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prometheus

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Prometheus.io client in Erlang

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prometheus src formats prometheus_protobuf_format.erl
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src/formats/prometheus_protobuf_format.erl 

%% @doc

%% Serializes Prometheus registry using protocol buffer format.

%% @end

-module(prometheus_protobuf_format).

-export([content_type/0,

         format/0,

         format/1]).



-include("prometheus.hrl").

-include("prometheus_model.hrl").



-behaviour(prometheus_format).



%%====================================================================

%% Format API

%%====================================================================



-spec content_type() -> binary().

%% @doc

%% Content type of the Protocol buffer format.

%% @end

content_type() ->

  <<"application/vnd.google.protobuf; "

    "proto=io.prometheus.client.MetricFamily; "

    "encoding=delimited">>.



%% @equiv format(default)

-spec format() -> binary().

%% @doc

%% Format `default' registry using Protocol buffer format.

%% @end

format() ->

  format(default).



-spec format(Registry :: prometheus_registry:registry()) -> binary().

%% @doc

%% Format `registry' using Protocol buffer format.

%% @end

format(Registry) ->

  {ok, Fd} = ram_file:open("", [write, read, binary]),

  Callback = fun (_, Collector) ->

                 registry_collect_callback(Fd, Registry, Collector)

             end,

  prometheus_registry:collect(Registry, Callback),

  {ok, Size} = ram_file:get_size(Fd),

  {ok, Buf} = file:pread(Fd, 0, Size),

  ok = file:close(Fd),

  Buf.



%%====================================================================

%% Private Parts

%%====================================================================



registry_collect_callback(Fd, Registry, Collector) ->

  Callback = fun (MF) -> file:write(Fd, delimited_encode_mf(MF)) end,

  prometheus_collector:collect_mf(Registry, Collector, Callback).



delimited_encode_mf(MF) ->

  IoRec = prometheus_model:encode_msg(MF),

  Size  = iolist_size(IoRec),

  [e_varint(Size, <<>>), IoRec].



e_varint(N, Bin) when N =< 127 -> <<Bin/binary, N>>;

e_varint(N, Bin) ->

  Bin2 = <<Bin/binary, (N band 127 bor 128)>>,

  e_varint(N bsr 7, Bin2).