Setting a Header to null
- doesn't change its count (stays at zero)
- doesn't change the Response output (header is not output)
However it will cause an error if a real value is added after:
app.Run(async (context) =>
{
var resposne = context.Response;
// Prints zero
Console.WriteLine(resposne.Headers["warning"].Count);
// Does not change response
resposne.Headers.Add("warning", new StringValues((string)null));
// Prints zero
Console.WriteLine(resposne.Headers["warning"].Count);
// Throws: System.ArgumentException: An item with the same key has already been added.
resposne.Headers.Add("warning", new StringValues("Hello"));
await context.Response.WriteAsync("Hello World!");
});If you can't smell it, see it, taste it, does it exist?
Should it not throw, but set the value? (as no value is set)
From aspnet/KestrelHttpServer#2347 (which was treating it as not set for perf reasons; i.e. don't expend extra cycles tracking nothing for no effect other than to just to throw an error on a second add)
/cc @halter73 @davidfowl
Setting a Header to null
However it will cause an error if a real value is added after:
If you can't smell it, see it, taste it, does it exist?
Should it not throw, but set the value? (as no value is set)
From aspnet/KestrelHttpServer#2347 (which was treating it as not set for perf reasons; i.e. don't expend extra cycles tracking nothing for no effect other than to just to throw an error on a second add)
/cc @halter73 @davidfowl