DynamicProxy

Dynamic HTTP Forward Proxy with Upstream Proxy Switching

🧭 Overview

DynamicProxy is a lightweight HTTP forward proxy designed for flexible upstream proxy switching based on request context. It was built to overcome limitations in environments where only a single static proxy can be configured — like in Mapsui with GDAL on Windows.

This proxy enables both internal and external geo services to work seamlessly without reconfiguring or restarting your app. It dynamically routes requests through the appropriate upstream proxy or direct connection, based on rules you define.

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💡 Use Case

While working with Mapsui + GDAL on Windows, we encountered a limitation: only one proxy could be configured globally, with no way to make exceptions. This was a problem because our application needed to access both:

• Internal geo-services (which required no proxy)
• External geo-services (which required a corporate proxy)

DynamicProxy solves this by acting as a smart middle layer:

• It listens as a local proxy.
• It inspects each request.
• Based on destination (or other rules), it forwards via the right upstream proxy — or bypasses it entirely.

🚀 Getting Started

To configure DynamicProxy, you need to set up the following environment variables:

• LISTEN_ADDR: The address where the proxy will listen for incoming requests (default: *:8080).
• UPSTREAM_PROXY: The upstream proxy address to use for external requests (e.g. corporate.proxy:8080).
• PROXY_EXCEPTIONS: A comma-separated list of hostnames or IPs that should bypass the upstream proxy (e.g. localhost,somehost1,somehost2).
• PROXY_AUTH: Optional authentication for the upstream proxy (currently only ntlm for windows is supported, e.g. ntlm).

You can then run the binary like usual:

./DynamicProxy

🛠️ Building from Source

To build DynamicProxy from source, ensure you have Go 1.24.5 or later installed and run the following commands:

go mod tidy
go build -o DynamicProxy ./cmd/main.go