Share Your Data Using Couchdb Replication

Experimental Feature

This feature may be removed or changed in the future. It might also have unhandled cases and cause corruption in your data. Be sure to backup your data constantly while using this.

Advanced Functionality

You're recommended to have some background knowledge about CouchDB before doing this.

Thanks to the power of CouchDB, sharing your whole database or parts of your data with another user can be easily done with CouchDB Replication, with the following use cases supported:

• Share items only in specific collections.

• Share items by custom rules.

• Share with read-only access.

• Share with read-write access.

However, it has the following limitations:

• One user must give their CouchDB database access to the other user, which means it's possible that a user can see or change everything in the other user's database.

• The people you shared your data with won't be able to change the Reference Number of your collection and items.

• If you set a Two-way Replication (Read-write Sharing), the person with whom you share your data with might be able to mess up with your unshared data if they know it's ID.

Prerequisite

Both you and the one you want to share data with must have CouchDB sync setup. The two CouchDB databases aren't required to be on the same server, but they should be reachable to one another.

Setup a One-way Replication - For Read-only Sharing

You'll need to create a replication document in the _replicator database on one of the servers. Here's a sample:

{
  "_id": "an_unique_id_for_your_replication",
  "source": {
    "url": "http://127.0.0.1:5984/soruce_database_name",
    "headers": {
      "Authorization": "Basic dXNlcm5hbWU6cGFzc3dvcmQ="
    }
  },
  "target": {
    "url": "https://127.0.0.1/target_database_name",
    "headers": {
      "Authorization": "Basic ZXhhbXBsZTpwYXNzd29yZA=="
    }
  },
  "continuous": true,
  "selector": {
    "type": { "$or": [{ "type": "collection" }, { "type": "item" }] }
  }
}

You can copy the JSON document above and paste it into the editor in http(s)://<your_couchdb_server>:<port>/_utils/#database/_replicator/_new (e.g. http://127.0.0.1:5984/_utils/#database/_replicator/_new).

Note that you'll need to change some of the fields in your document:

• _id: You can choose a recognizable ID for your replication. It should be unique.

• source: Set the connection of the source database, i.e., the database storing the items to be shared.

  • For the Authorization field, encode the username and password as username:password with Base64. For example, by running print -n 'example:password' | base64 in *nix.

• target: Set the connection of the target database, i.e., the database that you want to share the items with.

• selector: Use this to share every collection and item or specific collections and items. See examples below. This MUST be set to at least { "$or": [{ "type": "collection" }, { "type": "item" }] } to prevent overwriting everything in the target database. For more info, see https://docs.couchdb.org/en/stable/api/database/find.html#selector-syntax.

For more info, see https://docs.couchdb.org/en/stable/json-structure.html#replication-settings.

After saving the replication, you can see its status at http(s)://<your_couchdb_server>:<port>/_utils/#/replication (e.g. http://127.0.0.1:5984/_utils/#/replication).

Selector Examples

Replicate every collection and item

{ "$or": [{ "type": "collection" }, { "type": "item" }] }

Replicate specific collections, and items in those collecitons

{
  "$or": [
    {
      "type": "collection",
      "_id": {
        "$in": [
          "collection-<collection_id_1>",
          "collection-<collection_id_2>"
        ]
      }
    },
    {
      "type": "item",
      "data.collection_id": {
        "$in": [
          "<collection_id_1>",
          "<collection_id_2>"
        ]
      }
    },
    {
      "type": "item_image",
      "data._item_collection_id": {
        "$in": [
          "<collection_id_1>",
          "<collection_id_2>"
        ]
      }
    },
    {
      "type": "image",
      "data._item_collection_ids": {
        "$elemMatch": {
          "$in": [
            "<collection_id_1>",
            "<collection_id_2>"
          ]
        }
      }
    }
  ]
}

Note that you'll need to include the collection- prefix in the collection IDs under "type": "collection".

https://docs.couchdb.org/en/stable/replication/intro.html#controlling-which-documents-to-replicate asdf

Setup a Two-way Replication - For Read-write Sharing

1. Create a replication document the same as Setup a One-way Replication.
2. Create another replication document with the same content as step 1 but with the source and target databases swapped.

3. Ask the person you want to share data with for their Configuration UUID. The Configuration UUID can be found in the app (More -> Settings -> Configurations).

4. Create a document in your source database with _id set to db_sharing-<your_config_uuid>--<their_config_uuid>, as follows:

{
  "_id": "db_sharing-<your_config_uuid>--<their_config_uuid>",
  "data": {
    "permissions": ["read", "write"]
  }
}

Note: This document will not actually permit one to write into your database. It will just unblock the UI for editing.

1. Edit the replication document you created on step 1, and add the ID of step 4 to the selector section. For example:

   "selector": {
     "$or": [
+      { "_id": "db_sharing-<your_config_uuid>--<their_config_uuid>" },
       {
         "type": "collection",
         "_id": {
           "$in": ["collection-..."]
         }
       },
       {
         "type": "item",
         "data.collection_id": {
           "$in": ["..."]
         }
       }
     ]
   },

How to stop sharing?

1. Delete the db_sharing-<your_config_uuid>--<their_config_uuid> document in your database, if you had created one.

2. Remove the corresponding replications from the _replicator database.

3. Optionally, ask the person you shared data with to purge the documents that came from your database from their own database. Note: do not use delete, since the deletion will be replicated back to your database if you do replication from their database again.

Troubleshooting

Got error Save failed: Document update conflict. on creating a new replication document

Check if you have the _rev field in your new replication document. If so, delete it.