LYB (LibYang Binary) is a proprietary libyang binary data and file format. Its primary purpose is efficient serialization (printing) and deserialization (parsing). With this goal in mind, every term node value is stored in its new binary format specification according to its type. Following is the format for all types with explicit support out-of-the-box (meaning that have a special type plugin). Any derived types inherit the format of its closest type with explicit support (up to a built-in type).

Format of specific data type values

binary (built-in)

Size (B)	Mandatory	Type	Meaning
binary value size	yes	`void *`	value in binary

bits (built-in)

Size (B)	Mandatory	Type	Meaning
returned by lyplg_type_bits_bitmap_size()	yes	pointer to integer type of the specific size, if size more than 8 use `char *`	bitmap of the set bits

boolean (built-in)

Size (B)	Mandatory	Type	Meaning
1	yes	`int8_t *`	0 for false, otherwise true

decimal64 (built-in)

Size (B)	Mandatory	Type	Meaning
8	yes	`int64_t *`	little-endian value represented without floating point

empty (built-in)

Size (B)	Mandatory	Type	Meaning
0	yes	`void`	none

enumeration (built-in)

Size (B)	Mandatory	Type	Meaning
4	yes	`int32 *`	assigned little-endian value of the enum

identityref (built-in)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string JSON format of the identityref

instance-identifier (built-in)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string JSON format of the instance-identifier

instance-identifier-keys (yang)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string JSON format of the instance-identifier keys predicate

(u)int(8/16/32/64) (built-in)

Size (B)	Mandatory	Type	Meaning
1/2/4/8	yes	pointer to the specific integer type	little-endian integer value

leafref (built-in)

Size (B)	Mandatory	Type	Meaning
exact same format as the leafref target

string (built-in)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string itself

union (built-in)

Size (B)	Mandatory	Type	Meaning
4	yes	`uint32_t *`	little-endian index of the resolved type in lysc_type_union.types
exact same format as the resolved type

Note that loading union value in this format prevents it from changing its real (resolved) type.

ipv4-address (ietf-inet-types)

Size (B)	Mandatory	Type	Meaning
4	yes	`struct in_addr *`	IPv4 address in network-byte order
string length	no	`char *`	IPv4 address zone string

ipv4-address-no-zone (ietf-inet-types)

Size (B)	Mandatory	Type	Meaning
4	yes	`struct in_addr *`	IPv4 address in network-byte order

ipv6-address (ietf-inet-types)

Size (B)	Mandatory	Type	Meaning
16	yes	`struct in6_addr *`	IPv6 address in network-byte order
string length	no	`char *`	IPv6 address zone string

ipv6-address-no-zone (ietf-inet-types)

Size (B)	Mandatory	Type	Meaning
16	yes	`struct in6_addr *`	IPv6 address in network-byte order

ipv4-prefix (ietf-inet-types)

Size (B)	Mandatory	Type	Meaning
4	yes	`struct in_addr *`	IPv4 address in network-byte order
1	yes	`uint8_t *`	prefix length up to 32

ipv6-prefix (ietf-inet-types)

Size (B)	Mandatory	Type	Meaning
16	yes	`struct in6_addr *`	IPv6 address in network-byte order
1	yes	`uint8_t *`	prefix length up to 128

date-and-time (ietf-yang-types)

Size (B)	Mandatory	Type	Meaning
8	yes	`time_t *`	UNIX timestamp
1	no	`int8_t *`	flag whether the value is in the special -00:00 unknown timezone or not
string length	no	`char *`	string with the fraction digits of a second

phys-address, mac-address, hex-string, uuid (ietf-yang-types)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string itself

xpath1.0 (ietf-yang-types)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string JSON format of the XPath expression

node-instance-identifier (ietf-netconf-acm)

Size (B)	Mandatory	Type	Meaning
string length	yes	`char *`	string JSON format of the instance-identifier