pluginfw: Export .etherpad hooks (#4466)

* export support

* proper prefix

* just a basic example, needs working on still

* docs

* comments shouldnt be hard coded

doc/api/hooks_server-side.md

@@ -751,6 +751,21 @@ exports.exportHtmlAdditionalTagsWithData = function(hook, pad, cb){
 };
 ```
 
+## exportEtherpadAdditionalContent
+Called from src/node/utils/ExportEtherpad.js and src/node/utils/ImportEtherpad.js
+
+Things in context:
+
+Useful for exporting and importing non-pad centric data stored about a pad.  For example in ep_comments_page the comments are stored as comments:padId:uniqueIdOfComment and as such when you export .etherpad this data is not included.
+
+Example:
+```
+// Add support for exporting comments metadata
+exports.exportEtherpadAdditionalContent = function(hook_name, context, callback){
+  return callback(["comments"]);
+};
+```
+
 ## userLeave
 Called from src/node/handler/PadMessageHandler.js
 

src/node/utils/ExportEtherpad.js

@@ -16,6 +16,7 @@
 
 
 let db = require("../db/DB");
+let hooks = require('ep_etherpad-lite/static/js/pluginfw/hooks');
 
 exports.getPadRaw = async function(padId) {
 
@@ -58,5 +59,17 @@ exports.getPadRaw = async function(padId) {
     }
   }
 
+  await Promise.all([
+    // get content that has a different prefix IE comments:padId:foo
+    // a plugin would return something likle ["comments", "cakes"]
+    hooks.aCallAll('exportEtherpadAdditionalContent').then((prefixes) => {
+      prefixes.forEach(async function(prefix) {
+        let pluginContent = await db.get(prefix + ":" + padId);
+        data[prefix + ":" + padId] = pluginContent;
+      });
+    })
+  ]);
+
+
   return data;
 }

src/node/utils/ImportEtherpad.js

@@ -16,6 +16,7 @@
 
 var log4js = require('log4js');
 const db = require("../db/DB");
+const hooks = require('ep_etherpad-lite/static/js/pluginfw/hooks');
 
 exports.setPadRaw = function(padId, records)
 {
@@ -62,6 +63,19 @@ exports.setPadRaw = function(padId, records)
         // and create the value
         newKey = oldPadId.join(":"); // create the new key
       }
+
+      // is this a key that is supported through a plugin?
+      await Promise.all([
+        // get content that has a different prefix IE comments:padId:foo
+        // a plugin would return something likle ["comments", "cakes"]
+        hooks.aCallAll('exportEtherpadAdditionalContent').then((prefixes) => {
+          prefixes.forEach(async function(prefix) {
+            if(key.split(":")[0] === prefix){
+              newKey = prefix + ":" + padId;
+            }
+          });
+        })
+      ]);
     }
 
     // Write the value to the server