1 files changed, 175 insertions, 0 deletions
diff --git a/netlib/http/encoding.py b/netlib/http/encoding.py
new file mode 100644
index 00000000..e123a033
--- /dev/null
+++ b/netlib/http/encoding.py
@@ -0,0 +1,175 @@
+"""
+Utility functions for decoding response bodies.
+"""
+
+import codecs
+import collections
+from io import BytesIO
+
+import gzip
+import zlib
+import brotli
+
+from typing import Union
+
+
+# We have a shared single-element cache for encoding and decoding.
+# This is quite useful in practice, e.g.
+# flow.request.content = flow.request.content.replace(b"foo", b"bar")
+# does not require an .encode() call if content does not contain b"foo"
+CachedDecode = collections.namedtuple("CachedDecode", "encoded encoding errors decoded")
+_cache = CachedDecode(None, None, None, None)
+
+
+def decode(encoded: Union[str, bytes], encoding: str, errors: str='strict') -> Union[str, bytes]:
+    """
+    Decode the given input object
+
+    Returns:
+        The decoded value
+
+    Raises:
+        ValueError, if decoding fails.
+    """
+    if len(encoded) == 0:
+        return encoded
+
+    global _cache
+    cached = (
+        isinstance(encoded, bytes) and
+        _cache.encoded == encoded and
+        _cache.encoding == encoding and
+        _cache.errors == errors
+    )
+    if cached:
+        return _cache.decoded
+    try:
+        try:
+            decoded = custom_decode[encoding](encoded)
+        except KeyError:
+            decoded = codecs.decode(encoded, encoding, errors)
+        if encoding in ("gzip", "deflate", "br"):
+            _cache = CachedDecode(encoded, encoding, errors, decoded)
+        return decoded
+    except TypeError:
+        raise
+    except Exception as e:
+        raise ValueError("{} when decoding {} with {}: {}".format(
+            type(e).__name__,
+            repr(encoded)[:10],
+            repr(encoding),
+            repr(e),
+        ))
+
+
+def encode(decoded: Union[str, bytes], encoding: str, errors: str='strict') -> Union[str, bytes]:
+    """
+    Encode the given input object
+
+    Returns:
+        The encoded value
+
+    Raises:
+        ValueError, if encoding fails.
+    """
+    if len(decoded) == 0:
+        return decoded
+
+    global _cache
+    cached = (
+        isinstance(decoded, bytes) and
+        _cache.decoded == decoded and
+        _cache.encoding == encoding and
+        _cache.errors == errors
+    )
+    if cached:
+        return _cache.encoded
+    try:
+        try:
+            value = decoded
+            if isinstance(value, str):
+                value = decoded.encode()
+            encoded = custom_encode[encoding](value)
+        except KeyError:
+            encoded = codecs.encode(decoded, encoding, errors)
+        if encoding in ("gzip", "deflate", "br"):
+            _cache = CachedDecode(encoded, encoding, errors, decoded)
+        return encoded
+    except TypeError:
+        raise
+    except Exception as e:
+        raise ValueError("{} when encoding {} with {}: {}".format(
+            type(e).__name__,
+            repr(decoded)[:10],
+            repr(encoding),
+            repr(e),
+        ))
+
+
+def identity(content):
+    """
+        Returns content unchanged. Identity is the default value of
+        Accept-Encoding headers.
+    """
+    return content
+
+
+def decode_gzip(content):
+    gfile = gzip.GzipFile(fileobj=BytesIO(content))
+    return gfile.read()
+
+
+def encode_gzip(content):
+    s = BytesIO()
+    gf = gzip.GzipFile(fileobj=s, mode='wb')
+    gf.write(content)
+    gf.close()
+    return s.getvalue()
+
+
+def decode_brotli(content):
+    return brotli.decompress(content)
+
+
+def encode_brotli(content):
+    return brotli.compress(content)
+
+
+def decode_deflate(content):
+    """
+        Returns decompressed data for DEFLATE. Some servers may respond with
+        compressed data without a zlib header or checksum. An undocumented
+        feature of zlib permits the lenient decompression of data missing both
+        values.
+
+        http://bugs.python.org/issue5784
+    """
+    try:
+        return zlib.decompress(content)
+    except zlib.error:
+        return zlib.decompress(content, -15)
+
+
+def encode_deflate(content):
+    """
+        Returns compressed content, always including zlib header and checksum.
+    """
+    return zlib.compress(content)
+
+
+custom_decode = {
+    "none": identity,
+    "identity": identity,
+    "gzip": decode_gzip,
+    "deflate": decode_deflate,
+    "br": decode_brotli,
+}
+custom_encode = {
+    "none": identity,
+    "identity": identity,
+    "gzip": encode_gzip,
+    "deflate": encode_deflate,
+    "br": encode_brotli,
+}
+
+__all__ = ["encode", "decode"]