Windows async - handle trailing junk output (#85820)

Add handling for when a PowerShell module emits more than just the
module result JSON. The behaviour reflects the Python async wrapper
where trailing data after the module result will emit a warning.

changelogs/fragments/win_async-junk-output.yml

@@ -0,0 +1,3 @@
+bugfixes:
+  - >-
+    Windows async - Handle running PowerShell modules with trailing data after the module result

lib/ansible/executor/powershell/async_watchdog.ps1

@@ -67,14 +67,34 @@ try {
     $result.finished = $true
 
     if ($jobAsyncResult.IsCompleted) {
-        $jobOutput = $ps.EndInvoke($jobAsyncResult)
+        $jobOutput = @($ps.EndInvoke($jobAsyncResult) | Out-String) -join "`n"
         $jobError = $ps.Streams.Error
 
         # write success/output/error to result object
-        # TODO: cleanse leading/trailing junk
-        $moduleResult = $jobOutput | ConvertFrom-Json | Convert-JsonObject
+        $moduleResultJson = $jobOutput
+        $startJsonChar = $moduleResultJson.IndexOf([char]'{')
+        if ($startJsonChar -eq -1) {
+            throw "No start of json char found in module result"
+        }
+        $moduleResultJson = $moduleResultJson.Substring($startJsonChar)
+
+        $endJsonChar = $moduleResultJson.LastIndexOf([char]'}')
+        if ($endJsonChar -eq -1) {
+            throw "No end of json char found in module result"
+        }
+
+        $trailingJunk = $moduleResultJson.Substring($endJsonChar + 1).Trim()
+        $moduleResultJson = $moduleResultJson.Substring(0, $endJsonChar + 1)
+        $moduleResult = $moduleResultJson | ConvertFrom-Json | Convert-JsonObject
         # TODO: check for conflicting keys
         $result = $result + $moduleResult
+
+        if ($trailingJunk) {
+            if (-not $result.warnings) {
+                $result.warnings = @()
+            }
+            $result.warnings += "Module invocation had junk after the JSON data: $trailingJunk"
+        }
     }
     else {
         # We can't call Stop() as pwsh won't respond if it is busy calling a .NET
@@ -103,7 +123,7 @@ catch {
     $result.failed = $true
     $result.msg = "failure during async watchdog: $_"
     # return output back, if available, to Ansible to help with debugging errors
-    $result.stdout = $jobOutput | Out-String
+    $result.stdout = $jobOutput
     $result.stderr = $jobError | Out-String
 }
 finally {

test/integration/targets/win_async_wrapper/library/trailing_output.ps1

@@ -0,0 +1,6 @@
+#!powershell
+
+#AnsibleRequires -Wrapper
+
+[Console]::Out.WriteLine('{"changed": false, "test": 123}')
+'trailing junk after module result'

test/integration/targets/win_async_wrapper/tasks/main.yml

@@ -206,6 +206,21 @@
     - not success_async_custom_dir_poll.failed
     - success_async_custom_dir_poll.results_file == win_output_dir + '\\' + async_custom_dir_poll.ansible_job_id
 
+- name: test async with trailing output
+  trailing_output:
+  async: 10
+  poll: 1
+  register: async_trailing_output
+
+- name: assert test async with trailing output
+  assert:
+    that:
+    - async_trailing_output is not changed
+    - async_trailing_output.test == 123
+    - async_trailing_output.warnings | count == 1
+    - >-
+      async_trailing_output.warnings[0] is search('Module invocation had junk after the JSON data: trailing junk after module result')
+
 # FUTURE: figure out why the last iteration of this test often fails on shippable
 #- name: loop async success
 #  async_test: