Add TPROXY inbound (TCP and UDP) - #493
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Add a Linux TPROXY inbound listener for transparent proxying, enabled by the `inbound-tproxy` feature and configured as an inbound with protocol "tproxy". TCP: a listening socket with IP_TRANSPARENT accepts connections redirected by the iptables TPROXY target; the original destination is the accepted socket's local address. UDP: a socket with IP_TRANSPARENT and IP_RECVORIGDSTADDR receives redirected datagrams; the original destination is read from the IP_ORIGDSTADDR control message via recvmsg(2). Replies are sent from a transparent socket bound to the original destination, so the client sees the reply coming from the address it originally talked to.
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Adds a Linux TPROXY inbound listener so leaf can be used as a transparent proxy via the iptables
TPROXYtarget. The README lists TPROXY as "Coming soon"; this implements it for both TCP and UDP.How it works
TCP — a listening socket with
IP_TRANSPARENTaccepts connections redirected by theTPROXYtarget. The original destination is simply the accepted socket's local address.UDP — a socket with
IP_TRANSPARENT+IP_RECVORIGDSTADDRreceives redirected datagrams. The original destination is read from theIP_ORIGDSTADDRcontrol message viarecvmsg(2). Replies are sent from a transparent socket bound to the original destination, so the client sees the reply coming from the address it originally talked to.Usage
Enabled by the
inbound-tproxyfeature (Linux only; added toall-endpoints). Configured as a JSON inbound:{ "tag": "tproxy-in", "protocol": "tproxy", "address": "0.0.0.0", "port": 12345 }leaf needs
CAP_NET_ADMINto open transparent sockets. The usualip rule/ip route local/ iptablesTPROXYsetup is required.Testing
Verified in an isolated network-namespace setup (client ns → router ns running leaf+TPROXY → upstream): TCP transfers (256 KiB, md5-verified) and UDP datagrams were both proxied correctly, with the UDP reply source matching the original destination.
Notes
cfg-gated ontarget_os = "linux".confformat is not covered.