Add Lock to ReplaceACN. Minor Drone fixups

.drone.yml

@@ -14,7 +14,6 @@ pipeline:
       - wget https://git.openprivacy.ca/openprivacy/buildfiles/raw/master/tor/tor -P tmp/
       - chmod a+x tmp/tor
       - go mod download
-      - go get -u
   quality:
     when:
       repo: openprivacy/connectivity

.gitignore

@@ -4,5 +4,4 @@ tor/tor/
 vendor/
 *.cover.out
 tmp/
-testing/tor/torrc
 testing/tor/*

proxy_acn.go

@@ -2,6 +2,7 @@ package connectivity
 
 import (
 	"net"
+	"sync"
 )
 
 // ProxyACN because there is rarely a problem that can't be solved by another layer of indirection.
@@ -11,6 +12,10 @@ import (
 // ProxyACN - a wrapper around an ACN that allows safe replacement of a running ACN that is transparent to callers.
 type ProxyACN struct {
 	acn ACN
+
+	// All operations on the underlying acn are assumed to be thread safe, however changing the actual
+	// acn in ReplaceACN will lock to force an ordering of Close and Callback
+	lock sync.Mutex
 }
 
 func NewProxyACN(acn ACN) ProxyACN {
@@ -21,6 +26,8 @@ func NewProxyACN(acn ACN) ProxyACN {
 
 // ReplaceACN closes down the current ACN and replaces it with a new ACN.
 func (p *ProxyACN) ReplaceACN(acn ACN) {
+	p.lock.Lock()
+	defer p.lock.Unlock()
 	p.acn.Close()
 	acn.SetStatusCallback(p.acn.Callback())
 	p.acn = acn