From 383e70fc39a229aede3a39e4cbb10711248b092f Mon Sep 17 00:00:00 2001
From: Khaled Hosny <khaled@aliftype.com>
Date: Sat, 3 Jul 2021 13:47:41 +0200
Subject: [PATCH] [sstruct] Accept pad byte format character
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The list of format characters that sstruct accepts was missing “x” for
ignored pad bytes.
---
 Lib/fontTools/misc/sstruct.py | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/Lib/fontTools/misc/sstruct.py b/Lib/fontTools/misc/sstruct.py
index a0c36673b..9f1de8bcb 100644
--- a/Lib/fontTools/misc/sstruct.py
+++ b/Lib/fontTools/misc/sstruct.py
@@ -59,7 +59,7 @@ class Error(Exception):
 	pass
 
 def pack(fmt, obj):
-	formatstring, names, fixes = getformat(fmt)
+	formatstring, names, fixes = getformat(fmt, keep_pad_byte=True)
 	elements = []
 	if not isinstance(obj, dict):
 		obj = obj.__dict__
@@ -112,7 +112,7 @@ _elementRE = re.compile(
 		r"\s*"							# whitespace
 		r"([A-Za-z_][A-Za-z_0-9]*)"		# name (python identifier)
 		r"\s*:\s*"						# whitespace : whitespace
-		r"([cbB?hHiIlLqQfd]|"			# formatchar...
+		r"([xcbB?hHiIlLqQfd]|"			# formatchar...
 			r"[0-9]+[ps]|"				# ...formatchar...
 			r"([0-9]+)\.([0-9]+)(F))"	# ...formatchar
 		r"\s*"							# whitespace
@@ -132,7 +132,7 @@ _fixedpointmappings = {
 
 _formatcache = {}
 
-def getformat(fmt):
+def getformat(fmt, keep_pad_byte=False):
 	fmt = tostr(fmt, encoding="ascii")
 	try:
 		formatstring, names, fixes = _formatcache[fmt]
@@ -154,8 +154,9 @@ def getformat(fmt):
 				if not m:
 					raise Error("syntax error in fmt: '%s'" % line)
 				name = m.group(1)
-				names.append(name)
 				formatchar = m.group(2)
+				if keep_pad_byte or formatchar != "x":
+					names.append(name)
 				if m.group(3):
 					# fixed point
 					before = int(m.group(3))
@@ -184,6 +185,7 @@ def _test():
 		afloat: f; adouble: d	# multiple "statements" are allowed
 		afixed: 16.16F
 		abool: ?
+		apad: x
 	"""
 
 	print('size:', calcsize(fmt))