[PATCH] Add MsgPack ext types handling.

[Serge Petrenko <sergepetrenko@tarantool.org>]

Add the ability to encode/decode MsgPack ext types,
introduce the first extension type: MP_EXT_DECIMAL: it will be used to
store decimals in tarantool.

Needed-for tarantool/tarantool#692
---
https://github.com/tarantool/msgpuck/tree/sp/add-extension-types
https://github.com/tarantool/tarantool/issues/692

 hints.c        |  24 +++++++++
 msgpuck.c      |  20 +++++++-
 msgpuck.h      | 133 +++++++++++++++++++++++++++++++++++++++++++++++++
 test/msgpuck.c |   7 ++-
 4 files changed, 178 insertions(+), 6 deletions(-)

diff --git a/hints.c b/hints.c
index be859e9..0ab4f4d 100644
--- a/hints.c
+++ b/hints.c
@@ -672,3 +672,27 @@ const char *mp_char2escape[128] = {
 	NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
 	NULL, NULL, NULL, NULL, NULL, NULL, NULL, "\\u007f"
 };
+
+/*
+ * This lookup table is used by mp_encode_ext() to
+ * determine ext code (fixext 1, fixext 2, fixext 4, fixext 8,
+ * fixext 16) to encode using size.
+ */
+const uint8_t mp_ext_hint[16] = {
+	0xd4,  /*  1 */
+	0xd5,  /*  2 */
+	0xd6,  /*  3 */
+	0xd6,  /*  4 */
+	0xd7,  /*  5 */
+	0xd7,  /*  6 */
+	0xd7,  /*  7 */
+	0xd7,  /*  8 */
+	0xd8,  /*  9 */
+	0xd8,  /* 10 */
+	0xd8,  /* 11 */
+	0xd8,  /* 12 */
+	0xd8,  /* 13 */
+	0xd8,  /* 14 */
+	0xd8,  /* 15 */
+	0xd8   /* 16 */
+};
diff --git a/msgpuck.c b/msgpuck.c
index d0ffb83..04aeb0f 100644
--- a/msgpuck.c
+++ b/msgpuck.c
@@ -33,6 +33,17 @@
 #define MP_LIBRARY 1
 #include "msgpuck.h"
 
+const char *
+mp_ext_type_str(enum mp_ext_type type)
+{
+	switch(type) {
+	case MP_EXT_DECIMAL:
+		return "decimal";
+	default:
+		return "undefined";
+	}
+}
+
 size_t
 mp_vformat(char *data, size_t data_size, const char *format, va_list vl)
 {
@@ -298,9 +309,14 @@ next:										\
 		PRINTF("%lg", mp_decode_double(&data));				\
 		break;								\
 	case MP_EXT:								\
-		mp_next(&data);							\
-		PRINTF("undefined");						\
+	{									\
+		uint8_t type;							\
+		uint32_t len;							\
+		len = mp_decode_ext(&data, &len, &type);			\
+		PRINTF("%s", mp_ext_type_str(type));	    			\
+		data += len;							\
 		break;								\
+	}									\
 	default:								\
 		mp_unreachable();						\
 		return -1;							\
diff --git a/msgpuck.h b/msgpuck.h
index 6b29cd6..0a7d230 100644
--- a/msgpuck.h
+++ b/msgpuck.h
@@ -382,6 +382,13 @@ enum mp_type {
 	MP_EXT
 };
 
+/**
+ * \brief MsgPack extension data types.
+ */
+enum mp_ext_type {
+	MP_EXT_DECIMAL = 0
+};
+
 /**
  * \brief Determine MsgPack type by a first byte \a c of encoded data.
  *
@@ -532,6 +539,49 @@ mp_check_map(const char *cur, const char *end);
 MP_PROTO uint32_t
 mp_decode_map(const char **data);
 
+/**
+ * \brief calculate exact buffer size needed to store
+ * ext value of length \a len.
+ * \param len value length in bytes.
+ * \retval buffer size in bytes
+ */
+MP_PROTO uint32_t
+mp_sizeof_ext(uint32_t len);
+
+/**
+ * \brief Encode extension header with \a type and
+ * value length \a len.
+ * The value must be encoded after the header.
+ * \return \a data + \link mp_sizeof_ext() mp_sizeof_ext(size)\endlink
+ */
+MP_PROTO char *
+mp_encode_ext(char *data, uint8_t type, uint32_t len);
+
+/**
+ * \brief Check that \a cur buffer has enough bytes to decode a map header.
+ * \param cur buffer
+ * \param end end of the buffer
+ * \retval 0 - buffer has enough bytes
+ * \retval > 0 - the numbeer of remaining bytes to read
+ * \pre cur < end
+ * \pre mp_typeof(*cur) == MP_EXT
+ */
+MP_PROTO MP_PURE ptrdiff_t
+mp_check_ext(const char *cur, const char *end);
+
+/**
+ * \brief Decode an extension header from MsgPack \a data.
+ *
+ * The extension type value must be decoded after the header.
+ * \param data - the pointer to a buffer.
+ * \param len -  decoded length of the following value.
+ * \param type - decoded type of the following value.
+ * \retval - the length of the following ext value.
+ * \post *data = *data + mp_sizeof_ext(length)
+ */
+MP_PROTO uint32_t
+mp_decode_ext(const char **data, uint32_t *len, uint8_t *type);
+
 /**
  * \brief Calculate exact buffer size needed to store an integer \a num.
  * Maximum return value is 9. For performance reasons you can preallocate
@@ -1326,6 +1376,7 @@ mp_frame_advance(struct mp_frame *frame);
 extern const enum mp_type mp_type_hint[];
 extern const int8_t mp_parser_hint[];
 extern const char *mp_char2escape[];
+extern const uint8_t mp_ext_hint[];
 
 MP_IMPL MP_ALWAYSINLINE enum mp_type
 mp_typeof(const char c)
@@ -1462,6 +1513,88 @@ mp_decode_map(const char **data)
 	}
 }
 
+MP_IMPL uint32_t
+mp_sizeof_ext(uint32_t len)
+{
+	if (len <= 16) return 2;
+	if (len <= UINT8_MAX) return 3;
+	if (len <= UINT16_MAX) return 4;
+	else return 5;
+}
+
+MP_IMPL char *
+mp_encode_ext(char *data, uint8_t type, uint32_t len)
+{
+	/*
+	 * zero-length should be encoded in EXT 8, because
+	 * fixext always assumes exact length (1, 2, 4, 8 and 16).
+	 */
+	if (len <= 16 && len > 0) {
+		data = mp_store_u8(data, mp_ext_hint[len-1]);
+	} else if (len <= UINT8_MAX) {
+		data = mp_store_u8(data, 0xc7);
+		data = mp_store_u8(data, (uint8_t) len);
+	} else if (len <= UINT16_MAX) {
+		data = mp_store_u8(data, 0xc8);
+		data = mp_store_u16(data, (uint16_t) len);
+	} else {
+		data = mp_store_u8(data, 0xc9);
+		data = mp_store_u32(data, (uint32_t) len);
+	}
+	data = mp_store_u8(data, type);
+	return data;
+}
+
+MP_IMPL ptrdiff_t
+mp_check_ext(const char *cur, const char *end)
+{
+	assert(cur < end);
+	assert(mp_typeof(*cur) == MP_EXT);
+	uint8_t c = mp_load_u8(&cur);
+	switch (c) {
+	case 0xd4:
+	case 0xd5:
+	case 0xd6:
+	case 0xd7:
+	case 0xd8:
+	    return 1 - (end - cur);
+	case 0xc7:
+	case 0xc8:
+	    return c - 0xc4 - (end - cur);
+	case 0xc9:
+	    return 6 - (end - cur);
+	default:
+		mp_unreachable();
+	}
+}
+
+MP_IMPL uint32_t
+mp_decode_ext(const char **data, uint32_t *len, uint8_t *type) {
+	uint8_t c = mp_load_u8(data);
+	switch 	 (c) {
+	case 0xd4:
+	case 0xd5:
+	case 0xd6:
+	case 0xd7:
+	case 0xd8:
+		*len = 1u << (c - 0xd4);
+		break;
+	case 0xc7:
+		*len = mp_load_u8(data);
+		break;
+	case 0xc8:
+		*len = mp_load_u16(data);
+		break;
+	case 0xc9:
+		*len = mp_load_u32(data);
+		break;
+	default:
+		mp_unreachable();
+	}
+	*type = mp_load_u8(data);
+	return *len;
+}
+
 MP_IMPL uint32_t
 mp_sizeof_uint(uint64_t num)
 {
diff --git a/test/msgpuck.c b/test/msgpuck.c
index 3b31bfc..5ddaba7 100644
--- a/test/msgpuck.c
+++ b/test/msgpuck.c
@@ -789,9 +789,8 @@ test_mp_print()
 	d = mp_encode_double(d, 3.14);
 	d = mp_encode_uint(d, 100);
 	d = mp_encode_uint(d, 500);
-	*d++ = 0xd4; /* let's pack smallest fixed ext */
-	*d++ = 0;
-	*d++ = 0;
+	/* let's pack zero-length ext */
+	d = mp_encode_ext(d, MP_EXT_DECIMAL, 0);
 	char bin[] = "\x12test\x34\b\t\n\"bla\\-bla\"\f\r";
 	d = mp_encode_bin(d, bin, sizeof(bin));
 	d = mp_encode_map(d, 0);
@@ -800,7 +799,7 @@ test_mp_print()
 	const char *expected =
 		"[-5, 42, \"kill bill\", [], "
 		"{\"bool true\": true, \"bool false\": false, \"null\": null, "
-		"\"float\": 3.14, \"double\": 3.14, 100: 500}, undefined, "
+		"\"float\": 3.14, \"double\": 3.14, 100: 500}, decimal, "
 		"\"\\u0012test4\\b\\t\\n\\\"bla\\\\-bla\\\"\\f\\r\\u0000\", {}]";
 	int esize = strlen(expected);
 
-- 
2.20.1 (Apple Git-117)