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docs: Interface takes an interface IP, not an interface name

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UDPSServer parses Interface with inet_addr() to set IP_MULTICAST_IF, so
a name like "eth0" yields INADDR_NONE and Initialise fails. Every
example in UDPStreamer.md used "eth0", so anyone following the docs hit
that failure; the .cfg files in Test/ already used a dotted-quad.

Replace the examples with 192.168.1.10, state the dotted-quad
requirement in the parameter table and the Multicast section, and note
that receivers must join on the matching interface or they silently
receive nothing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Martino Ferrari
2026-08-17 08:09:21 +02:00
co-authored by Claude Opus 4.6
parent c827ecefff
commit 61a2aa3988
1 changed files with 12 additions and 4 deletions
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Docs/UDPStreamer.md
+12 -4
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@@ -36,7 +36,8 @@ thread.
// Multicast (optional — omit for unicast mode)
MulticastGroup = "239.0.0.1" // IPv4 multicast address (224.0.0.0/4)
Interface = "eth0" // Multicast-bound interface (mandatory when MulticastGroup is set)
Interface = "192.168.1.10" // Local IPv4 address of the outgoing interface
// (mandatory when MulticastGroup is set)
DataPort = 44501 // UDP port for multicast DATA (default: Port+1)
// Publishing mode (optional)
@@ -87,7 +88,7 @@ thread.
| `Port` | uint16 | 44500 | UDP server port (unicast) or TCP control port (multicast). Values ≤ 1024 produce a warning. |
| `MaxPayloadSize` | uint32 | 1400 | Max payload bytes per UDP datagram (min 18) |
| `MulticastGroup` | string | *(absent)* | IPv4 multicast address (e.g. `"239.0.0.1"`). Must be in 224.0.0.0/4. Absent or empty = unicast mode. |
| `Interface` | string | *(absent)* | Network interface for multicast binding (e.g. `"eth0"`). **Mandatory** when `MulticastGroup` is set. |
| `Interface` | string | *(absent)* | Local IPv4 address of the interface multicast DATA leaves from, in dotted-quad form (e.g. `"192.168.1.10"`, or `"127.0.0.1"` for loopback-only testing). **Not** an interface name — `"eth0"` is rejected. **Mandatory** when `MulticastGroup` is set. |
| `DataPort` | uint16 | Port+1 | UDP port for multicast DATA datagrams. Ignored in unicast mode. |
| `PublishingMode` | string | Strict | `Strict`: send every RT cycle. `Accumulate`: batch until size/time limit. `Decimate`: send every Nth cycle. |
| `MinRefreshRate` | float64| — | Flush frequency in Hz. **Required** when `PublishingMode` = `Accumulate`. |
@@ -147,7 +148,14 @@ CONNECT evicts the previous client.
### Multicast
Enabled by setting `MulticastGroup` to a valid IPv4 multicast address (224.0.0.0/4).
The `Interface` parameter is **mandatory** and specifies the network interface to bind.
The `Interface` parameter is **mandatory**. It is the local IPv4 address of the
interface DATA datagrams leave from, given in dotted-quad form — it sets
`IP_MULTICAST_IF` on the data socket and is parsed with `inet_addr()`, so an
interface *name* such as `"eth0"` is rejected and `Initialise` fails.
Receivers must join the group on the matching interface. A receiver that joins
with `INADDR_ANY` lets the kernel pick the default-route interface, and it will
silently receive nothing if that is not the interface named by `Interface`.
The server opens a TCP listener on `Port` for control traffic and a UDP socket aimed at
`MulticastGroup:DataPort` for data traffic. The client:
@@ -253,7 +261,7 @@ PrepareNextState() ← opens UDP server socket, starts background threa
Class = UDPStreamer
Port = 44500 // TCP control port
MulticastGroup = "239.0.0.1" // Enables multicast mode
Interface = "eth0" // Mandatory for multicast
Interface = "192.168.1.10" // Local IP of the outgoing interface (mandatory)
DataPort = 44501 // UDP data port (default: Port+1)
MaxPayloadSize = 1400
PublishingMode = "Accumulate"