chunk: Add helper to copy a chunk left-padded to a certain length

src/libstrongswan/tests/suites/test_chunk.c

@@ -573,6 +573,40 @@ START_TEST(test_increment)
 }
 END_TEST
 
+/*******************************************************************************
+ * chunk_copy_pad tests
+ */
+
+static struct {
+	size_t len;
+	u_char chr;
+	chunk_t src;
+	chunk_t exp;
+} copy_pad_data[] = {
+	{0, 0x00, { NULL, 0 }, { NULL, 0 }},
+	{4, 0x00, { NULL, 0 }, chunk_from_chars(0x00,0x00,0x00,0x00)},
+	{0, 0x00, chunk_from_chars(0x01), { NULL, 0 }},
+	{1, 0x00, chunk_from_chars(0x01), chunk_from_chars(0x01)},
+	{2, 0x00, chunk_from_chars(0x01), chunk_from_chars(0x00,0x01)},
+	{3, 0x00, chunk_from_chars(0x01), chunk_from_chars(0x00,0x00,0x01)},
+	{4, 0x00, chunk_from_chars(0x01), chunk_from_chars(0x00,0x00,0x00,0x01)},
+	{4, 0x02, chunk_from_chars(0x01), chunk_from_chars(0x02,0x02,0x02,0x01)},
+	{1, 0x00, chunk_from_chars(0x01,0x02,0x03,0x04), chunk_from_chars(0x04)},
+	{2, 0x00, chunk_from_chars(0x01,0x02,0x03,0x04), chunk_from_chars(0x03,0x04)},
+	{3, 0x00, chunk_from_chars(0x01,0x02,0x03,0x04), chunk_from_chars(0x02,0x03,0x04)},
+	{4, 0x00, chunk_from_chars(0x01,0x02,0x03,0x04), chunk_from_chars(0x01,0x02,0x03,0x04)},
+};
+
+START_TEST(test_copy_pad)
+{
+	chunk_t chunk;
+
+	chunk = chunk_copy_pad(chunk_alloca(copy_pad_data[_i].len),
+						   copy_pad_data[_i].src, copy_pad_data[_i].chr);
+	ck_assert_chunk_eq(chunk, copy_pad_data[_i].exp);
+}
+END_TEST
+
 /*******************************************************************************
  * chunk_printable tests
  */
@@ -1076,6 +1110,10 @@ Suite *chunk_suite_create()
 	tcase_add_loop_test(tc, test_increment, 0, countof(increment_data));
 	suite_add_tcase(s, tc);
 
+	tc = tcase_create("chunk_copy_pad");
+	tcase_add_loop_test(tc, test_copy_pad, 0, countof(copy_pad_data));
+	suite_add_tcase(s, tc);
+
 	tc = tcase_create("chunk_printable");
 	tcase_add_loop_test(tc, test_printable, 0, countof(printable_data));
 	tcase_add_loop_test(tc, test_printable_sanitize, 0, countof(printable_data));

src/libstrongswan/utils/chunk.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2013 Tobias Brunner
+ * Copyright (C) 2008-2019 Tobias Brunner
  * Copyright (C) 2005-2006 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * HSR Hochschule fuer Technik Rapperswil
@@ -752,6 +752,26 @@ bool chunk_increment(chunk_t chunk)
 	return TRUE;
 }
 
+/*
+ * Described in header
+ */
+chunk_t chunk_copy_pad(chunk_t dst, chunk_t src, u_char chr)
+{
+	if (dst.ptr)
+	{
+		if (dst.len > src.len)
+		{
+			memcpy(dst.ptr + dst.len - src.len, src.ptr, src.len);
+			memset(dst.ptr, chr, dst.len - src.len);
+		}
+		else
+		{
+			memcpy(dst.ptr, src.ptr + src.len - dst.len, dst.len);
+		}
+	}
+	return dst;
+}
+
 /**
  * Remove non-printable characters from a chunk.
  */

src/libstrongswan/utils/chunk.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2013 Tobias Brunner
+ * Copyright (C) 2008-2019 Tobias Brunner
  * Copyright (C) 2005-2008 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * HSR Hochschule fuer Technik Rapperswil
@@ -292,6 +292,16 @@ static inline chunk_t chunk_skip_zero(chunk_t chunk)
 	return chunk;
 }
 
+/**
+ * Copy the data from src to dst, left-padded with chr if dst is longer,
+ * otherwise data is copied truncated on the left.
+ *
+ * @param dst			data is copied here
+ * @param src			data is copied from here
+ * @param chr			value to use for padding if necessary
+ * @return				the destination chunk
+ */
+chunk_t chunk_copy_pad(chunk_t dst, chunk_t src, u_char chr);
 
 /**
  *  Compare two chunks, returns zero if a equals b