stats: rename statsns to clearer statsprefix

`statsns`, aside from being an unclear name, in its default behaviour,
doesn't use the namespace delimiter contaminates the root namespace
of the key.

Let's take care of that by deprecating `statsns` with its replacement,
`statsprefix`, that behaves properly.

src/init.cpp

@@ -777,8 +777,9 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-statshost=<ip>", strprintf("Specify statsd host (default: %s)", DEFAULT_STATSD_HOST), ArgsManager::ALLOW_ANY, OptionsCategory::STATSD);
     hidden_args.emplace_back("-statshostname");
     argsman.AddArg("-statsport=<port>", strprintf("Specify statsd port (default: %u)", DEFAULT_STATSD_PORT), ArgsManager::ALLOW_ANY, OptionsCategory::STATSD);
-    argsman.AddArg("-statsns=<ns>", strprintf("Specify additional namespace prefix (default: %s)", DEFAULT_STATSD_SUFFIX), ArgsManager::ALLOW_ANY, OptionsCategory::STATSD);
+    hidden_args.emplace_back("-statsns");
     argsman.AddArg("-statsperiod=<seconds>", strprintf("Specify the number of seconds between periodic measurements (default: %d)", DEFAULT_STATSD_PERIOD), ArgsManager::ALLOW_ANY, OptionsCategory::STATSD);
+    argsman.AddArg("-statsprefix=<string>", strprintf("Specify an optional string prepended to every stats key (default: %s)", DEFAULT_STATSD_PREFIX), ArgsManager::ALLOW_ANY, OptionsCategory::STATSD);
     argsman.AddArg("-statssuffix=<string>", strprintf("Specify an optional string appended to every stats key (default: %s)", DEFAULT_STATSD_SUFFIX), ArgsManager::ALLOW_ANY, OptionsCategory::STATSD);
 #if HAVE_DECL_FORK
     argsman.AddArg("-daemon", strprintf("Run in the background as a daemon and accept commands (default: %d)", DEFAULT_DAEMON), ArgsManager::ALLOW_BOOL, OptionsCategory::OPTIONS);

src/stats/client.cpp

@@ -79,15 +79,29 @@ std::unique_ptr<StatsdClient> InitStatsClient(const ArgsManager& args)
 
     auto sanitize_string = [](std::string& string) {
         // Remove key delimiters from the front and back as they're added back
-        // in formatting
         if (!string.empty()) {
             if (string.front() == STATSD_NS_DELIMITER) string.erase(string.begin());
             if (string.back() == STATSD_NS_DELIMITER) string.pop_back();
         }
     };
 
-    // Get our suffix and if we get nothing, try again with the deprecated
-    // argument. If we still get nothing, that's fine, suffixes are optional.
+    // Get our prefix and suffix and if we get nothing, try again with the
+    // deprecated argument. If we still get nothing, that's fine, they're optional.
+    auto prefix = args.GetArg("-statsprefix", DEFAULT_STATSD_PREFIX);
+    if (prefix.empty()) {
+        prefix = args.GetArg("-statsns", DEFAULT_STATSD_PREFIX);
+    } else {
+        // We restrict sanitization logic to our newly added arguments to
+        // prevent breaking changes.
+        sanitize_string(prefix);
+        // We need to add the delimiter here for backwards compatibility with
+        // the deprecated argument.
+        //
+        // TODO: Move this step into the constructor when removing deprecated
+        //       args support
+        prefix += STATSD_NS_DELIMITER;
+    }
+
     auto suffix = args.GetArg("-statssuffix", DEFAULT_STATSD_SUFFIX);
     if (suffix.empty()) {
         suffix = args.GetArg("-statshostname", DEFAULT_STATSD_SUFFIX);
@@ -102,15 +116,15 @@ std::unique_ptr<StatsdClient> InitStatsClient(const ArgsManager& args)
         args.GetArg("-statsport", DEFAULT_STATSD_PORT),
         args.GetArg("-statsbatchsize", DEFAULT_STATSD_BATCH_SIZE),
         args.GetArg("-statsduration", DEFAULT_STATSD_DURATION),
-        args.GetArg("-statsns", DEFAULT_STATSD_NAMESPACE),
+        prefix,
         suffix,
         is_enabled
     );
 }
 
 StatsdClient::StatsdClient(const std::string& host, uint16_t port, uint64_t batch_size, uint64_t interval_ms,
-                           const std::string& ns, const std::string& suffix, bool enabled) :
-    m_ns{ns},
+                           const std::string& prefix, const std::string& suffix, bool enabled) :
+    m_prefix{prefix},
     m_suffix{[suffix]() { return !suffix.empty() ? STATSD_NS_DELIMITER + suffix : suffix; }()}
 {
     if (!enabled) {
@@ -174,7 +188,7 @@ bool StatsdClient::send(const std::string& key, T1 value, const std::string& typ
     }
 
     // Construct the message and if our message isn't always-send, report the sample rate
-    RawMessage msg{strprintf("%s%s%s:%f|%s", m_ns, key, m_suffix, value, type)};
+    RawMessage msg{strprintf("%s%s%s:%f|%s", m_prefix, key, m_suffix, value, type)};
     if (!always_send) {
         msg += strprintf("|@%.2f", sample_rate);
     }

src/stats/client.h

@@ -21,7 +21,7 @@ static constexpr uint16_t DEFAULT_STATSD_PORT{8125};
 /** Default host assumed to be running a Statsd server */
 static const std::string DEFAULT_STATSD_HOST{"127.0.0.1"};
 /** Default prefix prepended to Statsd message keys */
-static const std::string DEFAULT_STATSD_NAMESPACE{""};
+static const std::string DEFAULT_STATSD_PREFIX{""};
 /** Default suffix appended to Statsd message keys */
 static const std::string DEFAULT_STATSD_SUFFIX{""};
 
@@ -40,7 +40,7 @@ class StatsdClient
 {
 public:
     explicit StatsdClient(const std::string& host, uint16_t port, uint64_t batch_size, uint64_t interval_ms,
-                          const std::string& ns, const std::string& suffix, bool enabled);
+                          const std::string& prefix, const std::string& suffix, bool enabled);
 
 public:
     /* Statsd-defined APIs */
@@ -68,7 +68,7 @@ class StatsdClient
     std::unique_ptr<RawSender> m_sender{nullptr};
 
     /* Phrase prepended to keys */
-    const std::string m_ns;
+    const std::string m_prefix{""};
     /* Phrase appended to keys */
     const std::string m_suffix{""};
 };