🔌 PicoServer.Nano (for .NET nanoFramework)

PicoServer.Nano (NuGet package: PicoServer.Nano) is a lightweight port of PicoServer to the .NET nanoFramework ecosystem. It is a zero-dependency "Web glue library" designed specifically for resource-constrained microcontrollers, with special adaptation and optimization for ESP32.

What is .NET nanoFramework?

A project under the Microsoft .NET Foundation that shrinks the full .NET runtime to a few hundred KB, enabling C# code to run on microcontrollers like ESP32 and STM32. You can develop projects in Visual Studio and deploy to boards with one click.

Difference from Official WebServer Library

PicoServer.Nano does not use reflection, has lower memory and CPU footprint, leaving limited resources for business logic.

Quick Start

1. Environment Setup

Install nanoFramework development environment:

1. Install nanoFramework Visual Studio Extension
2. Flash nanoFramework firmware to ESP32:

nanoff --target ESP32_S3_ALL --serialport COM5 --update --masserase

2. Add NuGet Package

dotnet add package PicoServer.Nano

3. Write Code

using PicoServer.Nano;
using System.Net;

var server = new WebAPIServer();
server.AddRoute("/hello", (req, res) => res.Write("Hello from MCU!"), "GET");
server.StartServer();
Console.WriteLine($"Server started: http://{server.GetIPAddress()}/");

Compile and deploy, then visit http://<device-IP>/hello in browser to see the response.

Core Capabilities

Feature	Supported
Route Mapping	✅ Exact routing
Custom Middleware	✅
Token Authentication	✅
Static File Hosting	✅
SSE Long Connection	✅
File Upload/Download	✅

Route Registration

server.AddRoute("/api/user", UserHandler, "GET");

private static void UserHandler(HttpListenerRequest req, HttpListenerResponse res)
{
    string token = req.GetToken();
    res.Write("{\"id\":1}");
}

Middleware

server.AddMiddleware((req, res) =>
{
    if (req.Headers["X-Key"] != "secret")
    {
        res.Write("Unauthorized", 401);
        return false;
    }
    return true;
});

Static File Hosting

Host an entire folder with one line:

server.AddStaticFiles("/web", "I:\\www", maxAge: 3600);

Visit http://device-IP/web/index.html to see the webpage.

Response Extensions

Method	Description
res.Write(content, contentType)	Write response and close
res.SendFile(filePath)	Send file (streaming)
res.WriteChunk(content)	Chunked push (SSE/long connection)

Request Extensions

Method	Description
req.GetToken()	Get Token from Authorization header
req.ReadBodyAsString()	Read request body as string
req.SaveFile(savePath)	Save uploaded file

Consistent C# Development Experience

PicoServer on Windows/Linux/macOS:

server.AddRoute("/hello", async (req, res) => await res.WriteAsync("Hello"));

PicoServer.Nano on ESP32/STM32:

server.AddRoute("/hello", (req, res) => res.Write("Hello"));

Almost the same API, enabling consistent Web development experience across desktop, cloud, and embedded microcontrollers.

Notes

1. Path Format: Use backslash \ in nanoFramework, e.g., "I:\\www"
2. Static File Hosting: Files must be deployed to device (set build action to "Content"), middleware executes in order, recommended to add first
3. Whitelist: Routes added to whitelist can skip authentication
4. Long Connection: Must call res.Close() after WriteChunk push completes

Resources

• NuGet: PicoServer.Nano https://www.nuget.org/packages/PicoServer.Nano
• Website: https://picoserver.cn
• nanoFramework Website: https://www.nanoframework.net