What is it?

go-repro is a reverse proxy that maps upstream hosts to public ports on the local machine, transparently rewriting requests and responses on the way to account for the mapping.

It was created as a tool for scenarios where you have a bunch of (v)hosts on a development machine that are resolved by local /etc/hosts entries. If you want to test such a setup on devices other than the development machine (e.g. mobile devices or even mobile emulators on the same machine), you will have to publish the host mapping to the testing device, either setting up DNS server or fiddling with the hosts file of the target device. go-repro presents a different solution for this problem by mapping the domains to public ports on the development machine that can be easily accessed from other devices without worrying about name resolution.

Consider for example two vhosts foo.bar.dev and huppe.hoppe.dev that are configured on your development machine. If you want to test your application with the android emulator, you will have to mess with the hosts setup of the emulated device or setup a DNS server. With go-repro, you can map these domains to local ports. Doing

go-repro -mappings '0.0.0.0:8081=http://foo.bar.dev,0.0.0.0:8082=http://huppe.hoppe.dev' -rewrite '.'

will forward these domains to ports 8081 and 8082, with go-repro listening on all interfaces. If there are references to the hosts in requests and / or responses, go-repro will transparently rewrite these in order to account for the mapping. In the android emulator, you can access the web application via 10.0.2.2:8081 (which is forwarded to the host listening on 127.0.0.1 by the emulator).

WARNING go-repro is developed as a debugging tool for web application development. Do not try to use it in a production environment!

Installation

Three ways lead to happiness.

Precompiled binaries

Just download precompiled binaries for your platform from github.

Go get

Provided that you sport an installation of golang, the latest version from master can be installed via

go get -d github.com/mayflower/go-repro/...
go generate github.com/mayflower/go-repro/...
go install github.com/mayflower/go-repro/cli/...

Isn't a simple go get github.com/mayflower/go-repro/cli/... sufficient, you ask? Indeed it is, but including the generate step detailed above will encode verbose version information in the binaries.

Git & Make

Clone the repository and do make. This will create a separate GOPATH in build and leave you with the binaries ready in build/bin. Of course, you need golang installed for this.

Usage

Configuration

Take a look at the command line help

go-repro -h

in order to get an overview over the available options.

If you get tired of specifying a complex rewriting config on the command line, you can also supply your setup as a YAML file

go-repro -config my_config.yaml

Please take a look at example_config.yaml if you want to go down this road.

Host mappings

Host mappings are configured with the -mappings option. This option takes a comma separated list of mapping entries. These are written as local_ip:local_port=remote_host where local_ip:local_port is the local IP/port on which go-repro will listen, while remote_host identifies the associated upstream host, including the protocol.

The local IP 0.0.0.0 causes the proxy to listen on all interfaces and is replaced with the actual IP targeted by the request (as specified the HTTP host header) during request rewriting.

Rewriting

Rewriting considers all configured mappings.

Headers

Headers are transparently translated for all requests handled by the proxy. The following headers are handled:

• Location for redirects
• Referer for all requests
• origin and access-control-allow-origin for requests that use the HTML5 CORS spec for cross origin requests.

Body content

Only routes that match one of the regular expressions provided via the -rewrite option (a comma separated list of regexes) are considered for body rewriting. There are two rewriters, one of which performs plain text replacements of all occurrences of the remote host URL (including the protocol!) within the response body. The second rewriter handles responses of MIME type application/json by decoding the JSON and subsequently replacing all occurences of the remote host within the JSON structure.

SSL

SSL encrypted connections to upstream hosts are supported. The -allow-insecure option can be specified in order to ignore any issues during cerificate validation (useful for self-signed certificates). The connection between client and proxy is always unencrypted.

Compression

gzip compression is supported. The proxy tries to compress upstream connections via gzip and will return gzip compressed content to the client if the client requested it with the accept-encoding header and the upstream server supplied a compressed response.

Logging

All rewrite steps are logged as a series of x-go-repro-log headers, e.g.

X-Go-Repro-Log:json rewriter: response rewritten
X-Go-Repro-Log:rewrote access-control-allow-origin
X-Go-Repro-Log:rewrote origin
X-Go-Repro-Log:rewrote referer

for a request in which the proxy rewrote referer and CORS headers as well as the JSON encoded server response.

You can disable logging by specifying the -no-logging option.

Limitations

• Body rewriting of non-JSON responses is a dumb text replacement on byte level. The rewriter is not encoding aware and does not parse HTML.
• The body of HTML redirects is not proxied. This is a open bug in the go standard library.
• Only gzip compression is supported
• q values in the accept-encoding header are not considered. In particular, q=0 is not correctly handled.

License

go-repro is released under the conditions of the MIT license.