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55 lines
1.9 KiB
Erlang
55 lines
1.9 KiB
Erlang
%%% Split the rec part of a possible version negotiation message into
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%%% the host name and a list of version integers.
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-module(util).
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-export([versions/1, rep_msg_type/1]).
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-include("rep_literals.hrl").
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versions(B) ->
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Host = lists:takewhile(fun (X) -> X /= 0 end, binary_to_list(B)),
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Skip = length(Host) + 1,
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case B of
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%%
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%% version negotiation proposal
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%%
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<<_H:Skip/binary, Vmin:32/big, Vmax:32/big,
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_Pad/binary>> ->
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{Host, [Vmin, Vmax]};
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%%
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%% version confirmation
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%%
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<<_H:Skip/binary, V:32/big, _Pad/binary>> ->
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{Host, V};
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%%
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%% legacy V1 handshake, with no extra version info
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%%
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_ ->
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Host
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end.
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%%% In release 4.7 of Berkeley DB the replication msg protocol was
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%%% changed. Previously it sent binary data in native format; now it
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%%% sends it in standard NBO. Each message is tagged with a version
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%%% number, identifying its format. Note that this presents a bit of
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%%% a "chicken-and-egg" problem: you need to know the version before
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%%% you can figure out how to read any of the data, *INCLUDING THE
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%%% VERSION NUMBER ITSELF*! However, we can get around this issue by
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%%% assuming native format. If we're on a big endian architecture, it
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%%% doesn't make any difference. If we're on a little endian, then if
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%%% we're wrong to assume native, then the number we see will look
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%%% like some huge number, with bits turned on in the high-order
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%%% byte. This should only happen with formats >= 4.7, so we'll take
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%%% the correct branch. (See also the comment in
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%%% __rep_process_message, rep/rep_record.c)
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%%%
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rep_msg_type(Control) ->
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<<MsgVersion:32/native, Remainder/binary>> = Control,
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if
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MsgVersion >= ?REPVERSION_47 ->
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<<_:3/unit:32, RecType:32/big, _/binary>> = Remainder;
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true ->
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<<_:3/unit:32, RecType:32/native, _/binary>> = Remainder
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end,
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RecType.
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