Azure Functions Middleware vs No Middleware — .NET 6 C# Comparison

A side-by-side comparison of two Azure Functions v4 projects on .NET 6: one using isolated worker middleware (WithMiddleware, built on IFunctionsWorkerMiddleware) and one without middleware (WithoutMiddleware, an in-process function). Both expose a SendMessage HTTP POST endpoint that greets the caller by name, but the middleware version transforms the name to uppercase before the function handler runs.

Projects

Project	Port	Description
WithMiddleware	7052	Registers UppercaseNameMiddleware; name is uppercased in middleware before reaching the handler
WithoutMiddleware	7162	In-process model (Microsoft.NET.Sdk.Functions), no middleware; the raw name field from the JSON body is used as-is

Middleware is a feature of the isolated worker model, which is why the baseline project uses the in-process model.

How the Middleware Works

UppercaseNameMiddleware implements IFunctionsWorkerMiddleware:

1. Reads the HTTP request body as a string
2. Parses it as JSON (JObject)
3. Converts the name property value to uppercase (or sets it to "name not found" if absent)
4. Stores the updated JObject in context.Items["updated_body"]
5. Resets the request body stream position
6. Calls next(context) to pass control to the function handler

The SendMessageFunction then reads context.Items["updated_body"] and returns Hello {name}.

Requirements

• .NET 6 SDK
• Azure Functions Core Tools v4
• A local.settings.json in each project (not committed to source control)

Minimum local.settings.json (WithMiddleware)

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
  }
}

For the in-process WithoutMiddleware project, set "FUNCTIONS_WORKER_RUNTIME": "dotnet" instead of "dotnet-isolated".

NuGet Packages (WithMiddleware)

Package	Version
Microsoft.Azure.Functions.Worker	1.19.0
Microsoft.Azure.Functions.Worker.Extensions.Http	3.0.13
Microsoft.Azure.Functions.Worker.Sdk	1.14.0
Newtonsoft.Json	13.0.1

WithoutMiddleware references only Microsoft.NET.Sdk.Functions 4.2.0.

Running Locally

From the Middleware folder:

# With middleware
cd Dotnet6/WithMiddleware
func start --port 7052

# Without middleware (separate terminal)
cd Dotnet6/WithoutMiddleware
func start --port 7162

Usage

# With middleware — name is returned in uppercase
curl -X POST http://localhost:7052/api/SendMessage \
  -H "Content-Type: application/json" \
  -d '{"name": "alice"}'

Response: Hello ALICE.

# Missing name field
curl -X POST http://localhost:7052/api/SendMessage \
  -H "Content-Type: application/json" \
  -d '{}'

Response: Hello name not found.

# Without middleware — name is used as-is
curl -X POST http://localhost:7162/api/SendMessage \
  -H "Content-Type: application/json" \
  -d '{"name": "alice"}'

Response: Hello, alice. This HTTP triggered function executed successfully. (with no name, it asks you to pass one).

Project Structure

Dotnet6/
├── WithMiddleware/
│   ├── Functions/
│   │   └── SendMessageFunction.cs      # Reads updated_body from context.Items
│   ├── Middlewares/
│   │   └── UppercaseNameMiddleware.cs  # Transforms name to uppercase
│   ├── Program.cs                      # Registers middleware
│   └── WithMiddleware.csproj
├── WithoutMiddleware/
│   ├── Functions/
│   │   └── SendMessageFunction.cs      # Reads name directly from request body
│   └── WithoutMiddleware.csproj
└── readme.md

Related Examples

• .NET 8 version with exception-handling middleware
• Azure Functions middleware overview
• Back to all C# and .NET code examples

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Documentation links

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