Reducing calls to malloc in AsyncSocket

Summary:
Reduce calls to string::operator+.
Constructing a single string by precalculating the size.

Reviewed By: yfeldblum

Differential Revision: D17573761

fbshipit-source-id: 3918d1774949873fab3ba702d47cdeb80b44ab1d

folly/io/async/AsyncSocket.cpp

@@ -2897,7 +2897,7 @@ std::ostream& operator<<(
   return os;
 }
 
-std::string AsyncSocket::withAddr(const std::string& s) {
+std::string AsyncSocket::withAddr(folly::StringPiece s) {
   // Don't use addr_ directly because it may not be initialized
   // e.g. if constructed from fd
   folly::SocketAddress peer, local;
@@ -2915,7 +2915,9 @@ std::string AsyncSocket::withAddr(const std::string& s) {
   } catch (...) {
     // ignore
   }
-  return s + " (peer=" + peer.describe() + ", local=" + local.describe() + ")";
+
+  return folly::to<std::string>(
+      s, " (peer=", peer.describe(), ", local=", local.describe(), ")");
 }
 
 void AsyncSocket::setBufferCallback(BufferCallback* cb) {

folly/io/async/AsyncSocket.h

@@ -1237,7 +1237,7 @@ class AsyncSocket : virtual public AsyncTransportWrapper {
   void invalidState(ReadCallback* callback);
   void invalidState(WriteCallback* callback);
 
-  std::string withAddr(const std::string& s);
+  std::string withAddr(folly::StringPiece s);
 
   void cacheLocalAddress() const;
   void cachePeerAddress() const;