Allocate receive buffers in on the fly

src/net.cpp

@@ -678,7 +678,6 @@ int CNetMessage::readHeader(const char *pch, unsigned int nBytes)
 
     // switch state to reading message data
     in_data = true;
-    vRecv.resize(hdr.nMessageSize);
 
     return nCopy;
 }
@@ -688,6 +687,11 @@ int CNetMessage::readData(const char *pch, unsigned int nBytes)
     unsigned int nRemaining = hdr.nMessageSize - nDataPos;
     unsigned int nCopy = std::min(nRemaining, nBytes);
 
+    if (vRecv.size() < nDataPos + nCopy) {
+        // Allocate up to 256 KiB ahead, but never more than the total message size.
+        vRecv.resize(std::min(hdr.nMessageSize, nDataPos + nCopy + 256 * 1024));
+    }
+
     memcpy(&vRecv[nDataPos], pch, nCopy);
     nDataPos += nCopy;