Tblue · September 4, 2025 21:07 · Mar 19, 2022 · Mar 19, 2022 · Jul 24, 2015 · Jul 23, 2015
diff --git a/mozlz4a.py b/mozlz4a.py
@@ -104,7 +104,9 @@ def get_argparser():
     p.add_argument(
         "out_file",
         type=BinFileArg("w"),
-        help="Path to output file. `-' means standard output."
+        nargs="?",
+        default="-",
+        help="Path to output file. `-' means standard output (and is the default)."
     )
 
     return p

diff --git a/mozlz4a.py b/mozlz4a.py
@@ -1,15 +1,28 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
+# vim: sw=4 ts=4 et tw=100 cc=+1
+#
+####################################################################################################
+#                                           DESCRIPTION                                            #
+####################################################################################################
 #
 # Decompressor/compressor for files in Mozilla's "mozLz4" format. Firefox uses this file format to
 # compress e. g. bookmark backups (*.jsonlz4).
 #
 # This file format is in fact just plain LZ4 data with a custom header (magic number [8 bytes] and
 # uncompressed file size [4 bytes, little endian]).
 #
-# This Python 3 script requires the LZ4 bindings for Python, see: https://pypi.python.org/pypi/lz4
+####################################################################################################
+#                                           DEPENDENCIES                                           #
+####################################################################################################
+#
+# - Tested with Python 3.10
+# - LZ4 bindings for Python, version 4.x: https://pypi.python.org/pypi/lz4
 #
+####################################################################################################
+#                                             LICENSE                                              #
+####################################################################################################
 #
-# Copyright (c) 2015, Tilman Blumenbach
+# Copyright (c) 2015-2022, Tilman Blumenbach
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without modification, are permitted
@@ -30,79 +43,105 @@
 # IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 # OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-import lz4
+import argparse
 import sys
 
-from argparse import ArgumentParser
+import lz4.block
 
 
-class MozLz4aError(Exception):
-    pass
+class BinFileArg:
+    def __init__(self, mode):
+        self._mode = mode
 
+    def __call__(self, arg):
+        objs = {
+            "r": sys.stdin.buffer,
+            "w": sys.stdout.buffer,
+        }
 
-class InvalidHeader(MozLz4aError):
-    def __init__(self, msg):
-        self.msg = msg
+        if arg == "-":
+            return objs[self._mode]
 
-    def __str__(self):
-        return self.msg
+        try:
+            return open(arg, self._mode + "b")
+        except OSError as e:
+            raise argparse.ArgumentTypeError(
+                "failed to open file for %s: %s" % (
+                    "reading" if self._mode == "r" else "writing",
+                    e
+                )
+            )
 
 
 def decompress(file_obj):
     if file_obj.read(8) != b"mozLz40\0":
-        raise InvalidHeader("Invalid magic number")
+        raise ValueError("Invalid magic number")
+
+    return lz4.block.decompress(file_obj.read())
 
-    return lz4.decompress(file_obj.read())
 
 def compress(file_obj):
-    compressed = lz4.compress(file_obj.read())
+    compressed = lz4.block.compress(file_obj.read())
     return b"mozLz40\0" + compressed
 
 
-if __name__ == "__main__":
-    argparser = ArgumentParser(description="MozLz4a compression/decompression utility")
-    argparser.add_argument(
-            "-d", "--decompress", "--uncompress",
-            action="store_true",
-            help="Decompress the input file instead of compressing it."
-        )
-    argparser.add_argument(
-            "in_file",
-            help="Path to input file."
-        )
-    argparser.add_argument(
-            "out_file",
-            help="Path to output file."
-        )
+def get_argparser():
+    p = argparse.ArgumentParser(
+        description="MozLz4a compression/decompression utility"
+    )
 
-    parsed_args = argparser.parse_args()
+    p.add_argument(
+        "-d", "--decompress", "--uncompress",
+        action="store_true",
+        help="Decompress the input file instead of compressing it."
+    )
 
+    p.add_argument(
+        "in_file",
+        type=BinFileArg("r"),
+        help="Path to input file. `-' means standard input."
+    )
+    p.add_argument(
+        "out_file",
+        type=BinFileArg("w"),
+        help="Path to output file. `-' means standard output."
+    )
 
-    try:
-        in_file = open(parsed_args.in_file, "rb")
-    except IOError as e:
-        print("Could not open input file `%s' for reading: %s" % (parsed_args.in_file, e), file=sys.stderr)
-        sys.exit(2)
-
-    try:
-        out_file = open(parsed_args.out_file, "wb")
-    except IOError as e:
-        print("Could not open output file `%s' for writing: %s" % (parsed_args.out_file, e), file=sys.stderr)
-        sys.exit(3)
+    return p
+
+
+def main():
+    args = get_argparser().parse_args()
 
     try:
-        if parsed_args.decompress:
-            data = decompress(in_file)
-        else:
-            data = compress(in_file)
+        with args.in_file as fh:
+            if args.decompress:
+                data = decompress(fh)
+            else:
+                data = compress(fh)
     except Exception as e:
-        print("Could not compress/decompress file `%s': %s" % (parsed_args.in_file, e), file=sys.stderr)
+        print(
+            "Could not compress/decompress file `%s': %s" % (
+                args.in_file.name,
+                e
+            ),
+            file=sys.stderr
+        )
         sys.exit(4)
 
     try:
-        out_file.write(data)
-    except IOError as e:
-        print("Could not write to output file `%s': %s" % (parsed_args.out_file, e), file=sys.stderr)
+        with args.out_file as fh:
+            fh.write(data)
+    except Exception as e:
+        print(
+            "Could not write to output file `%s': %s" % (
+                args.out_file.name,
+                e
+            ),
+            file=sys.stderr
+        )
         sys.exit(5)
-    finally:
-        out_file.close()
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/mozlz4a.py b/mozlz4a.py
@@ -34,7 +34,6 @@
 import sys
 
 from argparse import ArgumentParser
-from io import BytesIO
 
 
 class MozLz4aError(Exception):
@@ -56,12 +55,8 @@ def decompress(file_obj):
     return lz4.decompress(file_obj.read())
 
 def compress(file_obj):
-    out = BytesIO()
-
-    out.write(b"mozLz40\0")
-    out.write(lz4.compress(file_obj.read()))
-
-    return out.getbuffer()
+    compressed = lz4.compress(file_obj.read())
+    return b"mozLz40\0" + compressed
 
 
 if __name__ == "__main__":

diff --git a/mozlz4a.py b/mozlz4a.py
@@ -3,7 +3,7 @@
 # Decompressor/compressor for files in Mozilla's "mozLz4" format. Firefox uses this file format to
 # compress e. g. bookmark backups (*.jsonlz4).
 #
-# This file format is in fact just LZ4 data with a custom header (magic number [8 bytes] and
+# This file format is in fact just plain LZ4 data with a custom header (magic number [8 bytes] and
 # uncompressed file size [4 bytes, little endian]).
 #
 # This Python 3 script requires the LZ4 bindings for Python, see: https://pypi.python.org/pypi/lz4

diff --git a/mozlz4a.py b/mozlz4a.py
@@ -3,10 +3,10 @@
 # Decompressor/compressor for files in Mozilla's "mozLz4" format. Firefox uses this file format to
 # compress e. g. bookmark backups (*.jsonlz4).
 #
-# This file format is in fact just an LZ4 stream with a custom header (magic number [8 bytes] and
+# This file format is in fact just LZ4 data with a custom header (magic number [8 bytes] and
 # uncompressed file size [4 bytes, little endian]).
 #
-# This script requires the LZ4 bindings for Python, see: https://pypi.python.org/pypi/lz4
+# This Python 3 script requires the LZ4 bindings for Python, see: https://pypi.python.org/pypi/lz4
 #
 #
 # Copyright (c) 2015, Tilman Blumenbach

diff --git a/mozlz4a.py b/mozlz4a.py
@@ -0,0 +1,113 @@
+#!/usr/bin/env python
+#
+# Decompressor/compressor for files in Mozilla's "mozLz4" format. Firefox uses this file format to
+# compress e. g. bookmark backups (*.jsonlz4).
+#
+# This file format is in fact just an LZ4 stream with a custom header (magic number [8 bytes] and
+# uncompressed file size [4 bytes, little endian]).
+#
+# This script requires the LZ4 bindings for Python, see: https://pypi.python.org/pypi/lz4
+#
+#
+# Copyright (c) 2015, Tilman Blumenbach
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted
+# provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this list of conditions
+#    and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+#    conditions and the following disclaimer in the documentation and/or other materials provided
+#    with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import lz4
+import sys
+
+from argparse import ArgumentParser
+from io import BytesIO
+
+
+class MozLz4aError(Exception):
+    pass
+
+
+class InvalidHeader(MozLz4aError):
+    def __init__(self, msg):
+        self.msg = msg
+
+    def __str__(self):
+        return self.msg
+
+
+def decompress(file_obj):
+    if file_obj.read(8) != b"mozLz40\0":
+        raise InvalidHeader("Invalid magic number")
+
+    return lz4.decompress(file_obj.read())
+
+def compress(file_obj):
+    out = BytesIO()
+
+    out.write(b"mozLz40\0")
+    out.write(lz4.compress(file_obj.read()))
+
+    return out.getbuffer()
+
+
+if __name__ == "__main__":
+    argparser = ArgumentParser(description="MozLz4a compression/decompression utility")
+    argparser.add_argument(
+            "-d", "--decompress", "--uncompress",
+            action="store_true",
+            help="Decompress the input file instead of compressing it."
+        )
+    argparser.add_argument(
+            "in_file",
+            help="Path to input file."
+        )
+    argparser.add_argument(
+            "out_file",
+            help="Path to output file."
+        )
+
+    parsed_args = argparser.parse_args()
+
+
+    try:
+        in_file = open(parsed_args.in_file, "rb")
+    except IOError as e:
+        print("Could not open input file `%s' for reading: %s" % (parsed_args.in_file, e), file=sys.stderr)
+        sys.exit(2)
+
+    try:
+        out_file = open(parsed_args.out_file, "wb")
+    except IOError as e:
+        print("Could not open output file `%s' for writing: %s" % (parsed_args.out_file, e), file=sys.stderr)
+        sys.exit(3)
+
+    try:
+        if parsed_args.decompress:
+            data = decompress(in_file)
+        else:
+            data = compress(in_file)
+    except Exception as e:
+        print("Could not compress/decompress file `%s': %s" % (parsed_args.in_file, e), file=sys.stderr)
+        sys.exit(4)
+
+    try:
+        out_file.write(data)
+    except IOError as e:
+        print("Could not write to output file `%s': %s" % (parsed_args.out_file, e), file=sys.stderr)
+        sys.exit(5)
+    finally:
+        out_file.close()