Haskell bzlib-conduit/zlib-conduit示例 [英] Haskell bzlib-conduit/zlib-conduit example

问题描述

假设我们按如下方式创建文件a.txt.gz:

Let's assume we create the file a.txt.gz as follows:

$ echo "foobar" > a.txt
$ gzip a.txt

我打算使用 zlib-conduit 来在Haskell中模拟zcat

我正在寻找一个简单的示例，该示例也可以应用于 bzlib-conduit .

I'm looking for a simple example that can also be applied to bzlib-conduit.

注意:该问题以Q& A风格立即得到回答.因此，它故意不显示任何研究成果.

Note: This question was answered immediately in a Q&A-Style. Therefore it intentionally does not show any research effort.

推荐答案

如果您打算使用conduit s，我强烈建议您阅读优秀的

If you intend to work with conduits, I highly recommend to read the excellent Conduit overview by Michael Snoyman and the FP Complete tutorial on this topic first.

我已打开我的-vv标志，使其适合Haskell初学者(如我自己).

I've turned on my -vv flag to make this suitable for Haskell beginners (like myself).

您需要三件事:

• 文件源
• zlib减压过滤器
• 一个标准输出水槽

让我们从这个简单的文件复制示例开始:

Let's start off with this simple file copy example:

import Data.Conduit (runResourceT, ($$))
import qualified Data.Conduit.Binary as CB
import Data.Conduit.Zlib

main = do
    runResourceT $ CB.sourceFile "input.txt" $$ CB.sinkFile "output.txt"

我们需要在此处进行哪些修改?

What do we need to modify here?

• 输入的文件名不是a.txt.gz
• zlib解压缩器丢失
• 我们要输出到stdout，而不是output.txt

• The input filename is not a.txt.gz
• zlib decompressor is missing
• We want to output to stdout, not to output.txt

实际上是 decompress文档包含有关如何解压缩的示例.

Indeed the decompress documentation contains an example of how to decompress.

请注意，您不能将decompress用于gzip生成的文件. decompress解压缩由旧版compress UNIX程序生成的.Z文件.

Note that you can't use decompress for gzip-generated files. decompress decompresses .Z files generated by the old compress UNIX program.

修改上面的示例后，我们得到:

After modifying the above example we get:

import Data.Conduit (runResourceT, ($$), ($=))
import qualified Data.Conduit.Binary as CB
import Data.Conduit.Zlib
import System.IO

main = do
    runResourceT $ CB.sourceFile "a.txt.gz" $= ungzip $$ CB.sinkHandle stdout

使用bzlib-conduit时的差异很小:

import Data.Conduit (runResourceT, ($$), ($=))
import qualified Data.Conduit.Binary as CB
import Data.Conduit.BZlib
import System.IO

main = do
    runResourceT $ CB.sourceFile "a.txt.bz2" $= bunzip2 $$ CB.sinkHandle stdout

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