erl_marshal
This module contains functions for encoding Erlang terms into a sequence of bytes, and for decoding Erlang terms from a sequence of bytes.
Functions
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.
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.
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.
unsigned char *bufp;
This function returns the number of elements in an encoded term.
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 *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.
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.