blackbox: automatically rotate log files

If enabled, log rotation prevents the amount of space used by the
blackbox log from growing without bound. This becomes important in
cases where there are a lot of busy repositories managed by humans
and automation on many machines.

In large deployments, we cannot reasonably track all the repos where
blackbox logs need to be managed, so it is safer to have blackbox
manage its own logs than to move responsibility to an external tool
such as logrotate.

This change adds two configuration keys:

* blackbox.maxsize is the maximum allowable size of the current log

* blackbox.maxfiles is the number of log files to maintain

hgext/blackbox.py

@@ -21,11 +21,17 b' Examples:'
   [blackbox]
   track = incoming
 
+  [blackbox]
+  # limit the size of a log file
+  maxsize = 1.5 MB
+  # rotate up to N log files when the current one gets too big
+  maxfiles = 3
+
 """
 
 from mercurial import util, cmdutil
 from mercurial.i18n import _
-import os, re
+import errno, os, re
 
 cmdtable = {}
 command = cmdutil.command(cmdtable)
@@ -38,6 +44,38 b' def wrapui(ui):'
         def track(self):
             return self.configlist('blackbox', 'track', ['*'])
 
+        def _openlogfile(self):
+            def rotate(oldpath, newpath):
+                try:
+                    os.unlink(newpath)
+                except OSError, err:
+                    if err.errno != errno.ENOENT:
+                        self.debug("warning: cannot remove '%s': %s\n" %
+                                   (newpath, err.strerror))
+                try:
+                    if newpath:
+                        os.rename(oldpath, newpath)
+                except OSError, err:
+                    if err.errno != errno.ENOENT:
+                        self.debug("warning: cannot rename '%s' to '%s': %s\n" %
+                                   (newpath, oldpath, err.strerror))
+
+            fp = self._bbopener('blackbox.log', 'a')
+            maxsize = self.configbytes('blackbox', 'maxsize', 1048576)
+            if maxsize > 0:
+                st = os.fstat(fp.fileno())
+                if st.st_size >= maxsize:
+                    path = fp.name
+                    fp.close()
+                    maxfiles = self.configint('blackbox', 'maxfiles', 7)
+                    for i in xrange(maxfiles - 1, 1, -1):
+                        rotate(oldpath='%s.%d' % (path, i - 1),
+                               newpath='%s.%d' % (path, i))
+                    rotate(oldpath=path,
+                           newpath=maxfiles > 0 and path + '.1')
+                    fp = self._bbopener('blackbox.log', 'a')
+            return fp
+
         def log(self, event, *msg, **opts):
             global lastblackbox
             super(blackboxui, self).log(event, *msg, **opts)
@@ -49,7 +87,7 b' def wrapui(ui):'
                 blackbox = self._blackbox
             elif util.safehasattr(self, '_bbopener'):
                 try:
-                    self._blackbox = self._bbopener('blackbox.log', 'a')
+                    self._blackbox = self._openlogfile()
                 except (IOError, OSError), err:
                     self.debug('warning: cannot write to blackbox.log: %s\n' %
                                err.strerror)

tests/test-blackbox.t

@@ -131,5 +131,20 b' extension and python hooks - use the eol'
   1970/01/01 00:00:00 bob> exthook-update: echo hooked finished in * seconds (glob)
   1970/01/01 00:00:00 bob> update exited False after * seconds (glob)
 
+log rotation
+
+  $ echo '[blackbox]' >> .hg/hgrc
+  $ echo 'maxsize = 20 b' >> .hg/hgrc
+  $ echo 'maxfiles = 3' >> .hg/hgrc
+  $ hg status
+  $ hg status
+  $ hg status
+  $ hg tip -q
+  2:d02f48003e62
+  $ ls .hg/blackbox.log*
+  .hg/blackbox.log
+  .hg/blackbox.log.1
+  .hg/blackbox.log.2
+
 cleanup
   $ cd ..