beaglelogic: Add beaglelogic_tcp_drain function

The function drains off all the remaining data in the receive socket
and is triggered before starting a capture and after a capture is
completed. In the absence of this function, there is a possibility of
data corruption and also the NodeJS TCP server throws an error if the
buffer is not completely read out before the socket is closed.

Signed-off-by: Kumar Abhishek <abhishek@theembeddedkitchen.net>

src/hardware/beaglelogic/api.c

@@ -358,9 +358,11 @@ static int dev_acquisition_stop(struct sr_dev_inst *sdi)
 	/* Execute a stop on BeagleLogic */
 	devc->beaglelogic->stop(devc);
 
-	/* lseek to offset 0, flushes the cache */
+	/* Flush the cache */
 	if (devc->beaglelogic == &beaglelogic_native_ops)
 		lseek(devc->fd, 0, SEEK_SET);
+	else
+		beaglelogic_tcp_drain(devc);
 
 	/* Remove session source and send EOT packet */
 	sr_session_source_remove_pollfd(sdi->session, &devc->pollfd);

src/hardware/beaglelogic/beaglelogic.h

@@ -127,5 +127,6 @@ SR_PRIV extern const struct beaglelogic_ops beaglelogic_native_ops;
 SR_PRIV extern const struct beaglelogic_ops beaglelogic_tcp_ops;
 
 SR_PRIV int beaglelogic_tcp_detect(struct dev_context *devc);
+SR_PRIV int beaglelogic_tcp_drain(struct dev_context *devc);
 
 #endif

src/hardware/beaglelogic/beaglelogic_tcp.c

@@ -132,6 +132,32 @@ static int beaglelogic_tcp_read_data(struct dev_context *devc, char *buf,
 	return len;
 }
 
+SR_PRIV int beaglelogic_tcp_drain(struct dev_context *devc) {
+	char *buf = g_malloc(1024);
+	fd_set rset;
+	int ret, len = 0;
+	struct timeval tv;
+
+	FD_ZERO(&rset);
+	FD_SET(devc->socket, &rset);
+
+	/* 25ms timeout */
+	tv.tv_sec = 0;
+	tv.tv_usec = 25 * 1000;
+
+	do {
+		ret = select(devc->socket + 1, &rset, NULL, NULL, &tv);
+		if (ret > 0) {
+			len += beaglelogic_tcp_read_data(devc, buf, 1024);
+		}
+	} while (ret > 0);
+
+	sr_spew("Drained %d bytes of data.", len);
+
+	g_free(buf);
+	return SR_OK;
+}
+
 static int beaglelogic_tcp_get_string(struct dev_context *devc, const char *cmd,
 		char **tcp_resp) {
 	GString *response = g_string_sized_new(1024);
@@ -314,6 +340,7 @@ static int beaglelogic_get_lasterror(struct dev_context *devc) {
 }
 
 static int beaglelogic_start(struct dev_context *devc) {
+	beaglelogic_tcp_drain(devc);
 	return beaglelogic_tcp_send_cmd(devc, "get");
 }
 

src/hardware/beaglelogic/protocol.c

@@ -194,6 +194,10 @@ SR_PRIV int beaglelogic_tcp_receive_data(int fd, int revents, void *cb_data)
 		/* Send EOA Packet, stop polling */
 		std_session_send_df_end(sdi);
 		devc->beaglelogic->stop(devc);
+
+		/* Drain the receive buffer */
+		beaglelogic_tcp_drain(devc);
+
 		sr_session_source_remove_pollfd(sdi->session, &devc->pollfd);
 	}