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| author | Jelmer Vernooij <jelmer@samba.org> | 2008-10-21 14:51:13 +0200 |
|---|---|---|
| committer | Jelmer Vernooij <jelmer@samba.org> | 2008-10-21 14:51:13 +0200 |
| commit | 5209a846a9157e649fcdcb561f7eaf19c8c0e465 (patch) | |
| tree | b0a7e52b5646c8eec182dbc391e7934b6804488c /source4/lib/zlib/examples/zlib_how.html | |
| parent | 625359b2e266105022309df8985720108ecd6f67 (diff) | |
| parent | 2ee8d29d22bcb1c350ab59d71b0aee548489bc9c (diff) | |
| download | samba-5209a846a9157e649fcdcb561f7eaf19c8c0e465.tar.gz samba-5209a846a9157e649fcdcb561f7eaf19c8c0e465.tar.bz2 samba-5209a846a9157e649fcdcb561f7eaf19c8c0e465.zip | |
Merge branch 'master' of ssh://git.samba.org/data/git/samba into regsrv
Conflicts:
source4/lib/registry/ldb.c
source4/rpc_server/winreg/rpc_winreg.c
Diffstat (limited to 'source4/lib/zlib/examples/zlib_how.html')
| -rw-r--r-- | source4/lib/zlib/examples/zlib_how.html | 523 |
1 files changed, 0 insertions, 523 deletions
diff --git a/source4/lib/zlib/examples/zlib_how.html b/source4/lib/zlib/examples/zlib_how.html deleted file mode 100644 index 40998dbf08..0000000000 --- a/source4/lib/zlib/examples/zlib_how.html +++ /dev/null @@ -1,523 +0,0 @@ -<!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 <stdio.h> -#include <string.h> -#include <assert.h> -#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(&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(&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(&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(&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(&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(&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(&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(&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(&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(&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(&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 && 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] < source > dest\n", stderr); - return 1; - } -} -</b></pre> -<hr> -<i>Copyright (c) 2004 by Mark Adler<br>Last modified 13 November 2004</i> -</body> -</html> |