Via Syntax

Tags: wire, transport

© R.A.Sol

A via string identifies a transport endpoint.

Grammar

Full form:

scheme+host[:port]

Bare form (auto-negotiate transport):

host[:port]

Hostless form (used in HELLO Transport headers where host is already known):

scheme[:port]

HELLO transport header value:

via *(SP hint)

Known hints:

flow=session
flow=message
path=<absolute-path>

Unix domain socket:

unix+<absolute-path>

Schemes

Host

Host is a hostname, IPv4 address, or bracketed IPv6 address.

IPv6 bracket form: [::1] or [::1]:port.

Port

Port is optional. When omitted, the scheme default applies. Bare form defaults to 4777.

Hostless Resolution

Hostless forms appear in HELLO Transport headers. The client fills in the host from its existing connection. Examples:

• tcp — TCP on default port, same host
• udp:4777 — UDP on port 4777, same host
• quib:4776 — QUIB on port 4776, same host

HELLO Transport Hints

A Transport HELLO header starts with a via string or transport endpoint. Any remaining space-separated tokens are hints about that endpoint.

Known command-flow hints:

• flow=session — endpoint runs session command flow
• flow=message — endpoint runs message command flow

HTTP path hint:

• path=<absolute-path> — HTTP request path, default /hppr

path= applies only to HTTP unless another transport spec defines it. Unknown hints are ignored. Flow hints describe the command flow reachable at that transport endpoint, not the current endpoint that produced the HELLO.

Examples:

• Transport: tcp:4777 flow=session
• Transport: quib:4776 flow=session
• Transport: ws:4778 flow=session
• Transport: http:4778 flow=message path=/hppr
• Transport: udp:4777 flow=message

Display Form

The canonical display form is:

• scheme+host:port when a scheme is set
• host:port for auto-negotiate
• unix+<path> for Unix sockets

Examples