fix: make port transferables unique

packages/ipfs-message-port-client/README.md

@@ -102,7 +102,7 @@ values instead of copying.
 
 > **Note:** Transferring data will empty it on the sender side which can lead to
 > errors if that data is used again later. To avoid these errors transfer option
-> was added so user can explicitily give up reference when it is safe to do so.
+> was added so user can explicitly give up reference when it is safe to do so.
 
 ```js
 /**
@@ -115,7 +115,7 @@ const example = async (data) => {
 }
 ```
 
-It is however recommended to prefer web native [Blob][] / [File][] intances as
+It is however recommended to prefer web native [Blob][] / [File][] instances as
 most web APIs provide them as option & can be send across without copying
 underlying memory.
 

packages/ipfs-message-port-client/src/client/transport.js

@@ -178,7 +178,7 @@ module.exports = class MessageTransport {
         input: query.toJSON()
       },
       // @ts-ignore - TS seems to want second arg to postMessage to not be undefined
-      query.transfer()
+      [...new Set(query.transfer() || [])]
     )
   }
 

packages/ipfs-message-port-protocol/src/core.js

@@ -197,7 +197,7 @@ const decodeCallback = ({ port }) => {
    * @returns {void}
    */
   const callback = (args, transfer = []) => {
-    port.postMessage(args, transfer)
+    port.postMessage(args, [...new Set(transfer)])
   }
 
   return callback

packages/ipfs-message-port-server/package.json

@@ -50,6 +50,7 @@
   "devDependencies": {
     "@types/it-all": "^1.0.0",
     "aegir": "^28.2.0",
+    "cids": "^1.0.0",
     "rimraf": "^3.0.2",
     "typescript": "4.0.x"
   },

packages/ipfs-message-port-server/src/server.js

@@ -212,9 +212,12 @@ exports.Server = class Server {
     if (!query.signal.aborted) {
       try {
         const value = await query.result
+        const transfer = [...new Set(value.transfer || [])]
+        delete value.transfer
+
         port.postMessage(
           { type: 'result', id, result: { ok: true, value } },
-          value.transfer || []
+          transfer
         )
       } catch (error) {
         port.postMessage({

packages/ipfs-message-port-server/test/transfer.spec.js

@@ -0,0 +1,46 @@
+'use strict'
+
+/* eslint-env mocha */
+const { encodeCID } = require('ipfs-message-port-protocol/src/cid')
+const { expect } = require('aegir/utils/chai')
+
+const CID = require('cids')
+const { Query, Server } = require('../src/server')
+const { IPFSService } = require('../src/index')
+
+describe('Server', function () {
+  this.timeout(10 * 1000)
+
+  it('should be able to transfer multiple of the same CID instances', () => {
+    const cid = new CID("QmSnuWmxptJZdLJpKRarxBMS2Ju2oANVrgbr2xWbie9b2D")
+
+    return new Promise((resolve, reject) => {
+      const channel = process.browser
+        ? new MessageChannel()
+        : new (require('worker_threads').MessageChannel)()
+
+      channel.port1.onmessageerror = reject
+      channel.port1.onmessage = event => {
+        const result = event.data.result
+        result.ok ? resolve(result.value) : reject(new Error(result.error.message))
+      }
+
+      const service = new IPFSService()
+      const server = new Server(service)
+      const transfer = []
+
+      server.run = a => a
+      server.handleQuery(
+        "",
+        {
+          result: {
+            value: [ encodeCID(cid, transfer), encodeCID(cid, transfer) ],
+            transfer: transfer
+          },
+          signal: { aborted: false }
+        },
+        channel.port2
+      )
+    })
+  })
+})