GingerCal 1.1: apksigner v1 signing so Android 2.3 installs it; add Pangolin VPS setup notes

tools/check_dex.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+"""Checks the dex inside an APK the way Dalvik's dexopt does at install time:
+format version, file size, Adler-32 checksum, SHA-1 signature, and no post-035 sections.
+usage: check_dex.py app.apk"""
+import hashlib
+import struct
+import sys
+import zipfile
+import zlib
+
+d = zipfile.ZipFile(sys.argv[1]).read("classes.dex")
+problems = []
+if d[:8] != b"dex\n035\x00":
+    problems.append("dex version %r (Android 2.3 needs 035)" % d[:8])
+if struct.unpack("<I", d[32:36])[0] != len(d):
+    problems.append("file_size field wrong")
+if zlib.adler32(d[12:]) & 0xFFFFFFFF != struct.unpack("<I", d[8:12])[0]:
+    problems.append("Adler-32 checksum wrong")
+if hashlib.sha1(d[32:]).digest() != d[12:32]:
+    problems.append("SHA-1 signature wrong")
+map_off = struct.unpack("<I", d[52:56])[0]
+for i in range(struct.unpack("<I", d[map_off:map_off + 4])[0]):
+    t = struct.unpack("<H", d[map_off + 4 + i * 12:map_off + 6 + i * 12])[0]
+    if t in (7, 8):
+        problems.append("contains call_site/method_handle sections (needs Android 8+)")
+for p in problems:
+    print("DEX PROBLEM:", p)
+print("classes.dex: %d bytes, %s" % (len(d), "OK" if not problems else "REJECTED"))
+sys.exit(1 if problems else 0)