init

tools/_channel_patch.py

@@ -0,0 +1,74 @@
+"""Patch campaign / channel id embedded in type-0x01 secondary dylibs."""
+
+from __future__ import annotations
+
+import re
+import secrets
+
+# C-string keys immediately before the channel value in type-0x01 __cstring.
+CHANNEL_ANCHOR = b"u\x00d\x00f\x00s\x00c\x00"
+CHANNEL_LEN = 32
+_CHANNEL_RE = re.compile(rb"^[0-9a-f]{32}$")
+
+
+def gen_channel_id() -> str:
+    """32 lowercase hex chars (same width as campaign slot)."""
+    return secrets.token_hex(16)
+
+
+def validate_channel_id(value: str, *, name: str = "--channel-id") -> str:
+    if not isinstance(value, str) or not _CHANNEL_RE.fullmatch(value.encode("ascii")):
+        raise SystemExit(
+            f"{name} must be exactly {CHANNEL_LEN} lowercase hex chars "
+            f"(got {value!r})"
+        )
+    return value
+
+
+def find_channel_offsets(data: bytes, *, expect_old: bytes | None = None) -> list[int]:
+    """Return offsets of the 32-byte channel value after CHANNEL_ANCHOR."""
+    offsets: list[int] = []
+    start = 0
+    while True:
+        index = data.find(CHANNEL_ANCHOR, start)
+        if index < 0:
+            break
+        value_at = index + len(CHANNEL_ANCHOR)
+        value = data[value_at : value_at + CHANNEL_LEN]
+        if (
+            len(value) == CHANNEL_LEN
+            and _CHANNEL_RE.fullmatch(value)
+            and data[value_at + CHANNEL_LEN : value_at + CHANNEL_LEN + 1] == b"\x00"
+        ):
+            if expect_old is None or value == expect_old:
+                offsets.append(value_at)
+        start = index + 1
+    return offsets
+
+
+def patch_channel_in_dylib(
+    data: bytes,
+    new_channel: str,
+    *,
+    old_channel: str | None = None,
+    expect_hits: int = 1,
+    label: str = "dylib",
+) -> bytes:
+    """In-place replace channel C-string (must stay {CHANNEL_LEN} bytes)."""
+    new_channel = validate_channel_id(new_channel, name="channel")
+    new_b = new_channel.encode("ascii")
+    old_b = old_channel.encode("ascii") if old_channel else None
+    if old_b is not None:
+        validate_channel_id(old_channel, name="old channel")
+
+    offsets = find_channel_offsets(data, expect_old=old_b)
+    if len(offsets) != expect_hits:
+        raise SystemExit(
+            f"{label}: channel anchor hits={len(offsets)} (want {expect_hits}). "
+            "Secondary payload layout may have changed; re-adapt _channel_patch."
+        )
+
+    buf = bytearray(data)
+    for offset in offsets:
+        buf[offset : offset + CHANNEL_LEN] = new_b
+    return bytes(buf)