HttpSys crashes when Accept header has an empty value

[marcin-roman]

When receiving request with Accept header without value, http.sys crashes with the following stack trace:

at System.Text.UTF8Encoding.GetChars(Byte* bytes, Int32 byteCount, Char* chars, Int32 charCount) 
   at Microsoft.AspNetCore.Server.HttpSys.HeaderEncoding.GetString(SByte* pBytes, Int32 byteCount) 
   at Microsoft.AspNetCore.Server.HttpSys.NativeRequestContext.GetKnownHeader(HttpSysRequestHeader header) 
   at Microsoft.AspNetCore.Server.HttpSys.RequestHeaders.get_Accept() 
   at Microsoft.AspNetCore.Server.HttpSys.RequestHeaders.<PropertiesEnumerable>d__201.MoveNext() 
   at System.Linq.Enumerable.<ConcatIterator>d__58`1.MoveNext() 
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext() 
...

throwing and returning 500 Internal Server Error, preventing further execution. In our scenario, it happens when client invoke web method returning no-value (so Accept doesn't really matter, as no response is expected really).

IETF recommendations are not super-clear on empty values as header values though, but in this case, it feels right for it to correspond to Accept * / * reather than sending back error; it definitely should not crash with 500.

Given that application developers don't have control over clients in general, and that those invocated methods are not expected to return anything, we might want to serve requests with empty Accept header still.

It seems the similar issue was addressed in Kestrel too: aspnet/KestrelHttpServer#429

[Tratcher]

Duplicate of #381 that has already been fixed in 2.1.0-preview1.