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0.3.1
Macula HTTP/3 Mesh SDK — connect, subscribe, publish, call, advertise
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Files
src/observability/macula_metrics_http.erl
%%%-------------------------------------------------------------------
%%% @doc Prometheus text-format pull endpoint for {@link macula_metrics}.
%%%
%%% Phase 4.1 — see PLAN_MACULA_NET_PHASE4_1_OBSERVABILITY.md.
%%%
%%% Embeds an `inets' httpd listener that serves a single resource:
%%% `GET /metrics' returns the current snapshot in
%%% Prometheus text-exposition format (v0.0.4 / OpenMetrics-compatible).
%%%
%%% Defaults bind 127.0.0.1; remote scraping requires an explicit
%%% bind address via `start_link/1'.
%%% @end
%%%-------------------------------------------------------------------
-module(macula_metrics_http).
-behaviour(gen_server).
-export([start_link/0, start_link/1, stop/0, port/0, render/0]).
%% inets mod_* callback — exported so httpd can dispatch requests.
-export([do/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2]).
-define(DEFAULT_PORT, 9145).
-define(DEFAULT_BIND, {127,0,0,1}).
-record(state, {
httpd_pid :: pid() | undefined,
port :: inet:port_number(),
bind :: inet:ip_address()
}).
%% =============================================================================
%% Lifecycle
%% =============================================================================
-spec start_link() -> {ok, pid()} | {error, term()}.
start_link() -> start_link(#{}).
-spec start_link(map()) -> {ok, pid()} | {error, term()}.
start_link(Opts) ->
gen_server:start_link({local, ?MODULE}, ?MODULE, Opts, []).
-spec stop() -> ok.
stop() -> gen_server:stop(?MODULE).
%% @doc Returns the actual port the server is listening on (useful when
%% port=0 is passed for tests).
-spec port() -> inet:port_number().
port() ->
gen_server:call(?MODULE, port).
%% =============================================================================
%% gen_server
%% =============================================================================
init(Opts) ->
application:ensure_all_started(inets),
Port = maps:get(port, Opts, ?DEFAULT_PORT),
Bind = parse_bind(maps:get(bind, Opts, ?DEFAULT_BIND)),
{ok, Pid} = start_httpd(Port, Bind),
ActualPort = httpd_port(Pid),
{ok, #state{httpd_pid = Pid, port = ActualPort, bind = Bind}}.
handle_call(port, _From, #state{port = P} = S) ->
{reply, P, S};
handle_call(_, _From, S) ->
{reply, ok, S}.
handle_cast(_, S) -> {noreply, S}.
handle_info(_, S) -> {noreply, S}.
terminate(_, #state{httpd_pid = undefined}) -> ok;
terminate(_, #state{httpd_pid = Pid}) ->
_ = inets:stop(httpd, Pid),
ok.
%% =============================================================================
%% Inets mod_* callback
%% =============================================================================
-include_lib("inets/include/httpd.hrl").
%% inets calls do/1 with a #mod{} record per HTTP request.
-spec do(#mod{}) -> {proceed, list()}.
do(#mod{request_uri = "/metrics"} = Mod) ->
serve_metrics(Mod);
do(#mod{request_uri = "/metrics/"} = Mod) ->
serve_metrics(Mod);
do(#mod{} = _Mod) ->
{proceed, [{response, {404, "not found"}}]}.
serve_metrics(_Mod) ->
Body = iolist_to_binary(render()),
Length = integer_to_list(byte_size(Body)),
Headers = [
{code, 200},
{content_type, "text/plain; version=0.0.4; charset=utf-8"},
{content_length, Length}
],
{proceed, [{response, {response, Headers, [Body]}}]}.
%% @doc Render the current metric snapshot as Prometheus text format.
-spec render() -> iolist().
render() ->
[render_metric(M) || M <- macula_metrics:gather()].
%% =============================================================================
%% Prometheus text rendering
%% =============================================================================
render_metric(#{name := N, type := counter, help := H, samples := Ss}) ->
[help_line(N, H), type_line(N, <<"counter">>),
[counter_line(N, S) || S <- Ss]];
render_metric(#{name := N, type := gauge, help := H, samples := Ss}) ->
[help_line(N, H), type_line(N, <<"gauge">>),
[gauge_line(N, S) || S <- Ss]];
render_metric(#{name := N, type := histogram, help := H, samples := Ss}) ->
[help_line(N, H), type_line(N, <<"histogram">>),
[hist_lines(N, S) || S <- Ss]].
help_line(N, H) -> [<<"# HELP ">>, N, $\s, escape_help(H), $\n].
type_line(N, T) -> [<<"# TYPE ">>, N, $\s, T, $\n].
counter_line(N, #{labels := L, value := V}) ->
[N, render_labels(L), $\s, num(V), $\n].
gauge_line(N, #{labels := L, value := V}) ->
[N, render_labels(L), $\s, num(V), $\n].
hist_lines(N, #{labels := L, buckets := Bs, sum := Sum, count := Cnt}) ->
BucketLines = [hist_bucket_line(N, L, B, C) || {B, C} <- Bs],
InfLine = [N, <<"_bucket">>, render_labels_with_le(L, <<"+Inf">>),
$\s, num(Cnt), $\n],
SumLine = [N, <<"_sum">>, render_labels(L), $\s, num(Sum), $\n],
CountLine = [N, <<"_count">>, render_labels(L), $\s, num(Cnt), $\n],
[BucketLines, InfLine, SumLine, CountLine].
hist_bucket_line(N, L, B, C) ->
[N, <<"_bucket">>, render_labels_with_le(L, num(B)),
$\s, num(C), $\n].
render_labels([]) -> <<>>;
render_labels(L) -> [${, lists:join($,, [label_pair(K, V) || {K, V} <- L]), $}].
render_labels_with_le(L, LeBin) ->
LePair = [<<"le=\"">>, LeBin, $"],
Rest = [label_pair(K, V) || {K, V} <- L],
[${, lists:join($,, [LePair | Rest]), $}].
label_pair(K, V) when is_atom(K) ->
[atom_to_binary(K, utf8), <<"=\"">>, escape_label(V), $"].
escape_label(V) when is_binary(V) -> escape_label_bin(V, <<>>).
escape_label_bin(<<>>, Acc) -> Acc;
escape_label_bin(<<$\\, Rest/binary>>, Acc) -> escape_label_bin(Rest, <<Acc/binary, "\\\\">>);
escape_label_bin(<<$", Rest/binary>>, Acc) -> escape_label_bin(Rest, <<Acc/binary, "\\\"">>);
escape_label_bin(<<$\n, Rest/binary>>, Acc) -> escape_label_bin(Rest, <<Acc/binary, "\\n">>);
escape_label_bin(<<C, Rest/binary>>, Acc) -> escape_label_bin(Rest, <<Acc/binary, C>>).
escape_help(H) when is_binary(H) ->
%% HELP escapes only \ and \n
escape_help_bin(H, <<>>).
escape_help_bin(<<>>, Acc) -> Acc;
escape_help_bin(<<$\\, Rest/binary>>, Acc) -> escape_help_bin(Rest, <<Acc/binary, "\\\\">>);
escape_help_bin(<<$\n, Rest/binary>>, Acc) -> escape_help_bin(Rest, <<Acc/binary, "\\n">>);
escape_help_bin(<<C, Rest/binary>>, Acc) -> escape_help_bin(Rest, <<Acc/binary, C>>).
num(N) when is_integer(N) -> integer_to_binary(N);
num(N) when is_float(N) -> float_to_binary(N, [{decimals, 6}, compact]).
%% =============================================================================
%% Internals
%% =============================================================================
parse_bind({_,_,_,_} = Ip) -> Ip;
parse_bind({_,_,_,_,_,_,_,_} = Ip) -> Ip;
parse_bind(Bin) when is_binary(Bin) -> parse_bind(binary_to_list(Bin));
parse_bind(Str) when is_list(Str) ->
{ok, Ip} = inet:parse_address(Str),
Ip.
start_httpd(Port, Bind) ->
BindStr = inet:ntoa(Bind),
inets:start(httpd, [
{port, Port},
{bind_address, BindStr},
{server_name, "macula_metrics"},
{server_root, "/tmp"},
{document_root, "/tmp"},
{modules, [?MODULE]},
{mime_types, [{"txt", "text/plain"}]}
]).
httpd_port(Pid) ->
Info = httpd:info(Pid),
proplists:get_value(port, Info).