asahi_firmware.img4: New module for img4 extraction

Signed-off-by: Hector Martin <[email protected]>

Author: marcan

asahi_firmware/img4.py

@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: MIT
+
+from . import asn1
+
+def img4p_extract(data):
+    decoder = asn1.Decoder()
+    decoder.start(data)
+    tag = decoder.peek()
+    assert tag.nr == asn1.Numbers.Sequence
+    assert tag.typ == asn1.Types.Constructed
+    decoder.enter()
+
+    tag, value = decoder.read()
+    assert tag == asn1.Tag(asn1.Numbers.IA5String, asn1.Types.Primitive, 0)
+    assert value == "IM4P"
+
+    tag, name = decoder.read()
+    assert tag == asn1.Tag(asn1.Numbers.IA5String, asn1.Types.Primitive, 0)
+
+    tag, unk = decoder.read()
+    assert tag == asn1.Tag(asn1.Numbers.IA5String, asn1.Types.Primitive, 0)
+
+    tag, data = decoder.read()
+    assert tag == asn1.Tag(asn1.Numbers.OctetString, asn1.Types.Primitive, 0)
+
+    return name, data