java-manifest-py

Encode/decode Java's META-INF/MANIFEST.MF in Python.

Installation

To install the latest release on PyPI, run:

$ pip install java-manifest

Usage

A manifest is represented by a list of dictionaries, where each dictionary corresponds to an empty-line delimited section of the manifest and each dictionary has str keys and str values.

java_manifest.loads takes a string containing manifest-formatted data and returns a list of dictionaries, where each dictionary is a section in the manifest. java_manifest.load does the same, using any typing.TextIO readable object.

>>> import java_manifest
>>> manifest_str = """
... Name: README-Example-1
... Long-Line: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
...  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
...
... Name: README-Example-2
... Foo: Bar
... """
>>> manifest = java_manifest.loads(manifest_str)
>>> print(manifest)
[{'Name': 'README-Example-1', 'Long-Line': 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'}, {'Name': 'README-Example-2', 'Foo': 'Bar'}]

Similarly, java_manifest.dumps returns a string of manifest-formatted data from a list of dictionaries, where each dictionary is a section in the manifest. java_manifest.dump does the same, writing into any typing.TextIO writable object.

>>> import java_manifest
>>> manifest = [
...     {
...         "Name": "README-Example",
...         "Some-Str": "Some random string",
...     },
... ]
>>> manifest_str = java_manifest.dumps(manifest)
>>> print(manifest_str)
Name: README-Example
Some-Str: Some random string
<BLANKLINE>

There is also a from_jar function that finds the META-INF/MANIFEST.MF file within the jar and java_manifest.loads that.

>>> import java_manifest
>>> manifest = java_manifest.from_jar("test_files/simple.jar")

Custom Encoders/Decoders

Because Java's manifest file format does not deal with structured/typed values, specific uses of the format create ad-hoc encoding/decoding rules that convert structured/typed data to and from a string so it can be stored in a manifest. The encoder and decoder arguments for dumping and loading respectively are responsible for handling this. An encoder and decoder both take in a key-value pair. However, an encoder receives potentially structured/typed data as the value and returns a string, while a decoder receives string values and returns potentially structured/typed data.

As we have already see, the default encoder and decoder does no transformation and prevents you from attempting to dump non-string data.

>>> import java_manifest
>>> print(java_manifest.dumps([{"foo": "bar"}]))
foo: bar

>>> print(java_manifest.dumps([{"int": 1}]))
Traceback (most recent call last):
  ...
ValueError: key 'int' has type <class 'int'> value, expected str

You can however describe more custom encoders that support, for example, lists of strings.

>>> def encode(key, val):
...     if isinstance(val, list):
...         return ",".join(val)
...     return val
>>> print(java_manifest.dumps([{"foo": "bar", "names": ["alice", "bob", "charlie"]}], encoder=encode))
foo: bar
names: alice,bob,charlie
<BLANKLINE>

Similarly for custom decoders.

>>> import java_manifest
>>> def decode(key, val):
...     # In reality you'd probably want to target only specific keys, to avoid
...     # messing up random strings containing commas. This is just an example.
...     vals = val.split(",")
...     if len(vals) == 1:
...         return val
...     else:
...         return vals
>>> manifest = java_manifest.loads("foo: bar\r\nnames: alice,bob,charlie", decoder=decode)
>>> print(manifest)
[{'foo': 'bar', 'names': ['alice', 'bob', 'charlie']}]