Fix struct.pack with padding bytes

tannewt · tannewt · commit 5ccd5dc08b59 · 2021-04-16T12:39:23.000-07:00
It used to validate the following arg could fit in a single byte.
Now, it always uses zero to pad.
diff --git a/py/binary.c b/py/binary.c
@@ -371,11 +371,7 @@ void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte **
         }
     }
 
-    if (val_type == 'x') {
-        memset(p, 0, 1);
-    } else {
-        mp_binary_set_int(MIN((size_t)size, sizeof(val)), struct_type == '>', p, val);
-    }
+    mp_binary_set_int(MIN((size_t)size, sizeof(val)), struct_type == '>', p, val);
 }
 
 void mp_binary_set_val_array(char typecode, void *p, mp_uint_t index, mp_obj_t val_in) {
diff --git a/shared-module/struct/__init__.c b/shared-module/struct/__init__.c
@@ -153,9 +153,11 @@ void shared_modules_struct_pack_into(mp_obj_t fmt_in, byte *p, byte *end_p, size
             p += sz;
         } else {
             while (sz--) {
-                mp_binary_set_val(fmt_type, *fmt, args[i], &p);
                 // Pad bytes don't have a corresponding argument.
-                if (*fmt != 'x') {
+                if (*fmt == 'x') {
+                    mp_binary_set_val(fmt_type, *fmt, MP_OBJ_NEW_SMALL_INT(0), &p);
+                } else {
+                    mp_binary_set_val(fmt_type, *fmt, args[i], &p);
                     i++;
                 }
             }
diff --git a/tests/basics/struct1.py b/tests/basics/struct1.py
@@ -121,3 +121,5 @@
 
 # check padding bytes
 print(struct.pack("xb", 3))
+# Make sure pack doesn't reuse a larger value and error
+print(struct.pack("xH", 0x100))

Original file line number	Diff line number	Diff line change
`@@ -371,11 +371,7 @@ void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte **`
`371`	`371`	`}`
`372`	`372`	`}`
`373`	`373`
`374`		`- if (val_type == 'x') {`
`375`		`- memset(p, 0, 1);`
`376`		`- } else {`
`377`		`- mp_binary_set_int(MIN((size_t)size, sizeof(val)), struct_type == '>', p, val);`
`378`		`- }`
	`374`	`+ mp_binary_set_int(MIN((size_t)size, sizeof(val)), struct_type == '>', p, val);`
`379`	`375`	`}`
`380`	`376`
`381`	`377`	`void mp_binary_set_val_array(char typecode, void *p, mp_uint_t index, mp_obj_t val_in) {`
Original file line number	Diff line number	Diff line change
`@@ -153,9 +153,11 @@ void shared_modules_struct_pack_into(mp_obj_t fmt_in, byte p, byte end_p, size`
`153`	`153`	`p += sz;`
`154`	`154`	`} else {`
`155`	`155`	`while (sz--) {`
`156`		`- mp_binary_set_val(fmt_type, *fmt, args[i], &p);`
`157`	`156`	`// Pad bytes don't have a corresponding argument.`
`158`		`- if (*fmt != 'x') {`
	`157`	`+ if (*fmt == 'x') {`
	`158`	`+ mp_binary_set_val(fmt_type, *fmt, MP_OBJ_NEW_SMALL_INT(0), &p);`
	`159`	`+ } else {`
	`160`	`+ mp_binary_set_val(fmt_type, *fmt, args[i], &p);`
`159`	`161`	`i++;`
`160`	`162`	`}`
`161`	`163`	`}`