Extended types (xtypes) are user-defined data types equipped with mechanisms for parsing and printing.

Each xtype is described by a struct xtype, which contains properties of the type and several pointers to callback functions.

Xtypes are currently supported by the following modules:


Definitions of types

typedef const char * (*xtype_parser)(const char *str, void *dest, struct mempool *pool);

A parsing callback. Takes a string, interprets it as a value of the particular xtype and stores it where dest points. Returns NULL on success and an error message otherwise. It may allocate memory from the pool and the parsed value can contain pointers to this memory.

typedef const char * (*xtype_formatter)(void *src, u32 fmt, struct mempool *pool);

A formatting callback. Takes a value of the particular xtype and a formatting mode fmt (see below for how the modes work) and returns a string representation of the value. The string can be allocated from the pool, but it does not have to.

When fmt is set to XTYPE_FMT_DEFAULT, the resulting string should be parseable via the parsing callback and yield a semantically equivalent value.

enum xtype_fmt {
  XTYPE_FMT_DEFAULT = 0,        // Default format: readable, but not hostile to machine parsing
  XTYPE_FMT_RAW = 1,            // Raw data with no frills
  XTYPE_FMT_PRETTY = 2,         // Try to please humans (e.g., like "ls -h")
  XTYPE_FMT_CUSTOM = 0x80000000,

Formatting of values is controlled by a mode parameter, which is generally a 32-bit integer. If the most significant bit is clear, it is one of generic well-known modes (XTYPE_FMT_something), which can be passed to all formatters and if it is not understood, it acts like XTYPE_FMT_DEFAULT. When the most significant bit is set, the meaning of the mode is specific to the particular xtype.

typedef const char * (*xtype_fmt_parser)(const char *str, u32 *dest, struct mempool *pool);

A callback for parsing non-generic formatting modes. See xtype_parser for more details. It is usually called via xtype_parse_fmt, which handles the generic modes.

typedef const char * (*xtype_fmt_formatter)(u32 fmt, struct mempool *pool);

A callback for constructing a string representation of non-generic formatting modes, analogous to xtype_formatter. It is usually called via xtype_format_fmt, which handles the generic modes. Returns an empty string for unknown modes.

struct xtype {
  size_t size;                          // How many bytes does a single value occupy
  const char *name;                     // Name used in debug messages
  xtype_parser parse;                   // Parsing callback
  xtype_formatter format;               // Formatting callback
  xtype_fmt_parser parse_fmt;           // Format mode parsing callback (optional)
  xtype_fmt_formatter format_fmt;       // Format mode formatting callback (optional)

This structure describes an xtype. Among other things, it points to callback functions handling this xtype.

const char *xtype_parse_fmt(const struct xtype *xt, const char *str, u32 *dest, struct mempool *pool);

Construct a formatting mode from its string representation. It is a wrapper around the xtype_fmt_parser hook, which handles generic modes first.

The generic modes are called default, raw, and pretty.

const char *xtype_format_fmt(struct xtype *xt, u32 fmt, struct mempool *pool);

Construct a string representation of a formatting mode. It is a wrapper around the xtype_fmt_formatter hook, which handles generic modes first. Returns an empty string for unknown modes.

Basic pre-defined types

We provide xtypes for many basic data types:

  • xt_bool

  • xt_double — in addition to the generic formatting modes, you can use XT_DOUBLE_FMT_PREC(n) to generate a mode for fixed formatting with n decimal places.

  • xt_int

  • xt_intmax

  • xt_s64

  • xt_str — string, represented by a const char *

  • xt_u64

  • xt_uint

  • xt_uintmax

Tables of units

Various xtypes accept values accompanied by a unit of measure. Units by handled by the xtypes themselves, but we provide a couple of generic functions for their convenience.

struct unit_definition {
  const char *unit;             // Symbol (name of the unit, as appended to values)
  u64 num;                      // Numerator
  u64 denom;                    // Denominator

Each unit is defined by a conversion ratio, which is a fraction with 64-bit numerator and denominator. Therefore, a value of x units is interpreted as x * num / denon.

int xtype_unit_parser(const char *str, const struct unit_definition *units);

Given an array units of unit definitions (terminated by an all-zero entry), parse a name of a unit and return its index in the array, or -1 if it is not found.



xt_size is a size, possibly with a unit. Internally, it is represented as a u64.

enum size_units {


#define XT_SIZE_FMT_UNIT(_unit) (_unit | XT_SIZE_FMT_FIXED_UNIT)

Custom formatting mode: use a specified unit (XT_SIZE_UNIT_xxx). Textual representation of the mode is the name of the unit (case-insensitive).


xt_timestamp is a timestamp, internally represented as time_t.


Custom formatting mode: seconds since Unix epoch. Currently, this is the same as the raw format. Textual representation: timestamp or epoch.


Custom formatting mode: date and time. Currently, this is the same as the human-readable format. Textual representation: datetime.