Modernize HeaderChannel compression config handling

Summary: Improve efficiency and code clarity in HeaderChannel's compression configuration. Use move semantics to avoid unnecessary copies when setting compression config, mark preprocessHeader as const-correct since it doesn't modify the channel's state, and simplify codec initialization using emplace() pattern.

Reviewed By: praihan

Differential Revision: D89765894

fbshipit-source-id: bfd75be8df51d7299f68290b8e94ac9452d0c8a8

Author: Alex Snast

third-party/thrift/src/thrift/lib/cpp/transport/THeader.h

@@ -365,7 +365,7 @@ class THeader final {
       StringToStringMap& persistentReadHeaders);
 
   void setDesiredCompressionConfig(CompressionConfig compressionConfig) {
-    c_.compressionConfig_ = compressionConfig;
+    c_.compressionConfig_ = std::move(compressionConfig);
   }
 
   folly::Optional<CompressionConfig> getDesiredCompressionConfig() const {

third-party/thrift/src/thrift/lib/cpp2/async/HeaderChannel.cpp

@@ -61,7 +61,7 @@ void HeaderChannel::addRpcOptionHeaders(
 }
 
 void HeaderChannel::preprocessHeader(
-    apache::thrift::transport::THeader* header) {
+    apache::thrift::transport::THeader* header) const {
   header->mutableWriteHeaders().insert(
       persistentWriteHeaders_.begin(), persistentWriteHeaders_.end());
 
@@ -77,23 +77,18 @@ void HeaderChannel::preprocessHeader(
 
     if (!header->getDesiredCompressionConfig()) {
       apache::thrift::CompressionConfig compressionConfig;
-      switch (transform) {
-        case transport::THeader::ZLIB_TRANSFORM: {
-          apache::thrift::CodecConfig codec;
-          codec.zlibConfig() = apache::thrift::ZlibCompressionCodecConfig();
-          compressionConfig.codecConfig() = codec;
+      switch (auto&& codec = compressionConfig.codecConfig().emplace();
+              transform) {
+        case transport::THeader::ZLIB_TRANSFORM:
+          codec.zlibConfig().emplace();
           break;
-        }
-        case transport::THeader::ZSTD_TRANSFORM: {
-          apache::thrift::CodecConfig codec;
-          codec.zstdConfig() = apache::thrift::ZstdCompressionCodecConfig();
-          compressionConfig.codecConfig() = codec;
+        case transport::THeader::ZSTD_TRANSFORM:
+          codec.zstdConfig().emplace();
           break;
-        }
         default:
           LOG(DFATAL) << "Unsupported transform: " << transform;
       }
-      header->setDesiredCompressionConfig(compressionConfig);
+      header->setDesiredCompressionConfig(std::move(compressionConfig));
     }
   }
   if (loggingContext_) {

third-party/thrift/src/thrift/lib/cpp2/async/HeaderChannel.h

@@ -27,8 +27,6 @@ namespace apache::thrift {
  */
 class HeaderChannel {
  public:
-  HeaderChannel() {}
-
   void addRpcOptionHeaders(
       apache::thrift::transport::THeader* header, const RpcOptions& rpcOptions);
 
@@ -44,14 +42,15 @@ class HeaderChannel {
     loggingContext_ = std::move(loggingContext);
   }
 
-  const transport::THeader::StringToStringMap& getPersistentWriteHeaders() {
+  const transport::THeader::StringToStringMap& getPersistentWriteHeaders()
+      const {
     return persistentWriteHeaders_;
   }
 
-  void preprocessHeader(apache::thrift::transport::THeader* header);
+  void preprocessHeader(apache::thrift::transport::THeader* header) const;
 
  protected:
-  virtual ~HeaderChannel() {}
+  virtual ~HeaderChannel() = default;
 
   virtual bool clientSupportHeader() { return true; }