/* Part of SWI-Prolog Author: Jeffrey Rosenwald E-mail: jeffrose@acm.org WWW: http://www.swi-prolog.org Copyright (C): 2010, Jeffrey Rosenwald This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(protobufs, [ protobuf_message/2, % ?Template ?Codes protobuf_message/3 % ?Template ?Codes ?Rest ]). /** Google's Protocol Buffers Protocol buffers are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data -- think XML, but smaller, faster, and simpler. You define how you want your data to be structured once. This takes the form of a template that describes the data structure. You use this template to encode and decode your data structure into wire-streams that may be sent-to or read-from your peers. The underlying wire stream is platform independent, lossless, and may be used to interwork with a variety of languages and systems regardless of word size or endianness. Techniques exist to safely extend your data structure without breaking deployed programs that are compiled against the "old" format. The idea behind Google's Protocol Buffers is that you define your structured messages using a domain-specific language and tool set. In SWI-Prolog, you define your message template as a list of predefined Prolog terms that correspond to production rules in the Definite Clause Grammar (DCG) that realizes the interpreter. Each production rule has an equivalent rule in the protobuf grammar. The process is not unlike specifiying the format of a regular expression. To encode a template to a wire-stream, you pass a grounded template, =X=, and variable, =Y=, to protobuf_message/2. To decode a wire-stream, =Y=, you pass an ungrounded template, =X=, along with a grounded wire-stream, =Y=, to protobuf_message/2. The interpreter will unify the unbound variables in the template with values decoded from the wire-stream. For an overview and tutorial with examples, see protobufs_overview.txt. Examples of usage may also be found by inspecting test_protobufs.pl. @see http://code.google.com/apis/protocolbuffers @author: Jeffrey Rosenwald (JeffRose@acm.org) @license: LGPL2 (w/SWIPL library exception) @compat: SWI-Prolog */ :- require([ use_foreign_library/1 , atom_codes/2 , call/2 , float32_codes/2 , float64_codes/2 , int32_codes/2 , int64_codes/2 , integer_zigzag/2 , string_codes/2 , succ/2 , between/3 ]). :- use_foreign_library(foreign(protobufs)). :- use_module(library(utf8)). wire_type(varint, 0). wire_type(fixed64, 1). wire_type(length_delimited, 2). wire_type(start_group, 3). wire_type(end_group, 4). wire_type(fixed32, 5). % % deal with Google's method of encoding 2's complement integers % such that packed length is proportional to magnitude. We can handle up % to 63 bits, plus sign. Essentially moves sign-bit from MSB to LSB. % :- if(false). % now done in the C-support code zig_zag(Int, X) :- integer(Int), !, X is (Int << 1) xor (Int >> 63). zig_zag(Int, X) :- integer(X), Y is -1 * (X /\ 1), Int is (X >> 1) xor Y. :- endif. % % basic wire-type processing handled by C-support code % fixed_int32(X, [A0, A1, A2, A3 | Rest], Rest) :- int32_codes(X, [A0, A1, A2, A3]). fixed_int64(X, [A0, A1, A2, A3, A4, A5, A6, A7 | Rest], Rest) :- int64_codes(X, [A0, A1, A2, A3, A4, A5, A6, A7]). fixed_float64(X, [A0, A1, A2, A3, A4, A5, A6, A7 | Rest], Rest) :- float64_codes(X, [A0, A1, A2, A3, A4, A5, A6, A7]). fixed_float32(X, [A0, A1, A2, A3 | Rest], Rest) :- float32_codes(X, [A0, A1, A2, A3]). % % Start of the DCG % code_string(N, Codes, Rest, Rest1) :- length(Codes, N), append(Codes, Rest1, Rest), !. /* code_string(N, Codes) --> { length(Codes, N)}, Codes, !. */ % % deal with Google's method of packing unsigned integers in variable % length, modulo 128 strings. % % var_int and tag_type productions were rewritten in straight Prolog for % speed's sake. % var_int(A, [A | Rest], Rest) :- A < 128, !. var_int(X, [A | Rest], Rest1) :- nonvar(X), X1 is X >> 7, A is 128 + (X /\ 0x7f), var_int(X1, Rest, Rest1), !. var_int(X, [A | Rest], Rest1) :- var_int(X1, Rest, Rest1), X is (X1 << 7) + A - 128, !. % % tag_type(Tag, Type, Rest, Rest1) :- nonvar(Tag), nonvar(Type), wire_type(Type, X), A is Tag << 3 \/ X, var_int(A, Rest, Rest1), !. tag_type(Tag, Type, Rest, Rest1) :- var_int(A, Rest, Rest1), X is A /\ 0x07, wire_type(Type, X), Tag is A >> 3. % prolog_type(Tag, double) --> tag_type(Tag, fixed64). prolog_type(Tag, integer64) --> tag_type(Tag, fixed64). prolog_type(Tag, float) --> tag_type(Tag, fixed32). prolog_type(Tag, integer32) --> tag_type(Tag, fixed32). prolog_type(Tag, integer) --> tag_type(Tag, varint). prolog_type(Tag, unsigned) --> tag_type(Tag, varint). prolog_type(Tag, boolean) --> tag_type(Tag, varint). prolog_type(Tag, enum) --> tag_type(Tag, varint). prolog_type(Tag, atom) --> tag_type(Tag, length_delimited). prolog_type(Tag, codes) --> tag_type(Tag, length_delimited). prolog_type(Tag, utf8_codes) --> tag_type(Tag, length_delimited). prolog_type(Tag, string) --> tag_type(Tag, length_delimited). prolog_type(Tag, embedded) --> tag_type(Tag, length_delimited). % % The protobuf-2.1.0 grammar allows negative values in enums. % But they are encoded as unsigned in the golden message. % Encode as integer and lose. Encode as unsigned and win. % :- meta_predicate enumeration(1,*,*). enumeration(Type) --> { call(Type, Value) }, payload(unsigned, Value). payload(enum, A) --> enumeration(A). payload(double, A) --> fixed_float64(A). payload(integer64, A) --> fixed_int64(A). payload(float, A) --> fixed_float32(A). payload(integer32, A) --> fixed_int32(A). payload(integer, A) --> { nonvar(A), integer_zigzag(A,X) }, !, var_int(X). payload(integer, A) --> var_int(X), { integer_zigzag(A, X) }. payload(unsigned, A) --> { nonvar(A) -> A >= 0; true }, var_int(A). payload(codes, A) --> { nonvar(A), !, length(A, Len)}, var_int(Len), code_string(Len, A). payload(codes, A) --> var_int(Len), code_string(Len, A). payload(utf8_codes, A) --> { nonvar(A), !, phrase(utf8_codes(A), B) }, payload(codes, B). payload(utf8_codes, A) --> payload(codes, B), { phrase(utf8_codes(A), B) }. payload(atom, A) --> { nonvar(A), atom_codes(A, Codes) }, payload(utf8_codes, Codes), !. payload(atom, A) --> payload(utf8_codes, Codes), { atom_codes(A, Codes) }. payload(boolean, true) --> payload(unsigned, 1). payload(boolean, false) --> payload(unsigned, 0). payload(string, A) --> { nonvar(A) -> string_codes(A, Codes); true }, payload(codes, Codes), { string_codes(A, Codes) }. payload(embedded, protobuf(A)) --> { ground(A), phrase(protobuf(A), Codes) }, payload(codes, Codes), !. payload(embedded, protobuf(A)) --> payload(codes, Codes), { phrase(protobuf(A), Codes) }. start_group(Tag) --> tag_type(Tag, start_group). end_group(Tag) --> tag_type(Tag, end_group). % % nothing([]) --> [], !. protobuf([A | B]) --> { A =.. [ Type, Tag, Payload] }, message_sequence(Type, Tag, Payload), !, ( protobuf(B); nothing(B)). repeated_message_sequence(repeated_enum, Tag, Type, [A | B]) --> { Compound =.. [Type, A] }, message_sequence(enum, Tag, Compound), ( repeated_message_sequence(repeated_enum, Tag, Type, B); nothing(B)). repeated_message_sequence(Type, Tag, [A | B]) --> message_sequence(Type, Tag, A), repeated_message_sequence(Type, Tag, B). repeated_message_sequence(_Type, _Tag, A) --> nothing(A). % % message_sequence(repeated, Tag, enum(Compound)) --> { Compound =.. [ Type, List] }, repeated_message_sequence(repeated_enum, Tag, Type, List). message_sequence(repeated, Tag, Compound) --> { Compound =.. [Type, A] }, repeated_message_sequence(Type, Tag, A). message_sequence(group, Tag, A) --> start_group(Tag), protobuf(A), end_group(Tag), !. message_sequence(PrologType, Tag, Payload) --> prolog_type(Tag, PrologType), payload(PrologType, Payload). %% protobuf_message(?Template, ?Wire_stream) is semidet. %% protobuf_message(?Template, ?Wire_stream, ?Rest) is nondet. % % marshalls and unmarshalls byte streams encoded using Google's % Protobuf grammars. protobuf_message/2 provides a bi-directional % parser that marshalls a Prolog structure to Wire_stream, according to % rules specified by Template. It can also unmarshall Wire_stream into % a Prolog structure according to the same grammar. protobuf_message/3 % provides a difference list version. % % @param Template is a protobuf grammar specification. On decode, % unbound variables in the Template are unified with their respective % values in the Wire_stream. On encode, Template must be ground. % % @param Wire_stream is a code list that was generated by a protobuf % encoder using an equivalent template. % protobuf_message(protobuf(Template), Wirestream) :- must_be(list, Template), phrase(protobuf(Template), Wirestream), !. protobuf_message(protobuf(Template), Wirestream, Residue) :- must_be(list, Template), phrase(protobuf(Template), Wirestream, Residue).