Read specific HTTP header value from key/value collection in C#

Question

I'm trying to read two header values from an HTTP method and have a few gaps in my C# knowledge. I can see a Results View in the locals when debugging and I can also see it is a System.Collections.Generic but I don't know how to access this list to obtain my two values.

Here is my Azure Function App code:

[FunctionName("Tenant")]
public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "Tenant/{DomainName}")]HttpRequestMessage req, string DomainName, [Inject(typeof(ITableOps))]ITableOps _tableOps, TraceWriter log)
{
    var headers = req.Headers;
    var settings = _tableOps.GetTenantSettingsAsync(DomainName);
    return req.CreateResponse(HttpStatusCode.OK, settings.Result);
}

From this key/value list I'd like to get the key named apikey and domainName and I've tried all sorts of strange ways to do this:

 headers.ToList()[0]

or

var key = headers.Where(x => x.Key == "apikey")

Given the second example, key ends up being another list:

I've seen quite a few examples on using foreach loops but in my case I thought I could use a lambda to extract the value since I'm expecting two very specific key names. I realize this is easy to obtain but I'm at a loss on how to proceed.

Answer 1

Headers is a HttpRequestHeaders class, that class has a TryGetValues function that is for this exact situation.

[FunctionName("Tenant")]
public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "Tenant/{DomainName}")]HttpRequestMessage req, string DomainName, [Inject(typeof(ITableOps))]ITableOps _tableOps, TraceWriter log)
{
    var headers = req.Headers;
    if(!headers.TryGetValues("apiKey", out var apiKeys) ||
       !headers.TryGetValues("domain", out var domains))
    {
        return req.CreateResponse(HttpStatusCode.Forbidden);
    }
    var apiKey = apiKeys.First();
    var domain = domains.First();

    //Do something with apiKey and domain here.

    var settings = _tableOps.GetTenantSettingsAsync(DomainName);
    return req.CreateResponse(HttpStatusCode.OK, settings.Result);
}

There also is a GetValues function that could be used like

[FunctionName("Tenant")]
public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "Tenant/{DomainName}")]HttpRequestMessage req, string DomainName, [Inject(typeof(ITableOps))]ITableOps _tableOps, TraceWriter log)
{
    var headers = req.Headers;
    var apiKey = headers.GetValues("apiKey").First();
    var domain = headers.GetValues("domain").First();

    //Do something with apiKey and domain here.

    var settings = _tableOps.GetTenantSettingsAsync(DomainName);
    return req.CreateResponse(HttpStatusCode.OK, settings.Result);
}

However GetValues will throw a InvalidOperationException if the header was not sent with the request so doing a TryGetValues would be faster due to no exception overhead.

The HttpRequestHeaders is a kind of like a Dictionary<string, List<string> internally so a dictionary lookup would be the preferred way to do it.

Answer 2

One option is to get one item at the time is to use FirstOrDefault() which returns the first element from the list that matches your expression. If no elements exist it will return null.

var key = headers.FirstOrDefault(x => x.Key == "apikey");

To get both keys

var yourKeys = new List<string>{"apikey", "domainName"};
headers.Where(x => yourKeys.Contains(x.Key)).ToList();