Thursday, March 06, 2014

How to stop leaking your internal sites to Gravatar, while still use them.

Gravatar provides the ability for users to link an avatar to one or more email addresses and any website that wants to display user avatars can use Gravatar. This include not just public websites, but internal corporate websites and other private websites. When viewing a private website even when using ssl the browser will send a request to Gravatar that includes a referer headers which can leak information to Gravatar.

When you viewing the commits of a repository on GitHub such as this one you will see a Gravatar image next to each commit.  In Chrome if you open up the inspector and view the Network headers for the image's you will see along with other things that it is sending the header:
  1. Referer:

The past decade urls have for the better gained more meaning, but this can result in insider information leaking through the referer tag to a 3rd party. What if you were working for Apple and running a copy of GitHub internally, it might not be so good to be sending out to Gravatar. Even private repositories on are leaking information. If your repository is private, but you have ever browsed the files in your repository on GitHub you have leaked the directory structure to Gravatar.

While it seems common knowledge that you don't use 3rd party tools like Google's analytics on an internal corporate website, Gravatar images seem to slip by. Besides outright blocking one simple solution (of many no doubt) I have found is to make a simple proxy that strips the referer header and than point Gravatar traffic to this machine. For Apache that would look like the following

<virtualhost *:8080>
RequestHeader unset referer
RequestHeader unset User-Agent
ProxyPass /avatar

Edit: This post has spawned a number of emails as so I want to clarify my setup:

Using Chrome version 33 I browsed to a server running apache setup with ssl  (the url would looks like: https// and on that page it had a single image tag like so:

<img src="">

When fetching the image Chrome will send the referer header of to

While Chrome's inspector says it sends the header just to be sure it wasn't stripped right before the fetch I setup a fake gravatar server with ssl that dumped the headers received and pointed the page to it and found as expected the referer header were indeed being sent.

For all of those that told me to go look at the spec I would recommend that you too read it  rfc2616#section-15.1.3 where it only talks about secure to in-secure connections which is not the case we have here.

Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.

Thursday, January 23, 2014

Ben's Law

When every developer in a company is committing to the same branch the odds that a commit will break the build increases as more developers are hired.

Sunday, December 15, 2013

Tragedy of the commons in software

Unowned resources that are shared in software seem to inevitably end up disorganized.

A few instances of this I have seen include:
  • Shared libraries
  • Shared revision control repositories
  • Shared database
  • Shared folders
  • Shared log files
When different projects are using the same shared resource they often have different needs, goals, rules and cadences.  The resources themselves usually don't provide a way to split up the resource cleanly and one projects ends up spilling over into another one.  Two simple examples would be in a source code repository while one group might name their branches release/minor_release another group might follow build/* and in a shared library one project might declare static objects that eat up ram harming another group that is trying to reduce memory usage.
  The inevitable cleaning up of the shared resource grows to become a monumental and bureaucratic task.  Even what seems like a simple task of who maintains/own something can be a large task and at least once is found to be a guy that is no longer with the project (and by the way it is no longer used).
  Because the resource is shared by many different users it already takes up a decent amount of "stuff" (ram, hd space, bandwidth).  There is an admin team that is in charge of making sure more "stuff" is added when needed and the users inevitably take advantage of this to an extreme example where a user decided to check in a Visual Studio install into the revision control system (deep within the source too).  From their perspective they don't really feel the pain that everyone else might suddenly be burdened with an additional 10GB+.
  Some projects run very lean and clean.  They have very strict rules about how things should work and be stored, but there are many more that don't and as time marches on and new projects are added they end up having cruft all over the place and dependancies across what should have been the project divides.  This abuse of the shared resource ends up hurting all of the projects.  Rules are put in place and even if there is a good reason they are difficult to change.
  What seems inevitable is that slowly some projects start breaking off and using a different resource that is hopefully not shared and in the process the old shared resource gets less attention and is unlikely to ever recover as more and more becomes unmaintained.  Sadly it is often not a big thing, but many small problems that users put up with until one day they realize that abandoning everything will give them a significant boost.
  The only solutions to this problem I am aware of is to first recognize the problem early and second to have a steward, someone whose job it is to rapidly respond to problems and anticipate new ones before users start to leave.  The steward's job include occasionally striking down long held rules about the resource because they are found to be harmful and being the one that causes all the projects pain by forcing a migration.  It is only through these actions that the shared resource can maintain its viability in the long run.

Wednesday, April 03, 2013

Code analysis reporting tools don't work

Code analysis tools are good at highlighting code defects and technical debt, but it is when the issues are presented to the developer that determines how effective the tool will be at making the code better.  Tools that only generate reports nightly will be magnitudes less effective than tools that inform developers of errors before a change is put into the repository.

A few weeks ago I played with a code analysis tool that generates a website showing errors that it found in a codebase.  Like most reporting tools this one was made to run on a nightly cron job to generate its reports.  Upon reflection of my career I have never seen tools of this type produced more than a small improvement in a project.  After introduction there are a few developers that strive to keep the area they maintained clean and an even smaller pockets of developers that utilized the tools to raise the quality of their code to the next level, but they were the exception and not the norm.  A scenario I have seen several times over my career was a project that had tools to automatically run unit tests at night.  With this in place you would expect failures to be fixed the next day, but often I saw the failures continue for weeks or months and were only fixed right before a release.  Once the commit was in the repository the developer moves onto another task and considers it done. You could almost call it a law: Before a developer gets a commit into the repository they are willing to move the moon to make the patch right, but after it is in the repository the patch will have to destroy the moon before they will think about revisiting it and even in that case they will ask if you want to fix it so they don't have to.  This means that code analysis reporting tools are able to make only a small impact but no where near what the desired result is.

After pondering why the reporting tools do so poorly  and how they could be improved to make a bigger impact I finally figured out what was really nagging at me, these tools were created because our existing processes are failing.  If we could catch the issues sooner it would both be cheaper to fix the issue and eliminate a whole class of time wastes. While you could think about new developer training, better code review's, mentoring, etc all of which can be improved, a simpler solution would be to move the tools ability closer to the time when the change is made.

In 2007 I started a project that included local commit hooks with Git.  Anytime I had something that could have been automated it was added as a hook.  When you modify file foo.cpp it would run foo's unit tests, code style checking, project building, xml validation and more.  This idea was wildly successful and there were only a few times (~six?) in the lifetime of the project that the main branch failed to build on one of the three OS's or had failing unit tests.  More importantly the quality of the code was kept extremely high though out the project lifetime.   When working in a the much larger WebKit project when you put up a patch for review on the project's Bugzilla a bot would automatically grab the patch and run a gantlet of tests against it adding a comment to the patch when it was done.  Often it was done before the human reviewer even had a chance to look at the patch.  These bots would catch the same technical debt problems and the report tools, but because it was presented at the time of review it would be cleaned up right then and there when it was cheap and easy to do. Automatically reviewing patches after they are made but before they go into the main repository is a very successful way to prevent problems from ever appearing in the code base.

But why stop at commit time?  Many editors have built in warnings from code style to verification of code parsing.  A lot has been written about LLVM's improved compiler warnings and even John Carmack has written how powerful turning on /analyze is for providing static code analysis at compile time.  Much more could be done in this area to find and present issues to the developer in as soon as they create them or even in real time.

Code analysis reporting tools will always be useful because they can provide a view into legacy code, but for new code project using error reporting before commit time with hooks, bots, and editor integration will be able to actually prevent technical debt and do more for quality than nightly reports ever could.

Wednesday, August 22, 2012

The minimal amount of data needed to lock in users

I recently upgraded to OS X Mountain Lion only to find that RSS support wasn't just moved out of Mail, but out of Safari too.  RSS bookmarks were the only reason I was still using Safari on a daily basis so this removal is forcing me to migrate them somewhere else and in the process stopping my daily usage of Safari.

Stepping back, I realized how crazy it was that I was using Safari to read RSS.  The last five years I have been working on WebKit and browsers, three of those years (until RIM legal killed it) were spent making my very own browser called Arora.  And yet through all those years I still kept using Safari because the switching cost of the RSS feeds were "too high" (I had a mac around with safari so why not just keep using it...).  I even started hacking on a desktop RSS reader at one point.  RSS feed's are not locked into Safari, the Export Bookmarks action is right there in the File menu* and Safari doesn't keep feed data for more then about a month so it wasn't even the rss history I cared about, just the urls.

Here is a case of the bare minimum of data locking and yet it was able to keep a user that writes browsers (including rss feed plugins), uses a different OS as his primary desktop for years.  In the past when I thought about data lock in I thought about databases, custom scripts, iCloud, but with this I realize that the bar is much lower.  It wasn't until they forcefully took away the feature that I sat up in a daze wondering what I was doing and went looking for an alternative and in the process am going to abandon the application entirely.

Now imagine you are a Windows user and suddenly all your apps don't work on the new Metro arm based laptops.  It is probably the needed kick in the pants to sit up and go checkout what those mac's, web applications, and ipads are all about.  Scary stuff for Microsoft.

* You would think with Safari RSS users suddenly not having their RSS feeds apps like NetNewsWire would provide a bookmarks import, but oddly they don't (as of yesterday when I checked with the current version).

Wednesday, May 23, 2012

When publishing onto two platforms one will end up being the "lesser" of the two.

When a company produces a product for multiple platform invariably one of the platform is the primary platform. This can take on a number of forms such as:

  •  Releasing to one platform first.
  •  Releasing updates only to one platform.
  •  Releasing a reduced feature set for the later platforms.
  •  Releasing a product for a later platform that while works doesn't fit in or follow that platforms UI guidelines.
  •  The primary platform is stable while the secondary ones have bugs/crash.

Some big examples:

  • Video drivers: Windows XP v.s. Linux
  • Flash: Windows v.s. Linux
  • Video games: PS3/360 v.s. the Wii
  • Mobile apps: iphone v.s. android
  • Git: Linux v.s. Windows
  • Books: physical v.s. ebook
  • DVD's: U.S. v.s. Australia

There are many reasons for why this happens such as management believing that the primary platform will make more money, or the company (or the developers) have more experience in the primary platform or even as silly as the CEO getting the primary platform for christmas and mandating it is the primary. The secondary platforms are seen as nice to have and a possible extra source of revenue, but it would be foolish to think that they will have the same quality/features as the primary platform.

If the company has any hard times they will kill the secondary platform first.  If the product is ever killed it will almost always first be killed on the secondary platforms.

This is often a frustrating thing for the consumer as they typically can't do much about it, but at least realizing that you are on a secondary platform can help you schedule extra testing time and lower your expectations about what you will get.

The one nice thing is once you realize that product X is the future and its primary platform is not on your platform of choice and you believe that platform is the future then there is an opportunity.  The Wii can't run 360 games, but it does have a set of games that take advantage of its hardware that can't run on the 360.  ebooks coming from publishers wont replace traditional books, but a company that creates reading product that targets tablets first and physical books second will come to dominate ebooks.

Look around at the tools and products that you use.  What is their primary platform?  Is that your platform?

Tuesday, April 10, 2012

Patches with more than one fix will no longer be tolerated

Patches with more than one fix in them are a bad development practice and need to be stopped.

I was recently looking at Git commit in an open source project.  I was pretty sure part of the commit was wrong, but it was doing a bunch of other stuff which might have negated the issue I spotted.  I wasted fifteen minutes before I realized that the other stuff was actually actually a separate fix and the patch contained two different fixes.  The fixes touched the same code chunk and the commit message made it sound like both changes were effected by the same bug, but that was not the case.  I am pretty sure that fix number one is wrong, but because it is all munged in with fix number two I can't prove it to the original authors without investing significantly more time.  The commit could have been small and easy to talk about in a bug report, but now it will require several hours with multiple patches before it will be resolved.

I have seen this problem before and even given five minute lightning talks about the evil of multiple fixes in one commit, but it is clearly time to put the reasoning down in writing to help stop this behavior on a larger scale.

What is so wrong with a commit that fixes multiple different things?
  • It hurts the reviewer: When reviewing a patch that contains two separate bug fixes the reviewer have to mentally figure out which changes go to which fix. This makes reviewing harder and take longer than it has to be and mistakes are more likely to happen.  The worst mistake is if the reviewer only verifies one fix and not the other.
  • It hurts yourself: the first reviewer of any patch is yourself. The more complicated it is the higher the likeness you will miss something and look foolish later when you have to get patch #2 reviewed.
  • It hurts every future readers: In the future when someone else looks at that patch for whatever reason they will be in the same boat as the reviewer and have to take the extra time and effort and can make the same mistakes.  Except this time they don't have you to ask questions and probably wont lookup the bug in the bug database and will miss that discussion too further increasing the likely hood that they interoperate the patch incorrectly.
  • It hurts the project: It is rare for a patch to be perfect the first time around and the bigger they are the higher the likeliness that they will have a few rounds of tweaking before they can go in. If the patch has two separate fixes, one fix will usually be done before the other, but by tying them together in one commit you are denying the project the finished fix until the second one is ready. This might be an hour or a day, but it could be months.
  • It hurts you later if you they are at all wrong: Patches are not always perfect. Sometimes they are flat out wrong and need to be reverted. With a commit with two fixes you can not just do a "git revert [sha]", you have to dissect the patch and revert only half of it. Once again you have to mentally figure out what part of the patch goes to which fix. And because we are not perfect (hey we had to revert something remember) there is a chance that you will revert not all of the correct bits or revert something that didn't apply.  I have never seen someone that split a revert test that the other half they left behind still works now that I think of it!  Worst case scenario the person reverting the commit doesn't realize the commit is two fixes and reverts the whole patch assuming it only was a single fix and no one spots it until the regression bug report from the user rolls in.
Disclaimer: I have seen all of the above happen with my own eyes multiple times. These are not made up scenarios, they really happened, wastes my time and decreased my productivity.

This practice is typically found in cases where both fixes are in the same file.  With revision control systems like SVN or Perforce splitting multiple fixes in a single file was a non trivial task.  Typically you grudging commit files in your working tree with all of the changes.  But when using Git the situation is different.

If you are working in a file and notice something else there that needs to be changed you have options:

git branch - Branching in Git is cheap, make a branch for your existing code or commit and start a new branch for the new fix.

But if that is too much work, you can:

git stash - Git stash will store your changes in a hidden branch while you make the other fix in its own commit and then use Git stash apply your changes and continue your work.

But if that is still too much work, you can:

git add -p or git add -i - When it comes time to make the commits rather than adding the whole file to be committed, Git add -p will prompt you one by one through each chunk in the file to find out if it should be added to the staging.  Only add the relevant parts to a fix, commit and then do the same to the other fix.  A more detailed explanation with examples can be found on this blog entry on git add -p or in the git add man page.  (article bonus tip: git checkout -p exists and does exactly what you think it does)

Splitting commits

If you already have committed a patch and only realize after the fact that it should have been two Git is still there for you. If it was the last commit you can git reset HEAD^ and then use git commit -p to add them as two commits (You can even use git commit -c [sha] so you don't have to re-type the half of the commit message that matters). And if it isn't the top commit that is okay too, you can perform an interactive rebase and mark the commit to be edited. When the rebase reaches that commit, use git reset HEAD^, add the multiple new commits, and finish the rebase.  The git rebase man page has detailed instructions on how to split commits.

Why not a hook?

When making a commit message if you find yourself writing multiple paragraphs about different topics, listing multiple different bug id's, using words such as "while I was in this file I ..." or even just the word "Also" it is a pretty good hint that you probably want to step back and split your commit into two. Because Git is a distributed revision control system the infrastructure to support server side push hooks exists on your desktop too.   To use hooks and automate the process of spotting commits that should be split of you can whip up a one liner commit-msg hook that greps for the word "Also" and outputs a warning.  I have even tossed together a slightly more fancy version for the git-hooks project.

So now you have been warned.  Creating patches with multiple fixes is a bad practice that wastes time and can cause errors.  And if you are asked to review a commit that should be two, reject it and have them split it.  Patches with more than one fix will no longer be tolerated.

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