Add logical types. Minor improvements.

CMakeLists.txt

@@ -27,6 +27,7 @@ set(VELOCYPACK_URL_INFO_ABOUT "https://github.com/arangodb/velocypack")
 set(VELOCYPACK_CONTACT "hackers@arangodb.org")
 set(VELOCYPACK_FRIENDLY_STRING "VelocyPack - A fast & compact serialization format")
 
+set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 #Compiler Setting
 include(AR_CompilerSettings)

VelocyPack.md

@@ -104,7 +104,8 @@ reference, for arrays and objects see below for details:
  follow that encode in a little endian way the length of
  the mantissa in bytes. After that, same as positive long
  packed BCD-encoded float above.
- - 0xd8-0xef : reserved
+ - 0xd8-0xed : reserved
+ - 0xee-0xef : value tagging for logical types
  - 0xf0-0xff : custom types
 
 
@@ -556,6 +557,40 @@ There for the unholy nibble problem is solved and parsing (and indeed
 dumping) can be efficient.
 
 
+## Tagging
+
+Types 0xee-0xef are used for tagging of values to implement logical
+types.
+
+For example, if type 0x1c did not exist, the database driver could
+serialize a timestamp object (Date in JavaScript, Instant in Java, etc)
+into a Unix timestamp, a 64-bit integer. Assuming the lack of schema,
+upon deserialization it would not be possible to tell an integer from
+a timestamp and deserialize the value accordingly.
+
+Type tagging resolves this by attaching an integer tag to values that
+can then be read when deserializing the value, e.g. that tag=1 is a
+timestamp and the relevant timestamp class should be used.
+
+The tag values are specified separately and applications can also
+specify their own to have the database driver deserialize their specific
+data types into the appropriate classes (including models).
+
+Essentially this is object-relational mapping for parts of documents.
+
+The format of the type is:
+
+ 0xee
+ TAG number in 1 byte
+ sub VPack value
+
+or
+
+ 0xef
+ TAG number in 8 bytes, little-endian encoding
+ sub VPack value
+
+
 ## Custom types
 
 Note that custom types should usually not be used for data exchange but

include/velocypack/Buffer.h

@@ -56,7 +56,7 @@ class Buffer {
  Buffer(Buffer const& that) : Buffer() {
  if (that._size > 0) {
  if (that._size > sizeof(that._local)) {
- _buffer = static_cast<T*>(malloc(checkOverflow(that._size)));
+ _buffer = static_cast<T*>(velocypack_malloc(checkOverflow(that._size)));
  ensureValidPointer(_buffer);
  _capacity = that._size;
  } else {
@@ -76,13 +76,13 @@ class Buffer {
  memcpy(_buffer, that._buffer, checkOverflow(that._size));
  } else {
  // our own buffer is not big enough to hold the data
- T* buffer = static_cast<T*>(malloc(checkOverflow(that._size)));
+ T* buffer = static_cast<T*>(velocypack_malloc(checkOverflow(that._size)));
  ensureValidPointer(buffer);
  buffer[0] = '\x00';
  memcpy(buffer, that._buffer, checkOverflow(that._size));
 
  if (_buffer != _local) {
- free(_buffer);
+ velocypack_free(_buffer);
  }
  _buffer = buffer;
  _capacity = that._size;
@@ -113,7 +113,7 @@ class Buffer {
  Buffer& operator=(Buffer&& that) noexcept {
  if (this != &that) {
  if (_buffer != _local) {
- free(_buffer);
+ velocypack_free(_buffer);
  }
  if (that._buffer == that._local) {
  _buffer = _local;
@@ -135,7 +135,7 @@ class Buffer {
 
  ~Buffer() { 
  if (_buffer != _local) {
- free(_buffer);
+ velocypack_free(_buffer);
  }
  }
 
@@ -187,7 +187,7 @@ class Buffer {
  void clear() noexcept {
  _size = 0;
  if (_buffer != _local) {
- free(_buffer);
+ velocypack_free(_buffer);
  _buffer = _local;
  _capacity = sizeof(_local);
  poison(_buffer, _capacity);
@@ -289,11 +289,11 @@ class Buffer {
  VELOCYPACK_ASSERT(newLen > 0);
  T* p;
  if (_buffer != _local) {
- p = static_cast<T*>(realloc(_buffer, checkOverflow(newLen)));
+ p = static_cast<T*>(velocypack_realloc(_buffer, checkOverflow(newLen)));
  ensureValidPointer(p);
  // realloc will have copied the old data
  } else {
- p = static_cast<T*>(malloc(checkOverflow(newLen)));
+ p = static_cast<T*>(velocypack_malloc(checkOverflow(newLen)));
  ensureValidPointer(p);
  // copy existing data into buffer
  memcpy(p, _buffer, checkOverflow(_size));