- Constantine Sapuntzakis: The current implementation will always set

SO_SNDBUF to CURL_WRITE_SIZE even if the SO_SNDBUF starts out larger.  The
  patch doesn't do a setsockopt if SO_SNDBUF is already greater than
  CURL_WRITE_SIZE. This should help folks who have set up their computer with
  large send buffers.

lib/connect.c

@@ -664,6 +664,13 @@ static void nosigpipe(struct connectdata *conn,
 void Curl_sndbufset(curl_socket_t sockfd)
 {
   int val = CURL_MAX_WRITE_SIZE + 32;
+  int curval = 0;
+  int curlen = sizeof(curval);
+
+  if (getsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, (char *)&curval, &curlen) == 0)
+    if (curval > val)
+      return;
+
   setsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, (const char *)&val, sizeof(val));
 }
 #endif