core: Handle net::* errors as Fetch errors

  When making some network requests, we can encounter network errors
  that are not of the `FetchError` type but are `net` system errors
  (with error codes starting with `net::`).
  For example, when switching from one network to another during a file
  download from the Cozy, the downloading stream will throw an error
  with the `net::ERR_NETWORKD_CHANGED` code.

  We want to handle these errors as `FetchError` errors and can do do so
  by simply looking for the `net::` string in the error message.

core/remote/errors.js

@@ -188,7 +188,7 @@ const wrapError = (
   err /*: FetchError |  Error */,
   doc /*: ?SavedMetadata */
 ) /*: RemoteError */ => {
-  if (err.name === 'FetchError') {
+  if (isNetworkError(err)) {
     // $FlowFixMe FetchErrors missing status will fallback to the default case
     const { status } = err
 
@@ -379,6 +379,13 @@ function detail(err /*: FetchError */) /*: ?string */ {
   return detail
 }
 
+function isNetworkError(err /*: Error */) {
+  return (
+    err.name === 'FetchError' ||
+    (typeof err.message === 'string' && err.message.includes('net::'))
+  )
+}
+
 module.exports = {
   CozyDocumentMissingError,
   DirectoryNotFound,
@@ -405,5 +412,6 @@ module.exports = {
   UNKNOWN_REMOTE_ERROR_CODE,
   UNREACHABLE_COZY_CODE,
   USER_ACTION_REQUIRED_CODE,
+  isNetworkError,
   wrapError
 }

core/sync/errors.js

@@ -295,10 +295,10 @@ const wrapError = (
     return new SyncError({ sideName, err, code: INCOMPATIBLE_DOC_CODE, doc })
   } else if (err instanceof remoteErrors.ExcludedDirError) {
     return new SyncError({ sideName, err, code: EXCLUDED_DIR_CODE, doc })
-  } else if (sideName === 'remote' || err.name === 'FetchError') {
+  } else if (remoteErrors.isNetworkError(err)) {
     // FetchErrors can be raised from the LocalWriter when failing to download a
-    // file for example. In this case the sideName will be "local" but the error
-    // name will still be "FetchError".
+    // file for example. In this case the error name won't be "FetchError" but
+    // its message will still contain `net::`.
     // If err is a RemoteError, its code will be reused.
     return new SyncError({
       sideName,

test/unit/remote/errors.js

@@ -0,0 +1,18 @@
+/* eslint-env mocha */
+/* @flow */
+
+const should = require('should')
+
+const remoteErrors = require('../../../core/remote/errors')
+
+describe('Remote.wrapError', () => {
+  it('returns an UnreachableCozy error for net::ERR_NETWORKD_CHANGED errors', () => {
+    const netErr = new Error(
+      'Failed request, reason: net::ERR_NETWORKD_CHANGED'
+    )
+    should(remoteErrors.wrapError(netErr)).have.property(
+      'code',
+      remoteErrors.UNREACHABLE_COZY_CODE
+    )
+  })
+})

test/unit/sync/errors.js

@@ -0,0 +1,19 @@
+/* eslint-env mocha */
+/* @flow */
+
+const should = require('should')
+
+const remoteErrors = require('../../../core/remote/errors')
+const syncErrors = require('../../../core/sync/errors')
+
+describe('Sync.wrapError', () => {
+  it('returns an UnreachableCozy error for net::ERR_NETWORKD_CHANGED errors', () => {
+    const netErr = new Error(
+      'Failed request, reason: net::ERR_NETWORKD_CHANGED'
+    )
+    should(syncErrors.wrapError(netErr, 'local')).have.property(
+      'code',
+      remoteErrors.UNREACHABLE_COZY_CODE
+    )
+  })
+})