Shorten long SQL query to prevent oversized event

APM server allows events with a max size of 10000 characters. Shorten
queries traced in asyncpg to max allowed.

See: elastic#842

CHANGELOG.asciidoc

@@ -32,6 +32,11 @@ endif::[]
 [[release-notes-6.x]]
 === Python Agent version 6.x
 
+[float]
+===== Bug fixes
+
+* asyncpg: Limit SQL queries in context data to 10000 characters {pull}842[#842]
+
 [[release-notes-6.7.0]]
 === 6.7.0 - 2021-11-17
 

elasticapm/instrumentation/packages/asyncio/asyncpg.py

@@ -32,6 +32,7 @@
 from elasticapm.instrumentation.packages.asyncio.base import AsyncAbstractInstrumentedModule
 from elasticapm.instrumentation.packages.dbapi2 import extract_signature
 from elasticapm.utils import default_ports
+from elasticapm.utils.encoding import shorten
 
 
 class AsyncPGInstrumentation(AsyncAbstractInstrumentedModule):
@@ -63,7 +64,8 @@ def get_query(self, method, args):
     async def call(self, module, method, wrapped, instance, args, kwargs):
         query = self.get_query(method, args)
         name = extract_signature(query)
-        context = {"db": {"type": "sql", "statement": query}}
+        sql_string = shorten(query, string_length=10000)
+        context = {"db": {"type": "sql", "statement": sql_string}}
         action = "query"
         destination_info = {
             "address": kwargs.get("host", "localhost"),

tests/instrumentation/asyncio_tests/asyncpg_tests.py

@@ -139,3 +139,17 @@ async def test_fetch_methods(connection, elasticapm_client, method, verify):
     assert span["action"] == "query"
     assert span["sync"] is False
     assert span["name"] == "SELECT FROM test"
+
+
+async def test_truncate_long_sql(connection, elasticapm_client):
+    elasticapm_client.begin_transaction("test")
+    await connection.execute(
+        f"SELECT id, username FROM test WHERE username = {'x' * 10010};"
+    )
+    elasticapm_client.end_transaction("test", "OK")
+
+    transactions = elasticapm_client.events[constants.TRANSACTION]
+    spans = elasticapm_client.spans_for_transaction(transactions[0])
+
+    assert len(spans[0]["context"]["db"]["statement"]) == 10000
+    assert spans[0]["context"]["db"]["statement"].endswith("...")