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NAME
erl_marshal - Encoding and Decoding of Erlang terms
DESCRIPTION
This module contains functions for encoding Erlang terms into a sequence of bytes, and for
decoding Erlang terms from a sequence of bytes.
EXPORTS
int erl_compare_ext(bufp1, bufp2)
Types:
unsigned char *bufp1,*bufp2;
This function compares two encoded terms.
bufp1 is a buffer containing an encoded Erlang term term1.
bufp2 is a buffer containing an encoded Erlang term term2.
The function returns 0 if the terms are equal, -1 if term1 is less than term2, or 1
if term2 is less than term1.
ETERM *erl_decode(bufp)
ETERM *erl_decode_buf(bufpp)
Types:
unsigned char *bufp;
unsigned char **bufpp;
erl_decode() and erl_decode_buf() decode the contents of a buffer and return the
corresponding Erlang term. erl_decode_buf() provides a simple mechanism for dealing
with several encoded terms stored consecutively in the buffer.
bufp is a pointer to a buffer containing one or more encoded Erlang terms.
bufpp is the address of a buffer pointer. The buffer contains one or more
consecutively encoded Erlang terms. Following a successful call to
erl_decode_buf(), bufpp will be updated so that it points to the next encoded term.
erl_decode() returns an Erlang term corresponding to the contents of bufp on
success, or NULL on failure. erl_decode_buf() returns an Erlang term corresponding
to the first of the consecutive terms in bufpp and moves bufpp forward to point to
the next term in the buffer. On failure, each of the functions returns NULL.
int erl_encode(term, bufp)
int erl_encode_buf(term, bufpp)
Types:
ETERM *term;
unsigned char *bufp;
unsigned char **bufpp;
erl_encode() and erl_encode_buf() encode Erlang terms into external format for
storage or transmission. erl_encode_buf() provides a simple mechanism for encoding
several terms consecutively in the same buffer.
term is an Erlang term to be encoded.
bufp is a pointer to a buffer containing one or more encoded Erlang terms.
bufpp is a pointer to a pointer to a buffer containing one or more consecutively
encoded Erlang terms. Following a successful call to erl_encode_buf(), bufpp will
be updated so that it points to the position for the next encoded term.
These functions returns the number of bytes written to buffer if successful,
otherwise returns 0.
Note that no bounds checking is done on the buffer. It is the caller's
responsibility to make sure that the buffer is large enough to hold the encoded
terms. You can either use a static buffer that is large enough to hold the terms
you expect to need in your program, or use erl_term_len() to determine the exact
requirements for a given term.
The following can help you estimate the buffer requirements for a term. Note that
this information is implementation specific, and may change in future versions. If
you are unsure, use erl_term_len().
Erlang terms are encoded with a 1 byte tag that identifies the type of object, a 2-
or 4-byte length field, and then the data itself. Specifically:
Tuples:
need 5 bytes, plus the space for each element.
Lists:
need 5 bytes, plus the space for each element, and 1 additional byte for the
empty list at the end.
Strings and atoms:
need 3 bytes, plus 1 byte for each character (the terminating 0 is not
encoded). Really long strings (more than 64k characters) are encoded as lists.
Atoms cannot contain more than 256 characters.
Integers:
need 5 bytes.
Characters:
(integers < 256) need 2 bytes.
Floating point numbers:
need 32 bytes.
Pids:
need 10 bytes, plus the space for the node name, which is an atom.
Ports and Refs:
need 6 bytes, plus the space for the node name, which is an atom.
The total space required will be the result calculated from the information above,
plus 1 additional byte for a version identifier.
int erl_ext_size(bufp)
Types:
unsigned char *bufp;
This function returns the number of elements in an encoded term.
unsigned char erl_ext_type(bufp)
Types:
unsigned char *bufp;
This function identifies and returns the type of Erlang term encoded in a buffer.
It will skip a trailing magic identifier. Returns 0 if the type can't be determined
or one of
* ERL_INTEGER
* ERL_ATOM
* ERL_PID /* Erlang process identifier */
* ERL_PORT
* ERL_REF /* Erlang reference */
* ERL_EMPTY_LIST
* ERL_LIST
* ERL_TUPLE
* ERL_FLOAT
* ERL_BINARY
* ERL_FUNCTION
unsigned char *erl_peek_ext(bufp, pos)
Types:
unsigned char *bufp;
int pos;
This function is used for stepping over one or more encoded terms in a buffer, in
order to directly access a later term.
bufp is a pointer to a buffer containing one or more encoded Erlang terms.
pos indicates how many terms to step over in the buffer.
The function returns a pointer to a sub-term that can be used in a subsequent call
to erl_decode() in order to retrieve the term at that position. If there is no
term, or pos would exceed the size of the terms in the buffer, NULL is returned.
int erl_term_len(t)
Types:
ETERM *t;
This function determines the buffer space that would be needed by t if it were
encoded into Erlang external format by erl_encode().
The size in bytes is returned.