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;;; erlext.el --- Encoding and decoding of Erlang external term format
;; Copyleft (]) 2000-2002 Luke Gorrie <>
;; Version: $Id: erlext.el,v 1.1 2004/10/25 19:55:57 lukeg Exp $
;; Keywords: erlang
;;; Commentary:
;; Library for encoding/decoding elisp terms into erlang's external
;; term format. For format details see erts/emulator/internal_doc/ in
;; the Erlang/OTP sources.
;; Supported mappings from/to erlext to elisp:
;; atom -> symbol
;; string -> string
;; integer -> integer
;; list -> list
;; tuple -> (vector ...)
;; pid -> (vector ERL-TAG 'pid node id serial creation)
;; binary -> string
;; Not mapped/supported yet:
;; ref, port, float, bignum, function, ...
;; ----------------------------------------------------------------------
;; Revision history:
;; Originally written some time in 2000, borrowing lots of code that I
;; didn't understand from Lennart Staflin's nice elisp CORBA client.
;; May 2001: Added asynchronous networking support for the "shbuf"
;; program that shares emacs buffers on the network via an erlang
;; server.
;; March 2002: Big cleanup for use in distributed erlang. Removed the
;; old networking code.
(eval-when-compile (require 'cl))
(eval-when-compile (load "cl-extra"))
;; type tags
(defconst erlext-tag-alist
'((smallInt . 97)
(int . 98)
(float . 99)
(atom . 100)
(cached . 67)
(ref . 101)
(port . 102)
(pid . 103)
(smallTuple . 104)
(largeTuple . 105)
(null . 106)
(string . 107)
(list . 108)
(bin . 109)
(smallBig . 110)
(largeBig . 111)
(newRef . 114)))
(defconst erlext-max-atom-length 255 "The maximum length of an erlang atom.")
(defconst erlext-protocol-version 131)
(defconst empty-symbol (intern "")
"The zero-length lisp symbol.")
(defvar erl-tag (make-symbol "TYPE")
"Tag placed in the first element of a vector to indicate a non-tuple type.")
;; ------------------------------------------------------------
;; Encoding / decoding interface
;; ------------------------------------------------------------
(defun erlext-binary-to-term (string)
"Decode and return the elisp representation of `string'."
(assert (stringp string))
(let (default-enable-multibyte-characters)
(insert string)
(goto-char (point-min))
(defun erlext-term-to-binary (term)
"Encode `term' as erlext and return the result as a string."
(let (default-enable-multibyte-characters)
(insert erlext-protocol-version)
(erlext-write-obj term)
;; Tuple datatype: (tuple X Y Z) => [X Y Z]
(defun tuple (&rest elems)
(apply #'vector elems))
(defun tuple-to-list (x)
(assert (tuplep x))
(mapcar #'identity x))
(defun tuplep (x)
(and (vectorp x)
(or (zerop (length x))
(not (eq (elt x 0) erl-tag)))))
(defun tuple-arity (tuple)
(1- (length tuple)))
(defmacro tuple-elt (tuple index)
"Return element INDEX from TUPLE. Index starts from 1."
;; Defined as a macro just so that we get the setf of `elt' for free
`(elt ,tuple (1- ,index)))
;; ------------------------------------------------------------
;; Encoding
;; ------------------------------------------------------------
(defun erlext-write-obj (obj)
(cond ((listp obj) ; lists at top since (symbolp '()) => t
(erlext-write-list obj))
((stringp obj)
(erlext-write-string obj))
((symbolp obj)
(erlext-write-atom obj))
((vectorp obj)
(if (tuplep obj)
(erlext-write-tuple (tuple-to-list obj))
(let* ((list (mapcar #'identity obj))
(type (cadr list))
(elts (cddr list)))
(ecase type
(apply #'erlext-write-pid elts))
(apply #'erlext-write-port elts))
(apply #'erlext-write-ref elts))
(apply #'erlext-write-new-ref elts))
(erlext-write-binary (car elts)))))))
((integerp obj)
(erlext-write-int obj))
(error "erlext can't marshal %S" obj))))
(defun erlext-write1 (n)
(assert (integerp n))
(insert n))
(defun erlext-write2 (n)
(assert (integerp n))
(insert (logand (ash n -8) 255)
(logand n 255)))
(defun erlext-write4 (n)
(assert (integerp n))
(insert (logand (ash n -24) 255)
(logand (ash n -16) 255)
(logand (ash n -8) 255)
(logand n 255)))
(defun erlext-writen (bytes)
(assert (stringp bytes))
(insert bytes))
(defun erlext-insert4 (n offset)
(goto-char offset)
(erlext-write4 n)
(goto-char (point-max)))
(defun erlext-write-atom (atom)
(assert (symbolp atom))
(let* ((string (symbol-name atom))
(len (length string)))
(assert (<= len erlext-max-atom-length))
(erlext-write1 (erlext-get-code 'atom))
(erlext-write2 (length string))
(erlext-writen string)))
(defun erlext-write-int (n)
(assert (integerp n))
(cond ((= n (logand n 255))
(erlext-write1 (erlext-get-code 'smallInt))
(erlext-write1 n))
;; elisp has small numbers so 32bit on the wire is as far as
;; we need bother supporting
(erlext-write1 (erlext-get-code 'int))
(erlext-write4 n))))
(defun erlext-write-list (lst)
(assert (listp lst))
(if (null lst)
(progn (erlext-write-list-head (length lst))
(mapc 'erlext-write-obj lst)
(defun erlext-write-string (str)
(assert (stringp str))
(erlext-write1 (erlext-get-code 'string))
(erlext-write2 (length str))
(erlext-writen str))
(defun erlext-write-binary (str)
(assert (stringp str))
(erlext-write1 (erlext-get-code 'bin))
(erlext-write4 (length str))
(erlext-writen str))
(defun erlext-write-null ()
(erlext-write1 (erlext-get-code 'null)))
(defun erlext-write-list-head (arity)
(assert (> arity 0))
(erlext-write1 (erlext-get-code 'list))
(erlext-write4 arity))
(defun erlext-write-tuple (elts)
(assert (listp elts))
(let ((arity (length elts)))
(if (< arity 256)
(progn (erlext-write1 (erlext-get-code 'smallTuple))
(erlext-write1 arity))
(progn (erlext-write1 (erlext-get-code 'largeTuple))
(erlext-write4 arity))))
(mapc 'erlext-write-obj elts))
(defun erlext-write-pid (node id serial creation)
(erlext-write1 (erlext-get-code 'pid))
(erlext-write-obj node)
(erlext-write4 id)
(erlext-write4 serial)
(erlext-write1 creation))
(defun erlext-write-port (node id creation)
(erlext-write1 (erlext-get-code 'port))
(erlext-write-obj node)
(erlext-write4 id)
(erlext-write1 creation))
(defun erlext-write-ref (node id creation)
(erlext-write1 (erlext-get-code 'ref))
(erlext-write-obj node)
(erlext-write4 id)
(erlext-write1 creation))
(defun erlext-write-new-ref (node creation id)
(erlext-write1 (erlext-get-code 'newRef))
(erlext-write2 (/ (length id) 4))
(erlext-write-obj node)
(erlext-write1 creation)
(erlext-writen id))
;; ------------------------------------------------------------
;; Decoding
;; ------------------------------------------------------------
(if (fboundp 'char-int)
;; convert character to string
(defsubst erlext-read1 ()
(prog1 (char-int (following-char))
(forward-char 1)))
(defsubst erlext-read1 ()
(prog1 (following-char)
(forward-char 1)))))
(defun erlext-read-whole-obj ()
(let ((version (erlext-read1)))
(assert (= version erlext-protocol-version))
(defun erlext-read-obj ()
(let ((tag (erlext-get-tag (erlext-read1))))
(case tag
((smallInt) (erlext-read1))
((int) (erlext-read4))
((atom) (erlext-read-atom))
((smallTuple) (erlext-read-small-tuple))
((largeTuple) (erlext-read-large-tuple))
((list) (erlext-read-list))
((string) (erlext-read-string))
((bin) (erlext-read-binary))
((null) nil)
((nil) nil)
((pid) (vector erl-tag
(erlext-read-obj) ; node
(erlext-read4) ; id
(erlext-read4) ; serial
(erlext-read1))); creation
((port) (vector erl-tag
(erlext-read-obj) ; node
(erlext-read4) ; id
(erlext-read1))) ; creation
((ref) (vector erl-tag
(erlext-read-obj) ; node
(erlext-read4) ;id
(erlext-read1))) ; creation
((newRef) (erlext-read-newref))
((smallBig) (erlext-read-small-bignum))
((largeBig) (erlext-read-large-bignum))
(error "Unknown tag: %S" tag)))))
(defun erlext-read (size)
(case size
((1) (erlext-read1))
((2) (erlext-read2))
((4) (erlext-read4))))
;; read1 moved above so that it can be inlined
(defun erlext-read2 ()
(logior (ash (erlext-read1) 8)
(defun erlext-read4 ()
(logior (ash (erlext-read1) 24)
(ash (erlext-read1) 16)
(ash (erlext-read1) 8)
(defun erlext-readn (n)
(assert (integerp n))
(let ((start (point))
(end (+ (point) n)))
(prog1 (let ((string (buffer-substring start end)))
(if (featurep 'xemacs)
(string-as-unibyte string))) ; fixme: should be
; string-make-unibyte?
; Why is it necessary
; anyhow?
(goto-char end))))
(defun erlext-read-atom ()
(let ((length (erlext-read2)))
(intern (erlext-readn length))))
(defun erlext-read-small-tuple ()
(erlext-read-tuple (erlext-read1)))
(defun erlext-read-large-tuple ()
(erlext-read-tuple (erlext-read4)))
(defun erlext-read-list ()
(let ((arity (erlext-read4)))
(prog1 (loop for x from 1 to arity
collect (erlext-read-obj))
;; This seems fishy, I find nil's at the end of lists, not
;; included as elements, and no mention of how it works in the
;; erl_ext_dist.txt
(assert (eq (erlext-get-code 'null) (erlext-read1))))))
(defun erlext-read-tuple (arity)
(apply #'vector (loop for x from 1 to arity
collect (erlext-read-obj))))
(defun erlext-read-string ()
(erlext-readn (erlext-read2)))
(defun erlext-read-binary ()
(erlext-readn (erlext-read4)))
(defun erlext-read-newref ()
(let* ((len (erlext-read2))
(node (erlext-read-obj))
(creation (erlext-read1))
(id (erlext-readn (* 4 len))))
(vector erl-tag 'erl-new-ref node creation id)))
;; We don't actually support bignums. When we get one, we skip over it
;; and return the symbol {SMALL|LARGE}-BIGNUM.
(defun erlext-read-small-bignum ()
(erlext-read (erlext-read1))
(defun erlext-read-large-bignum ()
(erlext-read (erlext-read4))
;; ------------------------------------------------------------
;; Helpers
;; ------------------------------------------------------------
(defun erlext-get-tag (number)
(car (rassq number erlext-tag-alist)))
(defun erlext-get-code (tag)
(cdr (assq tag erlext-tag-alist)))
;; ------------------------------------------------------------
;; Testing
;; ------------------------------------------------------------
(defvar erlext-test-cases
`(1 foo "bar" [bar baz] [,erl-tag erl-pid someone@somehost 0 0 0] (1 foo ())
[,erl-tag erl-port someone@somehost 0 0]
(([1 2]) ([1 2]))))
(defun erlext-test ()
"Test each term in `erlext-test-cases' by encoding it and decoding
it and making sure that it's unchanged."
(mapc #'erlext-test-case erlext-test-cases)
(message "Smooth sailing"))
(defun erlext-test-case (term)
(condition-case x
(assert (equal term (erlext-binary-to-term (erlext-term-to-binary term))))
(error (error "test failed for %S: %S" term (error-message-string x)))))
(provide 'erlext)
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