Azure Functions Golang & SharePoint Sample

Prerequisites

• Azure Functions Core Tools, v4
• Go SDK
• Visual Studio Code & Azure Functions extension
• Azure CLI [optional]
• Terraform [optional, for IaC provisioning]

Mac or Linux machine, or Windows WSL2 are preferred. All the commands within the sample assumed running in bash.

Create Azure Function Resource

This flow is dev friendly when it comes to quick experiments. For production deployments please consider infrastructure as code and automation via DevOps.

In VS Code with Azure Functions extension installed:

• CMD+Shift+P type Azure Functions: Create Function App in Azure... (Advanced) and follow the wizard (further is the example of the steps)
• Select dev subscription
• Enter a globally unique name for the new function app
• Select a runtime stack: Custom Handler
• Select an OS: Linux
• Select a hosting plan: Consumption
• Create a new resource group
• Enter the name of the new resource group
• Create new storage account
• Enter the name of the new storage account
• Create new Application Insights resource
• Enter the name of the new Application Insights resource
• Select a location for new resources (closer to your location)

Don't forget to remove the resource group after experiments to avoid any unpredictable charges

Project structure highlights

• .vscode/ - VSCode settings folder, mostly standard, however, settings.json has important modification "azureFunctions.deploySubpath": "./functions" which changes root folder for functions deployment via ms-azuretools extension
• functions/ - everything related to Azure Functions, isolation makes things simpler while no mixing with custom handler related project files
  • Functions folders, containing function.json file
  • .funcignore - functions ignore file with handy ignore options
  • host.json - host configuration file, mostly standard, interesting and important section is customHandler, especially "enableForwardingHttpRequest": true which is not added by default
  • local.settings[.sample].json - contains configuration which is needed for local development and debug, local settings should be excluded from Git to avoid secrets leak
  • proxies.json - bypassing endpoints to external resources
• handlers/ - Handlers sub package grouping by extensible handlers methods
• debug.go - grabs Azure Functions settings to use when starting the handlers' server separately, is not included into production build
• main.go - Custom Handler Go server entry point
• mux.go - routes and handler binding configuration
• sp.go - SharePoint Client and authentication constructor
• Makefile - useful tasks/commands collection for project automation

Local start/debug

• Copy/rename local.settings.sample.json to local.settings.json.
• Provide authentication parameters:
  • SPAUTH_SITEURL
  • SPAUTH_CLIENTID
  • SPAUTH_CLIENTSECRET

Add-in Only auth is used as a sample.

• Start the local server with make start
• Navigate to one of the URL endpoints printed in the console

Debugging Go code

For breaking points debugging in VSCode a number of approaches can be used: attaching to process or connecting to server. In most cases, one would prefer restarting Go server without stoping and restarting func start session. Also, it's simpler to place a breakpoint, switch to main.go file, and launch debug. Such a scenario can be covered with:

make debug

The local function app is started without actually starting the Go side-car server, but mimicking the process for functions core utility.

Then, the Go application can be started or restarted as many times as needed, e.g. using go run ./ or launch debug UI.

Build and deploy

1. Run build command:

make build-prod

The assumption is that a Linux plan was selected for the function app.

The build creates bin/server binary with the Go custom handler.

2. In VSCode,

• CMD+Shift+P type Azure Functions: Deploy to Function App...
• Select subscription
• Select Function App in Azure
• Confirm deployment

Publish via CLI

Publishing via CLI is a faster and more robust scalable way.

make appname="functionapp_name" publish

where "functionapp_name" is the name of your Function App instance.

az CLI is required.

Configure environment variables

In the Azure Function app, create and provide the following environment variables:

• SPAUTH_SITEURL
• SPAUTH_CLIENTID
• SPAUTH_CLIENTSECRET

Depending on the SharePoint environment and use case, auth strategy can be different. For a production installation Azure Certificate Auth might be preferred.

sp.go/getSP handler should be aligned with authentication parameters.

Overriding host's settings

Azure Functions use .Net native approaches dealing with settings. Hierarchical settings can be overriden with environment variables.

E.g., you need server.exe locally but a Linux Functions host still needs server (without extention) in hosts.json, it can be redefined in local.settings.json with a value:

{
  // ...
  "Values": {
    // ...
    "AzureFunctionsJobHost__customHandler__description__defaultExecutablePath": "bin/server.exe"
  }
}

Adding new function

1. CMD+Shift+P type Azure Functions: Create Function...

2. Select a template for your function, e.g. HTTP trigger

3. Provide a function name. e.g. HttpTrigger1

4. Select authorization level, e.g. Function

A function's folder and bindings definition is created functions/HttpTrigger1/function.json:

{
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": ["get", "post"]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

5. Run make start and follow via http://localhost:7071/api/HttpTrigger1 for just created function's binding

The Echo service handler will response with URL path /api/HttpTrigger1, that's because created function is not processed with specific route Go custom handler yet.

Ctrl+C to stop running functions host.

6. Create handlers/HttpTrigger1.go and paste:

package handlers

import (
	"fmt"
	"net/http"
)

// HTTPTrigger1 handles a function's logic
func (h *Handlers) HTTPTrigger1(w http.ResponseWriter, r *http.Request) {
	name := r.URL.Query().Get("name")
	fmt.Fprintf(w, "Hello, %s!", name)
}

7. Bind a handler with a route in mux.go in API routes section:

http.HandleFunc("/api/HttpTrigger1", h.HTTPTrigger1)

8. Run make start and navigate to http://localhost:7071/api/HttpTrigger1?name=Function

Hello, Function! should be responded back.

SharePoint API in Go

Check handlers/fields.go and handlers/lists.go as samples of comuting with SharePoint instance.

In a handler, h.sp. exposes access to SharePoint object model.

The API layer is powered by gosip.

Reference

• Azure Functions custom handlers
• Create a Go function in Azure using VSCode
• Functions Custom Handlers (Go)
• Serverless Go in Azure Functions with custom handlers (video)
• Working with SharePoint in Go