rohmu: zstandard (zstd) compression support.

File interface is currently broken in python-zstandard: indygreg/python-zstandard#76
As a workaround using internal file wrapper.

rohmu/compressor.py

@@ -8,13 +8,19 @@
 from .errors import InvalidConfigurationError
 from .filewrap import Sink, Stream
 from .snappyfile import SnappyFile
+from .zstdfile import open as zstd_open
 import lzma
 
 try:
     import snappy
 except ImportError:
     snappy = None
 
+try:
+    import zstandard as zstd
+except ImportError:
+    zstd = None
+
 
 def CompressionFile(dst_fp, algorithm, level=0):
     """This looks like a class to users, but is actually a function that instantiates a class based on algorithm."""
@@ -24,6 +30,9 @@ def CompressionFile(dst_fp, algorithm, level=0):
     if algorithm == "snappy":
         return SnappyFile(dst_fp, "wb")
 
+    if algorithm == "zstd":
+        return zstd_open(dst_fp, "wb")
+
     if algorithm:
         raise InvalidConfigurationError("invalid compression algorithm: {!r}".format(algorithm))
 
@@ -39,6 +48,8 @@ def __init__(self, src_fp, algorithm, level=0):
             self._compressor = lzma.LZMACompressor(lzma.FORMAT_XZ, -1, level, None)
         elif algorithm == "snappy":
             self._compressor = snappy.StreamCompressor()
+        elif algorithm == "zstd":
+            self._compressor = zstd.ZstdCompressor(level=level).compressobj()
         else:
             InvalidConfigurationError("invalid compression algorithm: {!r}".format(algorithm))
 
@@ -57,6 +68,9 @@ def DecompressionFile(src_fp, algorithm):
     if algorithm == "snappy":
         return SnappyFile(src_fp, "rb")
 
+    if algorithm == "zstd":
+        return zstd_open(src_fp, "rb")
+
     if algorithm:
         raise InvalidConfigurationError("invalid compression algorithm: {!r}".format(algorithm))
 
@@ -73,6 +87,8 @@ def _create_decompressor(self, alg):
             return snappy.StreamDecompressor()
         elif alg == "lzma":
             return lzma.LZMADecompressor()
+        elif alg == "zstd":
+            return zstd.ZstdDecompressor().decompressobj()
         raise InvalidConfigurationError("invalid compression algorithm: {!r}".format(alg))
 
     def write(self, data):

rohmu/zstdfile.py

@@ -0,0 +1,87 @@
+"""
+rohmu - file-like interface for zstd
+
+Copyright (c) 2016 Ohmu Ltd
+See LICENSE for details
+"""
+
+from . import IO_BLOCK_SIZE
+from .filewrap import FileWrap
+import io
+
+try:
+    import zstandard as zstd
+except ImportError:
+    zstd = None
+
+
+class _ZstdFileWriter(FileWrap):
+
+    def __init__(self, next_fp, level):
+        self._zstd = zstd.ZstdCompressor(level=level).compressobj()
+        super().__init__(next_fp)
+
+    def close(self):
+        if self.closed:
+            return
+        data = self._zstd.flush() or b""
+        if data:
+            self.next_fp.write(data)
+        self.next_fp.flush()
+        super().close()
+
+    def write(self, data):
+        self._check_not_closed()
+        compressed_data = self._zstd.compress(data)
+        self.next_fp.write(compressed_data)
+        self.offset += len(data)
+        return len(data)
+
+    def writable(self):
+        return True
+
+
+class _ZtsdFileReader(FileWrap):
+
+    def __init__(self, next_fp):
+        self._zstd = zstd.ZstdDecompressor().decompressobj()
+        super().__init__(next_fp)
+        self._done = False
+
+    def close(self):
+        if self.closed:
+            return
+        super().close()
+
+    def read(self, size=-1):  # pylint: disable=unused-argument
+        # NOTE: size arg is ignored, random size output is returned
+        self._check_not_closed()
+        while not self._done:
+            compressed = self.next_fp.read(IO_BLOCK_SIZE)
+            if not compressed:
+                self._done = True
+                output = self._zstd.flush() or b""
+            else:
+                output = self._zstd.decompress(compressed)
+
+            if output:
+                self.offset += len(output)
+                return output
+
+        return b""
+
+    def readable(self):
+        return True
+
+
+def open(fp, mode, level=0):  # pylint: disable=redefined-builtin
+    if zstd is None:
+        raise io.UnsupportedOperation("zstd is not available")
+
+    if mode == "wb":
+        return _ZstdFileWriter(fp, level)
+
+    if mode == "rb":
+        return _ZtsdFileReader(fp)
+
+    raise io.UnsupportedOperation("unsupported mode for zstd")