What is the purpose of ProcessUUID in VLESS?

[kumahooks]

I am trying to understand the intent behind ProcessUUID in the VLESS validator:
https://github.com/XTLS/Xray-core/blob/main/proxy/vless/validator.go

It appears to normalize VLESS user IDs by zeroing bytes 6 and 7:

func ProcessUUID(id [16]byte) [16]byte {
	id[6] = 0
	id[7] = 0
	return id
}

If I understand correctly, this means the entire third UUID group is ignored for user matching. What is the reason for this normalization?

[krotname]

This looks intentional. Those two bytes are not part of the effective VLESS user identity in Xray; they are reserved for vlessRoute.

The flow is:

• MemoryValidator.Add() stores users under ProcessUUID(userID).
• MemoryValidator.Get() also looks up ProcessUUID(id).
• After the request is accepted, the inbound handler keeps the original bytes and sets inbound.VlessRoute = net.PortFromBytes(userSentID[6:8]).
• The router has a vlessRoute rule field and matches it through ctx.GetVlessRoute().

So yes, UUIDs that differ only in bytes 6 and 7 are treated as the same VLESS user. Those bytes become a 16-bit route value (7th<<8 | 8th) that the client can send per request without breaking user lookup.

Operationally, I would not create multiple users whose IDs only differ in the third UUID group. Use a distinct normalized UUID for user identity, and use bytes 6-7 only when you intentionally want to drive routing.rules[].vlessRoute.