Create a temporary FIFO (named pipe) in Python?

Question

How can you create a temporary FIFO (named pipe) in Python? This should work:

import tempfile

temp_file_name = mktemp()
os.mkfifo(temp_file_name)
open(temp_file_name, os.O_WRONLY)
# ... some process, somewhere, will read it ...

However, I'm hesitant because of the big warning in Python Docs 11.6 and potential removal because it's deprecated.

EDIT: It's noteworthy that I've tried tempfile.NamedTemporaryFile (and by extension tempfile.mkstemp), but os.mkfifo throws:

OSError -17: File already exists

when you run it on the files that mkstemp/NamedTemporaryFile have created.

Answer 1

os.mkfifo() will fail with exception OSError: [Errno 17] File exists if the file already exists, so there is no security issue here. The security issue with using tempfile.mktemp() is the race condition where it is possible for an attacker to create a file with the same name before you open it yourself, but since os.mkfifo() fails if the file already exists this is not a problem.

However, since mktemp() is deprecated you shouldn't use it. You can use tempfile.mkdtemp() instead:

import os, tempfile

tmpdir = tempfile.mkdtemp()
filename = os.path.join(tmpdir, 'myfifo')
print filename
try:
    os.mkfifo(filename)
except OSError, e:
    print "Failed to create FIFO: %s" % e
else:
    fifo = open(filename, 'w')
    # write stuff to fifo
    print >> fifo, "hello"
    fifo.close()
    os.remove(filename)
    os.rmdir(tmpdir)

EDIT: I should make it clear that, just because the mktemp() vulnerability is averted by this, there are still the other usual security issues that need to be considered; e.g. an attacker could create the fifo (if they had suitable permissions) before your program did which could cause your program to crash if errors/exceptions are not properly handled.

Answer 2

You may find it handy to use the following context manager, which creates and removes the temporary file for you:

import os
import tempfile
from contextlib import contextmanager


@contextmanager
def temp_fifo():
    """Context Manager for creating named pipes with temporary names."""
    tmpdir = tempfile.mkdtemp()
    filename = os.path.join(tmpdir, 'fifo')  # Temporary filename
    os.mkfifo(filename)  # Create FIFO
    yield filename
    os.unlink(filename)  # Remove file
    os.rmdir(tmpdir)  # Remove directory

You can use it, for example, like this:

with temp_fifo() as fifo_file:
    # Pass the fifo_file filename e.g. to some other process to read from.
    # Write something to the pipe 
    with open(fifo_file, 'w') as f:
        f.write("Hello\n")

Answer 3

How about using

d = mkdtemp()
t = os.path.join(d, 'fifo')

Answer 4

If it's for use within your program, and not with any externals, have a look at the Queue module. As an added benefit, python queues are thread-safe.

Answer 5

Effectively, all that mkstemp does is run mktemp in a loop and keeps attempting to exclusively create until it succeeds (see stdlib source code here). You can do the same with os.mkfifo:

import os, errno, tempfile

def mkftemp(*args, **kwargs):
    for attempt in xrange(1024):
        tpath = tempfile.mktemp(*args, **kwargs)

        try:
            os.mkfifo(tpath, 0600)
        except OSError as e:
            if e.errno == errno.EEXIST:
                # lets try again
                continue
            else:
                raise
        else:
           # NOTE: we only return the path because opening with
           # os.open here would block indefinitely since there 
           # isn't anyone on the other end of the fifo.
           return tpath
    else:
        raise IOError(errno.EEXIST, "No usable temporary file name found")

Answer 6

Why not just use mkstemp()?

For example:

import tempfile
import os

handle, filename = tempfile.mkstemp()
os.mkfifo(filename)
writer = open(filename, os.O_WRONLY)
reader = open(filename, os.O_RDONLY)
os.close(handle)