Bug 1696531 - [xpcshell] Fix some py3 related issues in toolkit/modules/subprocess/test/xpcshell/test_subprocess.js, r=bhearsum

Depends on D110546

Differential Revision: https://phabricator.services.mozilla.com/D109730

toolkit/modules/subprocess/test/xpcshell/data_test_script.py

@@ -1,5 +1,4 @@
-#!/usr/bin/env python2
-from __future__ import print_function
+#!/usr/bin/env python3
 
 import os
 import signal
@@ -7,15 +6,18 @@ import struct
 import sys
 
 
-def output(line):
-    sys.stdout.write(struct.pack("@I", len(line)))
-    sys.stdout.write(line)
-    sys.stdout.flush()
+def output(line, stream=sys.stdout, print_only=False):
+    if isinstance(line, str):
+        line = line.encode("utf-8", "surrogateescape")
+    if not print_only:
+        stream.buffer.write(struct.pack("@I", len(line)))
+    stream.buffer.write(line)
+    stream.flush()
 
 
 def echo_loop():
     while True:
-        line = sys.stdin.readline()
+        line = sys.stdin.buffer.readline()
         if not line:
             break
 
@@ -53,5 +55,5 @@ elif cmd == "ignore_sigterm":
 
             time.sleep(3600)
 elif cmd == "print":
-    sys.stdout.write(sys.argv[2])
-    sys.stderr.write(sys.argv[3])
+    output(sys.argv[2], stream=sys.stdout, print_only=True)
+    output(sys.argv[3], stream=sys.stderr, print_only=True)

toolkit/modules/subprocess/test/xpcshell/test_subprocess.js

@@ -693,6 +693,7 @@ add_task(async function test_subprocess_environment() {
     Object.assign(environment, {
       PATH: env.get("PATH"),
       PATHEXT: env.get("PATHEXT"),
+      SYSTEMROOT: env.get("SYSTEMROOT"),
     });
   }