feat(stats): extend connection support to IPv6, bail out earlier

Offloading `sockaddr` generation to `CService` lets us borrow its IPv6
`sockaddr` generation code but this requires us to first parse the host
before creating a socket.

As a bonus, as creating the socket is now the last step, we don't need
`m_init` anymore. We can just see if a socket is successfully
constructed and take that as our validity indicator.

We'll also move it out of the inner `send` function so we can bail out
before we bother with all the string processing and manipulation.

src/statsd_client.cpp

@@ -70,20 +70,12 @@ StatsdClient::StatsdClient(const std::string& host, const std::string& nodename,
         return;
     }
 
-    SOCKET hSocket = ::socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
-    if (hSocket == INVALID_SOCKET) {
-        LogPrintf("ERROR: Cannot create socket (socket() returned error %s), cannot init StatsdClient\n",
-                  NetworkErrorString(WSAGetLastError()));
-        return;
-    }
-    m_sock = std::make_unique<Sock>(hSocket);
-
     CNetAddr netaddr;
-    if (!LookupHost(m_host, netaddr, /*fAllowLookup=*/true)) {
+    if (!LookupHost(m_host, netaddr, /*fAllowLookup=*/false)) {
         LogPrintf("ERROR: Unable to lookup host %s, cannot init StatsdClient\n", m_host);
         return;
     }
-    if (!netaddr.IsIPv4()) {
+    if (!netaddr.IsIPv4() && !netaddr.IsIPv6()) {
         LogPrintf("ERROR: Host %s on unsupported network, cannot init StatsdClient\n", m_host);
         return;
     }
@@ -92,7 +84,13 @@ StatsdClient::StatsdClient(const std::string& host, const std::string& nodename,
         return;
     }
 
-    m_init = true;
+    SOCKET hSocket = ::socket(reinterpret_cast<struct sockaddr*>(&m_server.first)->sa_family, SOCK_DGRAM, IPPROTO_UDP);
+    if (hSocket == INVALID_SOCKET) {
+        LogPrintf("ERROR: Cannot create socket (socket() returned error %s), cannot init StatsdClient\n",
+                  NetworkErrorString(WSAGetLastError()));
+        return;
+    }
+    m_sock = std::make_unique<Sock>(hSocket);
 
     LogPrintf("StatsdClient initialized to transmit stats to %s:%d\n", m_host, m_port);
 }
@@ -140,6 +138,10 @@ int StatsdClient::timing(const std::string& key, uint32_t ms, float sample_rate)
 
 int StatsdClient::send(std::string key, uint32_t value, const std::string& type, float sample_rate)
 {
+    if (!m_sock) {
+        return -3;
+    }
+
     if (!ShouldSend(sample_rate)) {
         return 0;
     }
@@ -160,6 +162,10 @@ int StatsdClient::send(std::string key, uint32_t value, const std::string& type,
 
 int StatsdClient::sendDouble(std::string key, double value, const std::string& type, float sample_rate)
 {
+    if (!m_sock) {
+        return -3;
+    }
+
     if (!ShouldSend(sample_rate)) {
         return 0;
     }
@@ -180,8 +186,7 @@ int StatsdClient::sendDouble(std::string key, double value, const std::string& t
 
 int StatsdClient::send(const std::string& message)
 {
-    if (!m_init)
-        return -3;
+    assert(m_sock);
 
     if (::sendto(m_sock->Get(), message.data(), message.size(), /*flags=*/0,
                  reinterpret_cast<struct sockaddr*>(&m_server.first), m_server.second) == SOCKET_ERROR) {

src/statsd_client.h

@@ -63,7 +63,6 @@ class StatsdClient {
         mutable Mutex cs;
         mutable FastRandomContext insecure_rand GUARDED_BY(cs);
 
-        bool m_init{false};
         std::unique_ptr<Sock> m_sock{nullptr};
         std::pair<struct sockaddr_storage, socklen_t> m_server{{}, sizeof(struct sockaddr_storage)};