loggingutil: add basic logger backends

loggingutil: add basic logger backends

These classes will be used in command server. They are similar to
the blackboxlogger, but it can't be factored out since the blackbox is so
tightly coupled with a repo object.

--- a/mercurial/loggingutil.py	Tue Dec 04 17:13:01 2018 -0500
+++ b/mercurial/loggingutil.py	Sun Nov 18 18:58:06 2018 +0900
@@ -14,6 +14,12 @@
     pycompat,
 )
 
+from .utils import (
+    dateutil,
+    procutil,
+    stringutil,
+)
+
 def openlogfile(ui, vfs, name, maxfiles=0, maxsize=0):
     """Open log file in append mode, with optional rotation
 
@@ -49,6 +55,58 @@
                        newpath=maxfiles > 0 and path + '.1')
     return vfs(name, 'a', makeparentdirs=False)
 
+def _formatlogline(msg):
+    date = dateutil.datestr(format=b'%Y/%m/%d %H:%M:%S')
+    pid = procutil.getpid()
+    return b'%s (%d)> %s' % (date, pid, msg)
+
+def _matchevent(event, tracked):
+    return b'*' in tracked or event in tracked
+
+class filelogger(object):
+    """Basic logger backed by physical file with optional rotation"""
+
+    def __init__(self, vfs, name, tracked, maxfiles=0, maxsize=0):
+        self._vfs = vfs
+        self._name = name
+        self._trackedevents = set(tracked)
+        self._maxfiles = maxfiles
+        self._maxsize = maxsize
+
+    def tracked(self, event):
+        return _matchevent(event, self._trackedevents)
+
+    def log(self, ui, event, msg, opts):
+        line = _formatlogline(msg)
+        try:
+            with openlogfile(ui, self._vfs, self._name,
+                             maxfiles=self._maxfiles,
+                             maxsize=self._maxsize) as fp:
+                fp.write(line)
+        except IOError as err:
+            ui.debug(b'cannot write to %s: %s\n'
+                     % (self._name, stringutil.forcebytestr(err)))
+
+class fileobjectlogger(object):
+    """Basic logger backed by file-like object"""
+
+    def __init__(self, fp, tracked):
+        self._fp = fp
+        self._trackedevents = set(tracked)
+
+    def tracked(self, event):
+        return _matchevent(event, self._trackedevents)
+
+    def log(self, ui, event, msg, opts):
+        line = _formatlogline(msg)
+        try:
+            self._fp.write(line)
+            self._fp.flush()
+        except IOError as err:
+            ui.debug(b'cannot write to %s: %s\n'
+                     % (stringutil.forcebytestr(self._fp.name),
+                        stringutil.forcebytestr(err)))
+
 class proxylogger(object):
     """Forward log events to another logger to be set later"""