P4
ADDITIONAL SYSTEM INFORMATION :
At least Windows (supported versions), macOS/iOS, and Linux (including Android) support the system-level APIs to get this information, without requiring any special system privileges.
A DESCRIPTION OF THE PROBLEM :
Posix socket APIs make it possible to receive ancillary data alongside datagram packets, using the recvmsg() API. Recent Windows versions have a similar function, LPFN_WSARECVMSG.
Some of the ancillary data made available through these APIs are very important for implementing modern congestion control algorithms. For example, received ECN markings (available on Windows, Apple OSes, and Linux [including Android]) are needed for modern network-supported congestion avoidance algorithms such as L4S, and system receive timestamps are necessary to implement accurate timings for high-quality delay or round-trip time estimates in userspace applications. Windows, macOS/iOS, and Linux all support these ancillary data elements.
If Java wants to make it possible for modern protocols such as QUIC and thus HTTP/3, which are typically implemented in userspace, to be usable (outside of a JNI-type interface), these protocol elements will need to be visible to Java applications.
There should therefore be APIs so that Java implementations can receive all the OS-supported ancillary data in datagram packets, and also portable APIs to get common ancillary data such as ECN, TOS/TCLASS, timestamp, received IP address, received TTL, etc.
At least Windows (supported versions), macOS/iOS, and Linux (including Android) support the system-level APIs to get this information, without requiring any special system privileges.
A DESCRIPTION OF THE PROBLEM :
Posix socket APIs make it possible to receive ancillary data alongside datagram packets, using the recvmsg() API. Recent Windows versions have a similar function, LPFN_WSARECVMSG.
Some of the ancillary data made available through these APIs are very important for implementing modern congestion control algorithms. For example, received ECN markings (available on Windows, Apple OSes, and Linux [including Android]) are needed for modern network-supported congestion avoidance algorithms such as L4S, and system receive timestamps are necessary to implement accurate timings for high-quality delay or round-trip time estimates in userspace applications. Windows, macOS/iOS, and Linux all support these ancillary data elements.
If Java wants to make it possible for modern protocols such as QUIC and thus HTTP/3, which are typically implemented in userspace, to be usable (outside of a JNI-type interface), these protocol elements will need to be visible to Java applications.
There should therefore be APIs so that Java implementations can receive all the OS-supported ancillary data in datagram packets, and also portable APIs to get common ancillary data such as ECN, TOS/TCLASS, timestamp, received IP address, received TTL, etc.