windows: read the PATH env var of the child

The unix and windows process implementations diverge in their behavior
when dealing with subprocesses that are spawned with a relative path.
With unix the *child's* PATH environment variable is read, whereas
with windows the *parent's* environment variable is read.

This commit brings the two implementation in line with respect to
their behavior of reading PATH by having both read the *child's* PATH
environment variable. This involves looking into the user-provided
environment on windows and extracting the PATH variable specifically
so it can be inspected later on.

src/win/process.c

@@ -813,6 +813,20 @@ int make_program_env(char* env_block[], WCHAR** dst_ptr) {
   return 0;
 }
 
+/*
+ * Attempt to find the value of the PATH environment variable in the child's
+ * preprocessed environment.
+ *
+ * If found, a pointer into `env` is returned. If not found, NULL is returned.
+ */
+static WCHAR* find_path(WCHAR *env) {
+  for (; env != NULL && *env != 0; env += wcslen(env) + 1) {
+    if (wcsncmp(env, L"PATH=", 5) == 0)
+      return &env[5];
+  }
+
+  return NULL;
+}
 
 /*
  * Called on Windows thread-pool thread to indicate that
@@ -910,7 +924,7 @@ int uv_spawn(uv_loop_t* loop,
              const uv_process_options_t* options) {
   int i;
   int err = 0;
-  WCHAR* path = NULL;
+  WCHAR* path = NULL, *alloc_path = NULL;
   BOOL result;
   WCHAR* application_path = NULL, *application = NULL, *arguments = NULL,
          *env = NULL, *cwd = NULL;
@@ -984,7 +998,8 @@ int uv_spawn(uv_loop_t* loop,
   }
 
   /* Get PATH environment variable. */
-  {
+  path = find_path(env);
+  if (path == NULL) {
     DWORD path_len, r;
 
     path_len = GetEnvironmentVariableW(L"PATH", NULL, 0);
@@ -993,11 +1008,12 @@ int uv_spawn(uv_loop_t* loop,
       goto done;
     }
 
-    path = (WCHAR*) malloc(path_len * sizeof(WCHAR));
-    if (path == NULL) {
+    alloc_path = (WCHAR*) malloc(path_len * sizeof(WCHAR));
+    if (alloc_path == NULL) {
       err = ERROR_OUTOFMEMORY;
       goto done;
     }
+    path = alloc_path;
 
     r = GetEnvironmentVariableW(L"PATH", path, path_len);
     if (r == 0 || r >= path_len) {
@@ -1131,7 +1147,7 @@ int uv_spawn(uv_loop_t* loop,
   free(arguments);
   free(cwd);
   free(env);
-  free(path);
+  free(alloc_path);
 
   if (process->child_stdio_buffer != NULL) {
     /* Clean up child stdio handles. */

test/test-list.h

@@ -192,6 +192,7 @@ TEST_DECLARE   (spawn_stdout_to_file)
 TEST_DECLARE   (spawn_stdout_and_stderr_to_file)
 TEST_DECLARE   (spawn_auto_unref)
 TEST_DECLARE   (spawn_closed_process_io)
+TEST_DECLARE   (spawn_reads_child_path)
 TEST_DECLARE   (fs_poll)
 TEST_DECLARE   (fs_poll_getpath)
 TEST_DECLARE   (kill)
@@ -520,6 +521,7 @@ TASK_LIST_START
   TEST_ENTRY  (spawn_stdout_and_stderr_to_file)
   TEST_ENTRY  (spawn_auto_unref)
   TEST_ENTRY  (spawn_closed_process_io)
+  TEST_ENTRY  (spawn_reads_child_path)
   TEST_ENTRY  (fs_poll)
   TEST_ENTRY  (fs_poll_getpath)
   TEST_ENTRY  (kill)

test/test-spawn.c

@@ -1291,3 +1291,38 @@ TEST_IMPL(closed_fd_events) {
   return 0;
 }
 #endif  /* !_WIN32 */
+
+TEST_IMPL(spawn_reads_child_path) {
+  int r;
+  int len;
+  char path[1024];
+  char *env[2] = {path, NULL};
+
+  /* Set up the process, but make sure that the file to run is relative and */
+  /* requires a lookup into PATH */
+  init_process_options("spawn_helper1", exit_cb);
+  options.file = "run-tests";
+  args[0] = "run-tests";
+
+  /* Set up the PATH env variable */
+  for (len = strlen(exepath);
+       exepath[len - 1] != '/' && exepath[len - 1] != '\\';
+       len--);
+  exepath[len] = 0;
+  strcpy(path, "PATH=");
+  strcpy(path + 5, exepath);
+
+  options.env = env;
+
+  r = uv_spawn(uv_default_loop(), &process, &options);
+  ASSERT(r == 0);
+
+  r = uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+  ASSERT(r == 0);
+
+  ASSERT(exit_cb_called == 1);
+  ASSERT(close_cb_called == 1);
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}