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POData.ByteString.Lazy.Char8 newline conversion on Windows---is the documentation misleading?
 

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    <p>I have a question about the Data.ByteString.Lazy.Char8 library in the bytestring library. Specifically, my question concerns the readFile function, which is documented as follows:</p> <blockquote> <p>Read an entire file lazily into a ByteString. Use 'text mode' on Windows to interpret newlines </p> </blockquote> <p>I'm interested in the claim that this function will 'use text mode on Windows to interpret newlines'. The source code for the function is as follows:</p> <pre><code>-- | Read an entire file /lazily/ into a 'ByteString'. Use 'text mode' -- on Windows to interpret newlines readFile :: FilePath -&gt; IO ByteString readFile f = openFile f ReadMode &gt;&gt;= hGetContents </code></pre> <p>and we see that, in one sense, the claim in the documentation is perfectly true: the <code>openFile</code> function (as opposed to <code>openBinaryFile</code>) has been used, and so newline conversion will be enabled for the file. </p> <p><em>But</em>, the file will then be passed to hGetContents. This will call <code>Data.ByteString.hGetNonBlocking</code> (see the source code <a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.1.5/doc/html/src/Data-ByteString-Lazy.html#hGetContents" rel="nofollow">here</a> and <a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.1.5/doc/html/src/Data-ByteString-Lazy.html#hGetContentsN" rel="nofollow">here</a>), which is meant to be a non blocking version of <code>Data.ByteString.hGet</code> (see <a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.1.7/doc/html/Data-ByteString.html#v%3ahGetNonBlocking" rel="nofollow">the documentation</a>); and (finally) <code>Data.ByteString.hGet</code> calls <code>GHC.IO.Handle.hGetBuf</code> (see <a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.1.7/doc/html/Data-ByteString.html#v%3ahGet" rel="nofollow">the documentation</a> or <a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.1.7/doc/html/src/Data-ByteString.html#hGet" rel="nofollow">the source code</a>). This function's <a href="http://hackage.haskell.org/packages/archive/base/4.2.0.2/doc/html/GHC-IO-Handle.html#v%3ahGetBuf" rel="nofollow">documentation</a> says that </p> <blockquote> <p>hGetBuf ignores whatever TextEncoding the Handle is currently using, and reads bytes directly from the underlying IO device.</p> </blockquote> <p>which suggests that the fact that we opened the file using <code>readFile</code> rather than <code>readBinaryFile</code> is irrelevant: the data will be read without transforming newlines, notwithstanding the claim in the documentation referred to at the beginning of the question.</p> <p>So, the nub of the question: 1. Am I missing something? Is there some sense in which the statement 'that Data.ByteString.Lazy.Char8.readFile uses text mode on Windows to interpret newlines' is true? Or is the documentation just misleading?</p> <p>P.S. Testing also indicates that this function, at least when used naively as I was using it, does no newline conversion on Windows.</p>
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