How to get an specific header value from the HttpResponseMessage

Question

I'm making an HTTP call. My response contains a session code X-BB-SESSION in the header section of the HttpResponseMessage object. How do I get that specific header value?

I am using a foreach statement to iterate through all the headers (MSDN link). However the compiler keeps saying that it cannot be done:

foreach statement cannot operate on variables of type
  System.net.http.headers.cachecontrolheadervalue because
  'System.net.http.headers.cachecontrolheadervalue' doesn't contain
  a public definition for 'GetEnumerator'

This is the code I'm trying:

//Connection code to BaasBox

HttpResponseMessage response = await client.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead);
if (response.IsSuccessStatusCode)
{
    //get the headers
    HttpResponseHeaders responseHeadersCollection = response.Headers;
    foreach (var value in responseHeadersCollection.CacheControl)  --> HERE
    {
        string sTemp = String.Format("CacheControl {0}={1}", value.Name, value.Value);
    } else
{
    Console.WriteLine("X-BB-SESSION: NOT Found");
}

The header content from where I'm trying to get the value (X-BB-SESSION value) is something like:

Access-Control-Allow-Origin: *    
Access-Control-Allow-Headers: X-Requested-With    
X-BB-SESSION: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Answer 1

You should be able to use the TryGetValues method.

HttpHeaders headers = response.Headers;
IEnumerable<string> values;
if (headers.TryGetValues("X-BB-SESSION", out values))
{
  string session = values.First();
}

Answer 2

Though Sam's answer is correct. It can be somewhat simplified, and avoid the unneeded variable.

IEnumerable<string> values;
string session = string.Empty;
if (response.Headers.TryGetValues("X-BB-SESSION", out values))
{
    session = values.FirstOrDefault();
}

Or, using a single statement with a ternary operator (as commented by @SergeySlepov):

string session = response.Headers.TryGetValues("X-BB-SESSION", out var values) ? values.FirstOrDefault() : null;

Answer 3

Using Linq aswell, this is how I solved it.

string operationLocation = response.Headers.GetValues("Operation-Location").FirstOrDefault();

I think it's clean and not too long.

Answer 4

You are trying to enumerate one header (CacheControl) instead of all the headers, which is strange. To see all the headers, use

foreach (var value in responseHeadersCollection)
{
    Debug.WriteLine("CacheControl {0}={1}", value.Name, value.Value);
}

to get one specific header, convert the Headers to a dictionary and then get then one you want

Debug.WriteLine(response.Headers.ToDictionary(l=>l.Key,k=>k.Value)["X-BB-SESSION"]);

This will throw an exception if the header is not in the dictionary so you better check it using ContainsKey first

Answer 5

If someone like method-based queries then you can try:

    var responseValue = response.Headers.FirstOrDefault(i=>i.Key=="X-BB-SESSION").Value.FirstOrDefault();