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<title>skalibs: the allreadwrite library interface</title>
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<a href="../index.html">skalibs</a><br />
<a href="http://skarnet.org/software/">Software</a><br />
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<h1> The <tt>allreadwrite</tt> library interface </h1>
<p>
The following functions are declared in the <tt>skalibs/allreadwrite.h</tt> header,
and implemented in the <tt>libskarnet.a</tt> or <tt>libskarnet.so</tt> library.
</p>
<h2> General information </h2>
<p>
<tt>allreadwrite</tt> is a set of IO function helpers. It's the
basis for safe reading and writing, either in blocking or in
non-blocking mode. The <a href="buffer.html">buffer</a> interface
relies heavily on <tt>allreadwrite</tt>.
</p>
<p>
Unless the IO you need is very simple, you generally should not
be using the <tt>allreadwrite</tt> functions directly; you should
use higher-level APIs such as <a href="buffer.html>buffer</a> and
<a href="bufalloc.html">bufalloc</a>.
</p>
<h2> Function types </h2>
<p>
<code> typedef ssize_t iofunc_t (int fd, char *buf, size_t len) </code> <br />
This is the simplified type of IO functions such as
<a href="http://www.opengroup.org/onlinepubs/9699919799/functions/read.html">read()</a>
and
<a href="http://www.opengroup.org/onlinepubs/9699919799/functions/write.html">write()</a>.
</p>
<p>
<code> typedef size_t alliofunc_t (int fd, char *buf, size_t len) </code> <br />
This is the type of an IO operation that expects <em>all</em> of its
<em>len</em> bytes to be sent or received, and that will loop around a
lower-level IO function until either <em>len</em> bytes have been
transmitted or an error has occurred. The return value is the actual
number of transmitted bytes; if this value is lesser than <em>len</em>,
it means that an error has occurred and <tt>errno</tt> is set.
</p>
<h2> Functions </h2>
<p>
<code> ssize_t sanitize_read (ssize_t r) </code> <br />
Reading functions such as <tt>read()</tt> and <tt>fd_read</tt> return
a positive number when they succeed, -1 when they fail, and 0 when they
read an EOF. No data available on the descriptor when reading in
non-blocking mode is treated as a failure: -1 EWOULDBLOCK. But sometimes
(namely, in asynchronous IO loops) it's preferrable to handle EOF as an
exception condition and EWOULDBLOCK as a normal condition.
<tt>sanitize_read()</tt>, when applied to the result of a basic reading
function, returns 0 if <em>r</em> is -1 and errno is EWOULDBLOCK (or
EAGAIN). If <em>r</em> is zero, it returns -1 EPIPE. Else it returns <em>r</em>.
</p>
<p>
(No system reading function can ever set errno to EPIPE, and the
semantics are appropriate, so EPIPE is a good candidate to signal EOF
on reading.)
</p>
<p>
<code> size_t allreadwrite (iofunc_t *f, int fd, char *s, size_t len) </code> <br />
*<em>f</em> must be a basic reading or writing function such as
<tt>fd_read</tt> or <tt>fd_write</tt>. <tt>allreadwrite()</tt> performs
*<em>f</em> on <em>fd</em>, <em>s</em> and <em>len</em> until <em>len</em>
bytes have been read or written, or until an error occurs. It returns the
total number of handled bytes, and sets errno if this number is not
<em>len</em>. <tt>allreadwrite</tt> may block if <em>fd</em> is in
blocking mode; if <em>fd</em> is in non-blocking mode, it might
set errno to EWOULDBLOCK or EAGAIN.
</p>
<p>
<code> ssize_t fd_read (int fd, char *s, size_t len) </code> <br />
<a href="safewrappers.html">Safe wrapper</a> around the
<a href="http://www.opengroup.org/onlinepubs/9699919799/functions/read.html">read()</a>
function.
</p>
<p>
<code> ssize_t fd_write (int fd, char const *s, size_t len) </code> <br />
<a href="safewrappers.html">Safe wrapper</a> around the
<a href="http://www.opengroup.org/onlinepubs/9699919799/functions/write.html">write()</a>
function.
</p>
<p>
<code> ssize_t fd_recv (int fd, char *s, size_t len, unsigned int flags) </code> <br />
<a href="safewrappers.html">Safe wrapper</a> around the
<a href="http://www.opengroup.org/onlinepubs/9699919799/functions/recv.html">recv()</a>
function.
</p>
<p>
<code> ssize_t fd_send (int fd, char const *s, size_t len, unsigned int flags) </code> <br />
<a href="safewrappers.html">Safe wrapper</a> around the
<a href="http://www.opengroup.org/onlinepubs/9699919799/functions/send.html">send()</a>
function.
</p>
<p>
<code> size_t allread (int fd, char *s, size_t len) </code> <br />
Equivalent to <code> allreadwrite(&fd_read, fd, s, len) </code>: attempts
to read <em>len</em> bytes from <em>fd</em> into <em>s</em>, looping around
<tt>fd_read()</tt> if necessary, until either <em>len</em> bytes are read or
an error occurs. EOF is reported as EPIPE.
</p>
<p>
<code> size_t allwrite (int fd, char const *s, size_t len) </code> <br />
Equivalent to <code> allreadwrite((iofunc_t *)&fd_write, fd, s, len) </code>:
attempts to write <em>len</em> bytes from <em>s</em> to <em>fd</em>, looping
around <tt>fd_write()</tt> if necessary, until either <em>len</em> bytes are
written or an error occurs.
</p>
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