camo 
Camo is all about making insecure assets look secure. This is an SSL image proxy to prevent mixed content warnings on secure pages served from GitHub.
We want to allow people to keep embedding images in comments/issues/READMEs.
There's more info on the GitHub blog.
Using a shared key, proxy URLs are authenticated with hmac so we can bust caches/ban/rate limit if needed.
Camo currently runs on node version 0.10.29 at GitHub on heroku.
Features
- Max size for proxied images
- Follow redirects to a certain depth
- Restricts proxied images content-types to a whitelist
- Forward images regardless of HTTP status code
At GitHub we render markdown and replace all of the src attributes on the img tags with the appropriate URL to hit the proxies. There's example code for creating URLs in the tests.
URL Formats
Camo supports two distinct URL formats:
http://example.org/<digest>?url=<image-url>
http://example.org/<digest>/<image-url>
The <digest> is a 40 character hex encoded HMAC digest generated with a shared
secret key and the unescaped <image-url> value. The <image-url> is the
absolute URL locating an image. In the first format, the <image-url> should be
URL escaped aggressively to ensure the original value isn't mangled in transit.
In the second format, each byte of the <image-url> should be hex encoded such
that the resulting value includes only characters [0-9a-f].
Configuration
Camo is configured through environment variables.
PORT: The port number Camo should listen on. (default: 8081)CAMO_HEADER_VIA: The string for Camo to include in theViaandUser-Agentheaders it sends in requests to origin servers. (default:Camo Asset Proxy <version>)CAMO_KEY: A shared key consisting of a random string, used to generate the HMAC digest.CAMO_LENGTH_LIMIT: The maximumContent-LengthCamo will proxy. (default: 5242880)CAMO_LOGGING_ENABLED: The logging level used for reporting debug or error information. Options aredebuganddisabled. (default:disabled)CAMO_MAX_REDIRECTS: The maximum number of redirects Camo will follow while fetching an image. (default: 4)CAMO_SOCKET_TIMEOUT: The maximum number of seconds Camo will wait before giving up on fetching an image. (default: 10)CAMO_TIMING_ALLOW_ORIGIN: The string for Camo to include in theTiming-Allow-Originheader it sends in responses to clients. The header is omitted if this environment variable is not set. (default: not set)CAMO_HOSTNAME: TheCamo-Hostheader value that Camo will send. (default:unknown)CAMO_KEEP_ALIVE: Whether or not to enable keep-alive session. (default:false)
Testing Functionality
Bundle Everything
% rake bundle
Start the server
% coffee server.coffee
In another shell
% rake
Debugging
To see the full URL restclient is hitting etc, try this.
% RESTCLIENT_LOG=stdout rake
Deployment
You should run this on heroku.
To enable useful line numbers in stacktraces you probably want to compile the server.coffee file to native javascript when deploying.
% coffee -c server.coffee
% /usr/bin/env PORT=9090 CAMO_KEY="<my application key>" node server.js
Docker
A Dockerfile is included, you can build and run it with:
docker build -t camo .
docker run --env CAMO_KEY=YOUR_KEY -t camo