Working Around Bugs

by Tykling

02. nov 2017 14:47 UTC

This is the story of a bug I found in Djangos Daphne HTTP and Websocket terminating server, where I had to work around the bug for months while waiting for the fix to make it into a release.

Daphne is part of the Channels project which is Djangos cool websocket thing that recently got adopted as a part of the official Django project. We've been using Channels for a while on the the Schedule part of the BornHack website, which is how I found this Daphne bug to begin with.

X-Forwarded-For and Friends

I run all my stuff seperated in FreeBSD jails with an nginx proxy in front. This means that I make heavy use of the X-Forwarded-* HTTP headers to see the real client IP in my requests. Basically the nginx proxy receives the request, and does a new request to the backend Django server to get the response, and then passes that response back to the client. The proxy nginx adds a couple of headers to the request called X-Forwarded-For and X-Forwarded-Port and the backend nginx and Django instances can use those headers instead of the client ip (which points to the proxy).

The Problem

The websocket requests handled by Daphne were seen with the proxy IP as client IP, not respecting X-Forwarded-For. This was weird because looking over the code it appeared to have support for those headers, and it turned out to be a bug related to Python2/3 support and encoding of a dict of headers. I fixed the bug back in April and did a pull request which was recently accepted into Daphne. But I needed a solution there and then, I couldn't sit around and wait for the next Daphne release.

Git Fun

What I needed was a way to get pip to install the latest Daphne 1.3.0 release (which is based on the 1.3.0 tag on Github) with my patch on top. I could do this by hand of course, but that is not how I work. I need something I can put into Ansible and deploy automatically and repeatedly without any fuzz. Fortunately it is easy to make pip install a package from a Github branch. But first I need to Fork.

So the first thing I did was go to Github and press Fork on the Daphne repo. Then I cloned my new fork onto my laptop:

user@dev:~/devel$ git clone
Cloning into 'daphne'...
remote: Counting objects: 1086, done.
remote: Total 1086 (delta 0), reused 0 (delta 0), pack-reused 1086
Receiving objects: 100% (1086/1086), 239.07 KiB | 0 bytes/s, done.
Resolving deltas: 100% (711/711), done.

I check that the 1.3.0 tag is present:

user@dev:~/devel/daphne$ git tag | grep 1.3.0

Cool. Then I make a new branch called ws-x-forwarded-for-bugfix based on the upstream tag 1.3.0 to hold my bugfix:

user@dev:~/devel$ cd daphne/
user@dev:~/devel/daphne$ git checkout -b ws-x-forwarded-for-bugfix 1.3.0
Switched to a new branch 'ws-x-forwarded-for-bugfix'

Finally I git cherry-pick the latest commit from master and add it to my branch:

user@dev:~/devel/daphne$ git cherry-pick master
[ws-x-forwarded-for-bugfix fe7c7df] Make sure headers are always correctly encoded
 Date: Thu Oct 12 20:06:18 2017 +0200
 1 file changed, 10 insertions(+), 5 deletions(-)

My bugfix just happened to be the latest commit on the master branch of the upstream Daphne repo, otherwise I would have to add some flags to the git cherry-pick command.

Finally I push the new branch to my fork on Github:

user@dev:~/devel/daphne$ git push --set-upstream origin ws-x-forwarded-for-bugfix
Counting objects: 4, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 654 bytes | 0 bytes/s, done.
Total 4 (delta 3), reused 0 (delta 0)
remote: Resolving deltas: 100% (3/3), completed with 3 local objects.
 * [new branch]      ws-x-forwarded-for-bugfix -> ws-x-forwarded-for-bugfix
Branch ws-x-forwarded-for-bugfix set up to track remote branch ws-x-forwarded-for-bugfix from origin.

Fixing requirements.txt

All that remains is to make my deployments use my fork until there is a new release of Daphne on pip. This snippet from requirements.txt shows how I disabled the regular Daphne and made it use my fork from Github:

#temp fix for

Thats all. It works and will keep things running until a new Daphne release hits the streets. Until then!

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