caddyhttp: Fix listener overlap detection on Linux

Sigh, apparently Linux is incapable of distinguishing host interfaces in socket addresses, even though it works fine on Mac. I suppose we just have to assume that any listeners with the same port are the same address, completely ignoring the host interface on Linux... oh well.

Matthew Holt committed Apr 26, 2020 at 22:28 UTC 83c85c53f583906e438bb9eb30fc0ab57bf59108

1 file changed +25 -2

modules/caddyhttp/server.go

+25 -2

@@ -21,6 +21,7 @@ import (

21 "net"

22 "net/http"

23 "net/url"

24 + "runtime"

25 "strings"

26 "time"

@@ -307,8 +308,30 @@ func (s *Server) hasListenerAddress(fullAddr string) bool {

308 continue

309 }

310

310 - // host must be the same and port must fall within port range

311 - if (thisAddrs.Host == laddrs.Host) &&

311 + // Apparently, Linux requires all bound ports to be distinct

312 + // *regardless of host interface* even if the addresses are

313 + // in fact different; binding "192.168.0.1:9000" and then

314 + // ":9000" will fail for ":9000" because "address is already

315 + // in use" even though it's not, and the same bindings work

316 + // fine on macOS. I also found on Linux that listening on

317 + // "[::]:9000" would fail with a similar error, except with

318 + // the address "0.0.0.0:9000", as if deliberately ignoring

319 + // that I specified the IPv6 interface explicitly. This seems

320 + // to be a major bug in the Linux network stack and I don't

321 + // know why it hasn't been fixed yet, so for now we have to

322 + // special-case ourselves around Linux like a doting parent.

323 + // The second issue seems very similar to a discussion here:

324 + // https://github.com/nodejs/node/issues/9390

325 + //

326 + // This is very easy to reproduce by creating an HTTP server

327 + // that listens to both addresses or just one with a host

328 + // interface; or for a more confusing reproduction, try

329 + // listening on "127.0.0.1:80" and ":443" and you'll see

330 + // the error, if you take away the GOOS condition below.

331 + //

332 + // So, an address is equivalent if the port is in the port

333 + // range, and if not on Linux, the host is the same... sigh.

334 + if (runtime.GOOS == "linux" || thisAddrs.Host == laddrs.Host) &&

335 (laddrs.StartPort <= thisAddrs.EndPort) &&

336 (laddrs.StartPort >= thisAddrs.StartPort) {

337 return true