DCC Transfers getting stuck

Sometimes, mostly around the 500MB mark, the DCC transfers seem to get stuck at

`connection.send_bytes(struct.pack("!I", self.received_bytes))`

The previous package is received and then execution just stops at the above function.
It's a little hard to debug since a few thousand packages go through so manually stepping through is not feasable.

Is this related to the warning that TCP Buffers can block?

Here are my relevant functions. Any Idea would be appreciated.

```python
def on_ctcp(self, connection, event):
print(event)
if (event.arguments[0] == "VERSION"):
connection.ctcp_reply(event.source, "VERSION Niblette 0.1a")
return

payload = event.arguments[1]
parts = shlex.split(payload)
command, filename, peer_address, peer_port, size = parts

if (command != "SEND"):
return

showName, season = determineStructure(filename)

if (isWindows):
fullpath = filename
else:
showPath = f"/usr/download/Anime/{showName}"
seasonPath = f"/usr/download/Anime/{showName}/{season}"
fullpath = f"/usr/download/Anime/{showName}/{season}/{filename}"
if (not os.path.exists(showPath)):
os.mkdir(showPath)
if (not os.path.exists(seasonPath)):
os.mkdir(seasonPath)

print("Receiving a file. Potential location: ", fullpath)
if (os.path.exists(fullpath)):
print("A file named", fullpath, "already exists. Refusing to save it.")
return
print("Downloading ", filename)
self.total_bytes = int(size)
print(f"Size: {self.total_bytes}")
self.received_bytes = 0
if (self.file is not None):
self.file.close()
self.file = open(fullpath, "wb")
peer_address = irc.client.ip_numstr_to_quad(peer_address)
peer_port = int(peer_port)
self.downloader = self.dcc("raw")
self.downloader = self.downloader.connect(peer_address, peer_port)

def on_dccmsg(self, connection, event):
try:
if (len(event.arguments) != 1):
print(f"Error while downloading, error: {event.arguments}")
self.file.close()
self.downloader.disconnect()
data = event.arguments[0]
self.file.write(data)
self.received_bytes = self.received_bytes + len(data)

connection.send_bytes(struct.pack("!I", self.received_bytes))

if (self.received_bytes == self.total_bytes):
print("")
print("Finished, disconnecting.")
self.file.close()
self.downloader.disconnect()
except Exception as ex:
print(f"Error: {ex}")
```

Start with the on_ctcp and on_dccmsg entry points shown in the issue, especially the connection.send_bytes call after each received packet. Reproduce the transfer near the reported size and inspect whether the send operation blocks or raises an error. Done means identifying the cause of the stalled transfer and documenting or fixing a reproducible behavior in the library.

Written by the indexing model from the issue text.