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TECH-279: Adds OTEL middleware for swag's cowboy server #65

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TECH-279: Adds OTEL middleware for swag's cowboy server #65

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11 changes: 1 addition & 10 deletions apps/capi/src/capi_handler.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -66,8 +66,7 @@

-spec authorize_api_key(operation_id(), swag_server:api_key(), request_context(), handler_opts()) ->
Result :: false | {true, capi_auth:preauth_context()}.
authorize_api_key(OperationID, ApiKey, Context, _HandlerOpts) ->
ok = set_otel_context(Context),
authorize_api_key(OperationID, ApiKey, _Context, _HandlerOpts) ->
%% Since we require the request id field to create a woody context for our trip to token_keeper
%% it seems it is no longer possible to perform any authorization in this method.
%% To gain this ability back be would need to rewrite the swagger generator to perform its
Expand Down Expand Up @@ -296,14 +295,6 @@ process_general_error(Class, Reason, Stacktrace, Req, SwagContext) ->
),
{error, server_error(500)}.

set_otel_context(#{cowboy_req := Req}) ->
Headers = cowboy_req:headers(Req),
%% Implicitly puts OTEL context into process dictionary.
%% Since cowboy does not reuse process for other requests, we don't care
%% about cleaning it up.
_OtelCtx = otel_propagator_text_map:extract(maps:to_list(Headers)),
ok.

-spec set_context_meta(processing_context()) -> ok.
set_context_meta(Context) ->
AuthContext = capi_handler_utils:get_auth_context(Context),
Expand Down
87 changes: 87 additions & 0 deletions apps/capi/src/capi_otel_middleware.erl
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Original file line number Diff line number Diff line change
@@ -0,0 +1,87 @@
-module(capi_otel_middleware).

-behaviour(cowboy_middleware).

-export([execute/2]).

-behaviour(otel_propagator_text_map).

-export([fields/1]).
-export([inject/4]).
-export([extract/5]).

-spec execute(Req, Env) -> {ok, Req, Env} | {stop, Req} when Req :: cowboy_req:req(), Env :: cowboy_middleware:env().
execute(#{headers := Headers} = Req, Env) ->
Propagator =
{otel_propagator_text_map_composite, [
%% First try getting OTEL context from x-ray trace header
?MODULE,
%% But if trace context headers are present, then get current span context from there
otel_propagator:builtin_to_module(tracecontext)
]},
OtelCtx = otel_propagator_text_map:extract_to(otel_ctx:new(), Propagator, maps:to_list(Headers)),
%% Implicitly puts OTEL context into process dictionary.
%% Since cowboy does not reuse process for other requests, we don't care
%% about cleaning it up.
_Token = otel_ctx:attach(OtelCtx),
{ok, Req, Env}.

-define(HEADER_KEY, <<"x-amzn-trace-id">>).

-spec fields(otel_propagator_text_map:propagator_options()) -> [unicode:latin1_binary()].
fields(_) ->
[?HEADER_KEY].

-spec inject(
otel_ctx:t(),
otel_propagator:carrier(),
otel_propagator_text_map:carrier_set(),
otel_propagator_text_map:propagator_options()
) -> no_return().
inject(_Ctx, _Carrier, _CarrierSet, _Options) ->
erlang:error(not_implemented).

-spec extract(
otel_ctx:t(),
otel_propagator:carrier(),
otel_propagator_text_map:carrier_keys(),
otel_propagator_text_map:carrier_get(),
otel_propagator_text_map:propagator_options()
) -> otel_ctx:t().
extract(Ctx, Carrier, _CarrierKeysFun, CarrierGet, _Options) ->
case CarrierGet(?HEADER_KEY, Carrier) of
undefined ->
Ctx;
XRayTrace ->
case decode(string:trim(XRayTrace)) of
undefined ->
Ctx;
SpanCtx ->
otel_tracer:set_current_span(Ctx, SpanCtx)
end
end.

%%

decode(
%% NOTE Version is expected to be always single char "1"
<<"Root=", _Version:1/binary, "-", Timestamp:8/binary, "-", RootId:24/binary, ";Parent=", ParentId:16/binary,
";Sampled=", Sampled:1/binary, _/binary>>
) ->
try
TraceId = binary_to_integer(<<Timestamp/binary, RootId/binary>>, 16),
SpanId = binary_to_integer(ParentId, 16),
TraceFlags =
case Sampled of
<<"1">> -> 1;
<<"0">> -> 0;
_ -> error(badarg)
end,
otel_tracer:from_remote_span(TraceId, SpanId, TraceFlags)
catch
%% to integer from base 16 string failed
error:badarg ->
undefined
end;
decode(_) ->
undefined.
3 changes: 2 additions & 1 deletion apps/capi/src/capi_swagger_server.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,8 @@ get_cowboy_config(AdditionalRoutes, LogicHandler, SwaggerHandlerOpts) ->
middlewares => [
cowboy_router,
cowboy_cors,
cowboy_handler
cowboy_handler,
capi_otel_middleware
],
stream_handlers => [
cowboy_access_log_h,
Expand Down
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