Fix connection abort if device buffer is full

When trying to upload a IPSW filesystem to an iPad, the process would
randomly stop somewhere at 3% or 10%. It is possible that the receive
buffer of the iPad is full. To prevent erroring out because size ==
conn->sendable == 0, skip reading from the client.

There is a similar case where the clients is ready to accept data, but
the device has no data to send. Apply a similar fix there.

Hopefully the device is fast enough to reply in the next main loop
iteration, otherwise the CPU usage of usbmux will spike because the
client socket is ready while there is no data to process...

1 files changed, 4 insertions, 3 deletions

diff --git a/src/device.c b/src/device.c
index e36509e..1c8ec8c 100644
--- a/src/device.c
+++ b/src/device.c
@@ -424,9 +424,9 @@ void device_client_process(int device_id, struct mux_client *client, short event
 
 	int res;
 	int size;
-	if(events & POLLOUT) {
+	if((events & POLLOUT) && conn->ib_size > 0) {
 		// Client is ready to receive data, send what we have
-		// in the client's connection buffer
+		// in the client's connection buffer (if there is any)
 		size = client_write(conn->client, conn->ib_buf, conn->ib_size);
 		if(size <= 0) {
 			usbmuxd_log(LL_DEBUG, "error writing to client (%d)", size);
@@ -441,9 +441,10 @@ void device_client_process(int device_id, struct mux_client *client, short event
 			memmove(conn->ib_buf, conn->ib_buf + size, conn->ib_size);
 		}
 	}
-	if(events & POLLIN) {
+	if((events & POLLIN) && conn->sendable > 0) {
 		// There is inbound trafic on the client socket,
 		// convert it to tcp and send to the device
+		// (if the device's input buffer is not full)
 		size = client_read(conn->client, conn->ob_buf, conn->sendable);
 		if(size <= 0) {
 			if (size < 0) {