我可以从HTTP（s）octetstream读取拼花吗？

Question

某些后端端点返回八位字节流中的拼花文件

在熊猫中，我可以这样做：

result = requests.get("https://..../file.parquet")
df = pd.read_parquet(io.BytesIO(result.content))

我能在达斯克做吗

此代码：

dd.read_parquet("https://..../file.parquet")

引发异常（显然，这是一个类似字节的对象）：

  File "to_parquet_dask.py", line 153, in <module>
    main(*parser.parse_args())
  File "to_parquet_dask.py", line 137, in main
    download_parquet(
  File "to_parquet_dask.py", line 121, in download_parquet
    dd.read_parquet(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/dask/dataframe/io/parquet/core.py", line 313, in read_parquet
    read_metadata_result = engine.read_metadata(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/dask/dataframe/io/parquet/fastparquet.py", line 733, in read_metadata
    parts, pf, gather_statistics, base_path = _determine_pf_parts(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/dask/dataframe/io/parquet/fastparquet.py", line 148, in _determine_pf_parts
    elif fs.isdir(paths[0]):
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fsspec/asyn.py", line 88, in wrapper
    return sync(self.loop, func, *args, **kwargs)
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fsspec/asyn.py", line 69, in sync
    raise result[0]
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fsspec/asyn.py", line 25, in _runner
    result[0] = await coro
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fsspec/implementations/http.py", line 418, in _isdir
    return bool(await self._ls(path))
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fsspec/implementations/http.py", line 195, in _ls
    out = await self._ls_real(url, detail=detail, **kwargs)
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fsspec/implementations/http.py", line 150, in _ls_real
    text = await r.text()
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/aiohttp/client_reqrep.py", line 1082, in text
    return self._body.decode(encoding, errors=errors)  # type: ignore
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x90 in position 7: invalid start byte

UPD

由于@mdurant answer对fsspec进行了更改，我得到了一个错误

ValueError: Cannot seek streaming HTTP file

所以我把“simplecache:：”放在我的url上，然后我面对下一个：

Traceback (most recent call last):
  File "to_parquet_dask.py", line 161, in <module>
    main(*parser.parse_args())
  File "to_parquet_dask.py", line 145, in main
    download_parquet(
  File "to_parquet_dask.py", line 128, in download_parquet
    dd.read_parquet(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/dask/dataframe/io/parquet/core.py", line 313, in read_parquet
    read_metadata_result = engine.read_metadata(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/dask/dataframe/io/parquet/fastparquet.py", line 733, in read_metadata
    parts, pf, gather_statistics, base_path = _determine_pf_parts(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/dask/dataframe/io/parquet/fastparquet.py", line 185, in _determine_pf_parts
    pf = ParquetFile(
  File "/home/bc30138/Documents/CODE/flexydrive/driver_style/.venv/lib/python3.8/site-packages/fastparquet/api.py", line 127, in __init__
    raise ValueError("Opening directories without a _metadata requires"
ValueError: Opening directories without a _metadata requiresa filesystem compatible with fsspec

临时解决方案

也许这种方式是肮脏的，不是最佳的，但有些工作：

@dask.delayed
def parquet_from_http(url, token):
    result = requests.get(
        url,
        headers={'Authorization': token}
    )
    return pd.read_parquet(io.BytesIO(result.content))
    
delayed_download = parquet_from_http(url, token)
df = dd.from_delayed(delayed_download, meta=meta)

在这种方法中，p.s.元参数是必要的，因为否则dask将使用此函数两次：查找元，而不是计算，因此将发出两个请求

Answer 1

这不是一个答案，但我相信fsspec中的以下更改将解决您的问题。如果您愿意尝试并确认，我们可以制作一个补丁

 - a/fsspec/implementations/http.py
+++ b/fsspec/implementations/http.py
@@ -472,7 +472,10 @@ class HTTPFileSystem(AsyncFileSystem):

     async def _isdir(self, path):
         # override, since all URLs are (also) files
-        return bool(await self._ls(path))
+        try:
+            return bool(await self._ls(path))
+        except (FileNotFoundError, ValueError):
+            return False

（如果这样便于安装，我们可以将其放在分支中）

-编辑-

第二个问题（在两个拼花引擎中都是一样的）源于服务器要么不提供文件的大小，要么不允许范围获取。拼花地板格式需要随机访问数据才能读取。解决这个问题的唯一方法（除了改进服务器）是在本地复制整个文件，例如，在URL前面加上“simplecache:：”