test: write test to validate buffer size is respected

Author: kwvg

tests/testStatsdClient.cpp

@@ -58,6 +58,72 @@ void testErrorConditions() {
     throwOnError(client, false, "Should not be able to resolve a ridiculous ip");
 }
 
+void testOverflow() {
+    StatsdServer mock_server;
+    std::vector<std::string> messages, expected;
+    std::thread server(mock, std::ref(mock_server), std::ref(messages), /*split=*/false);
+
+    // Set a new config that has the client send messages to a proper address that can be resolved
+    StatsdClient client("localhost", 8125, /*prefix=*/"", /*batchsize=*/48, /*sendInterval=*/0, /*gaugePrecision=*/3);
+    throwOnError(client);
+
+    // Send message that exhausts most of the batch limit (40/48)
+    client.increment("stat.timesWeUsed40CharsOfBufferSpace");
+    throwOnError(client);
+    expected.emplace_back("stat.timesWeUsed40CharsOfBufferSpace:1|c");
+
+    // Send message that would go over the batch limit (50/48)
+    // The second message shouldn't fit the batch and must be part of the next batch
+    client.increment("stat.i");
+    throwOnError(client);
+    expected.emplace_back("stat.i:1|c");
+
+    // Flush messages
+    client.flush();
+
+    // Send messages that would exactly fit in the batch, newlines included (48/48)
+    // Everything should be part of the same batch
+    expected.emplace_back();
+    for (int idx = 0; idx < 5; idx++) {
+        client.increment("silly");
+        throwOnError(client);
+        expected.back().append("silly:1|c\n");
+    }
+    expected.back().pop_back();
+
+    // Flush messages
+    client.flush();
+
+    // With all messages flushed, send one giant message that would exceed the batch (50/48)
+    // The message should arrive intact in one batch
+    client.increment("stat.veryImportantIfIncrementedComputerExplode");
+    throwOnError(client);
+    expected.emplace_back("stat.veryImportantIfIncrementedComputerExplode:1|c");
+
+    // Flush messages
+    client.flush();
+
+    // Signal the mock server we are done (and flush so that the signal is sent)
+    client.timing("DONE", 0);
+    client.flush();
+
+    // Wait for the server to stop
+    server.join();
+
+    // Make sure we get the exactly correct output
+    if (messages != expected) {
+        std::cerr << "Unexpected stats received by server, got:" << std::endl;
+        for (const auto& message : messages) {
+            std::cerr << "- " << message << std::endl;
+        }
+        std::cerr << std::endl << "But we expected:" << std::endl;
+        for (const auto& message : expected) {
+            std::cerr << "- " << message << std::endl;
+        }
+        throw std::runtime_error("Unexpected stats");
+    }
+}
+
 void testReconfigure() {
     StatsdServer server;
     throwOnError(server);
@@ -181,6 +247,8 @@ int main() {
 
     // general things that should be errors
     testErrorConditions();
+    // ensure batch size is respected
+    testOverflow();
     // reconfiguring how you are sending
     testReconfigure();
     // no batching