Move string compression to Python

... so that the script can know its uncompressed size and calculate the
appropriate buffer size.

Translations/lzfx.py

@@ -0,0 +1,91 @@
+import ctypes
+import functools
+import os
+from pathlib import Path
+
+HERE = Path(__file__).resolve().parent
+
+
+@functools.lru_cache(maxsize=None)
+def _liblzfx():
+    so_path = os.path.join(HERE, "../source/Objects/host/lzfx/liblzfx.so")
+    liblzfx = ctypes.cdll.LoadLibrary(so_path)
+    return liblzfx
+
+
+@functools.lru_cache(maxsize=None)
+def _fn_lzfx_compress():
+    """Returns the lzfx_compress C function.
+    ::
+
+        /*  Buffer-to buffer compression.
+
+            Supply pre-allocated input and output buffers via ibuf and obuf, and
+            their size in bytes via ilen and olen.  Buffers may not overlap.
+
+            On success, the function returns a non-negative value and the argument
+            olen contains the compressed size in bytes.  On failure, a negative
+            value is returned and olen is not modified.
+        */
+        int lzfx_compress(const void* ibuf, unsigned int ilen,
+                                void* obuf, unsigned int *olen);
+    """
+
+    fn = _liblzfx().lzfx_compress
+    fn.argtype = [
+        ctypes.c_char_p,
+        ctypes.c_uint,
+        ctypes.c_char_p,
+        ctypes.POINTER(ctypes.c_uint),
+    ]
+    fn.restype = ctypes.c_int
+    return fn
+
+
+def compress(data: bytes) -> bytes:
+    """Returns a bytes object of the lzfx-compressed data."""
+
+    fn_compress = _fn_lzfx_compress()
+
+    output_buffer_len = len(data) + 8
+
+    ibuf = data
+    ilen = len(ibuf)
+    obuf = ctypes.create_string_buffer(output_buffer_len)
+    olen = ctypes.c_uint(output_buffer_len)
+
+    res = fn_compress(ibuf, ilen, obuf, ctypes.byref(olen))
+
+    if res < 0:
+        raise LzfxError(res)
+    else:
+        return bytes(obuf[: olen.value])  # type: ignore
+
+
+class LzfxError(Exception):
+    """Exception raised for lzfx compression or decompression error.
+
+    Attributes:
+        error_code -- The source error code, which is a negative integer
+        error_name -- The constant name of the error
+        message -- explanation of the error
+    """
+
+    # define LZFX_ESIZE      -1      /* Output buffer too small */
+    # define LZFX_ECORRUPT   -2      /* Invalid data for decompression */
+    # define LZFX_EARGS      -3      /* Arguments invalid (NULL) */
+
+    def __init__(self, error_code):
+        self.error_code = error_code
+        if error_code == -1:
+            self.error_name = "LZFX_ESIZE"
+            self.message = "Output buffer too small"
+        elif error_code == -2:
+            self.error_name = "LZFX_ECORRUPT"
+            self.message = "Invalid data for decompression"
+        elif error_code == -3:
+            self.error_name = "LZFX_EARGS"
+            self.message = "Arguments invalid (NULL)"
+        else:
+            self.error_name = "UNKNOWN"
+            self.message = "Unknown error"