Precompiled functions

Azure Functions supports pre-compiled functions, which enables the use of .NET assemblies containing the function implementation, bypassing the dynamic compilation process.

In order to use pre-compiled functions, your function.json file must have the scriptFile and entryPoint properties set, pointing to the assembly file and fully qualified method name, respectively:

Sample function.json

{
    "scriptFile": "PreCompiledFunctionSample.dll",
    "entryPoint": "PreCompiledFunctionSample.MyFunction.Run",
    "bindings": [
        {
            "authLevel": "function",
            "name": "req",
            "type": "httpTrigger",
            "direction": "in"
        },
        {
            "name": "$return",
            "type": "http",
            "direction": "out"
        }
    ],
    "disabled": false
}

Sample function implementation

using System.Net;
using System.Linq;
using System.Threading.Tasks;
using System.Net.Http;

namespace PreCompiledFunctionSample
{
    public class MyFunction
    {
        public static async Task<HttpResponseMessage> Run(HttpRequestMessage req)
        {
            // parse query parameter
            string name = req.GetQueryNameValuePairs()
                .FirstOrDefault(q => string.Compare(q.Key, "name", true) == 0)
                .Value;

            // Get request body
            dynamic data = await req.Content.ReadAsAsync<object>();

            // Set name to query string or body data
            name = name ?? data?.name;

            return name == null
                ? req.CreateResponse(HttpStatusCode.BadRequest, "Please pass a name on the query string or in the request body")
                : req.CreateResponse(HttpStatusCode.OK, "Hello " + name);
        }
    }
}

With this approach, functions can be developed as a regular class library, using any .NET language. For the above sample, the function folder contained the function.json and the assembly file, PreCompiledFunctionSample.dll

A sample project with the above function is available here