Returning screenshots in Gitlab CI (and Travis CI)


Our code base includes a large suite of functional tests using Lettuce, Selenium and PhantomJS. When a test fails, we have a hook that captures the current screen contents and writes it to a file. In an ideal CI system these would be collected as a failure artifact (along with the stack trace, etc.) but that’s not currently possible withGitlab CI (hint hint Gitlab team, investigate Subunit for streaming test output).

Instead what we do on Gitlab is output our images as base64 encoded text:

if $SUCCESS; then
    echo "Success"
    echo "Failed ------------------------------------"
    for i in Test*.html; do echo $i; cat "$i"; done
    for i in Test*.png; do echo $i; base64 "$i"; echo "EOF"; done

Of course now you have test output full of meaningless base64’ed data. Enter Greasemonkey.

// ==UserScript==
// @name View CI Images
// @namespace
// @description View CI Images
// @version 1
// @match https://gitlabci/projects/*/builds/*
// ==/UserScript==

(function ($) {
    var text = $('#build-trace').html();
    text = text.replace(/(Test_.+\.png)\n([A-Za-z0-9\n\/\+=]+)\nEOF\n/g,
                        '<h2>$1</h2><img src="data:image/png;base64,$2" ' +
                        'style="display:block; max-width:800px; width: auto; height: auto;" ' +

Web browsers (handily) can already display base64’ed images. This little user script will match builds on the CI server you specify and then replace those huge chunks of base64 with the image they represent.

This technique could easily be replicated on Travis CI by updating the jQuery selector.

Author: Danielle

Danielle is an Australian software engineer, computer scientist and feminist. She doesn't really work on GNOME any more (sadly). Opinions and writing are solely her own and so not represent her employer, the GNOME Foundation, or anyone else but herself.