Add option to show traffic stats from server perspective

[german2285]

Is your feature request related to a problem? Please describe.

The Traffic Stats API shows traffic from the client's perspective (tx = client upload, rx = client download), but this creates problems when comparing with server monitoring tools and hosting provider reports.

Real example - after downloading a 100MB file:

• Hysteria Traffic Stats: rx: 105MB, tx: 0.7MB = 105.7 MB total
• vnstat (server): tx: 177MB, rx: 102MB = 279 MB total
• My hosting provider billing: matches vnstat (279 MB), not Hysteria!

The critical problem:
If I rely only on Traffic Stats API to monitor my 15TB/month VPS limit, I would think I used only 105.7 MB, but actually consumed 279 MB (2.6x more!). This makes it impossible to predict when I'll hit my traffic limit and avoid overage fees.

Describe the solution you'd like

Add an option to show stats from server perspective:

trafficStats:
  perspective: server  # or "client" (default)

Or: GET /traffic?perspective=server

With perspective: server:

• tx = bytes sent by server (matches what hosting provider counts)
• rx = bytes received by server
• Total would match vnstat and hosting billing

Describe alternatives you've considered

Using wrapper scripts to swap tx/rx, but this is error-prone and doesn't solve the traffic calculation mismatch (server sees 279 MB while API shows only 105.7 MB due to protocol overhead).

Additional context

Server administrators need stats that match OS-level tools (vnstat, iptables) and hosting provider billing to:

• Accurately track bandwidth against VPS limits
• Set correct usage alerts (e.g., 90% of 15TB)
• Avoid surprise overage charges
• Fairly distribute bandwidth among users

[haruue]

That's because the traffic stats only account for traffic between the Hysteria server and the Hysteria client.

However, when you access a website, the Hysteria server needs to send and receive a similar amount of traffic to and from the website server. This doubles the traffic, but it is not counted by the Hysteria traffic stats.

[german2285]

Yes, I understood this from the documentation and during testing. This issue is simply a feature request. As a VPN provider, I'm interested in selling VPN service based on traffic consumption.