Flexy Proxy

An easy-to-start, YAML-based flexible proxy server for software development. Return customized responses for specific URLs.

Features

• Customizable Responses: Set responses for specific URLs using one of the following methods:
  • File: Return any file stored on the storage.
  • Rewrite: Rewrite the URL to another URL like a reverse proxy.
  • Content: Directly return a string content as the response.
  • Transform: Apply a transformation command to the response content.
• Regex Based Matching:
  • Use regex to route URLs.
  • Dynamically change the reverse proxy destination using variables.
• Default Route Configuration: Choose the behavior when no routing matches.
  • Connect to the internet.
  • Connect to another proxy.
  • Deny access.

Installation

Binary Download

You can download the binary files from the GitHub Releases page. Choose the version that suits your operating system and architecture.

Build from Source with Go

If you prefer to build from source, you can install Flexy Proxy using go install.

go install github.com/kajikentaro/flexy-proxy@latest

Usage

1. Prepare the executable and add it to your PATH
   Make sure the flexy binary is either in your system's PATH or moved to a location like /usr/local/bin.

2. Create a config.yaml file
   Define your routes and responses in a config.yaml file. For example:

   routes:
     - url: "http://sample.test"
       regex: false
       response:
         content: "hello world\n"

3. Run the proxy with your config file
   Execute flexy with the -f flag pointing to your configuration file:

   flexy -f config.yaml

4. Use the proxy
   Now, you can use the proxy with a tool like curl:

   $ curl http://sample.test -x http://localhost:8888
   hello world

Configurations

For more details on configurations, visit: https://kajikentaro.github.io/flexy-proxy/output/

Example

config.yaml

default_route:
  deny_access: true

log_level: "INFO"
always_mitm: true

routes:
  # if the request URL is "https://example.com/user/[user_id]/post/[post_id]",
  # reverse proxy to "https://example.com/api?user=[user_id]&post=[post_id]".
  - url: "https://example.com/user/[^/]+/post/[^/]"
    regex: true
    response:
      rewrite:
        from: '^https://example\\.com/user/([^/]+)/post/([^/]+)'
        to: "https://example.com/api?user=$1&post=$2"
        regex: true
  # if the request URL is "https://example.com/not-found",
  # return the content "not found" with 404 status code.
  - url: "https://example.com/not-found"
    regex: false
    response:
      content: "not found"
      content_type: "text/plain"
      status: 404
  # if the request URL is "https://example.com/[any character].png",
  # return the file: "./sample.png"
  - url: 'https://example.com/.*\.png'
    regex: true
    response:
      file: "sample.png"
  # if the request URL is "https://example.com/proxy",
  # reverse proxy to "https://example.com/api" using a specific proxy.
  - url: "https://example.com/proxy"
    regex: false
    response:
      rewrite:
        from: "https://example.com/proxy"
        to: "https://example.com/api"
        regex: false
        proxy: "http://proxy.example.com"
  # if the request URL is "https://content.test",
  # return the content "basic" with a custom header.
  - url: "https://content.test"
    regex: false
    response:
      content: "basic"
      headers:
        "Access-Control-Allow-Origin": "*"
  # if the request URL is "https://content.test/",
  # return the content "foo" transformed to "bar".
  - url: "https://content.test/"
    regex: false
    response:
      content: "foo"
      transform: "sed -E 's/foo/bar/g'"

Certificates

The following commands create a private key (server.key) and a certificate (server.csr). By specifying options, Flexy Proxy can use this private key and certificate to generate new certificates for the requested hostname and use them for communication. By installing the server.csr certificate on your PC or browser, responses from Flexy Proxy will be considered secure.

openssl genrsa -out server.key
openssl req -new -key server.key -out server.csr -subj "/C=JP/ST=Tokyo/L=Minato/O=Example Company/OU=IT Department/CN=example.com"
openssl x509 -req -days 3650 -signkey server.key -in server.csr -out server.crt

Specify the certificates in the YAML file as follows:

certificate: "server.crt"
certificate_key: "server.key"