Listen on both IPv4 and IPv6 in standalone mode by default

socat binds a single family unless told which one: up to 1.7.x the
default IP version for TCP-LISTEN is 4, and 1.8.0 made it "no
preference", which resolves to whatever getaddrinfo and bindv6only
happen to give. So an order carrying both an IPv4 and an IPv6
identifier could never pass both http-01 challenges.

Bind one socket per family instead, with ipv6only on the IPv6 one so
the two do not collide. IPv4-mapped IPv6 addresses are not a portable
alternative, OpenBSD does not support them at all. The IPv6 listener
is best effort, a host without IPv6 still gets the IPv4 one. The
python fallback does the same. --listen-v4 and --listen-v6 keep
forcing a single family, and passing both now means both.

Le_Listen_V4 and Le_Listen_V6 were mutually exclusive in the domain
conf, which silently dropped one of them on renewal, and
_starttlsserver let -4 win when both were set.

Fixes #7185

acme.sh

@@ -2715,6 +2715,21 @@ _clearcaconf() {
   _clear_conf "$CA_CONF" "$1"
 }
 
+#Starts a socat listener in the background, the pid is set to _socat_pid.
+#It uses the content, _content_len, _NC and _SOCAT_ERR of _startserver.
+#options
+_startsocat() {
+  _socat_opts="$1"
+  _debug "_NC" "$_NC $_socat_opts"
+  $_NC $_socat_opts SYSTEM:"sleep 1; \
+echo 'HTTP/1.0 200 OK'; \
+echo 'Content-Length\: $_content_len'; \
+echo ''; \
+printf '%s' '$content';" 2>>"$_SOCAT_ERR" &
+  _socat_pid="$!"
+  _debug "_socat_pid" "$_socat_pid"
+}
+
 # content localaddress
 _startserver() {
   content="$1"
@@ -2728,16 +2743,24 @@ _startserver() {
   _debug Le_Listen_V4 "$Le_Listen_V4"
   _debug Le_Listen_V6 "$Le_Listen_V6"
 
+  _serverproc_v6=""
   if _exists "socat"; then
     _NC="socat"
-    if [ "$Le_Listen_V6" ]; then
+    SOCAT_OPTIONS6=""
+    if [ "$Le_Listen_V6" ] && [ -z "$Le_Listen_V4" ]; then
       _NC="$_NC -6"
       SOCAT_OPTIONS=TCP6-LISTEN
-    elif [ "$Le_Listen_V4" ]; then
+    elif [ "$Le_Listen_V4" ] && [ -z "$Le_Listen_V6" ]; then
       _NC="$_NC -4"
       SOCAT_OPTIONS=TCP4-LISTEN
-    else
+    elif [ "$ncaddr" ]; then
+      #a single local address belongs to a single family, let socat pick it
       SOCAT_OPTIONS=TCP-LISTEN
+    else
+      #listen on both ipv4 and ipv6, with one socket for each family:
+      #ipv4-mapped ipv6 addresses are not available everywhere.
+      SOCAT_OPTIONS=TCP4-LISTEN
+      SOCAT_OPTIONS6=TCP6-LISTEN
     fi
 
     if [ "$DEBUG" ] && [ "$DEBUG" -gt "1" ]; then
@@ -2745,6 +2768,10 @@ _startserver() {
     fi
 
     SOCAT_OPTIONS=$SOCAT_OPTIONS:$Le_HTTPPort,crlf,reuseaddr,fork
+    if [ "$SOCAT_OPTIONS6" ]; then
+      #ipv6only keeps this socket from colliding with the ipv4 one
+      SOCAT_OPTIONS6=$SOCAT_OPTIONS6:$Le_HTTPPort,crlf,reuseaddr,fork,ipv6only=1
+    fi
 
     #Adding bind to local-address
     if [ "$ncaddr" ]; then
@@ -2753,14 +2780,14 @@ _startserver() {
 
     _content_len="$(printf "%s" "$content" | wc -c)"
     _debug _content_len "$_content_len"
-    _debug "_NC" "$_NC $SOCAT_OPTIONS"
     export _SOCAT_ERR="$(_mktemp)"
-    $_NC $SOCAT_OPTIONS SYSTEM:"sleep 1; \
-echo 'HTTP/1.0 200 OK'; \
-echo 'Content-Length\: $_content_len'; \
-echo ''; \
-printf '%s' '$content';" 2>"$_SOCAT_ERR" &
-    serverproc="$!"
+    _startsocat "$SOCAT_OPTIONS"
+    serverproc="$_socat_pid"
+    if [ "$SOCAT_OPTIONS6" ]; then
+      #best effort, the host may have no ipv6 support at all
+      _startsocat "$SOCAT_OPTIONS6"
+      _serverproc_v6="$_socat_pid"
+    fi
   else
     _PYTHON=""
     if _exists "python3"; then
@@ -2772,21 +2799,40 @@ printf '%s' '$content';" 2>"$_SOCAT_ERR" &
     fi
     if [ "$_PYTHON" ]; then
       _debug "Using python: $_PYTHON"
-      _AF="socket.AF_INET"
-      _BIND_ADDR="0.0.0.0"
-      if [ "$Le_Listen_V6" ]; then
-        _AF="socket.AF_INET6"
+      #a comma separated list of addresses to listen on, one socket for each
+      _BIND_ADDR="0.0.0.0,::"
+      if [ "$Le_Listen_V6" ] && [ -z "$Le_Listen_V4" ]; then
         _BIND_ADDR="::"
+      elif [ "$Le_Listen_V4" ] && [ -z "$Le_Listen_V6" ]; then
+        _BIND_ADDR="0.0.0.0"
       fi
       if [ "$ncaddr" ]; then
         _BIND_ADDR="$ncaddr"
       fi
+      _debug "_BIND_ADDR" "$_BIND_ADDR"
       export _SOCAT_ERR="$(_mktemp)"
-      $_PYTHON -c "import socket,sys;s=socket.socket($_AF,socket.SOCK_STREAM);s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1);s.bind((sys.argv[2],int(sys.argv[1])));s.listen(5);res='HTTP/1.0 200 OK\r\nContent-Length: '+str(len(sys.argv[3]))+'\r\n\r\n'+sys.argv[3];
+      $_PYTHON -c "import socket,sys,select
+res='HTTP/1.0 200 OK\r\nContent-Length: '+str(len(sys.argv[3]))+'\r\n\r\n'+sys.argv[3]
+ads=sys.argv[2].split(',')
+ls=[]
+for ad in ads:
+ try:
+  sk=socket.socket(socket.AF_INET6 if ':' in ad else socket.AF_INET,socket.SOCK_STREAM)
+  sk.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
+  if ':' in ad and len(ads)>1:
+   sk.setsockopt(socket.IPPROTO_IPV6,socket.IPV6_V6ONLY,1)
+  sk.bind((ad,int(sys.argv[1])))
+  sk.listen(5)
+  ls.append(sk)
+ except Exception:
+  sys.stderr.write(str(sys.exc_info()[1])+'\n')
+if not ls:
+ sys.exit(1)
 while True:
- c,a=s.accept()
- c.sendall(res.encode() if hasattr(res, 'encode') else res)
- c.close()" "$Le_HTTPPort" "$_BIND_ADDR" "$content" 2>"$_SOCAT_ERR" &
+ for sk in select.select(ls,[],[])[0]:
+  c,a=sk.accept()
+  c.sendall(res.encode() if hasattr(res, 'encode') else res)
+  c.close()" "$Le_HTTPPort" "$_BIND_ADDR" "$content" 2>"$_SOCAT_ERR" &
       serverproc="$!"
       _NC="$_PYTHON"
     else
@@ -2809,6 +2855,11 @@ while True:
 _stopserver() {
   pid="$1"
   _debug "pid" "$pid"
+  if [ "$_serverproc_v6" ]; then
+    _debug "_serverproc_v6" "$_serverproc_v6"
+    kill $_serverproc_v6 >/dev/null 2>&1
+    _serverproc_v6=""
+  fi
   if [ -z "$pid" ]; then
     rm -f "$_SOCAT_ERR"
     return
@@ -2882,9 +2933,11 @@ _starttlsserver() {
 
   _debug Le_Listen_V4 "$Le_Listen_V4"
   _debug Le_Listen_V6 "$Le_Listen_V6"
-  if [ "$Le_Listen_V4" ]; then
+  #openssl s_server binds a single socket, so both options together can only
+  #mean: do not force a family, same as when neither of them is given.
+  if [ "$Le_Listen_V4" ] && [ -z "$Le_Listen_V6" ]; then
     __S_OPENSSL="$__S_OPENSSL -4"
-  elif [ "$Le_Listen_V6" ]; then
+  elif [ "$Le_Listen_V6" ] && [ -z "$Le_Listen_V4" ]; then
     __S_OPENSSL="$__S_OPENSSL -6"
   fi
 
@@ -5986,12 +6039,17 @@ $_authorizations_map"
     _clearaccountconf "HTTPS_INSECURE"
   fi
 
-  if [ "$Le_Listen_V4" ]; then
-    _savedomainconf "Le_Listen_V4" "$Le_Listen_V4"
-    _cleardomainconf Le_Listen_V6
-  elif [ "$Le_Listen_V6" ]; then
-    _savedomainconf "Le_Listen_V6" "$Le_Listen_V6"
-    _cleardomainconf Le_Listen_V4
+  if [ "$Le_Listen_V4" ] || [ "$Le_Listen_V6" ]; then
+    if [ "$Le_Listen_V4" ]; then
+      _savedomainconf "Le_Listen_V4" "$Le_Listen_V4"
+    else
+      _cleardomainconf Le_Listen_V4
+    fi
+    if [ "$Le_Listen_V6" ]; then
+      _savedomainconf "Le_Listen_V6" "$Le_Listen_V6"
+    else
+      _cleardomainconf Le_Listen_V6
+    fi
   fi
 
   if [ "$Le_ForceNewDomainKey" = "1" ]; then
@@ -8172,8 +8230,9 @@ Parameters:
   --ocsp, --ocsp-must-staple        Generate OCSP-Must-Staple extension.
   --always-force-new-domain-key     Generate new domain key on renewal. Otherwise, the domain key is not changed by default.
   --auto-upgrade [0|1]              Valid for '--upgrade' command, indicating whether to upgrade automatically in future. Defaults to 1 if argument is omitted.
-  --listen-v4                       Force standalone/tls server to listen at ipv4.
-  --listen-v6                       Force standalone/tls server to listen at ipv6.
+  --listen-v4                       Force standalone/tls server to listen at ipv4 only.
+                                      By default the standalone server listens on both ipv4 and ipv6.
+  --listen-v6                       Force standalone/tls server to listen at ipv6 only.
   --request-v4                      Force client requests to use ipv4 to connect to the CA server.
   --request-v6                      Force client requests to use ipv6 to connect to the CA server.
   --openssl-bin <file>              Specifies a custom openssl bin location.