Calls func once for each header value in this.
Beware that unlike [[email protected]_list], this processes the headers in exactly the way they were added, rather than concatenating multiple same-named headers into a single value. (This is intentional; it ensures that if you call [ [email protected]] multiple times with the same name, then the I/O code will output multiple copies of the header when sending the message to the remote implementation, which may be required for interoperability in some cases.)
You may not modify the headers from func.
| this | |
| func |
callback function to run for each header |
| user_data |
data to pass to |