feat: add gzip compression tracking to User-Agent metrics

- Add test to verify 'L' metric appears in User-Agent when gzip compression is used
- Enable compression in test setup and mock client
- Validate business metrics tracking for request compression feature

Author: kai-ion

src/aws-cpp-sdk-core/include/aws/core/client/UserAgent.h

@@ -31,6 +31,7 @@ enum class UserAgentFeature {
   ACCOUNT_ID_MODE_DISABLED,
   ACCOUNT_ID_MODE_REQUIRED,
   RESOLVED_ACCOUNT_ID,
+  GZIP_REQUEST_COMPRESSION,
 };
 
 class AWS_CORE_API UserAgent {

src/aws-cpp-sdk-core/source/client/AWSClient.cpp

@@ -910,6 +910,9 @@ void AWSClient::BuildHttpRequest(const Aws::AmazonWebServiceRequest& request, co
             if (compressOutcome.IsSuccess()) {
                 Aws::String compressionAlgorithmId = Aws::Client::GetCompressionAlgorithmId(selectedCompressionAlgorithm);
                 AppendHeaderValueToRequest(httpRequest, CONTENT_ENCODING_HEADER, compressionAlgorithmId);
+                if (selectedCompressionAlgorithm == Aws::Client::CompressionAlgorithm::GZIP) {
+                  request.AddUserAgentFeature(Aws::Client::UserAgentFeature::GZIP_REQUEST_COMPRESSION);
+                }
                 AddContentBodyToRequest(
                     httpRequest, compressOutcome.GetResult(),
                     request.ShouldComputeContentMd5(),

src/aws-cpp-sdk-core/source/client/UserAgent.cpp

@@ -41,6 +41,7 @@ const std::pair<UserAgentFeature, const char*> BUSINESS_METRIC_MAPPING[] = {
     {UserAgentFeature::ACCOUNT_ID_MODE_DISABLED , "Q"},
     {UserAgentFeature::ACCOUNT_ID_MODE_REQUIRED, "R"},
     {UserAgentFeature::RESOLVED_ACCOUNT_ID, "T"},
+    {UserAgentFeature::GZIP_REQUEST_COMPRESSION, "L"},
 };
 
 Aws::String BusinessMetricForFeature(UserAgentFeature feature) {

tests/aws-cpp-sdk-core-tests/monitoring/MonitoringTest.cpp

@@ -196,6 +196,8 @@ class MonitoringTestSuite : public Aws::Testing::AwsCppSdkGTestSuite
         config.scheme = Scheme::HTTP;
         config.connectTimeoutMs = 30000;
         config.requestTimeoutMs = 30000;
+        config.requestCompressionConfig.useRequestCompression = UseRequestCompression::ENABLE;
+        config.requestCompressionConfig.requestMinCompressionSizeBytes = 10240;
         auto countedRetryStrategy = Aws::MakeShared<CountedRetryStrategy>(ALLOCATION_TAG);
         config.retryStrategy = std::static_pointer_cast<DefaultRetryStrategy>(countedRetryStrategy);
 
@@ -330,3 +332,31 @@ TEST_F(MonitoringTestSuite, TestHttpClientMetrics)
     ASSERT_STREQ("SslLatency", GetHttpClientMetricNameByType(HttpClientMetricsType::SslLatency).c_str());
     ASSERT_STREQ("Unknown", GetHttpClientMetricNameByType(HttpClientMetricsType::Unknown).c_str());
 }
+
+TEST_F(MonitoringTestSuite, TestUserAgentCompressionTracking)
+{
+  HeaderValueCollection responseHeaders;
+  AmazonWebServiceRequestMock request;
+
+  // Create large request body to trigger compression
+  std::string largeBody(20000, 'A');
+  auto bodyStream = Aws::MakeShared<Aws::StringStream>(ALLOCATION_TAG);
+  *bodyStream << largeBody;
+  request.SetBody(bodyStream);
+
+  QueueMockResponse(HttpResponseCode::OK, responseHeaders);
+  const auto outcome = client->MakeRequest(request);
+  AWS_ASSERT_SUCCESS(outcome);
+
+  const auto requestSeen = mockHttpClient->GetMostRecentHttpRequest();
+  EXPECT_TRUE(requestSeen.HasUserAgent());
+  const auto& userAgent = requestSeen.GetUserAgent();
+  EXPECT_TRUE(!userAgent.empty());
+  const auto userAgentParsed = Aws::Utils::StringUtils::Split(userAgent, ' ');
+
+  // Check for gzip compression business metric (L) in user agent
+  auto businessMetrics = std::find_if(userAgentParsed.begin(), userAgentParsed.end(),
+      [](const Aws::String& value) { return value.find("m/") != Aws::String::npos && value.find("L") != Aws::String::npos; });
+  EXPECT_TRUE(businessMetrics != userAgentParsed.end());
+}
+

tests/testing-resources/include/aws/testing/mocks/aws/client/MockAWSClient.h

@@ -54,6 +54,18 @@ class AmazonWebServiceRequestMock : public Aws::AmazonWebServiceRequest
         auto bodyString = ss.str();
         return bodyString.find("TestErrorInBodyOfResponse") != std::string::npos;
     }
+    
+    Aws::Client::CompressionAlgorithm GetSelectedCompressionAlgorithm(Aws::Client::RequestCompressionConfig config) const override {
+        if (config.useRequestCompression == Aws::Client::UseRequestCompression::ENABLE && m_body) {
+            m_body->seekg(0, m_body->end);
+            size_t bodySize = m_body->tellg();
+            m_body->seekg(0, m_body->beg);
+            if (bodySize >= config.requestMinCompressionSizeBytes) {
+                return Aws::Client::CompressionAlgorithm::GZIP;
+            }
+        }
+        return Aws::Client::CompressionAlgorithm::NONE;
+    }
 
 private:
     std::shared_ptr<Aws::IOStream> m_body;