utils: T8018: add unbuffered output support to popen()

Instead of executing the command passed to popen() and waiting for it to
finish before printing its output, add a function argument to disable
buffered mode.

When buffered mode (the default) is turned off, each line emitted by the
process is flushed immediately to the calling TTY.

1 files changed, 47 insertions, 26 deletions

diff --git a/python/vyos/utils/process.py b/python/vyos/utils/process.py
index 86a2747af..158371024 100644
--- a/python/vyos/utils/process.py
+++ b/python/vyos/utils/process.py
@@ -32,7 +32,8 @@ def get_wrapper(vrf, netns):
 
 
 def popen(command, flag='', shell=None, input=None, timeout=None, env=None,
-          stdout=PIPE, stderr=PIPE, decode='utf-8', vrf=None, netns=None):
+          stdout=PIPE, stderr=PIPE, decode='utf-8', vrf=None, netns=None,
+          buffered=True):
     """
     popen is a wrapper helper around subprocess.Popen
     with it default setting it will return a tuple (out, err)
@@ -58,6 +59,9 @@ def popen(command, flag='', shell=None, input=None, timeout=None, env=None,
              the default is explicitely utf-8 which is python's own default
     vrf:     run command in a VRF context
     netns:   run command in the named network namespace
+    buffered: define how process output shall be presented to stdout
+               - true: buffer output and return once after command finished
+               - false: immediately output strings on stdout - give live feedback
 
     usage:
     get both stdout and stderr: popen('command', stdout=PIPE, stderr=STDOUT)
@@ -104,38 +108,54 @@ def popen(command, flag='', shell=None, input=None, timeout=None, env=None,
         stdin = PIPE
         input = input.encode() if type(input) is str else input
 
+    text = None
+    bufsize = -1 # default: means the system default of io.DEFAULT_BUFFER_SIZE will be used
+    if not buffered:
+        text = True # Treat output as strings (not bytes)
+        bufsize = 1 # Enable line buffering
+
     p = Popen(command, stdin=stdin, stdout=stdout, stderr=stderr,
-              env=env, shell=use_shell)
+              env=env, shell=use_shell, text=text, bufsize=bufsize)
 
-    pipe = p.communicate(input, timeout)
+    if buffered:
+        pipe = p.communicate(input, timeout)
+        rc = p.returncode
 
-    pipe_out = b''
-    if stdout == PIPE:
-        pipe_out = pipe[0]
+        pipe_out = b''
+        if stdout == PIPE:
+            pipe_out = pipe[0]
 
-    pipe_err = b''
-    if stderr == PIPE:
-        pipe_err = pipe[1]
+        pipe_err = b''
+        if stderr == PIPE:
+            pipe_err = pipe[1]
 
-    str_out = pipe_out.decode(decode).replace('\r\n', '\n').strip()
-    str_err = pipe_err.decode(decode).replace('\r\n', '\n').strip()
+        str_out = pipe_out.decode(decode).replace('\r\n', '\n').strip()
+        str_err = pipe_err.decode(decode).replace('\r\n', '\n').strip()
 
-    out_msg = f"returned (out):\n{str_out}"
-    if str_out:
-        debug.message(out_msg, flag)
+        out_msg = f"returned (out):\n{str_out}"
+        if str_out:
+            debug.message(out_msg, flag)
 
-    if str_err:
-        from sys import stderr
-        err_msg = f"returned (err):\n{str_err}"
-        # this message will also be send to syslog via airbag
-        debug.message(err_msg, flag, destination=stderr)
+        if str_err:
+            from sys import stderr
+            err_msg = f"returned (err):\n{str_err}"
+            # this message will also be send to syslog via airbag
+            debug.message(err_msg, flag, destination=stderr)
 
-        # should something go wrong, report this too via airbag
-        airbag.noteworthy(cmd_msg)
-        airbag.noteworthy(out_msg)
-        airbag.noteworthy(err_msg)
+            # should something go wrong, report this too via airbag
+            airbag.noteworthy(cmd_msg)
+            airbag.noteworthy(out_msg)
+            airbag.noteworthy(err_msg)
+    else:
+        output_lines = []
+        for line in p.stdout:
+            print(line, end='', flush=True)  # print each line as it arrives
+            output_lines.append(line)
+        p.stdout.close()
+        rc = p.wait()
+        str_out = ''.join(output_lines)
 
-    return str_out, p.returncode
+    return str_out, rc
 
 
 def run(command, flag='', shell=None, input=None, timeout=None, env=None,
@@ -191,9 +211,9 @@ def cmd(command, flag='', shell=None, input=None, timeout=None, env=None,
             raise raising(feedback)
     return decoded
 
-
 def rc_cmd(command, flag='', shell=None, input=None, timeout=None, env=None,
-           stdout=PIPE, stderr=STDOUT, decode='utf-8', vrf=None, netns=None):
+           stdout=PIPE, stderr=STDOUT, decode='utf-8', vrf=None, netns=None,
+           buffered=True):
     """
     A wrapper around popen, which returns the return code
     of a command and stdout
@@ -211,6 +231,7 @@ def rc_cmd(command, flag='', shell=None, input=None, timeout=None, env=None,
         decode=decode,
         vrf=vrf,
         netns=netns,
+        buffered=buffered,
     )
     return code, out