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.
Using a shared key, proxy URLs are encrypted 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.
- 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.
Camo supports two distinct URL formats:
<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
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 the
User-Agentheaders it sends in requests to origin servers. (default:
Camo Asset Proxy <version>)
CAMO_KEY: The shared key used to generate the HMAC digest.
CAMO_LENGTH_LIMIT: The maximum
Content-LengthCamo will proxy. (default: 5242880)
CAMO_LOGGING_ENABLED: The logging level used for reporting debug or error information. Options are
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 the
Timing-Allow-Originheader it sends in responses to clients. The header is omitted if this environment variable is not set. (default: not set)
Camo-Hostheader value that Camo will send. (default:
CAMO_KEEP_ALIVE: Whether or not to enable keep-alive session. (default:
NODE_TLS_REJECT_UNAUTHORIZED: If set to
0, camo will also forward images from hosts with a bad SSL implementation. (default:
% rake bundle
Start the server
% coffee server.coffee
In another shell
To see the full URL restclient is hitting etc, try this.
% RESTCLIENT_LOG=stdout rake
You should run this on heroku.
% coffee -c server.coffee % /usr/bin/env PORT=9090 CAMO_KEY="<my application key>" node server.js
Dockerfile is included, you can build and run it with:
docker build -t camo . docker run --env CAMO_KEY=YOUR_KEY -t camo