Add public API to retrieve trace parent header.

[diegosperes]

What does this pull request do?

Add a new public API to easily return the trace parent header of the current transaction, currently it's necessary to dig into the project and understand how it works.

Code necessary to get the current trace parent header without the new function.

from elasticapm.traces import execution_context

transaction = execution_context.get_transaction().
trace_parent_header = transaction .trace_parent.to_string() if transaction and transaction.trace_parent else None

Related issues

#954

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Build stats

• Build Cause: [Started by user Benjamin Wohlwend, Replayed #7]

• Start Time: 2020-10-28T11:50:24.612+0000

• Duration: 22 min 36 sec

Test stats 🧪

Test	Results
Failed	0
Passed	11238
Skipped	8409
Total	19647

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• Name: Shell Script

  • Description: ./tests/scripts/docker/run_tests.sh pypy-3 django-1.11

  • Duration: 3 min 58 sec

  • Start Time: 2020-10-28T11:55:51.496+0000

  • log

[diegosperes]

Couldn't find which place I should add the unit test, does someone has any suggestion? I think there isn't a test case for public API.

[beniwohli]

Hey @diegosperes. This looks like a nice addition to the public API! You're right, the testing for public APIs isn't very extensive, but there are a few here that might serve as inspiration:

apm-agent-python/tests/instrumentation/transactions_store_tests.py

Lines 363 to 442 in 65e8b7c

	def test_set_transaction_name(elasticapm_client):
	elasticapm_client.begin_transaction("test")
	elasticapm_client.end_transaction("test_name", 200)
	elasticapm_client.begin_transaction("test")
	elasticapm.set_transaction_name("another_name")
	elasticapm_client.end_transaction("test_name", 200)
	transactions = elasticapm_client.events[TRANSACTION]
	assert transactions[0]["name"] == "test_name"
	assert transactions[1]["name"] == "another_name"
	def test_set_transaction_custom_data(elasticapm_client):
	elasticapm_client.begin_transaction("test")
	elasticapm.set_custom_context({"foo": "bar"})
	elasticapm_client.end_transaction("foo", 200)
	transactions = elasticapm_client.events[TRANSACTION]
	assert transactions[0]["context"]["custom"] == {"foo": "bar"}
	def test_set_transaction_custom_data_merge(elasticapm_client):
	elasticapm_client.begin_transaction("test")
	elasticapm.set_custom_context({"foo": "bar", "bar": "baz"})
	elasticapm.set_custom_context({"bar": "bie", "boo": "biz"})
	elasticapm_client.end_transaction("foo", 200)
	transactions = elasticapm_client.events[TRANSACTION]
	assert transactions[0]["context"]["custom"] == {"foo": "bar", "bar": "bie", "boo": "biz"}
	def test_set_user_context(elasticapm_client):
	elasticapm_client.begin_transaction("test")
	elasticapm.set_user_context(username="foo", email="foo@example.com", user_id=42)
	elasticapm_client.end_transaction("foo", 200)
	transactions = elasticapm_client.events[TRANSACTION]
	assert transactions[0]["context"]["user"] == {"username": "foo", "email": "foo@example.com", "id": 42}
	def test_set_user_context_merge(elasticapm_client):
	elasticapm_client.begin_transaction("test")
	elasticapm.set_user_context(username="foo", email="bar@example.com")
	elasticapm.set_user_context(email="foo@example.com", user_id=42)
	elasticapm_client.end_transaction("foo", 200)
	transactions = elasticapm_client.events[TRANSACTION]
	assert transactions[0]["context"]["user"] == {"username": "foo", "email": "foo@example.com", "id": 42}
	def test_callable_context_ignored_when_not_sampled(elasticapm_client):
	callable_data = mock.Mock()
	callable_data.return_value = {"a": "b"}
	transaction = elasticapm_client.begin_transaction("test")
	transaction.is_sampled = False
	elasticapm.set_context({"c": "d"})
	elasticapm.set_context(callable_data)
	elasticapm_client.end_transaction("test", "OK")
	transaction = elasticapm_client.events[TRANSACTION][0]
	assert callable_data.call_count == 0
	assert "context" not in transaction
	def test_dedot_context_keys(elasticapm_client):
	elasticapm_client.begin_transaction("test")
	elasticapm.set_context({"d.o.t": "d_o_t", "s*t*a*r": "s_t_a_r", "q*u*o*t*e": "q_u_o_t_e"})
	elasticapm_client.end_transaction("foo", 200)
	transaction = elasticapm_client.events[TRANSACTION][0]
	assert transaction["context"]["custom"] == {"s_t_a_r": "s_t_a_r", "q_u_o_t_e": "q_u_o_t_e", "d_o_t": "d_o_t"}

It would also be great if you could add an entry in the traceparent docs here: https://github.com/elastic/apm-agent-python/blob/master/docs/api.asciidoc#traceparent.

[diegosperes]

@beniwohli thanks for guide me, I added a few missing test to the public API also a new entry for this function in the traceparent docs.

[apmmachine]

💚 Flaky test report

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Test stats 🧪

Test	Results
Failed	0
Passed	11238
Skipped	8409
Total	19647

[beniwohli]

This is great work, thanks a lot!

@basepi ok with merging this?