[dnsapi] Support adding / removing multiple TXT values for Gandi

Gandi supports setting multiple entries by setting multiple array items
for the rrset_values field in their API. Modify the dns_gandi_livedns.sh
script so that it checks for existing entries, appends new ones if
needed, and removes existing ones individually. This enabled wildcard
certificate support on Gandi.

Fixes the dns_gandi_livedns part of #1261.

Tested for creating a multidomain, multiple wild-card certificate on
Gandi and using a test script executing only the dns_gandi_livedns_add
and dns_gandi_livedns_rm functions.

dnsapi/dns_gandi_livedns.sh

@@ -7,6 +7,7 @@
 # Requires GANDI API KEY set in GANDI_LIVEDNS_KEY set as environment variable
 #
 #Author: Frédéric Crozat <fcrozat@suse.com>
+#        Dominik Röttsches <drott@google.com>
 #Report Bugs here: https://github.com/fcrozat/acme.sh
 #
 ########  Public functions #####################
@@ -36,9 +37,7 @@ dns_gandi_livedns_add() {
   _debug domain "$_domain"
   _debug sub_domain "$_sub_domain"
 
-  _gandi_livedns_rest PUT "domains/$_domain/records/$_sub_domain/TXT" "{\"rrset_ttl\": 300, \"rrset_values\":[\"$txtvalue\"]}" \
-    && _contains "$response" '{"message": "DNS Record Created"}' \
-    && _info "Add $(__green "success")"
+  _dns_gandi_append_record "$_domain" "$_sub_domain" "$txtvalue"
 }
 
 #Usage: fulldomain txtvalue
@@ -56,9 +55,23 @@ dns_gandi_livedns_rm() {
   _debug fulldomain "$fulldomain"
   _debug domain "$_domain"
   _debug sub_domain "$_sub_domain"
+  _debug txtvalue "$txtvalue"
 
-  _gandi_livedns_rest DELETE "domains/$_domain/records/$_sub_domain/TXT" ""
-
+  if ! _dns_gandi_existing_rrset_values "$_domain" "$_sub_domain"; then
+    return 1
+  fi
+  _new_rrset_values=$(echo "$_rrset_values" | sed "s/...$txtvalue...//g")
+  # Cleanup dangling commata.
+  _new_rrset_values=$(echo "$_new_rrset_values" | sed "s/, ,/ ,/g")
+  _new_rrset_values=$(echo "$_new_rrset_values" | sed "s/, *\]/\]/g")
+  _new_rrset_values=$(echo "$_new_rrset_values" | sed "s/\[ *,/\[/g")
+  _debug "New rrset_values" "$_new_rrset_values"
+
+  _gandi_livedns_rest PUT \
+    "domains/$_domain/records/$_sub_domain/TXT" \
+    "{\"rrset_ttl\": 300, \"rrset_values\": $_new_rrset_values}" \
+    && _contains "$response" '{"message": "DNS Record Created"}' \
+    && _info "Removing record $(__green "success")"
 }
 
 ####################  Private functions below ##################################
@@ -98,6 +111,45 @@ _get_root() {
   return 1
 }
 
+_dns_gandi_append_record() {
+  domain=$1
+  sub_domain=$2
+  txtvalue=$3
+
+  if _dns_gandi_existing_rrset_values "$domain" "$sub_domain"; then
+    _debug "Appending new value"
+    _rrset_values=$(echo "$_rrset_values" | sed "s/\"]/\",\"$txtvalue\"]/")
+  else
+    _debug "Creating new record" "$_rrset_values"
+    _rrset_values="[\"$txtvalue\"]"
+  fi
+  _debug new_rrset_values "$_rrset_values"
+  _gandi_livedns_rest PUT "domains/$_domain/records/$sub_domain/TXT" \
+    "{\"rrset_ttl\": 300, \"rrset_values\": $_rrset_values}" \
+    && _contains "$response" '{"message": "DNS Record Created"}' \
+    && _info "Adding record $(__green "success")"
+}
+
+_dns_gandi_existing_rrset_values() {
+  domain=$1
+  sub_domain=$2
+  if ! _gandi_livedns_rest GET "domains/$domain/records/$sub_domain"; then
+    return 1
+  fi
+  if ! _contains "$response" '"rrset_type": "TXT"'; then
+    _debug "Does not have a _acme-challenge TXT record yet."
+    return 1
+  fi
+  if _contains "$response" '"rrset_values": \[\]'; then
+    _debug "Empty rrset_values for TXT record, no previous TXT record."
+    return 1
+  fi
+  _debug "Already has TXT record."
+  _rrset_values=$(echo "$response" | _egrep_o 'rrset_values.*\[.*\]' \
+    | _egrep_o '\[".*\"]')
+  return 0
+}
+
 _gandi_livedns_rest() {
   m=$1
   ep="$2"