[THRIFT-5673] TZlibTransport.py gets into infinite loop if underlying transport ends unexpectedly.

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Python - Library
• Assignee: Unassigned
• Reporter: Benjamin Mahler
• Created: 13/Dec/22 23:10
• Updated: 14/Dec/22 17:14

Description

In python, when using a thrift client composed as follows, the TZlibTransport.py logic can enter an infinite loop when the response closes prematurely (e.g. disconnection):

class GzipTransport(TZlibTransport.TZlibTransport):
  def _init_zlib(self):
    """Override of internal method for setting up the zlib compression and
    decompression objects, to support 'gzip' content encoding.
    """
    self._zcomp_read = zlib.decompressobj(wbits=zlib.MAX_WBITS + 16)
    self._zcomp_write = zlib.compressobj(self.compresslevel, wbits=zlib.MAX_WBITS + 16)

http_client.setCustomHeaders({"Content-Encoding": "gzip", "Accept-Encoding": "gzip"})
transport = GzipTransport(http_client)
transport = TTransport.TBufferedTransport(transport, rbuf_size=1024 * 1024)
thriftClient = ReadOnlyScheduler.Client(protocol)
httpClient.open()
try:
  transport.open()
  return thriftClient.getFoo(FooQuery(...))
finally:
  transport.close()

We observed that when the server shuts down at the same time as the response is being read, the program spins on the following stack trace:

  File: "client.py", line 47, in query_scheduler_api
    return thrift_client_method(thrift_client, *args)
  File: "gen/apache/aurora/api/ReadOnlyScheduler.py", line 198, in getJobSummary
    return self.recv_getJobSummary()
  File: "gen/apache/aurora/api/ReadOnlyScheduler.py", line 210, in recv_getJobSummary
    (fname, mtype, rseqid) = iprot.readMessageBegin()
  File: "thrift/protocol/TJSONProtocol.py", line 417, in readMessageBegin
    self.readJSONArrayStart()
  File: "thrift/protocol/TJSONProtocol.py", line 405, in readJSONArrayStart
    self.readJSONSyntaxChar(LBRACKET)
  File: "thrift/protocol/TJSONProtocol.py", line 253, in readJSONSyntaxChar
    current = self.reader.read()
  File: "thrift-0.13.0-cp37-cp37m-linux_x86_64.whl/thrift/protocol/TJSONProtocol.py", line 164, in read
    self.data = self.protocol.trans.read(1)
  File: "thrift/transport/TTransport.py", line 164, in read
    self.__rbuf = BufferIO(self.__trans.read(max(sz, self.__rbuf_size)))
  File: "thrift/transport/TZlibTransport.py", line 191, in read
    if self.readComp(sz):
  File: "thrift/transport/TZlibTransport.py", line 208, in readComp
    return False

Essentially, it appears that when the json protocol asks to read 1 byte, and there's always 0 bytes returned from the http response (EOF), then the zlib transport will spin in a loop here: https://github.com/apache/thrift/blob/v0.17.0/lib/py/src/transport/TZlibTransport.py#L190-L192

It seems like this is a bug, and the zlib transport should treat 0 bytes coming back from the underlying transport as EOF, at which point it closes its compression streams and tells the caller about the remaining data and EOF (possibly throwing an exception if the EOF does not cleanly finish the decompression stream).

In our case, the underlying transport is ultimately the HttpClient's response, and that doesn't appear to throw an exception when the response is cut short, it just appears to return 0 bytes repeatedly.

We use thrift 0.13.0 but I see the same logic in the latest release and the bug appears unfixed there as well.