[patch] detect when Enscript is not installed

[techtonik <techtonik@…>]

trac.log is full of tracebacks about failed Enscript executions. Enscript is not installed and won't be. The patch here checks if Enscript is installed before reporting supported mimetypes.

2008-10-23 00:24:01,436 Trac[__init__] WARNING: HTML preview using <trac.mimeview.enscript.EnscriptRenderer object at 0x40edae8c> failed (Running (enscript --color -h -q --language=html -p - -Ecpp) failed: 127, sh: line 1: enscript: command not found
.)
Traceback (most recent call last):
  File "/home/.december/trex/inst/lib/python2.4/site-packages/Trac-0.11.1-py2.4.egg/trac/mimeview/api.py", line 635, in render
    rendered_content, filename, url)
  File "/home/.december/trex/inst/lib/python2.4/site-packages/Trac-0.11.1-py2.4.egg/trac/mimeview/enscript.py", line 145, in render
    raise Exception, err
Exception: Running (enscript --color -h -q --language=html -p - -Ecpp) failed: 127, sh: line 1: enscript: command not found

[techtonik <techtonik@…>]

check if enscript command is available

[Christian Boos]

Good idea, but I'd rather do something like an auto-disable after the first failure.

[techtonik <techtonik@…>]

Is it possible to disable a component? I thought it is not, because components do not return anything on initialization and TracDev/ComponentArchitecture is also silent about this.

[Remy Blank]

Patch against 0.11-stable disabling enscript after the first execution error

[Remy Blank]

The patch above disables EnscriptRenderer when invocation of enscript fails. An environment reload is required to re-enable it.

Christian, is that what you had in mind?

[techtonik@…]

Seems good, but it would be even better if log message is expanded with the information that Enscript is getting disabled. And it's still would be nice to look for enscript executable in PATHs.

[Christian Boos]

Replying to rblank:

The patch above disables EnscriptRenderer when invocation of enscript fails. An environment reload is required to re-enable it.

Christian, is that what you had in mind?

Yes, something similar:

trac/mimeview/enscript.py

@@ -140 +140 @@
 
         np = NaivePopen(cmdline, content.encode('utf-8'), capturestderr=1)
         if np.errorlevel or np.err:
+            self.env.enabled[self.__class__] = False
             err = 'Running (%s) failed: %s, %s.' % (cmdline, np.errorlevel,
                                                     np.err)
             raise Exception, err

(sorry untested, not much time for Trac those days ;-) )

[Remy Blank]

Fixed in [7719] by disabling the component in the ComponentManager. I have also made clear in the error message that EnscriptRenderer is disabled.

About searching for enscript on PATH, this is already done, as enscript is run through os.system(), which uses exec() which uses PATH to find the executable if it doesn't contain a /. At least it works on *nix, not sure about Windows. I have enscript_path = enscript in my trac.ini and the executable is found.

[techtonik <techtonik@…>]

find_executable() function looks for executable in PATH without executing it, because it is not a good idea to spawn a new system process just to ensure that executable is not available.

find_executable() returns full path for executable. This path can then be executed without shell environment with functions other than os.system() that allow to intercept input/output stream directly instead of file reading/writing/reading cycle as it is now.

It is also ​recommended to replace os.system() calls with functions from subprocess module.