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

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