Specialize *Protocol::readStringBody for std::string

Summary: `folly::resizeWithoutInitialization` allows us to make this slightly more efficient than the general code

Reviewed By: robertroeser

Differential Revision: D68296464

fbshipit-source-id: a33d849336caa497b256bc5dab6e68559776d0d3

Author: iahs

thrift/lib/cpp2/protocol/BinaryProtocol-inl.h

@@ -580,32 +580,7 @@ inline void BinaryProtocolReader::readBinary(folly::IOBuf& str) {
 template <typename StrType>
 inline void BinaryProtocolReader::readStringBody(StrType& str, int32_t size) {
   checkStringSize(size);
-
-  // Catch empty string case
-  if (size == 0) {
-    str.clear();
-    return;
-  }
-
-  if (static_cast<int32_t>(in_.length()) < size) {
-    if (!in_.canAdvance(size)) {
-      protocol::TProtocolException::throwTruncatedData();
-    }
-    str.reserve(size); // only reserve for multi iter case below
-  }
-  str.clear();
-  size_t size_left = size;
-  while (size_left > 0) {
-    auto data = in_.peekBytes();
-    auto data_avail = std::min(data.size(), size_left);
-    if (data.empty()) {
-      TProtocolException::throwTruncatedData();
-    }
-
-    str.append((const char*)data.data(), data_avail);
-    size_left -= data_avail;
-    in_.skipNoAdvance(data_avail);
-  }
+  detail::readStringBody(str, in_, size);
 }
 
 inline bool BinaryProtocolReader::advanceToNextField(

thrift/lib/cpp2/protocol/CompactProtocol-inl.h

@@ -736,25 +736,8 @@ inline void CompactProtocolReader::readStringSize(int32_t& size) {
 
 template <typename StrType>
 inline void CompactProtocolReader::readStringBody(StrType& str, int32_t size) {
-  if (static_cast<int32_t>(in_.length()) < size) {
-    if (!in_.canAdvance(size)) {
-      protocol::TProtocolException::throwTruncatedData();
-    }
-    str.reserve(size); // only reserve for multi iter case below
-  }
-  str.clear();
-  size_t size_left = size;
-  while (size_left > 0) {
-    auto data = in_.peekBytes();
-    auto data_avail = std::min(data.size(), size_left);
-    if (data.empty()) {
-      TProtocolException::throwTruncatedData();
-    }
-
-    str.append((const char*)data.data(), data_avail);
-    size_left -= data_avail;
-    in_.skipNoAdvance(data_avail);
-  }
+  assert(size >= 0); // Checked in readStringSize
+  detail::readStringBody(str, in_, size);
 }
 
 template <typename StrType>

thrift/lib/cpp2/protocol/Protocol.h

@@ -20,15 +20,15 @@
 #include <sys/types.h>
 
 #include <cstdint>
-#include <map>
 #include <memory>
 #include <string>
-#include <vector>
 
 #include <glog/logging.h>
 
+#include <folly/io/Cursor.h>
 #include <folly/io/IOBuf.h>
 #include <folly/io/IOBufQueue.h>
+#include <folly/memory/UninitializedMemoryHacks.h>
 #include <folly/portability/GFlags.h>
 #include <thrift/lib/cpp/Thrift.h>
 #include <thrift/lib/cpp/protocol/TProtocol.h>
@@ -400,6 +400,47 @@ struct StringTraits<std::unique_ptr<folly::IOBuf>> {
   }
 };
 
+namespace detail {
+
+template <typename StrType>
+inline void readStringBody(StrType& str, folly::io::Cursor& in, size_t size) {
+  // Catch empty string case
+  if (size == 0) {
+    str.clear();
+    return;
+  }
+
+  if (in.length() < size) {
+    if (!in.canAdvance(size)) {
+      protocol::TProtocolException::throwTruncatedData();
+    }
+    str.reserve(size); // only reserve for multi iter case below
+  }
+  str.clear();
+  size_t size_left = size;
+  while (size_left > 0) {
+    auto data = in.peekBytes();
+    auto data_avail = std::min(data.size(), size_left);
+    if (data.empty()) {
+      TProtocolException::throwTruncatedData();
+    }
+
+    str.append((const char*)data.data(), data_avail);
+    size_left -= data_avail;
+    in.skipNoAdvance(data_avail);
+  }
+}
+
+inline void readStringBody(
+    std::string& str, folly::io::Cursor& in, size_t size) {
+  folly::resizeWithoutInitialization(str, size);
+  if (in.pullAtMost(str.data(), size) < size) {
+    str.clear();
+    protocol::TProtocolException::throwTruncatedData();
+  }
+}
+} // namespace detail
+
 } // namespace apache::thrift
 
 #endif