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Simple HTTP client with HTTP/1.1, HTTP/2, and HTTP/3 support
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Files
src/hackney_metrics_prometheus.erl
%%% -*- erlang -*-
%%%
%%% This file is part of hackney released under the Apache 2 license.
%%% See the NOTICE for more information.
%%%
%%% Copyright (c) 2012-2026 Benoît Chesneau <benoitc@e-engura.org>
%%%
-module(hackney_metrics_prometheus).
-author("benoitc").
-behaviour(hackney_metrics_backend).
%% hackney_metrics_backend callbacks
-export([
counter_inc/2,
counter_inc/3,
gauge_set/3,
gauge_inc/2,
gauge_dec/2,
histogram_observe/3,
declare_counter/3,
declare_gauge/3,
declare_histogram/3,
declare_histogram/4
]).
%% Default histogram buckets for duration metrics (in seconds)
-define(DEFAULT_BUCKETS, [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0]).
%% Counter operations
counter_inc(Name, Labels) ->
counter_inc(Name, Labels, 1).
counter_inc(Name, Labels, Value) ->
try
prometheus_counter:inc(Name, labels_to_list(Labels), Value)
catch
_:_ -> ok
end.
%% Gauge operations
gauge_set(Name, Labels, Value) ->
try
prometheus_gauge:set(Name, labels_to_list(Labels), Value)
catch
_:_ -> ok
end.
gauge_inc(Name, Labels) ->
try
prometheus_gauge:inc(Name, labels_to_list(Labels))
catch
_:_ -> ok
end.
gauge_dec(Name, Labels) ->
try
prometheus_gauge:dec(Name, labels_to_list(Labels))
catch
_:_ -> ok
end.
%% Histogram operations
histogram_observe(Name, Labels, Value) ->
try
prometheus_histogram:observe(Name, labels_to_list(Labels), Value)
catch
_:_ -> ok
end.
%% Metric lifecycle - declarations are idempotent in prometheus
declare_counter(Name, Help, LabelKeys) ->
try
prometheus_counter:declare([
{name, Name},
{help, Help},
{labels, LabelKeys}
])
catch
_:_ -> ok
end.
declare_gauge(Name, Help, LabelKeys) ->
try
prometheus_gauge:declare([
{name, Name},
{help, Help},
{labels, LabelKeys}
])
catch
_:_ -> ok
end.
declare_histogram(Name, Help, LabelKeys) ->
declare_histogram(Name, Help, LabelKeys, ?DEFAULT_BUCKETS).
declare_histogram(Name, Help, LabelKeys, Buckets) ->
try
prometheus_histogram:declare([
{name, Name},
{help, Help},
{labels, LabelKeys},
{buckets, Buckets}
])
catch
_:_ -> ok
end.
%% Internal helpers
%% Convert a map of labels to a list of values in the order expected by prometheus
%% The order is determined by the keys when sorted alphabetically
labels_to_list(Labels) when is_map(Labels) ->
lists:map(fun({_K, V}) -> V end, lists:keysort(1, maps:to_list(Labels))).