Add helpers for working with Base16 (i.e. hex) encoded data.

LAYOUT

@@ -4,6 +4,7 @@ Directory	Description
 =============	=============================================================
 common		Non-specific functionality that is of general interest, e.g.
 		the logging system, test infrastructure and Buffer class.
+common/data	Data formats and encodings.
 common/thread	Threading infrastructure.
 common/timer	Time sampling infrastructure.
 common/uuid	UUID API.

common/Makefile

@@ -1,3 +1,4 @@
+SUBDIR+=data
 SUBDIR+=thread
 SUBDIR+=timer
 SUBDIR+=uuid

common/data/Makefile

@@ -0,0 +1,3 @@
+SUBDIR+=
+
+include ../../common/subdir.mk

common/data/base16.h

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2016 Juli Mallett. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef	COMMON_DATA_BASE16_H
+#define	COMMON_DATA_BASE16_H
+
+/*
+ * Base16 (i.e. hex) encoding and decoding for Buffers.
+ */
+struct Base16 {
+	static bool decode(Buffer *out, const Buffer *in)
+	{
+		if (in->length() % 2 != 0) {
+			ERROR("/base16") << "Refusing to decode data with odd number of hex digits.";
+			return (false);
+		}
+
+		/*
+		 * We use a temporary buffer rather than maintaining a
+		 * lot of internal state to avoid copies.  The Buffer
+		 * code itself much more sophisticated than we need to
+		 * be here and gets the job done easily.
+		 */
+		Buffer encoded(*in);
+		Buffer decoded;
+		while (encoded.length() >= 2) {
+			uint8_t d[2];
+
+			encoded.moveout(d, sizeof d);
+
+			uint8_t b = 0x00;
+
+			if (d[0] >= '0' && d[0] <= '9')
+				b |= d[0] - '0';
+			else if (d[0] >= 'a' && d[0] <= 'f')
+				b |= 0xa + (d[0] - 'a');
+			else if (d[0] >= 'A' && d[0] <= 'F')
+				b |= 0xa + (d[0] - 'A');
+			else {
+				ERROR("/base16") << "Could not decode data with malformed hex digit (0 in pair.)";
+				return (false);
+			}
+			b <<= 4;
+
+			if (d[1] >= '0' && d[1] <= '9')
+				b |= d[1] - '0';
+			else if (d[1] >= 'a' && d[1] <= 'f')
+				b |= 0xa + (d[1] - 'a');
+			else if (d[1] >= 'A' && d[1] <= 'F')
+				b |= 0xa + (d[1] - 'A');
+			else {
+				ERROR("/base16") << "Could not decode data with malformed hex digit (1 in pair.)";
+				return (false);
+			}
+
+			decoded.append(b);
+		}
+
+		decoded.moveout(out);
+		return (true);
+	}
+
+	static Buffer encode(const Buffer *in)
+	{
+		static const char hexchars[] = "0123456789abcdef";
+		Buffer out;
+
+		Buffer::SegmentIterator iter(in->segments());
+		while (!iter.end()) {
+			const BufferSegment *seg = *iter;
+			const uint8_t *p;
+
+			for (p = seg->data(); p < seg->end(); p++) {
+				out.append((uint8_t)hexchars[(*p & 0xf0) >> 4]);
+				out.append((uint8_t)hexchars[*p & 0xf]);
+			}
+
+			iter.next();
+		}
+
+		return (out);
+	}
+};
+
+#endif /* !COMMON_DATA_BASE16_H */