feat: replace base64url with percent encoding

Author: git-developer

README.md

@@ -104,29 +104,30 @@ The following values are used in the examples:
   ```
 
 #### Send a text message to a group
-* Topic: `<TOPIC_PREFIX>/<MQTT_SUBSCRIBE_TOPIC>/group/<BASE64URL_ENCODED_GROUP_ID>`
-* Note: The group id (which is `base64` encoded) must be converted to `base64url` encoding
-  by applying the following replacements:
-  - `+` (plus) becomes `-` (minus)
-  - `/` (slash) becomes `_` (underscore)
+* Topic: `<TOPIC_PREFIX>/<MQTT_SUBSCRIBE_TOPIC>/group/<PERCENT_ENCODED_GROUP_ID>`
+* Note: The group-id must be percent-encoded.
+  A group-id (which is base64 encoded) may be converted to percent encoding by applying the following replacements:
+  - `+` (plus) becomes `%2B`
+  - `/` (slash) becomes `%2F`
+  - `=` (equals) becomes `%3D`
 * Example:
   ```sh
-  $ mosquitto_pub -h broker -t signal/send/group/LS0-YWRtaW5zPz8_Cg== -m 'Outgoing message'
+  $ mosquitto_pub -h broker -t signal/send/group/LS0%2BYWRtaW5zPz8%2FCg%3D%3D -m 'Outgoing message'
   ```
   The text _Outgoing message_ is sent to the group _Admins_.
 
 #### Receive a text message from a group
-* Topic: `<TOPIC_PREFIX>/<MQTT_PUBLISH_TOPIC>/<PHONE_NUMBER_WITHOUT_LEADING_PLUS>/timestamp/<TIMESTAMP>/group/<BASE64URL_ENCODED_GROUP_ID>`
-* Note: The last segment of the topic is `base64url` encoded.
-  To retrieve the group id, it must be converted to `base64` encoding
-  by applying the following replacements:
-  - `-` (minus) becomes `+` (plus)
-  - `_` (underscore) becomes `/` (slash)
+* Topic: `<TOPIC_PREFIX>/<MQTT_PUBLISH_TOPIC>/<PHONE_NUMBER_WITHOUT_LEADING_PLUS>/timestamp/<TIMESTAMP>/group/<PERCENT_ENCODED_GROUP_ID>`
+* Note: The last segment of the topic is percent-encoded.
+  It may be converted into a (base64 encoded) group-id by applying the following replacements:
+  - `%2B` becomes `+` (plus)
+  - `%2F` becomes `/` (slash)
+  - `%3D` becomes `=` (equals)
 * Example:
   The text _Incoming message_ is sent from the phone to the group _Admins_.
   ```sh
   $ mosquitto_sub -v -h broker -t signal/#
-  signal/receive/491713920000/timestamp/1577882096000/group/LS0-YWRtaW5zPz8_Cg== Incoming message
+  signal/receive/491713920000/timestamp/1577882096000/group/LS0%2BYWRtaW5zPz8%2FCg%3D%3D Incoming message
   ```
 
 #### Receive a quotation message

image/signal-mqtt

@@ -45,31 +45,26 @@ _build_json_send() {
   '{jsonrpc:"2.0", method:"send", params:{($name):$value, message:$message}}'
 }
 
-#
-# base64url encoding is required when a base64-encoded string
-# (e.g. group-id) is used as part of an mqtt topic.
-#
-
 #######################################
-# Convert a text from base64 to base64url.
+# Encode a text to percent-encoding.
 # Arguments:
-#   1: Text in base64 encoding
+#   1: Text
 # Outputs:
-#   Text in base64url encoding
+#   Text in percent-encoding
 #######################################
-_to_base64url() {
-  printf '%s' "${1}" | tr '/+' '_-'
+percent_encode() {
+  printf '%s' "${1}" | jq -sRr @uri
 }
 
 #######################################
-# Convert a text from base64url to base64.
+# Decode a text from percent-encoding.
 # Arguments:
-#   1: Text in base64url encoding
+#   1: Text in percent-encoding
 # Outputs:
-#   Text in base64 encoding
+#   Decoded Text
 #######################################
-_from_base64url() {
-  printf '%s' "${1}" | tr '_-' '/+'
+percent_decode() {
+  printf '%s' "${1}" | printf '%b\n' "$(sed -E -e 's/\+/ /g' -e 's/%([0-9a-fA-F]{2})/\\x\1/g')"
 }
 
 #######################################
@@ -121,7 +116,7 @@ mqtt_publish() {
               topic="${topic}/timestamp/${timestamp}"
             fi
             if [ "${group_id}" ]; then
-              topic="${topic}/group/$(_to_base64url "${group_id}")"
+              topic="${topic}/group/$(percent_encode "${group_id}")"
             fi
             if [ "${quote_timestamp}" ]; then
               topic="${topic}/quote/${quote_timestamp}"
@@ -150,7 +145,7 @@ mqtt_subscribe() {
     case "${topic}" in
       "${MQTT_SUBSCRIBE_TOPIC}") printf '%s\n' "${payload}" ;;
       "${MQTT_SUBSCRIBE_TOPIC}"/group/*)
-        _build_json_send "${payload}" groupId "$(_from_base64url "${topic##*/}")"
+        _build_json_send "${payload}" groupId "$(percent_decode "${topic##*/}")"
         ;;
       "${MQTT_SUBSCRIBE_TOPIC}"/*)
         _build_json_send "${payload}" recipient "+${topic##*/}"