unix: do not set environ unless one is provided

Currently, `uv_spawn` will set `environ` to the value of `options.env`, even if
`options.env` is `NULL`.  This results in child processes for whom `environ ==
NULL`, which can cause a variety of unexpected issues.

This is a back-port of commit 1d85815 from the master branch.

src/unix/process.c

@@ -260,7 +260,9 @@ static void uv__process_child_init(uv_process_options_t options,
     _exit(127);
   }
 
-  environ = options.env;
+  if (options.env) {
+    environ = options.env;
+  }
 
   execvp(options.file, options.args);
   perror("execvp()");

test/run-tests.c

@@ -134,5 +134,18 @@ static int maybe_run_test(int argc, char **argv) {
     return 1;
   }
 
+  if (strcmp(argv[1], "spawn_helper7") == 0) {
+    int r;
+    char *test;
+    /* Test if the test value from the parent is still set */
+    test = getenv("ENV_TEST");
+    ASSERT(test != NULL);
+
+    r = fprintf(stdout, "%s", test);
+    ASSERT(r > 0);
+
+    return 1;
+  }
+
   return run_test(argv[1], TEST_TIMEOUT, 0);
 }

test/test-list.h

@@ -133,6 +133,7 @@ TEST_DECLARE   (spawn_and_kill)
 TEST_DECLARE   (spawn_detached)
 TEST_DECLARE   (spawn_and_kill_with_std)
 TEST_DECLARE   (spawn_and_ping)
+TEST_DECLARE   (spawn_preserve_env)
 TEST_DECLARE   (spawn_setuid_fails)
 TEST_DECLARE   (spawn_setgid_fails)
 TEST_DECLARE   (spawn_stdout_to_file)
@@ -362,6 +363,7 @@ TASK_LIST_START
   TEST_ENTRY  (spawn_detached)
   TEST_ENTRY  (spawn_and_kill_with_std)
   TEST_ENTRY  (spawn_and_ping)
+  TEST_ENTRY  (spawn_preserve_env)
   TEST_ENTRY  (spawn_setuid_fails)
   TEST_ENTRY  (spawn_setgid_fails)
   TEST_ENTRY  (spawn_stdout_to_file)

test/test-spawn.c

@@ -373,6 +373,44 @@ TEST_IMPL(spawn_and_kill) {
   return 0;
 }
 
+
+TEST_IMPL(spawn_preserve_env) {
+  int r;
+  uv_pipe_t out;
+  uv_stdio_container_t stdio[2];
+
+  init_process_options("spawn_helper7", exit_cb);
+
+  uv_pipe_init(uv_default_loop(), &out, 0);
+  options.stdio = stdio;
+  options.stdio[0].flags = UV_IGNORE;
+  options.stdio[1].flags = UV_CREATE_PIPE | UV_WRITABLE_PIPE;
+  options.stdio[1].data.stream = (uv_stream_t*) &out;
+  options.stdio_count = 2;
+
+  ASSERT(setenv("ENV_TEST", "testval", 1) == 0);
+  /* Explicitly set options.env to NULL to test for env clobbering. */
+  options.env = NULL;
+
+  r = uv_spawn(uv_default_loop(), &process, options);
+  ASSERT(r == 0);
+
+  r = uv_read_start((uv_stream_t*) &out, on_alloc, on_read);
+  ASSERT(r == 0);
+
+  r = uv_run(uv_default_loop());
+  ASSERT(r == 0);
+
+  ASSERT(exit_cb_called == 1);
+  ASSERT(close_cb_called == 2);
+
+  printf("output is: %s", output);
+  ASSERT(strcmp("testval", output) == 0);
+
+  return 0;
+}
+
+
 TEST_IMPL(spawn_detached) {
   int r;
   uv_err_t err;