yprox is a versatile TCP proxy server tool and a Rust library, designed for modifying and multiplexing network traffic. It allows users to track and analyze traffic for different backend systems, aiding in performance monitoring and system emulation. yprox can be seamlessly used both as a standalone executable and as an integrated library in Rust applications.

yprox is currently under active development. The tool's primary aim is to facilitate the monitoring of multiple backend behaviors by capturing and comparing traffic between the original system and a secondary system designed to replicate the original's functionality.

Install yprox easily using Cargo, Rust's package manager:

cargo install yprox

yprox supports configuration through a TOML file. By default, it searches for a file named yprox.toml in the current directory. This file allows you to specify the server settings in a structured format.

Here is the structure of yprox.toml:

# Example yprox.toml configuration
bind = "ip:port"                   # The bind address
backends = ["ip:port", "ip:port"]  # List of backends
default_backend = "backendName"    # Optional: Default backend name

You can also provide backends as a TOML table:

backends = { primary = "127.0.0.1:27017", secondary = "127.0.0.1:27016" }

This way you can name each backend.

If you prefer not to use a configuration file, yprox can also be configured via command line arguments:

1. Configuration File Path:
   Optionally specify a custom configuration file path. If not set, yprox looks for yprox.toml in the current directory.

   --config <path/to/config.toml>
   

2. Bind Address:
   Set the bind address in ip:port format. This is required if specifying backends via command line.

   --bind <ip:port>
   

3. Backend Addresses:
   Specify one or more backend addresses, either as ip:port or name=ip:port. Unnamed backends are automatically named backend1, backend2, etc.

   --backend <backend_address>
   

4. Default Backend:
   Name the default backend. If not specified, the first backend will be used.

   --default <backend_name>
   

Example Usage:

yprox --bind 127.0.0.1:8080 --backend 127.0.0.1:9000 --backend 127.0.0.1:9001

In this example, responses from 127.0.0.1:9001 will be returned to clients.

Naming Backends:

For better log clarity, backends can be named using the key=value format:

yprox --bind 127.0.0.1:8080 --backend qa=127.0.0.1:9000 --backend test=127.0.0.1:9001 

Unspecified backends will be automatically assigned default names such as backendN.

Setting a Default Backend:

The default backend refers to the chosen backend whose response is forwarded back to the client. In the absence of a specified default, the first backend is automatically selected.

To set a default backend, use:

yprox                               \
    --bind 127.0.0.1:8080           \
    --backend qa=127.0.0.1:9000     \
    --backend test=127.0.0.1:9001   \
    --default test

In this example, responses from 127.0.0.1:9001 will be returned to clients.