1 files changed, 166 insertions, 0 deletions
diff --git a/hlvr/patch-hlvr b/hlvr/patch-hlvr
new file mode 100755
index 0000000..5339157
--- /dev/null
+++ b/hlvr/patch-hlvr
@@ -0,0 +1,166 @@
+#!/usr/bin/env python3
+# SPDX-FileCopyrightText: 2026 Tomasz Kramkowski <tomasz@kramkow.ski>
+# SPDX-License-Identifier: CC0-1.0
+
+"""A Half-Life: Alyx launch wrapper that patches the game.
+
+For build 26283546.
+
+Use at your own risk!
+"""
+
+import hashlib
+import os
+import stat
+import subprocess
+import sys
+import tempfile
+from dataclasses import dataclass
+from pathlib import Path
+
+NAME = Path(__file__).name
+MARKER = b"Valve, please fix."
+
+
+@dataclass(frozen=True)
+class Edit:
+    offset: int
+    replacement: bytes
+
+
+@dataclass(frozen=True)
+class Patch:
+    original_hash: bytes
+    patched_hash: bytes
+    edits: tuple[Edit, ...]
+
+    def apply_to(self, data: bytes) -> bytes:
+        payload = data.removesuffix(MARKER)
+        digest = sha256(payload)
+        if digest == self.patched_hash:
+            return payload + MARKER
+        if digest != self.original_hash:
+            if payload != data:
+                raise LookupError(
+                    "already patched with another set of patches: verify file integrity and restart"
+                )
+            raise LookupError("unrecognized build: this wrapper may need updating")
+        result = bytearray(payload)
+        for edit in self.edits:
+            end = edit.offset + len(edit.replacement)
+            if edit.offset < 0 or end > len(result):
+                raise ValueError("patch extends outside the file")
+            result[edit.offset : end] = edit.replacement
+        if sha256(result) != self.patched_hash:
+            raise ValueError("patched file checksum mismatch")
+        return bytes(result) + MARKER
+
+
+def patch(
+    original_hash: str, patched_hash: str, edits: tuple[tuple[int, str], ...]
+) -> Patch:
+    return Patch(
+        bytes.fromhex(original_hash),
+        bytes.fromhex(patched_hash),
+        tuple(
+            Edit(offset, bytes.fromhex(replacement)) for offset, replacement in edits
+        ),
+    )
+
+
+PATCHES = {
+    "game/bin/linuxsteamrt64/libscenesystem.so": patch(
+        "6d395e42a86d352eed03a794bb877f3fd21e84d4be494daa309ad986208e5c48",
+        "7e47f2c0ba97e60cbedcb154df4017feaf04ad1d2528b942f46da15b7303bbc6",
+        (
+            # Only advance the instance count after a successful allocation.
+            (0x163C41, "0f86ad0000006690"),
+            (0x163CF4, "89b30c5f0000e9a1ffffff"),
+            # Skip this batch of instances if allocation fails.
+            (0x25BA30, "e929b8ffff90"),
+            (0x25725E, "89853cb7ffff4883bd58b7ffff000f844d490000e9bf470000"),
+        ),
+    ),
+    "game/bin/linuxsteamrt64/libnetworksystem.so": patch(
+        "adab8ab904bb6e751ab98943a707e9df0e3f5cd2a084ff223bb563e8ef91f08d",
+        "cc4d9e260f9ead33b764c1e56f4f0ed03a87ef1a98b54149008f1b14d5b591e9",
+        (
+            # Use the 8-byte snappy fast path for offsets below 16.
+            (0x1FAEB5, "0f"),
+            (0x1FAEBA, "86"),
+        ),
+    ),
+}
+
+
+def sha256(data):
+    return hashlib.sha256(data).digest()
+
+
+def notify(message):
+    print(f"{NAME}: {message}", file=sys.stderr)
+    try:
+        subprocess.run(
+            ["notify-send", NAME, message],
+            check=False,
+            timeout=3,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+        )
+    except (OSError, subprocess.TimeoutExpired):
+        pass
+
+
+def replace(path, data):
+    mode = stat.S_IMODE(path.stat().st_mode)
+    with tempfile.NamedTemporaryFile(
+        dir=path.parent, prefix=path.name + ".", delete=False
+    ) as f:
+        temporary = Path(f.name)
+        try:
+            f.write(data)
+            f.flush()
+            os.fchmod(f.fileno(), mode)
+            os.fsync(f.fileno())
+            os.replace(temporary, path)
+        finally:
+            temporary.unlink(missing_ok=True)
+
+
+def main(command):
+    diagnostics = []
+    if not command:
+        print(f"Usage: {NAME} command [args...]", file=sys.stderr)
+        return 2
+    try:
+        root = Path.cwd()
+        pending = []
+        for relative, patch in PATCHES.items():
+            path = (root / relative).resolve()
+            try:
+                original = path.read_bytes()
+            except FileNotFoundError as e:
+                diagnostics.append(f"Skipped `{relative}`: {e}")
+                continue
+            try:
+                updated = patch.apply_to(original)
+            except ValueError as e:
+                raise ValueError(f"Patching `{relative}` failed: {e}") from e
+            except LookupError as e:
+                diagnostics.append(f"Skipped `{relative}`: {e}")
+                continue
+            if updated != original:
+                pending.append((path, updated))
+        for path, updated in pending:
+            replace(path, updated)
+            diagnostics.append(f"Patched {path}")
+        if diagnostics:
+            notify("\n".join(diagnostics))
+    except (OSError, ValueError) as e:
+        notify("\n".join([f"Encountered an error: {e}", *diagnostics]))
+        return 1
+    os.execvp(command[0], command)
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))