[bitbake-devel] [PATCH] knotty: Add automatic paging for bitbake -s and -e

[Rob Woolley]

The bitbake show environment and show versions commands provide a
large volume of output to the user.  The knotty user interface changes
the output it provides based on whether it detects a TTY.

By checking for the presense of a TTY, we can automatically pipe
the output to a child process that pages the output for the user.
The logic for the automatic paging is based on pager.c found in git.

Some users may have a preferred pager already set in the PAGER
environment variable.  If it is set, found in PATH, and executable
then we use the user's preferred pager.  If it is set to "cat", then
paging is disabled.  If no pager is set, then we set it to "less" as
the default.

The LESS and LV environment variables are also set with sane defaults
in the event that either of these pagers are used.

We cleanly close the pipe before the summary message is displayed.  This
is done intentionally so that the user does not miss any of the summary
information if they close the pipe early.

Tested with both bitbake -s and -e with and without an explicit pipe
to a pager.  This includes testing broken pipe conditions caused by
quitting the pager before the full output has been sent through the pipe.

A custom logging handler was added for Python 3 to ensure that the data
going into the subprocess pipe was utf-8 encoded.  Without this encoding
no data is displayed by the subprocess.

Pagers tested include: less, more, cat, more, lv, and vim less.sh

[ YOCTO #9203 ]

Signed-off-by: Rob Woolley <rob.woolley at windriver.com>
---
 lib/bb/ui/knotty.py | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 63 insertions(+), 3 deletions(-)

diff --git a/lib/bb/ui/knotty.py b/lib/bb/ui/knotty.py
index a19c3b3b..d3587435 100644
--- a/lib/bb/ui/knotty.py
+++ b/lib/bb/ui/knotty.py
@@ -32,6 +32,7 @@ import fcntl
 import struct
 import copy
 import atexit
+import subprocess
 
 from bb.ui import uihelper
 
@@ -40,6 +41,22 @@ featureSet = [bb.cooker.CookerFeatures.SEND_SANITYEVENTS]
 logger = logging.getLogger("BitBake")
 interactive = sys.stdout.isatty()
 
+class UnicodeStreamHandler(logging.StreamHandler):
+    terminator = '\n'
+
+    def __init__(self, stream=None):
+        super().__init__(stream)
+
+    def emit(self, record):
+        try:
+            msg = self.format(record).encode('utf-8')
+            stream = self.stream
+            stream.write(msg)
+            stream.write(self.terminator.encode('utf-8'))
+            self.flush()
+        except Exception:
+            self.handleError(record)
+
 class BBProgress(progressbar.ProgressBar):
     def __init__(self, msg, maxval, widgets=None, extrapos=-1, resize_handler=None):
         self.msg = msg
@@ -166,7 +183,7 @@ class TerminalFilter(object):
         self.helper = helper
         self.cuu = None
         self.stdinbackup = None
-        self.interactive = sys.stdout.isatty()
+        self.interactive = console.stream.isatty()
         self.footer_present = False
         self.lastpids = []
         self.lasttime = None
@@ -351,8 +368,43 @@ def main(server, eventHandler, params, tf = TerminalFilter):
 
     helper = uihelper.BBUIHelper()
 
-    console = logging.StreamHandler(sys.stdout)
-    errconsole = logging.StreamHandler(sys.stderr)
+    pager_bin = None
+    pager_process = None
+
+    if (os.getenv("PAGER")):
+        pager_bin = os.getenv("PAGER")
+    else:
+        pager_bin = "less"
+
+    if pager_bin == "cat":
+        pager_bin = None
+
+    if pager_bin and (not os.path.isfile(pager_bin) or not os.access(pager_bin, os.X_OK)):
+        found_pager = False
+        for path in os.environ["PATH"].split(os.pathsep):
+             pager_path = os.path.join(path,pager_bin)
+             if os.path.isfile(pager_path) and os.access(pager_path, os.X_OK):
+                 found_pager = True
+                 break
+
+        if not found_pager:
+            pager_bin = None
+
+    if (os.getenv("LESS") == None):
+        os.environ['LESS'] = 'FRX'
+
+    if (os.getenv("LV") == None):
+        os.environ['LV'] = '-c'
+
+    if interactive and pager_bin and (params.options.show_versions or params.options.show_environment):
+        pager_process = subprocess.Popen(pager_bin, stdin=subprocess.PIPE, stdout=sys.stdout)
+        console = UnicodeStreamHandler(pager_process.stdin)
+        errconsole = UnicodeStreamHandler(pager_process.stdin)
+        console.setLevel(logging.DEBUG)
+    else:
+        console = logging.StreamHandler(sys.stdout)
+        errconsole = logging.StreamHandler(sys.stderr)
+
     format_str = "%(levelname)s: %(message)s"
     format = bb.msg.BBLogFormatter(format_str)
     if params.options.quiet == 0:
@@ -711,6 +763,14 @@ def main(server, eventHandler, params, tf = TerminalFilter):
                 _, error = server.runCommand(["stateForceShutdown"])
             main.shutdown = 2
             return_value = 1
+
+    if pager_process:
+        try:
+            pager_process.stdin.close()
+            pager_process.wait()
+        except(BrokenPipeError, IOError):
+            pass
+
     try:
         termfilter.clearFooter()
         summary = ""
-- 
2.11.0