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prometheus

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Prometheus.io client in Erlang

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prometheus src formats prometheus_text_format.erl
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src/formats/prometheus_text_format.erl 

-module(prometheus_text_format).

-export([content_type/0,

         format/0,

         format/1]).



-ifdef(TEST).

-export([escape_metric_help/1,

         escape_label_value/1]).

-endif.



-include("prometheus.hrl").

-include("prometheus_model.hrl").



-behaviour(prometheus_format).



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

%% Format API

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



-spec content_type() -> binary().

content_type() ->

  <<"text/plain; version=0.0.4">>.



%% @equiv format(default)

-spec format() -> binary().

format() ->

  format(default).



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

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),

  file:write(Fd, io_lib:format("\n", [])),

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

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

  ok = file:close(Fd),

  Str.



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

%% Private Parts

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



registry_collect_callback(Fd, Registry, Collector) ->

  Callback = fun (MF) ->

                 emit_mf_prologue(Fd, MF),

                 emit_mf_metrics(Fd, MF)

             end,

  prometheus_collector:collect_mf(Collector, Callback, Registry).



emit_mf_prologue(Fd, #'MetricFamily'{name=Name, help=Help, type=Type}) ->

  Bytes = io_lib:format("# TYPE ~s ~s\n# HELP ~s ~s\n",

                        [Name, string_type(Type),

                         Name, escape_metric_help(Help)]),

  file:write(Fd, Bytes).



emit_mf_metrics(Fd, #'MetricFamily'{name=Name, metric = Metrics}) ->

  [emit_metric(Fd, Name, Metric) || Metric <- Metrics].



emit_metric(Fd, Name, #'Metric'{label=Labels,

                                counter=#'Counter'{value=Value}}) ->

  emit_series(Fd, Name, Labels, Value);

emit_metric(Fd, Name, #'Metric'{label=Labels, gauge=#'Gauge'{value=Value}}) ->

  emit_series(Fd, Name, Labels, Value);

emit_metric(Fd, Name, #'Metric'{label=Labels,

                                summary=#'Summary'{sample_count=Count,

                                                   sample_sum=Sum}}) ->

  emit_series(Fd, [Name, "_count"], Labels, Count),

  emit_series(Fd, [Name, "_sum"], Labels, Sum);

emit_metric(Fd, Name, #'Metric'{label=Labels,

                                histogram=#'Histogram'{sample_count=Count,

                                                       sample_sum=Sum,

                                                       bucket=Buckets}}) ->

  [emit_histogram_bucket(Fd, Name, Labels, Bucket) || Bucket <- Buckets],

  emit_series(Fd, [Name, "_count"], Labels, Count),

  emit_series(Fd, [Name, "_sum"], Labels, Sum).



emit_histogram_bucket(Fd, Name, Labels, #'Bucket'{cumulative_count=BCount,

                                                  upper_bound=BBound}) ->

  BLValue = bound_to_label_value(BBound),

  emit_series(Fd, [Name, "_bucket"],

              Labels ++ [#'LabelPair'{name="le", value=BLValue}], BCount).



string_type('COUNTER') ->

  "counter";

string_type('GAUGE') ->

  "gauge";

string_type('SUMMARY') ->

  "summary";

string_type('HISTOGRAM') ->

  "histogram";

string_type('UNTYPED') ->

  "untyped".



labels_string([])     -> "";

labels_string(Labels) ->

  Fun = fun (#'LabelPair'{name=Name, value=Value}) ->

            io_lib:format("~s=\"~s\"", [Name, escape_label_value(Value)])

        end,

  "{" ++ string:join(lists:map(Fun, Labels), ",") ++ "}".



emit_series(Fd, Name, Labels, undefined) ->

  LString = labels_string(Labels),

  file:write(Fd, io_lib:format("~s" ++ LString ++ " NaN\n", [Name]));

emit_series(Fd, Name, Labels, Value) ->

  LString = labels_string(Labels),

  file:write(Fd, io_lib:format("~s" ++ LString ++ " ~p\n", [Name, Value])).



escape_metric_help(Help) ->

  sub(sub(Help, "\\", "\\\\\\\\"), "\n", "\\\\n").



bound_to_label_value(Bound) when is_number(Bound) ->

  Bound;

bound_to_label_value(infinity) ->

  "+Inf".



-spec escape_label_value(binary() | iolist() | undefined) -> string().

escape_label_value(LValue) when is_list(LValue)->

  sub(sub(sub(LValue, "\\", "\\\\\\\\"), "\n", "\\\\n"), "\"", "\\\\\"");

escape_label_value(LValue) when is_binary(LValue) ->

  escape_label_value(binary_to_list(LValue));

escape_label_value(LValue) ->

  escape_label_value(io_lib:format("~p", [LValue])).



-spec sub(string() | atom(), string(), string()) -> string().

sub(Str, Old, New) when is_atom(Str) ->

  sub(atom_to_list(Str), Old, New);

sub(Str, Old, New) ->

  RegExp = "\\Q" ++ Old ++ "\\E",

  re:replace(Str, RegExp, New, [global, {return, list}]).