Send command and parameters in single operation.

This significantly improves the performance because it reduces the
number of round trips needed.

Author: smarsching

src/xvc_client.cpp

@@ -267,20 +267,16 @@ ssize_t XVC_client::xfer_pkt(const string &instr,
 		uint8_t *rx, uint32_t rx_size)
 {
 	ssize_t len = tx_size;
+	vector<uint8_t> buffer(instr.size() + (tx) ? tx_size : 0);
+	memcpy(buffer.data(), instr.c_str(), instr.size());
+	if (tx)
+		memcpy(buffer.data() + instr.size(), tx, tx_size);
 
-	/* 1. instruction */
-	if (sendall(_sock, instr.c_str(), instr.size(), 0) == -1) {
-		printError("Send instruction failed");
+	if (sendall(_sock, buffer.data(), buffer.size(), 0) == -1) {
+		printError("Send failed");
 		return -1;
 	}
 
-	if (tx) {
-		if (sendall(_sock, tx, tx_size, 0) == -1) {
-			printError("Send error");
-			return -1;
-		}
-	}
-
 	if (rx) {
 		len = recv(_sock, rx, rx_size, 0);
 		if (len < 0) {