Looks up the "Content-Type" header in hdrs, parses it, and returns its value in *content_type and *params.
params can be null if you are only interested in the content type itself.
return location for the Content-Type parameters (eg, "charset"), or null
a string with the value of the "Content-Type" header or null if hdrs does not contain that header or it cannot be parsed (in which case *params will be unchanged).
Looks up the "Content-Type" header in hdrs, parses it, and returns its value in *content_type and *params.
params can be null if you are only interested in the content type itself.