Test: Cases on ID and metadata triggering

tests/test_source.liq

+#!/usr/bin/env liquidsoap
+#
+# Aura Engine (https://gitlab.servus.at/aura/engine)
+#
+# Copyright (C) 2017-now() - The Aura Engine Team.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+%include "base_config.liq"
+
+url = "https://orf-live.ors-shoutcast.at/oe1-q2a"
+input_stream = input.http(id="input_stream", url, start=true)
+def handle_meta1(meta) =
+    print("Called metadata handler1 and got: #{meta}")
+end
+def handle_meta2(meta) =
+    print("Called metadata handler2 and got: #{meta}")
+end
+
+
+### SOURCE ID ###
+
+# Test retrieving ID via getter
+id = input_stream.id()
+print("Source ID: #{id}")
+assertEquals(id, "input_stream")
+
+# Test retrieving ID via `source.id`
+id = source.id(input_stream)
+print("Source ID: #{id}")
+assertEquals(id, "input_stream")
+
+
+### ON_METADATA ###
+
+# Two variants of metadata event handling
+# See https://github.com/savonet/liquidsoap/discussions/2509
+
+# Variant A.) Attach `on_metadata` handler directly: handlers registered
+# directly using the source method will be called whenever the source is being consumed
+input_stream.on_metadata(handle_meta1)
+print("Source ID: #{input_stream.id()}")
+assertEquals(id, "input_stream")
+
+# Variant B.) Source returned by `on_metadata`: Handlers are only called
+# when the returned source is being used
+input_stream = source.on_metadata(id="input_stream", input_stream, handle_meta2)
+print("Source ID: #{input_stream.id()}")
+assertEquals(id, "input_stream")
+
+
+# IMPORTANT: If this is commented out, only "handle_meta1" will be called
+output.alsa(device="default", mksafe(mixer), bufferize=true)
+
+# The same is true for a mixer i.e. when the source is not selected/not audible:
+# mixer = mix(id="mixer", [input_stream])
+# output.alsa(device="default", mksafe(mixer), bufferize=true)
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