fix loading of string content saved as binary

src/services/blob.js

@@ -1,5 +1,6 @@
 const becca = require('../becca/becca');
 const NotFoundError = require("../errors/not_found_error");
+const protectedSessionService = require("./protected_session");
 
 function getBlobPojo(entityName, entityId, opts = {}) {
     opts.preview = !!opts.preview;
@@ -10,19 +11,47 @@ function getBlobPojo(entityName, entityId, opts = {}) {
         throw new NotFoundError(`Entity ${entityName} '${entityId}' was not found.`);
     }
 
-    const blob = becca.getBlob(entity.blobId);
+    const blob = becca.getBlob(entity);
 
     const pojo = blob.getPojo();
 
     if (!entity.hasStringContent()) {
         pojo.content = null;
-    } else if (opts.preview && pojo.content.length > 10000) {
-        pojo.content = `${pojo.content.substr(0, 10000)}\r\n\r\n... and ${pojo.content.length - 10000} more characters.`;
+    } else {
+        pojo.content = processContent(pojo.content, entity.isProtected, true);
+
+        if (opts.preview && pojo.content.length > 10000) {
+            pojo.content = `${pojo.content.substr(0, 10000)}\r\n\r\n... and ${pojo.content.length - 10000} more characters.`;
+        }
     }
 
     return pojo;
 }
 
+function processContent(content, isProtected, isStringContent) {
+    if (isProtected) {
+        if (protectedSessionService.isProtectedSessionAvailable()) {
+            content = content === null ? null : protectedSessionService.decrypt(content);
+        } else {
+            content = "";
+        }
+    }
+
+    if (isStringContent) {
+        return content === null ? "" : content.toString("utf-8");
+    } else {
+        // see https://github.com/zadam/trilium/issues/3523
+        // IIRC a zero-sized buffer can be returned as null from the database
+        if (content === null) {
+            // this will force de/encryption
+            content = Buffer.alloc(0);
+        }
+
+        return content;
+    }
+}
+
 module.exports = {
-    getBlobPojo
+    getBlobPojo,
+    processContent
 };