Swarm::update_swarms(const all_swarms_t& swarms) {
 swarm_id_t get_swarm_by_pk(const std::vector<SwarmInfo>& all_swarms,
                            const std::string& pk) {
 
-    // TODO: handle errors
-    // TODO: get rid of allocations?
+    if (pk.size() != 66) {
+        throw std::invalid_argument("invalid pub key size");
+    }
 
-    std::string pk0_str = std::string(pk.c_str() + 2, 16);
-    std::string pk1_str = std::string(pk.c_str() + 2 + 16, 16);
-    std::string pk2_str = std::string(pk.c_str() + 2 + 32, 16);
-    std::string pk3_str = std::string(pk.c_str() + 2 + 48, 16);
+    /// Create a buffer for 64 characters plus 4 nulls on 8-byte boundaries
+    char buf[68] = {};
 
-    uint64_t pk0 = std::stoull(pk0_str, 0, 16);
-    uint64_t pk1 = std::stoull(pk1_str, 0, 16);
-    uint64_t pk2 = std::stoull(pk2_str, 0, 16);
-    uint64_t pk3 = std::stoull(pk3_str, 0, 16);
+    /// Note: pk is expected to contain two leading characters
+    /// (05 for the messenger) that do not participate in mapping
 
-    uint64_t res = pk0 ^ pk1 ^ pk2 ^ pk3;
+    memcpy(buf, pk.c_str() + 2, 16);
+    memcpy(buf + 17, pk.c_str() + 2 + 16, 16);
+    memcpy(buf + 34, pk.c_str() + 2 + 32, 16);
+    memcpy(buf + 51, pk.c_str() + 2 + 48, 16);
 
-    swarm_id_t cur_best = 0;
-    uint64_t cur_min = std::numeric_limits<uint64_t>::max();
+    /// Note: if conversion is not possible, we will still
+    /// get a value in res (possibly 0 or UINT64_MAX), which
+    /// we are not handling at the moment
+    uint64_t res = strtoull(buf, nullptr, 16);
+    res ^= strtoull(buf + 17, nullptr, 16);
+    res ^= strtoull(buf + 34, nullptr, 16);
+    res ^= strtoull(buf + 51, nullptr, 16);
+
+    /// We reserve UINT64_MAX as a sentinel swarm id for unassigned snodes
+    constexpr swarm_id_t MAX_ID = std::numeric_limits<uint64_t>::max() - 1;
+    constexpr swarm_id_t SENTINEL_ID = std::numeric_limits<uint64_t>::max();
+
+    swarm_id_t cur_best = SENTINEL_ID;
+    uint64_t cur_min = SENTINEL_ID;
+
+    /// We don't require that all_swarms is sorted, so we find
+    /// the smallest/largest elements in the same loop
+    swarm_id_t leftmost_id = SENTINEL_ID;
+    swarm_id_t rightmost_id = 0;
 
     for (const auto& si : all_swarms) {
 
@@ -149,16 +167,30 @@ swarm_id_t get_swarm_by_pk(const std::vector<SwarmInfo>& all_swarms,
             cur_best = si.swarm_id;
             cur_min = dist;
         }
+
+        /// Find the letfmost
+        if (si.swarm_id < leftmost_id) {
+            leftmost_id = si.swarm_id;
+        }
+
+        if (si.swarm_id > rightmost_id) {
+            rightmost_id = si.swarm_id;
+        }
     }
 
     // handle special case
-
-    if (res > all_swarms[0].swarm_id) {
-        uint64_t dist =
-            std::numeric_limits<uint64_t>::max() - res + all_swarms[0].swarm_id;
-
+    if (res > leftmost_id) {
+        uint64_t dist = (MAX_ID - res) + leftmost_id;
         if (dist < cur_min) {
-            return all_swarms[0].swarm_id;
+            cur_best = leftmost_id;
+        }
+    } else {
+        // since rightmost is at least as large as leftmost,
+        // res <= rightmost in this branch, so the value will
+        // not overflow
+        uint64_t dist = res + (MAX_ID - rightmost_id);
+        if (dist < cur_min) {
+            cur_best = rightmost_id;
         }
     }