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authorJelmer Vernooij <jelmer@samba.org>2008-10-21 14:51:13 +0200
committerJelmer Vernooij <jelmer@samba.org>2008-10-21 14:51:13 +0200
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-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
- "http://www.w3.org/TR/REC-html40/loose.dtd">
-<html>
-<head>
-<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
-<title>zlib Usage Example</title>
-<!-- Copyright (c) 2004 Mark Adler. -->
-</head>
-<body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#00A000">
-<h2 align="center"> zlib Usage Example </h2>
-We often get questions about how the <tt>deflate()</tt> and <tt>inflate()</tt> functions should be used.
-Users wonder when they should provide more input, when they should use more output,
-what to do with a <tt>Z_BUF_ERROR</tt>, how to make sure the process terminates properly, and
-so on. So for those who have read <tt>zlib.h</tt> (a few times), and
-would like further edification, below is an annotated example in C of simple routines to compress and decompress
-from an input file to an output file using <tt>deflate()</tt> and <tt>inflate()</tt> respectively. The
-annotations are interspersed between lines of the code. So please read between the lines.
-We hope this helps explain some of the intricacies of <em>zlib</em>.
-<p>
-Without further adieu, here is the program <a href="zpipe.c"><tt>zpipe.c</tt></a>:
-<pre><b>
-/* zpipe.c: example of proper use of zlib's inflate() and deflate()
- Not copyrighted -- provided to the public domain
- Version 1.2 9 November 2004 Mark Adler */
-
-/* Version history:
- 1.0 30 Oct 2004 First version
- 1.1 8 Nov 2004 Add void casting for unused return values
- Use switch statement for inflate() return values
- 1.2 9 Nov 2004 Add assertions to document zlib guarantees
- */
-</b></pre><!-- -->
-We now include the header files for the required definitions. From
-<tt>stdio.h</tt> we use <tt>fopen()</tt>, <tt>fread()</tt>, <tt>fwrite()</tt>,
-<tt>feof()</tt>, <tt>ferror()</tt>, and <tt>fclose()</tt> for file i/o, and
-<tt>fputs()</tt> for error messages. From <tt>string.h</tt> we use
-<tt>strcmp()</tt> for command line argument processing.
-From <tt>assert.h</tt> we use the <tt>assert()</tt> macro.
-From <tt>zlib.h</tt>
-we use the basic compression functions <tt>deflateInit()</tt>,
-<tt>deflate()</tt>, and <tt>deflateEnd()</tt>, and the basic decompression
-functions <tt>inflateInit()</tt>, <tt>inflate()</tt>, and
-<tt>inflateEnd()</tt>.
-<pre><b>
-#include &lt;stdio.h&gt;
-#include &lt;string.h&gt;
-#include &lt;assert.h&gt;
-#include "zlib.h"
-</b></pre><!-- -->
-<tt>CHUNK</tt> is simply the buffer size for feeding data to and pulling data
-from the <em>zlib</em> routines. Larger buffer sizes would be more efficient,
-especially for <tt>inflate()</tt>. If the memory is available, buffers sizes
-on the order of 128K or 256K bytes should be used.
-<pre><b>
-#define CHUNK 16384
-</b></pre><!-- -->
-The <tt>def()</tt> routine compresses data from an input file to an output file. The output data
-will be in the <em>zlib</em> format, which is different from the <em>gzip</em> or <em>zip</em>
-formats. The <em>zlib</em> format has a very small header of only two bytes to identify it as
-a <em>zlib</em> stream and to provide decoding information, and a four-byte trailer with a fast
-check value to verify the integrity of the uncompressed data after decoding.
-<pre><b>
-/* Compress from file source to file dest until EOF on source.
- def() returns Z_OK on success, Z_MEM_ERROR if memory could not be
- allocated for processing, Z_STREAM_ERROR if an invalid compression
- level is supplied, Z_VERSION_ERROR if the version of zlib.h and the
- version of the library linked do not match, or Z_ERRNO if there is
- an error reading or writing the files. */
-int def(FILE *source, FILE *dest, int level)
-{
-</b></pre>
-Here are the local variables for <tt>def()</tt>. <tt>ret</tt> will be used for <em>zlib</em>
-return codes. <tt>flush</tt> will keep track of the current flushing state for <tt>deflate()</tt>,
-which is either no flushing, or flush to completion after the end of the input file is reached.
-<tt>have</tt> is the amount of data returned from <tt>deflate()</tt>. The <tt>strm</tt> structure
-is used to pass information to and from the <em>zlib</em> routines, and to maintain the
-<tt>deflate()</tt> state. <tt>in</tt> and <tt>out</tt> are the input and output buffers for
-<tt>deflate()</tt>.
-<pre><b>
- int ret, flush;
- unsigned have;
- z_stream strm;
- char in[CHUNK];
- char out[CHUNK];
-</b></pre><!-- -->
-The first thing we do is to initialize the <em>zlib</em> state for compression using
-<tt>deflateInit()</tt>. This must be done before the first use of <tt>deflate()</tt>.
-The <tt>zalloc</tt>, <tt>zfree</tt>, and <tt>opaque</tt> fields in the <tt>strm</tt>
-structure must be initialized before calling <tt>deflateInit()</tt>. Here they are
-set to the <em>zlib</em> constant <tt>Z_NULL</tt> to request that <em>zlib</em> use
-the default memory allocation routines. An application may also choose to provide
-custom memory allocation routines here. <tt>deflateInit()</tt> will allocate on the
-order of 256K bytes for the internal state.
-(See <a href="zlib_tech.html"><em>zlib Technical Details</em></a>.)
-<p>
-<tt>deflateInit()</tt> is called with a pointer to the structure to be initialized and
-the compression level, which is an integer in the range of -1 to 9. Lower compression
-levels result in faster execution, but less compression. Higher levels result in
-greater compression, but slower execution. The <em>zlib</em> constant Z_DEFAULT_COMPRESSION,
-equal to -1,
-provides a good compromise between compression and speed and is equivalent to level 6.
-Level 0 actually does no compression at all, and in fact expands the data slightly to produce
-the <em>zlib</em> format (it is not a byte-for-byte copy of the input).
-More advanced applications of <em>zlib</em>
-may use <tt>deflateInit2()</tt> here instead. Such an application may want to reduce how
-much memory will be used, at some price in compression. Or it may need to request a
-<em>gzip</em> header and trailer instead of a <em>zlib</em> header and trailer, or raw
-encoding with no header or trailer at all.
-<p>
-We must check the return value of <tt>deflateInit()</tt> against the <em>zlib</em> constant
-<tt>Z_OK</tt> to make sure that it was able to
-allocate memory for the internal state, and that the provided arguments were valid.
-<tt>deflateInit()</tt> will also check that the version of <em>zlib</em> that the <tt>zlib.h</tt>
-file came from matches the version of <em>zlib</em> actually linked with the program. This
-is especially important for environments in which <em>zlib</em> is a shared library.
-<p>
-Note that an application can initialize multiple, independent <em>zlib</em> streams, which can
-operate in parallel. The state information maintained in the structure allows the <em>zlib</em>
-routines to be reentrant.
-<pre><b>
- /* allocate deflate state */
- strm.zalloc = Z_NULL;
- strm.zfree = Z_NULL;
- strm.opaque = Z_NULL;
- ret = deflateInit(&amp;strm, level);
- if (ret != Z_OK)
- return ret;
-</b></pre><!-- -->
-With the pleasantries out of the way, now we can get down to business. The outer <tt>do</tt>-loop
-reads all of the input file and exits at the bottom of the loop once end-of-file is reached.
-This loop contains the only call of <tt>deflate()</tt>. So we must make sure that all of the
-input data has been processed and that all of the output data has been generated and consumed
-before we fall out of the loop at the bottom.
-<pre><b>
- /* compress until end of file */
- do {
-</b></pre>
-We start off by reading data from the input file. The number of bytes read is put directly
-into <tt>avail_in</tt>, and a pointer to those bytes is put into <tt>next_in</tt>. We also
-check to see if end-of-file on the input has been reached. If we are at the end of file, then <tt>flush</tt> is set to the
-<em>zlib</em> constant <tt>Z_FINISH</tt>, which is later passed to <tt>deflate()</tt> to
-indicate that this is the last chunk of input data to compress. We need to use <tt>feof()</tt>
-to check for end-of-file as opposed to seeing if fewer than <tt>CHUNK</tt> bytes have been read. The
-reason is that if the input file length is an exact multiple of <tt>CHUNK</tt>, we will miss
-the fact that we got to the end-of-file, and not know to tell <tt>deflate()</tt> to finish
-up the compressed stream. If we are not yet at the end of the input, then the <em>zlib</em>
-constant <tt>Z_NO_FLUSH</tt> will be passed to <tt>deflate</tt> to indicate that we are still
-in the middle of the uncompressed data.
-<p>
-If there is an error in reading from the input file, the process is aborted with
-<tt>deflateEnd()</tt> being called to free the allocated <em>zlib</em> state before returning
-the error. We wouldn't want a memory leak, now would we? <tt>deflateEnd()</tt> can be called
-at any time after the state has been initialized. Once that's done, <tt>deflateInit()</tt> (or
-<tt>deflateInit2()</tt>) would have to be called to start a new compression process. There is
-no point here in checking the <tt>deflateEnd()</tt> return code. The deallocation can't fail.
-<pre><b>
- strm.avail_in = fread(in, 1, CHUNK, source);
- if (ferror(source)) {
- (void)deflateEnd(&amp;strm);
- return Z_ERRNO;
- }
- flush = feof(source) ? Z_FINISH : Z_NO_FLUSH;
- strm.next_in = in;
-</b></pre><!-- -->
-The inner <tt>do</tt>-loop passes our chunk of input data to <tt>deflate()</tt>, and then
-keeps calling <tt>deflate()</tt> until it is done producing output. Once there is no more
-new output, <tt>deflate()</tt> is guaranteed to have consumed all of the input, i.e.,
-<tt>avail_in</tt> will be zero.
-<pre><b>
- /* run deflate() on input until output buffer not full, finish
- compression if all of source has been read in */
- do {
-</b></pre>
-Output space is provided to <tt>deflate()</tt> by setting <tt>avail_out</tt> to the number
-of available output bytes and <tt>next_out</tt> to a pointer to that space.
-<pre><b>
- strm.avail_out = CHUNK;
- strm.next_out = out;
-</b></pre>
-Now we call the compression engine itself, <tt>deflate()</tt>. It takes as many of the
-<tt>avail_in</tt> bytes at <tt>next_in</tt> as it can process, and writes as many as
-<tt>avail_out</tt> bytes to <tt>next_out</tt>. Those counters and pointers are then
-updated past the input data consumed and the output data written. It is the amount of
-output space available that may limit how much input is consumed.
-Hence the inner loop to make sure that
-all of the input is consumed by providing more output space each time. Since <tt>avail_in</tt>
-and <tt>next_in</tt> are updated by <tt>deflate()</tt>, we don't have to mess with those
-between <tt>deflate()</tt> calls until it's all used up.
-<p>
-The parameters to <tt>deflate()</tt> are a pointer to the <tt>strm</tt> structure containing
-the input and output information and the internal compression engine state, and a parameter
-indicating whether and how to flush data to the output. Normally <tt>deflate</tt> will consume
-several K bytes of input data before producing any output (except for the header), in order
-to accumulate statistics on the data for optimum compression. It will then put out a burst of
-compressed data, and proceed to consume more input before the next burst. Eventually,
-<tt>deflate()</tt>
-must be told to terminate the stream, complete the compression with provided input data, and
-write out the trailer check value. <tt>deflate()</tt> will continue to compress normally as long
-as the flush parameter is <tt>Z_NO_FLUSH</tt>. Once the <tt>Z_FINISH</tt> parameter is provided,
-<tt>deflate()</tt> will begin to complete the compressed output stream. However depending on how
-much output space is provided, <tt>deflate()</tt> may have to be called several times until it
-has provided the complete compressed stream, even after it has consumed all of the input. The flush
-parameter must continue to be <tt>Z_FINISH</tt> for those subsequent calls.
-<p>
-There are other values of the flush parameter that are used in more advanced applications. You can
-force <tt>deflate()</tt> to produce a burst of output that encodes all of the input data provided
-so far, even if it wouldn't have otherwise, for example to control data latency on a link with
-compressed data. You can also ask that <tt>deflate()</tt> do that as well as erase any history up to
-that point so that what follows can be decompressed independently, for example for random access
-applications. Both requests will degrade compression by an amount depending on how often such
-requests are made.
-<p>
-<tt>deflate()</tt> has a return value that can indicate errors, yet we do not check it here. Why
-not? Well, it turns out that <tt>deflate()</tt> can do no wrong here. Let's go through
-<tt>deflate()</tt>'s return values and dispense with them one by one. The possible values are
-<tt>Z_OK</tt>, <tt>Z_STREAM_END</tt>, <tt>Z_STREAM_ERROR</tt>, or <tt>Z_BUF_ERROR</tt>. <tt>Z_OK</tt>
-is, well, ok. <tt>Z_STREAM_END</tt> is also ok and will be returned for the last call of
-<tt>deflate()</tt>. This is already guaranteed by calling <tt>deflate()</tt> with <tt>Z_FINISH</tt>
-until it has no more output. <tt>Z_STREAM_ERROR</tt> is only possible if the stream is not
-initialized properly, but we did initialize it properly. There is no harm in checking for
-<tt>Z_STREAM_ERROR</tt> here, for example to check for the possibility that some
-other part of the application inadvertently clobbered the memory containing the <em>zlib</em> state.
-<tt>Z_BUF_ERROR</tt> will be explained further below, but
-suffice it to say that this is simply an indication that <tt>deflate()</tt> could not consume
-more input or produce more output. <tt>deflate()</tt> can be called again with more output space
-or more available input, which it will be in this code.
-<pre><b>
- ret = deflate(&amp;strm, flush); /* no bad return value */
- assert(ret != Z_STREAM_ERROR); /* state not clobbered */
-</b></pre>
-Now we compute how much output <tt>deflate()</tt> provided on the last call, which is the
-difference between how much space was provided before the call, and how much output space
-is still available after the call. Then that data, if any, is written to the output file.
-We can then reuse the output buffer for the next call of <tt>deflate()</tt>. Again if there
-is a file i/o error, we call <tt>deflateEnd()</tt> before returning to avoid a memory leak.
-<pre><b>
- have = CHUNK - strm.avail_out;
- if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
- (void)deflateEnd(&amp;strm);
- return Z_ERRNO;
- }
-</b></pre>
-The inner <tt>do</tt>-loop is repeated until the last <tt>deflate()</tt> call fails to fill the
-provided output buffer. Then we know that <tt>deflate()</tt> has done as much as it can with
-the provided input, and that all of that input has been consumed. We can then fall out of this
-loop and reuse the input buffer.
-<p>
-The way we tell that <tt>deflate()</tt> has no more output is by seeing that it did not fill
-the output buffer, leaving <tt>avail_out</tt> greater than zero. However suppose that
-<tt>deflate()</tt> has no more output, but just so happened to exactly fill the output buffer!
-<tt>avail_out</tt> is zero, and we can't tell that <tt>deflate()</tt> has done all it can.
-As far as we know, <tt>deflate()</tt>
-has more output for us. So we call it again. But now <tt>deflate()</tt> produces no output
-at all, and <tt>avail_out</tt> remains unchanged as <tt>CHUNK</tt>. That <tt>deflate()</tt> call
-wasn't able to do anything, either consume input or produce output, and so it returns
-<tt>Z_BUF_ERROR</tt>. (See, I told you I'd cover this later.) However this is not a problem at
-all. Now we finally have the desired indication that <tt>deflate()</tt> is really done,
-and so we drop out of the inner loop to provide more input to <tt>deflate()</tt>.
-<p>
-With <tt>flush</tt> set to <tt>Z_FINISH</tt>, this final set of <tt>deflate()</tt> calls will
-complete the output stream. Once that is done, subsequent calls of <tt>deflate()</tt> would return
-<tt>Z_STREAM_ERROR</tt> if the flush parameter is not <tt>Z_FINISH</tt>, and do no more processing
-until the state is reinitialized.
-<p>
-Some applications of <em>zlib</em> have two loops that call <tt>deflate()</tt>
-instead of the single inner loop we have here. The first loop would call
-without flushing and feed all of the data to <tt>deflate()</tt>. The second loop would call
-<tt>deflate()</tt> with no more
-data and the <tt>Z_FINISH</tt> parameter to complete the process. As you can see from this
-example, that can be avoided by simply keeping track of the current flush state.
-<pre><b>
- } while (strm.avail_out == 0);
- assert(strm.avail_in == 0); /* all input will be used */
-</b></pre><!-- -->
-Now we check to see if we have already processed all of the input file. That information was
-saved in the <tt>flush</tt> variable, so we see if that was set to <tt>Z_FINISH</tt>. If so,
-then we're done and we fall out of the outer loop. We're guaranteed to get <tt>Z_STREAM_END</tt>
-from the last <tt>deflate()</tt> call, since we ran it until the last chunk of input was
-consumed and all of the output was generated.
-<pre><b>
- /* done when last data in file processed */
- } while (flush != Z_FINISH);
- assert(ret == Z_STREAM_END); /* stream will be complete */
-</b></pre><!-- -->
-The process is complete, but we still need to deallocate the state to avoid a memory leak
-(or rather more like a memory hemorrhage if you didn't do this). Then
-finally we can return with a happy return value.
-<pre><b>
- /* clean up and return */
- (void)deflateEnd(&amp;strm);
- return Z_OK;
-}
-</b></pre><!-- -->
-Now we do the same thing for decompression in the <tt>inf()</tt> routine. <tt>inf()</tt>
-decompresses what is hopefully a valid <em>zlib</em> stream from the input file and writes the
-uncompressed data to the output file. Much of the discussion above for <tt>def()</tt>
-applies to <tt>inf()</tt> as well, so the discussion here will focus on the differences between
-the two.
-<pre><b>
-/* Decompress from file source to file dest until stream ends or EOF.
- inf() returns Z_OK on success, Z_MEM_ERROR if memory could not be
- allocated for processing, Z_DATA_ERROR if the deflate data is
- invalid or incomplete, Z_VERSION_ERROR if the version of zlib.h and
- the version of the library linked do not match, or Z_ERRNO if there
- is an error reading or writing the files. */
-int inf(FILE *source, FILE *dest)
-{
-</b></pre>
-The local variables have the same functionality as they do for <tt>def()</tt>. The
-only difference is that there is no <tt>flush</tt> variable, since <tt>inflate()</tt>
-can tell from the <em>zlib</em> stream itself when the stream is complete.
-<pre><b>
- int ret;
- unsigned have;
- z_stream strm;
- char in[CHUNK];
- char out[CHUNK];
-</b></pre><!-- -->
-The initialization of the state is the same, except that there is no compression level,
-of course, and two more elements of the structure are initialized. <tt>avail_in</tt>
-and <tt>next_in</tt> must be initialized before calling <tt>inflateInit()</tt>. This
-is because the application has the option to provide the start of the zlib stream in
-order for <tt>inflateInit()</tt> to have access to information about the compression
-method to aid in memory allocation. In the current implementation of <em>zlib</em>
-(up through versions 1.2.x), the method-dependent memory allocations are deferred to the first call of
-<tt>inflate()</tt> anyway. However those fields must be initialized since later versions
-of <em>zlib</em> that provide more compression methods may take advantage of this interface.
-In any case, no decompression is performed by <tt>inflateInit()</tt>, so the
-<tt>avail_out</tt> and <tt>next_out</tt> fields do not need to be initialized before calling.
-<p>
-Here <tt>avail_in</tt> is set to zero and <tt>next_in</tt> is set to <tt>Z_NULL</tt> to
-indicate that no input data is being provided.
-<pre><b>
- /* allocate inflate state */
- strm.zalloc = Z_NULL;
- strm.zfree = Z_NULL;
- strm.opaque = Z_NULL;
- strm.avail_in = 0;
- strm.next_in = Z_NULL;
- ret = inflateInit(&amp;strm);
- if (ret != Z_OK)
- return ret;
-</b></pre><!-- -->
-The outer <tt>do</tt>-loop decompresses input until <tt>inflate()</tt> indicates
-that it has reached the end of the compressed data and has produced all of the uncompressed
-output. This is in contrast to <tt>def()</tt> which processes all of the input file.
-If end-of-file is reached before the compressed data self-terminates, then the compressed
-data is incomplete and an error is returned.
-<pre><b>
- /* decompress until deflate stream ends or end of file */
- do {
-</b></pre>
-We read input data and set the <tt>strm</tt> structure accordingly. If we've reached the
-end of the input file, then we leave the outer loop and report an error, since the
-compressed data is incomplete. Note that we may read more data than is eventually consumed
-by <tt>inflate()</tt>, if the input file continues past the <em>zlib</em> stream.
-For applications where <em>zlib</em> streams are embedded in other data, this routine would
-need to be modified to return the unused data, or at least indicate how much of the input
-data was not used, so the application would know where to pick up after the <em>zlib</em> stream.
-<pre><b>
- strm.avail_in = fread(in, 1, CHUNK, source);
- if (ferror(source)) {
- (void)inflateEnd(&amp;strm);
- return Z_ERRNO;
- }
- if (strm.avail_in == 0)
- break;
- strm.next_in = in;
-</b></pre><!-- -->
-The inner <tt>do</tt>-loop has the same function it did in <tt>def()</tt>, which is to
-keep calling <tt>inflate()</tt> until has generated all of the output it can with the
-provided input.
-<pre><b>
- /* run inflate() on input until output buffer not full */
- do {
-</b></pre>
-Just like in <tt>def()</tt>, the same output space is provided for each call of <tt>inflate()</tt>.
-<pre><b>
- strm.avail_out = CHUNK;
- strm.next_out = out;
-</b></pre>
-Now we run the decompression engine itself. There is no need to adjust the flush parameter, since
-the <em>zlib</em> format is self-terminating. The main difference here is that there are
-return values that we need to pay attention to. <tt>Z_DATA_ERROR</tt>
-indicates that <tt>inflate()</tt> detected an error in the <em>zlib</em> compressed data format,
-which means that either the data is not a <em>zlib</em> stream to begin with, or that the data was
-corrupted somewhere along the way since it was compressed. The other error to be processed is
-<tt>Z_MEM_ERROR</tt>, which can occur since memory allocation is deferred until <tt>inflate()</tt>
-needs it, unlike <tt>deflate()</tt>, whose memory is allocated at the start by <tt>deflateInit()</tt>.
-<p>
-Advanced applications may use
-<tt>deflateSetDictionary()</tt> to prime <tt>deflate()</tt> with a set of likely data to improve the
-first 32K or so of compression. This is noted in the <em>zlib</em> header, so <tt>inflate()</tt>
-requests that that dictionary be provided before it can start to decompress. Without the dictionary,
-correct decompression is not possible. For this routine, we have no idea what the dictionary is,
-so the <tt>Z_NEED_DICT</tt> indication is converted to a <tt>Z_DATA_ERROR</tt>.
-<p>
-<tt>inflate()</tt> can also return <tt>Z_STREAM_ERROR</tt>, which should not be possible here,
-but could be checked for as noted above for <tt>def()</tt>. <tt>Z_BUF_ERROR</tt> does not need to be
-checked for here, for the same reasons noted for <tt>def()</tt>. <tt>Z_STREAM_END</tt> will be
-checked for later.
-<pre><b>
- ret = inflate(&amp;strm, Z_NO_FLUSH);
- assert(ret != Z_STREAM_ERROR); /* state not clobbered */
- switch (ret) {
- case Z_NEED_DICT:
- ret = Z_DATA_ERROR; /* and fall through */
- case Z_DATA_ERROR:
- case Z_MEM_ERROR:
- (void)inflateEnd(&amp;strm);
- return ret;
- }
-</b></pre>
-The output of <tt>inflate()</tt> is handled identically to that of <tt>deflate()</tt>.
-<pre><b>
- have = CHUNK - strm.avail_out;
- if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
- (void)inflateEnd(&amp;strm);
- return Z_ERRNO;
- }
-</b></pre>
-The inner <tt>do</tt>-loop ends when <tt>inflate()</tt> has no more output as indicated
-by not filling the output buffer, just as for <tt>deflate()</tt>. In this case, we cannot
-assert that <tt>strm.avail_in</tt> will be zero, since the deflate stream may end before the file
-does.
-<pre><b>
- } while (strm.avail_out == 0);
-</b></pre><!-- -->
-The outer <tt>do</tt>-loop ends when <tt>inflate()</tt> reports that it has reached the
-end of the input <em>zlib</em> stream, has completed the decompression and integrity
-check, and has provided all of the output. This is indicated by the <tt>inflate()</tt>
-return value <tt>Z_STREAM_END</tt>. The inner loop is guaranteed to leave <tt>ret</tt>
-equal to <tt>Z_STREAM_END</tt> if the last chunk of the input file read contained the end
-of the <em>zlib</em> stream. So if the return value is not <tt>Z_STREAM_END</tt>, the
-loop continues to read more input.
-<pre><b>
- /* done when inflate() says it's done */
- } while (ret != Z_STREAM_END);
-</b></pre><!-- -->
-At this point, decompression successfully completed, or we broke out of the loop due to no
-more data being available from the input file. If the last <tt>inflate()</tt> return value
-is not <tt>Z_STREAM_END</tt>, then the <em>zlib</em> stream was incomplete and a data error
-is returned. Otherwise, we return with a happy return value. Of course, <tt>inflateEnd()</tt>
-is called first to avoid a memory leak.
-<pre><b>
- /* clean up and return */
- (void)inflateEnd(&amp;strm);
- return ret == Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
-}
-</b></pre><!-- -->
-That ends the routines that directly use <em>zlib</em>. The following routines make this
-a command-line program by running data through the above routines from <tt>stdin</tt> to
-<tt>stdout</tt>, and handling any errors reported by <tt>def()</tt> or <tt>inf()</tt>.
-<p>
-<tt>zerr()</tt> is used to interpret the possible error codes from <tt>def()</tt>
-and <tt>inf()</tt>, as detailed in their comments above, and print out an error message.
-Note that these are only a subset of the possible return values from <tt>deflate()</tt>
-and <tt>inflate()</tt>.
-<pre><b>
-/* report a zlib or i/o error */
-void zerr(int ret)
-{
- fputs("zpipe: ", stderr);
- switch (ret) {
- case Z_ERRNO:
- if (ferror(stdin))
- fputs("error reading stdin\n", stderr);
- if (ferror(stdout))
- fputs("error writing stdout\n", stderr);
- break;
- case Z_STREAM_ERROR:
- fputs("invalid compression level\n", stderr);
- break;
- case Z_DATA_ERROR:
- fputs("invalid or incomplete deflate data\n", stderr);
- break;
- case Z_MEM_ERROR:
- fputs("out of memory\n", stderr);
- break;
- case Z_VERSION_ERROR:
- fputs("zlib version mismatch!\n", stderr);
- }
-}
-</b></pre><!-- -->
-Here is the <tt>main()</tt> routine used to test <tt>def()</tt> and <tt>inf()</tt>. The
-<tt>zpipe</tt> command is simply a compression pipe from <tt>stdin</tt> to <tt>stdout</tt>, if
-no arguments are given, or it is a decompression pipe if <tt>zpipe -d</tt> is used. If any other
-arguments are provided, no compression or decompression is performed. Instead a usage
-message is displayed. Examples are <tt>zpipe < foo.txt > foo.txt.z</tt> to compress, and
-<tt>zpipe -d < foo.txt.z > foo.txt</tt> to decompress.
-<pre><b>
-/* compress or decompress from stdin to stdout */
-int main(int argc, char **argv)
-{
- int ret;
-
- /* do compression if no arguments */
- if (argc == 1) {
- ret = def(stdin, stdout, Z_DEFAULT_COMPRESSION);
- if (ret != Z_OK)
- zerr(ret);
- return ret;
- }
-
- /* do decompression if -d specified */
- else if (argc == 2 &amp;&amp; strcmp(argv[1], "-d") == 0) {
- ret = inf(stdin, stdout);
- if (ret != Z_OK)
- zerr(ret);
- return ret;
- }
-
- /* otherwise, report usage */
- else {
- fputs("zpipe usage: zpipe [-d] &lt; source &gt; dest\n", stderr);
- return 1;
- }
-}
-</b></pre>
-<hr>
-<i>Copyright (c) 2004 by Mark Adler<br>Last modified 13 November 2004</i>
-</body>
-</html>