1# Copyright (c) 2012 The Chromium OS Authors.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4#
5# Copyright (c) 2003-2005 by Peter Astrand <astrand@lysator.liu.se>
6# Licensed to PSF under a Contributor Agreement.
7# See http://www.python.org/2.4/license for licensing details.
8
9"""Subprocress execution
10
11This module holds a subclass of subprocess.Popen with our own required
12features, mainly that we get access to the subprocess output while it
13is running rather than just at the end. This makes it easiler to show
14progress information and filter output in real time.
15"""
16
17import errno
18import os
19import pty
20import select
21import subprocess
22import sys
23import unittest
24
25
26# Import these here so the caller does not need to import subprocess also.
27PIPE = subprocess.PIPE
28STDOUT = subprocess.STDOUT
29PIPE_PTY = -3     # Pipe output through a pty
30stay_alive = True
31
32
33class Popen(subprocess.Popen):
34    """Like subprocess.Popen with ptys and incremental output
35
36    This class deals with running a child process and filtering its output on
37    both stdout and stderr while it is running. We do this so we can monitor
38    progress, and possibly relay the output to the user if requested.
39
40    The class is similar to subprocess.Popen, the equivalent is something like:
41
42        Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
43
44    But this class has many fewer features, and two enhancement:
45
46    1. Rather than getting the output data only at the end, this class sends it
47         to a provided operation as it arrives.
48    2. We use pseudo terminals so that the child will hopefully flush its output
49         to us as soon as it is produced, rather than waiting for the end of a
50         line.
51
52    Use CommunicateFilter() to handle output from the subprocess.
53
54    """
55
56    def __init__(self, args, stdin=None, stdout=PIPE_PTY, stderr=PIPE_PTY,
57                 shell=False, cwd=None, env=None, **kwargs):
58        """Cut-down constructor
59
60        Args:
61            args: Program and arguments for subprocess to execute.
62            stdin: See subprocess.Popen()
63            stdout: See subprocess.Popen(), except that we support the sentinel
64                    value of cros_subprocess.PIPE_PTY.
65            stderr: See subprocess.Popen(), except that we support the sentinel
66                    value of cros_subprocess.PIPE_PTY.
67            shell: See subprocess.Popen()
68            cwd: Working directory to change to for subprocess, or None if none.
69            env: Environment to use for this subprocess, or None to inherit parent.
70            kwargs: No other arguments are supported at the moment.    Passing other
71                    arguments will cause a ValueError to be raised.
72        """
73        stdout_pty = None
74        stderr_pty = None
75
76        if stdout == PIPE_PTY:
77            stdout_pty = pty.openpty()
78            stdout = os.fdopen(stdout_pty[1])
79        if stderr == PIPE_PTY:
80            stderr_pty = pty.openpty()
81            stderr = os.fdopen(stderr_pty[1])
82
83        super(Popen, self).__init__(args, stdin=stdin,
84                stdout=stdout, stderr=stderr, shell=shell, cwd=cwd, env=env,
85                **kwargs)
86
87        # If we're on a PTY, we passed the slave half of the PTY to the subprocess.
88        # We want to use the master half on our end from now on.    Setting this here
89        # does make some assumptions about the implementation of subprocess, but
90        # those assumptions are pretty minor.
91
92        # Note that if stderr is STDOUT, then self.stderr will be set to None by
93        # this constructor.
94        if stdout_pty is not None:
95            self.stdout = os.fdopen(stdout_pty[0])
96        if stderr_pty is not None:
97            self.stderr = os.fdopen(stderr_pty[0])
98
99        # Insist that unit tests exist for other arguments we don't support.
100        if kwargs:
101            raise ValueError("Unit tests do not test extra args - please add tests")
102
103    def CommunicateFilter(self, output):
104        """Interact with process: Read data from stdout and stderr.
105
106        This method runs until end-of-file is reached, then waits for the
107        subprocess to terminate.
108
109        The output function is sent all output from the subprocess and must be
110        defined like this:
111
112            def Output([self,] stream, data)
113            Args:
114                stream: the stream the output was received on, which will be
115                        sys.stdout or sys.stderr.
116                data: a string containing the data
117
118        Note: The data read is buffered in memory, so do not use this
119        method if the data size is large or unlimited.
120
121        Args:
122            output: Function to call with each fragment of output.
123
124        Returns:
125            A tuple (stdout, stderr, combined) which is the data received on
126            stdout, stderr and the combined data (interleaved stdout and stderr).
127
128            Note that the interleaved output will only be sensible if you have
129            set both stdout and stderr to PIPE or PIPE_PTY. Even then it depends on
130            the timing of the output in the subprocess. If a subprocess flips
131            between stdout and stderr quickly in succession, by the time we come to
132            read the output from each we may see several lines in each, and will read
133            all the stdout lines, then all the stderr lines. So the interleaving
134            may not be correct. In this case you might want to pass
135            stderr=cros_subprocess.STDOUT to the constructor.
136
137            This feature is still useful for subprocesses where stderr is
138            rarely used and indicates an error.
139
140            Note also that if you set stderr to STDOUT, then stderr will be empty
141            and the combined output will just be the same as stdout.
142        """
143
144        read_set = []
145        write_set = []
146        stdout = None # Return
147        stderr = None # Return
148
149        if self.stdin:
150            # Flush stdio buffer.    This might block, if the user has
151            # been writing to .stdin in an uncontrolled fashion.
152            self.stdin.flush()
153            if input:
154                write_set.append(self.stdin)
155            else:
156                self.stdin.close()
157        if self.stdout:
158            read_set.append(self.stdout)
159            stdout = []
160        if self.stderr and self.stderr != self.stdout:
161            read_set.append(self.stderr)
162            stderr = []
163        combined = []
164
165        input_offset = 0
166        while read_set or write_set:
167            try:
168                rlist, wlist, _ = select.select(read_set, write_set, [], 0.2)
169            except select.error, e:
170                if e.args[0] == errno.EINTR:
171                    continue
172                raise
173
174            if not stay_alive:
175                    self.terminate()
176
177            if self.stdin in wlist:
178                # When select has indicated that the file is writable,
179                # we can write up to PIPE_BUF bytes without risk
180                # blocking.    POSIX defines PIPE_BUF >= 512
181                chunk = input[input_offset : input_offset + 512]
182                bytes_written = os.write(self.stdin.fileno(), chunk)
183                input_offset += bytes_written
184                if input_offset >= len(input):
185                    self.stdin.close()
186                    write_set.remove(self.stdin)
187
188            if self.stdout in rlist:
189                data = ""
190                # We will get an error on read if the pty is closed
191                try:
192                    data = os.read(self.stdout.fileno(), 1024)
193                except OSError:
194                    pass
195                if data == "":
196                    self.stdout.close()
197                    read_set.remove(self.stdout)
198                else:
199                    stdout.append(data)
200                    combined.append(data)
201                    if output:
202                        output(sys.stdout, data)
203            if self.stderr in rlist:
204                data = ""
205                # We will get an error on read if the pty is closed
206                try:
207                    data = os.read(self.stderr.fileno(), 1024)
208                except OSError:
209                    pass
210                if data == "":
211                    self.stderr.close()
212                    read_set.remove(self.stderr)
213                else:
214                    stderr.append(data)
215                    combined.append(data)
216                    if output:
217                        output(sys.stderr, data)
218
219        # All data exchanged.    Translate lists into strings.
220        if stdout is not None:
221            stdout = ''.join(stdout)
222        else:
223            stdout = ''
224        if stderr is not None:
225            stderr = ''.join(stderr)
226        else:
227            stderr = ''
228        combined = ''.join(combined)
229
230        # Translate newlines, if requested.    We cannot let the file
231        # object do the translation: It is based on stdio, which is
232        # impossible to combine with select (unless forcing no
233        # buffering).
234        if self.universal_newlines and hasattr(file, 'newlines'):
235            if stdout:
236                stdout = self._translate_newlines(stdout)
237            if stderr:
238                stderr = self._translate_newlines(stderr)
239
240        self.wait()
241        return (stdout, stderr, combined)
242
243
244# Just being a unittest.TestCase gives us 14 public methods.    Unless we
245# disable this, we can only have 6 tests in a TestCase.    That's not enough.
246#
247# pylint: disable=R0904
248
249class TestSubprocess(unittest.TestCase):
250    """Our simple unit test for this module"""
251
252    class MyOperation:
253        """Provides a operation that we can pass to Popen"""
254        def __init__(self, input_to_send=None):
255            """Constructor to set up the operation and possible input.
256
257            Args:
258                input_to_send: a text string to send when we first get input. We will
259                    add \r\n to the string.
260            """
261            self.stdout_data = ''
262            self.stderr_data = ''
263            self.combined_data = ''
264            self.stdin_pipe = None
265            self._input_to_send = input_to_send
266            if input_to_send:
267                pipe = os.pipe()
268                self.stdin_read_pipe = pipe[0]
269                self._stdin_write_pipe = os.fdopen(pipe[1], 'w')
270
271        def Output(self, stream, data):
272            """Output handler for Popen. Stores the data for later comparison"""
273            if stream == sys.stdout:
274                self.stdout_data += data
275            if stream == sys.stderr:
276                self.stderr_data += data
277            self.combined_data += data
278
279            # Output the input string if we have one.
280            if self._input_to_send:
281                self._stdin_write_pipe.write(self._input_to_send + '\r\n')
282                self._stdin_write_pipe.flush()
283
284    def _BasicCheck(self, plist, oper):
285        """Basic checks that the output looks sane."""
286        self.assertEqual(plist[0], oper.stdout_data)
287        self.assertEqual(plist[1], oper.stderr_data)
288        self.assertEqual(plist[2], oper.combined_data)
289
290        # The total length of stdout and stderr should equal the combined length
291        self.assertEqual(len(plist[0]) + len(plist[1]), len(plist[2]))
292
293    def test_simple(self):
294        """Simple redirection: Get process list"""
295        oper = TestSubprocess.MyOperation()
296        plist = Popen(['ps']).CommunicateFilter(oper.Output)
297        self._BasicCheck(plist, oper)
298
299    def test_stderr(self):
300        """Check stdout and stderr"""
301        oper = TestSubprocess.MyOperation()
302        cmd = 'echo fred >/dev/stderr && false || echo bad'
303        plist = Popen([cmd], shell=True).CommunicateFilter(oper.Output)
304        self._BasicCheck(plist, oper)
305        self.assertEqual(plist [0], 'bad\r\n')
306        self.assertEqual(plist [1], 'fred\r\n')
307
308    def test_shell(self):
309        """Check with and without shell works"""
310        oper = TestSubprocess.MyOperation()
311        cmd = 'echo test >/dev/stderr'
312        self.assertRaises(OSError, Popen, [cmd], shell=False)
313        plist = Popen([cmd], shell=True).CommunicateFilter(oper.Output)
314        self._BasicCheck(plist, oper)
315        self.assertEqual(len(plist [0]), 0)
316        self.assertEqual(plist [1], 'test\r\n')
317
318    def test_list_args(self):
319        """Check with and without shell works using list arguments"""
320        oper = TestSubprocess.MyOperation()
321        cmd = ['echo', 'test', '>/dev/stderr']
322        plist = Popen(cmd, shell=False).CommunicateFilter(oper.Output)
323        self._BasicCheck(plist, oper)
324        self.assertEqual(plist [0], ' '.join(cmd[1:]) + '\r\n')
325        self.assertEqual(len(plist [1]), 0)
326
327        oper = TestSubprocess.MyOperation()
328
329        # this should be interpreted as 'echo' with the other args dropped
330        cmd = ['echo', 'test', '>/dev/stderr']
331        plist = Popen(cmd, shell=True).CommunicateFilter(oper.Output)
332        self._BasicCheck(plist, oper)
333        self.assertEqual(plist [0], '\r\n')
334
335    def test_cwd(self):
336        """Check we can change directory"""
337        for shell in (False, True):
338            oper = TestSubprocess.MyOperation()
339            plist = Popen('pwd', shell=shell, cwd='/tmp').CommunicateFilter(oper.Output)
340            self._BasicCheck(plist, oper)
341            self.assertEqual(plist [0], '/tmp\r\n')
342
343    def test_env(self):
344        """Check we can change environment"""
345        for add in (False, True):
346            oper = TestSubprocess.MyOperation()
347            env = os.environ
348            if add:
349                env ['FRED'] = 'fred'
350            cmd = 'echo $FRED'
351            plist = Popen(cmd, shell=True, env=env).CommunicateFilter(oper.Output)
352            self._BasicCheck(plist, oper)
353            self.assertEqual(plist [0], add and 'fred\r\n' or '\r\n')
354
355    def test_extra_args(self):
356        """Check we can't add extra arguments"""
357        self.assertRaises(ValueError, Popen, 'true', close_fds=False)
358
359    def test_basic_input(self):
360        """Check that incremental input works
361
362        We set up a subprocess which will prompt for name. When we see this prompt
363        we send the name as input to the process. It should then print the name
364        properly to stdout.
365        """
366        oper = TestSubprocess.MyOperation('Flash')
367        prompt = 'What is your name?: '
368        cmd = 'echo -n "%s"; read name; echo Hello $name' % prompt
369        plist = Popen([cmd], stdin=oper.stdin_read_pipe,
370                shell=True).CommunicateFilter(oper.Output)
371        self._BasicCheck(plist, oper)
372        self.assertEqual(len(plist [1]), 0)
373        self.assertEqual(plist [0], prompt + 'Hello Flash\r\r\n')
374
375    def test_isatty(self):
376        """Check that ptys appear as terminals to the subprocess"""
377        oper = TestSubprocess.MyOperation()
378        cmd = ('if [ -t %d ]; then echo "terminal %d" >&%d; '
379                'else echo "not %d" >&%d; fi;')
380        both_cmds = ''
381        for fd in (1, 2):
382            both_cmds += cmd % (fd, fd, fd, fd, fd)
383        plist = Popen(both_cmds, shell=True).CommunicateFilter(oper.Output)
384        self._BasicCheck(plist, oper)
385        self.assertEqual(plist [0], 'terminal 1\r\n')
386        self.assertEqual(plist [1], 'terminal 2\r\n')
387
388        # Now try with PIPE and make sure it is not a terminal
389        oper = TestSubprocess.MyOperation()
390        plist = Popen(both_cmds, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
391                shell=True).CommunicateFilter(oper.Output)
392        self._BasicCheck(plist, oper)
393        self.assertEqual(plist [0], 'not 1\n')
394        self.assertEqual(plist [1], 'not 2\n')
395
396if __name__ == '__main__':
397    unittest.main()
398