2020-03-02 11:50:34 -05:00
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<title>BIO_read</title>
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<p><a name="__index__"></a></p>
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<ul>
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<li><a href="#name">NAME</a></li>
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<li><a href="#synopsis">SYNOPSIS</a></li>
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<li><a href="#description">DESCRIPTION</a></li>
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<li><a href="#return_values">RETURN VALUES</a></li>
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<li><a href="#notes">NOTES</a></li>
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<li><a href="#see_also">SEE ALSO</a></li>
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<li><a href="#history">HISTORY</a></li>
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<li><a href="#copyright">COPYRIGHT</a></li>
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<hr />
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<h1><a name="name">NAME</a></h1>
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<p>BIO_read_ex, BIO_write_ex, BIO_read, BIO_write, BIO_gets, BIO_puts
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- BIO I/O functions</p>
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<p>
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</p>
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<hr />
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<h1><a name="synopsis">SYNOPSIS</a></h1>
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<pre>
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#include <openssl/bio.h></pre>
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<pre>
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int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes);
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int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written);</pre>
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<pre>
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int BIO_read(BIO *b, void *data, int dlen);
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int BIO_gets(BIO *b, char *buf, int size);
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int BIO_write(BIO *b, const void *data, int dlen);
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int BIO_puts(BIO *b, const char *buf);</pre>
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<p>
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</p>
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<hr />
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<h1><a name="description">DESCRIPTION</a></h1>
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<p><code>BIO_read_ex()</code> attempts to read <strong>dlen</strong> bytes from BIO <strong>b</strong> and places the data
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in <strong>data</strong>. If any bytes were successfully read then the number of bytes read is
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stored in <strong>*readbytes</strong>.</p>
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<p><code>BIO_write_ex()</code> attempts to write <strong>dlen</strong> bytes from <strong>data</strong> to BIO <strong>b</strong>. If
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successful then the number of bytes written is stored in <strong>*written</strong>.</p>
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<p><code>BIO_read()</code> attempts to read <strong>len</strong> bytes from BIO <strong>b</strong> and places
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the data in <strong>buf</strong>.</p>
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<p><code>BIO_gets()</code> performs the BIOs "gets" operation and places the data
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in <strong>buf</strong>. Usually this operation will attempt to read a line of data
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from the BIO of maximum length <strong>size-1</strong>. There are exceptions to this,
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however; for example, <code>BIO_gets()</code> on a digest BIO will calculate and
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return the digest and other BIOs may not support <code>BIO_gets()</code> at all.
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The returned string is always NUL-terminated and the '\n' is preserved
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if present in the input data.</p>
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<p><code>BIO_write()</code> attempts to write <strong>len</strong> bytes from <strong>buf</strong> to BIO <strong>b</strong>.</p>
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<p><code>BIO_puts()</code> attempts to write a NUL-terminated string <strong>buf</strong> to BIO <strong>b</strong>.</p>
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<p>
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</p>
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<hr />
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<h1><a name="return_values">RETURN VALUES</a></h1>
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<p><code>BIO_read_ex()</code> and <code>BIO_write_ex()</code> return 1 if data was successfully read or
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written, and 0 otherwise.</p>
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<p>All other functions return either the amount of data successfully read or
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written (if the return value is positive) or that no data was successfully
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read or written if the result is 0 or -1. If the return value is -2 then
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the operation is not implemented in the specific BIO type. The trailing
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NUL is not included in the length returned by <code>BIO_gets()</code>.</p>
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<p>
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</p>
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<hr />
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<h1><a name="notes">NOTES</a></h1>
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<p>A 0 or -1 return is not necessarily an indication of an error. In
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particular when the source/sink is non-blocking or of a certain type
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it may merely be an indication that no data is currently available and that
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the application should retry the operation later.</p>
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<p>One technique sometimes used with blocking sockets is to use a system call
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(such as <code>select()</code>, <code>poll()</code> or equivalent) to determine when data is available
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and then call <code>read()</code> to read the data. The equivalent with BIOs (that is call
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<code>select()</code> on the underlying I/O structure and then call <code>BIO_read()</code> to
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read the data) should <strong>not</strong> be used because a single call to <code>BIO_read()</code>
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can cause several reads (and writes in the case of SSL BIOs) on the underlying
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I/O structure and may block as a result. Instead <code>select()</code> (or equivalent)
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should be combined with non blocking I/O so successive reads will request
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a retry instead of blocking.</p>
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<p>See <em>BIO_should_retry(3)</em> for details of how to
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determine the cause of a retry and other I/O issues.</p>
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<p>If the <code>BIO_gets()</code> function is not supported by a BIO then it possible to
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work around this by adding a buffering BIO <em>BIO_f_buffer(3)</em>
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to the chain.</p>
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<p>
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</p>
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<hr />
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<h1><a name="see_also">SEE ALSO</a></h1>
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<p><em>BIO_should_retry(3)</em></p>
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<p>
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</p>
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<hr />
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<h1><a name="history">HISTORY</a></h1>
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<p><code>BIO_gets()</code> on 1.1.0 and older when called on <code>BIO_fd()</code> based BIO does not
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keep the '\n' at the end of the line in the buffer.</p>
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<p>
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</p>
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<hr />
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<h1><a name="copyright">COPYRIGHT</a></h1>
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<p>Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.</p>
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2020-03-02 12:19:21 -05:00
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<p>Licensed under the OpenSSL license (the "License"). You may not use
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2020-03-02 11:50:34 -05:00
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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<a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>
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