With this function you can get a certain header that has been sent by the client. You specify the header you want to get using the key parameter. If the key parameter isn't a string it'll throw a TypeError and when the header wasn't found it'll return undefined.

This function returns if the client has sent the specified header. You can specify the header you want to check using the key parameter. If the key parameter isn't a string it'll throw a TypeError.

This function returns an array of the names of all the headers that were sent by the client.