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https://github.com/atmos/camo

:lock: an http proxy to route images through SSL
https://github.com/atmos/camo

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:lock: an http proxy to route images through SSL

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# camo [![Build Status](https://travis-ci.org/atmos/camo.svg?branch=master)](https://travis-ci.org/atmos/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](https://github.com).



![camo](https://cloud.githubusercontent.com/assets/38/24514552/88f29edc-1529-11e7-832f-6d2942144c87.gif)



We want to allow people to keep embedding images in comments/issues/READMEs.



[There's more info on the GitHub blog](https://github.com/blog/743-sidejack-prevention-phase-3-ssl-proxied-assets).



Using a shared key, proxy URLs are authenticated with [hmac](http://en.wikipedia.org/wiki/HMAC) so we can bust caches/ban/rate limit if needed.



Camo currently runs on node version 0.10.29 at GitHub on [heroku](http://heroku.com).



[![Deploy to Heroku](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/atmos/camo)



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](https://github.com/atmos/camo/blob/master/test/proxy_test.rb).



## URL Formats



Camo supports two distinct URL formats:



    http://example.org/?url=

    http://example.org//



The `` is a 40 character hex encoded HMAC digest generated with a shared

secret key and the unescaped `` value. The `` is the

absolute URL locating an image. In the first format, the `` should be

URL escaped aggressively to ensure the original value isn't mangled in transit.

In the second format, each byte of the `` 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 the `Via` and `User-Agent` headers it sends in requests to origin servers. (default: `Camo Asset Proxy `)

* `CAMO_KEY`: A shared key consisting of a random string, used to generate the HMAC digest.

* `CAMO_LENGTH_LIMIT`: The maximum `Content-Length` Camo will proxy. (default: 5242880)

* `CAMO_LOGGING_ENABLED`: The logging level used for reporting debug or error information. Options are `debug` and `disabled`. (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 the [`Timing-Allow-Origin` header](http://www.w3.org/TR/resource-timing/#cross-origin-resources) it sends in responses to clients. The header is omitted if this environment variable is not set. (default: not set)

* `CAMO_HOSTNAME`: The `Camo-Host` header 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="" node server.js



### Docker



A `Dockerfile` is included, you can build and run it with:



```bash

docker build -t camo .

docker run --env CAMO_KEY=YOUR_KEY -t camo

```



## Examples

* Ruby - https://github.com/ankane/camo

* PHP - https://github.com/willwashburn/Phpamo