Entries tagged development

Related tags: cmail, console, debian, debugging, desktops, ipv6, lua, mail, software, todo.

Using the compiler to help you debug segfaults

Friday, 5 August 2016

Recently somebody reported that my console-based mail-client was segfaulting when opening an IMAP folder, and then when they tried with a local Maildir-hierarchy the same fault was observed.

I couldn't reproduce the problem at all, as neither my development host (read "my personal desktop"), nor my mail-host had been crashing at all, both being in use to read my email for several months.

Debugging crashes with no backtrace, or real hint of where to start, is a challenge. Even when downloading the same Maildir samples I couldn't see a problem. It was only when I decided to see if I could add some more diagnostics to my code that I came across a solution.

My intention was to make it easier to receive a backtrace, by adding more compiler options:

  -fsanitize=address -fno-omit-frame-pointer

I added those options and my mail-client immediately started to segfault on my own machine(s), almost as soon as it started. Ultimately I found three pieces of code where I was allocating C++ objects and passing them to the Lua stack, a pretty fundamental part of the code, which were buggy. Once I'd tracked down the areas of code that were broken and fixed them the user was happy, and I was happy too.

Its interesting that I've been running for over a year with these bogus things in place, which "just happened" to not crash for me or anybody else. In the future I'll be adding these options to more of my C-based projects, as there seems to be virtually no downside.

In related news my console editor has now achieved almost everything I want it to, having gained:

  • Syntax highlighting via Lua + LPEG
  • Support for TAB completion of Lua-code and filenames.
  • Bookmark support.
  • Support for setting the mark and copying/cutting regions.

The only outstanding feature, which is a biggy, is support for Undo which I need to add.

Happily no segfaults here, so far..



Planning how to configure my next desktop

Thursday, 6 November 2014

I recently setup a bunch of IPv6-only accessible hosts, which I mentioned in my previous blog post.

In the end I got them talking to the IPv4/legacy world via the installation of an OpenVPN server - they connect over IPv6 get a private IP address, and that is masqueraded via the OpenVPN-gateway.

But the other thing I've been planning recently is how to configure my next desktop system. I generally do all development, surfing, etc, on one desktop system. I use virtual desktops to organize things, and I have a simple scripting utility to juggle windows around into the correct virtual-desktop as they're launched.

Planning a replacement desktop means installing a fresh desktop, then getting all the software working again. These days I'd probably use docker images to do development within, along with a few virtual machines (such as the pbuilder host I used to release all my Debian packages).

But there are still niggles. I'd like to keep the base system lean, with few packages, but you can't run xine remotely, similarly I need mpd/sonata for listening to music, emacs for local stuff, etc, etc.

In short there is always the tendency to install yet-another package, service, or application on the desktop, which makes migration a pain.

I'm not sure I could easily avoid that, but it is worth thinking about. I guess I could configure a puppet/slaughter/cfengine host and use that to install the desktop - but I've always done desktops "manually" and servers "magically" so it's a bit of a change in thinking.



After you've started it seems like a bad idea?

Tuesday, 30 April 2013

To recap: given the absence of other credible alternatives I had two options:

  • Re-hack mutt to give me a sidebar that will show only folders containing new messages.
  • Look at writing a "simple mail client". Haha. Ha. Hah.

I think there is room for a new console client, because mutt is showing its age and does feel like it should have a real extension language - be it guile, lisp, javascript(!), Lua, or something else.

So I distilled what I thought I wanted into three sections:

  • mode-ful. There would be a "folder-browsing mode", a "message-browsing mode" and a "read-a-single-message" mode.
  • There would be scripting. Real scripting. I chose Lua.
  • You give it ~/Maildir as the configuration. Nothing else. If the damn computer cannot find your mailboxes something is wrong.

So how did I do? I wrote a ncurses-based client which has Lua backed into it. You can fully explore the sidebar-mode - which lets you select multiple folders.

From there you can view the messages in a list.

What you can't do is anything "real":

  • Update a messages flags. new -> read, etc.
  • GPG-validation.
  • MIME-handling.
  • Attachment viewing.

For a two-day hack it is remarkably robust, and allowing scripting shows awesomeness. Consider this:

-- show all folders in the Maildir-list.
function all()
   -- ensure that the sidebar displays all folders
   sidebar_mode = "all";
   -- we're going to be in "maildir browsing mode"
   cmail_mode = "sidebar";

-- Test code, show that the pattern-searching works.
-- To use this press ":" to enter the prompt, then enter "livejournal".
-- OR press "l" when in the sidebar-mode.
function livejournal()
   sidebar_pattern = "/.livejournal.2";
   sidebar_mode = "pattern";

-- There is a different table for each mode.
keymap = {}
keymap['sidebar'] = {}
keymap['index']   = {}
keymap['message'] = {}

-- In the sidebar-mode "b" toggles the sidebar <-> index.
-- ":" invokes the evaluator.
-- "q" quits the browser and goes to the index-mode.
-- "Q" quits the program entirely.
keymap['sidebar'][':'] = "prompt-eval"
keymap['sidebar']['b'] = "toggle"
keymap['sidebar']['q'] = "toggle"
keymap['sidebar']['Q'] = "exit"

-- show all/unread/livejournal folders
keymap['sidebar']['a'] = "all"
keymap['sidebar']['u'] = "unread"
keymap['sidebar']['l'] = "livejournal"

Neat, huh? See the cmail.lua file on github for more details.

My decision hasn't really progressed any further, though I can see that if this client were complete I'd love to use it. Its just that the remaining parts are the fiddly ones.

I guess I'll re-hack mutt, and keep this on the back-burner.

The code is ropey in places, but should you wish to view:

And damn C is kicking my ass.



A good cockerel always points north

Monday, 11 February 2008

I spent a while yesterday thinking over the software projects that I'm currently interested in. It is a reasonably short list.

At the time I just looked over the packages that I've got installed and the number of bugs. I'm a little disappointed to see that the bugfixes that I applied to GNU screen have been mostly ignored.

Still I have the day off work on Thursday and Friday this week and would probbly spend it releasing the pending advisories I've got in my queue, and then fixing N bugs in a single package.

The alternative is to build a quick GPG-based mailing list manager.

I'd like a simple system which allowed users to subscribe, and only accepted GPG-signed mails. The subscriber could choose to receive their messages either signed (as-is) by the submitter or encrypted to them.

So to join you'd do something like this:

subscribe foo@example.org [encrypted]

There is the risk, with a large enough number of users, that a list could DOS the host if it had to encrypt each message to each subscribers. But if the submissions were validated as being signed by a user with a known key it should be minimal, unless there is a lot of traffic.

The cases are simple:

  • foo-subscribe => Add the user to the list, assuming valid key data found
  • foo-unsubscribe => Do the reverse.
  • foo:
    • If the message is signed accept and either mail to each recipient, or encrypt on a per-recipient basis.
    • If the message is not signed, or signed by a non-subscriber drop it.

There are some random hacks out there for this, including a mailman patch (did I mention how much I detest mailman yet today?) but nothing recent.

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