pymemcache.exceptions.MemcacheUnknownCommandError: b'get' when hitting maximum number of connections

[cbowal]

Hello!

I'm using:

• django v4.2
• memcache v1.6.22
• pymemcache v4.0.0

I started seeing errors like this pop up:

  File "django/core/cache/backends/memcached.py", line 96, in get_many
          ret = self._cache.get_multi(key_map.keys())
  File "pymemcache/client/hash.py", line 398, in get_many
              result = self._safely_run_func(client, get_func, {}, *new_args, **kwargs)
  File "pymemcache/client/hash.py", line 211, in _safely_run_func
              result = func(*args, **kwargs)
  File "pymemcache/client/base.py", line 706, in get_many
          return self._fetch_cmd(b"get", keys, False, key_prefix=self.key_prefix)
  File "pymemcache/client/base.py", line 1149, in _fetch_cmd
                  self._raise_errors(line, name)
  File "pymemcache/client/base.py", line 1034, in _raise_errors
              raise MemcacheUnknownCommandError(name)
pymemcache.exceptions.MemcacheUnknownCommandError: b'get'

This was weird since 'get' is obviously a valid command.

Looking at the logs of the memcache instance I noticed that this is happening when I've hit the maximum number of connections. I'm seeing these memcache error logs:
ts=2023-11-16T19:27:25.256Z caller=exporter.go:771 level=error msg="Could not query stats settings" err="memcache: unexpected stats line format \"ERROR Too many open connections\\r\\n\""

I'm not too familiar with the pymemcache internals but it seems to be incorrectly raising MemcacheUnknownCommandError. I'm not sure what the expected error is when there's no available connection, perhaps MemcacheServerError or MemcacheUnexpectedCloseError.

[jogo]

The current code scan the response for lines that start with 'ERROR,' and sounds like that logic doesn't work in this case.

Do you have the full steps to reproduce the issue? If so I can take a look and work on a fix.

https://github.com/pinterest/pymemcache/blob/v4.0.0/pymemcache/client/base.py#L1149

pymemcache/pymemcache/client/base.py

Line 1032 in 4e5db4b

def _raise_errors(self, line: bytes, name: bytes) -> None:

[dforce]

I have the same issue.
`from pymemcache.client.base import Client

client = Client(('localhost', 11211))
hits = client.stats('get_hits')
misses = client.stats('get_misses')
print(f'Hits: {hits}')
print(f'Misses: {misses}')

Got error "pymemcache.exceptions.MemcacheUnknownCommandError: b'stats'"

[AnnaAngeline]

In _recv method socket.recv() raising ERROR\r\n

cmd = name
        if prefixed_keys:
            cmd += b" " + b" ".join(prefixed_keys)
        cmd += b"\r\n"

In above code for cmd we are sending args to now cmd will be b'stats get_hits\r\n' we are sending this cmd to socket.sendall() so socket.recv(size) raise issue MemcacheUnknownCommandError

After making changes comment out below lines

 if prefixed_keys:
            cmd += b" " + b" ".join(prefixed_keys)

PR Raised for this issue fix