ash: fix 'read' shell built-in (1)

Consider this test case:

   { echo -n te; sleep 3; echo st; } | (read -t 1 x; echo "$x")

- bash echoes "te" after 1 second.

- Upstream BusyBox echoes an empty "$x" after 1 second.

- busybox-w32 echoes an empty "$x" after 3 seconds.

The delayed echo in busybox-w32 arises because the 'read' shell
built-in omits the code to poll for input.

Rearrange the code so that polling takes place.  This doesn't address
the difference between BusyBox and bash.

Costs 48-64 bytes.

1 files changed, 7 insertions, 16 deletions

diff --git a/shell/shell_common.c b/shell/shell_common.c
index 99e56a050..657ee9969 100644
--- a/shell/shell_common.c
+++ b/shell/shell_common.c
@@ -195,7 +195,6 @@ shell_builtin_read(struct builtin_read_params *params)
                         }
                 }
 
-#if !ENABLE_PLATFORM_MINGW32
                 /* We must poll even if timeout is -1:
                  * we want to be interrupted if signal arrives,
                  * regardless of SA_RESTART-ness of that signal!
@@ -209,13 +208,7 @@ shell_builtin_read(struct builtin_read_params *params)
                         retval = (const char *)(uintptr_t)1;
                         goto ret;
                 }
-                if (read(fd, &buffer[bufpos], 1) != 1) {
-                        err = errno;
-                        retval = (const char *)(uintptr_t)1;
-                        break;
-                }
-#else
-                errno = 0;
+#if ENABLE_PLATFORM_MINGW32
                 if (isatty(fd)) {
                         int64_t key;
 
@@ -245,15 +238,13 @@ shell_builtin_read(struct builtin_read_params *params)
                                 /* echo input if not in silent mode */
                                 console_write(buffer + bufpos, 1);
                         }
-                }
-                else {
-                        if (read(fd, &buffer[bufpos], 1) != 1) {
-                                err = errno;
-                                retval = (const char *)(uintptr_t)1;
-                                break;
-                        }
-                }
+                } else
 #endif
+                if (read(fd, &buffer[bufpos], 1) != 1) {
+                        err = errno;
+                        retval = (const char *)(uintptr_t)1;
+                        break;
+                }
 
                 c = buffer[bufpos];
 #if ENABLE_PLATFORM_MINGW32