passage
=======

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[![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)

[OpenTraceing](http://opentracing.io/) API for Erlang

[Documentation](https://hexdocs.pm/passage/)

Examples
---------

```erlang
%% Registers `tracer`
Context = passage_span_context_null,
Sampler = passage_sampler_all:new(),
Reporter = passage_reporter_process:new(self(), span),
ok = passage_tracer_registry:register(tracer, Context, Sampler, Reporter),

%% Starts a root span
RootSpan = passage:start_root_span(example_root, tracer),

%% Starts a child span
ChildSpan = passage:start_span(example_child, {child_of, RootSpan}),

%% Finishes spans
passage:finish_span(ChildSpan),
passage:finish_span(RootSpan),

%% Receives the finished spans
receive {span, FinishedChildSpan} -> ok end,
receive {span, FinishedRootSpan} -> ok end.
```

### Process Dictionary Version

```erlang
%% Registers `tracer`
Context = passage_span_context_null,
Sampler = passage_sampler_all:new(),
Reporter = passage_reporter_process:new(self(), span),
ok = passage_tracer_registry:register(tracer, Context, Sampler, Reporter),

%% Starts a root span
ok = passage_pd:start_root_span(example_root, tracer),

%% Starts a child span
ok = passage_pd:start_span(example_child),

%% Finishes spans
passage_pd:finish_span(),  % child
passage_pd:finish_span(),  % root

%% Receives the finished spans
receive {span, FinishedChildSpan} -> ok end,
receive {span, FinishedRootSpan} -> ok end.
```

### Parse Transform

```erlang
-module(example).

-compile({parse_transform, passage_transform}). % Enables `passage_transform'

-passage_trace([{tags, #{foo => bar}}, {eval_tags, #{size => "byte_size(Bin)"}}]).
-spec foo(binary()) -> binary().
foo(Bin) ->
  <<"foo", Bin/binary>>.
```

The above foo function will be transformed as follows:
```erlang
foo(Bin) ->
  try
    passage_pd:start_span(foo, [{tags, #{application => example, module => example}}]),
    passage_pd:set_tags(#{process => self(), size => byte_size(Bin)}),
    <<"foo", Bin/binary>>
  after
    passage_pd:finish_span()
  end.
```

References
-----------

- [The OpenTracing Semantic Specification(v1.1)](https://github.com/opentracing/specification/blob/1.1/specification.md)