pmb.helpers.run_core: add output=pipe (MR 1996)

This adds a new output mode "pipe" that is identical to the existing
"background" mode except for that its stdout is redirected into a
pipe so that it can be retrieved.

pmb/helpers/run_core.py

@@ -20,7 +20,7 @@ def sanity_checks(output="log", output_return=False, check=None,
     Raise an exception if the parameters passed to core() don't make sense
     (all parameters are described in core() below).
     """
-    if output not in ["log", "stdout", "interactive", "tui", "background"]:
+    if output not in ["log", "stdout", "interactive", "tui", "background", "pipe"]:
         raise RuntimeError("Invalid output value: " + str(output))
 
     # Prevent setting the check parameter with output="background".
@@ -45,6 +45,14 @@ def background(args, cmd, working_dir=None):
     return ret
 
 
+def pipe(args, cmd, working_dir=None):
+    """ Run a subprocess in background and redirect its output to a pipe. """
+    ret = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=args.logfd,
+                           cwd=working_dir)
+    logging.verbose(f"New background process: pid={ret.pid}, output=pipe")
+    return ret
+
+
 def pipe_read(args, process, output_to_stdout=False, output_return=False,
               output_return_buffer=False):
     """
@@ -215,14 +223,16 @@ def core(args, log_message, cmd, working_dir=None, output="log",
                    "stdout", "interactive", "background"), so it's easy to
                    trace what pmbootstrap does.
 
-                   The exception is "tui" (text-based user interface), where
+                   The exceptions are "tui" (text-based user interface), where
                    it does not make sense to write to the log file (think of
-                   ncurses UIs, such as "menuconfig").
+                   ncurses UIs, such as "menuconfig") and "pipe" where the
+                   output is written to a pipe for manual asynchronous
+                   consumption by the caller.
 
-                   When the output is not set to "interactive", "tui" or
-                   "background", we kill the process if it does not output
-                   anything for 5 minutes (time can be set with "pmbootstrap
-                   --timeout").
+                   When the output is not set to "interactive", "tui",
+                   "background" or "pipe", we kill the process if it does not
+                   output anything for 5 minutes (time can be set with
+                   "pmbootstrap --timeout").
 
                    The table below shows all possible values along with
                    their properties. "wait" indicates that we wait for the
@@ -235,18 +245,20 @@ def core(args, log_message, cmd, working_dir=None, output="log",
                    "interactive" |         | x          | x             | x
                    "tui"         |         |            | x             | x
                    "background"  |         | x          |               |
+                   "pipe"        |         |            |               |
 
     :param output_return: in addition to writing the program's output to the
                           destinations above in real time, write to a buffer
                           and return it as string when the command has
                           completed. This is not possible when output is
-                          "background" or "tui".
+                          "background", "pipe" or "tui".
     :param check: an exception will be raised when the command's return code
                   is not 0. Set this to False to disable the check. This
-                  parameter can not be used when the output is "background".
+                  parameter can not be used when the output is "background" or
+                  "pipe".
     :param kill_as_root: use sudo to kill the process when it hits the timeout.
     :returns: * program's return code (default)
-              * subprocess.Popen instance (output is "background")
+              * subprocess.Popen instance (output is "background" or "pipe")
               * the program's entire output (output_return is True)
     """
     sanity_checks(output, output_return, check, kill_as_root)
@@ -259,6 +271,10 @@ def core(args, log_message, cmd, working_dir=None, output="log",
     if output == "background":
         return background(args, cmd, working_dir)
 
+    # Pipe
+    if output == "pipe":
+        return pipe(args, cmd, working_dir)
+
     # Foreground
     output_after_run = ""
     if output == "tui":

test/test_run_core.py

@@ -56,6 +56,20 @@ def test_background(args):
     assert process.poll() is None
 
 
+def test_pipe(args):
+    # Sleep in background
+    process = pmb.helpers.run_core.pipe(args, ["sleep", "1"], "/")
+
+    # Check if it is still running
+    assert process.poll() is None
+
+    # Print output in background
+    process = pmb.helpers.run_core.pipe(args, ["echo", "-n", "hello"], "/")
+
+    # Read output
+    assert process.communicate()[0].decode('utf-8') == "hello"
+
+
 def test_foreground_pipe(args):
     func = pmb.helpers.run_core.foreground_pipe
     cmd = ["echo", "test"]