[[PageOutline]]

= File compression =
== BOINC-supplied compression ==
=== Compression of input files === #compress-input
Starting with version 5.4, the BOINC client is able to handle HTTP `Content-Encoding` types 'deflate'
(zlib algorithm) and 'gzip' (gzip algorithm).
The client decompresses these files 'on the fly' and stores them on disk in uncompressed form.
This can be used in the following two ways.

Both methods store files uncompressed on the client.
If you need compression on the client, you must do it at the application level (see below).

==== gzip encoding ====
To use this method, gzip your downloadable files, giving them a filename suffix such as '.gz'.
(The name used in your `<file_info>` elements, however, is the original filename without '.gz').

This method has the advantage of reducing server disk usage and server CPU load,
but it will only work with 5.4+ clients.
BOINC clients older than 5.4 won't be able to download files.
Use the 'min_core_client_version' entry in config.xml to enforce this.

==== Apache mod_deflate ====
You can use the Apache 2.0 mod_deflate module to automatically compress files on the fly.
See http://httpd.apache.org/docs/2.0/mod/mod_deflate.html.
This method will work with all BOINC clients, but it will do compression only for 5.4+ clients.

You can use this in conjunction with gzip encoding because the mod_deflate module
allows you to exempt certain filetypes from on-the-fly compression.

This method increases CPU load on the web server, but this is typically not significant.

==== Configuration File ====

You'll need to modify your `httpd.conf` file; example:

{{{
# Enable module
LoadModule deflate_module modules/mod_deflate.so

# Log file compression
DeflateFilterNote Input instream
DeflateFilterNote Output outstream
DeflateFilterNote Ratio ratio

LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate
CustomLog logs/deflate_log deflate

# Use low settings for compression to make sure impact on server is low
DeflateMemLevel 2
DeflateCompressionLevel 2

# Add encoding type
AddEncoding x-gzip .gz

Alias /boinc/download /path/to/files/download

<Directory /path/to/files/download>
Options Indexes FollowSymlinks MultiViews
AllowOverride AuthConfig
Order allow,deny
Allow from all

RewriteEngine on
RewriteCond %{HTTP:Accept-Encoding} gzip.*deflate|deflate.*gzip
RewriteCond %{REQUEST_FILENAME} "\.(vmdk|exe|dll|pdb)$"
RewriteCond %{REQUEST_FILENAME}.gz -f
RewriteRule ^.*$ %{REQUEST_URI}.gz [L]

<FilesMatch ".*\.(vmdk|exe|dll|pdb)\.gz$">
ForceType application/octet-stream
Header set Content-Encoding gzip
</FilesMatch>

SetOutputFilter DEFLATE
SetEnvIfNoCase Request_URI \.(?:gz|gif|jpg|jpeg|png)$ no-gzip dont-vary
</Directory>
}}}
This configuration tells Apache to redirect to the statically compressed files
if the extension is vmdk, exe, dll, or pdb.
All other files are compressed on-the-fly from the download direction except for files
that end with `gz`,`gif`,`jpg`,`jpeg` and `png`.

An alternate way to specify the files is the following:
{{{
Alias /boinc/download /path/to/files/download

<Directory /path/to/files/download>
AddOutputFilter DEFLATE .faa .mask
</Directory>
}}}
This configuration tells Apache to compress only the file types `.faa` and `.mask`
served from the download directory.

=== Compression of output files === #compress-output
If you include the `<gzip_when_done>` tag in an [wiki:XmlFormat#Files output file description],
the file will be gzip-compressed after it has been generated.

The gzip_when_done is only supported in client version 5.8+.
If you receive files from clients that do not support the gzip_when_done flag,
then you should open the files with a function similar to this to your validator/assimilator:

{{{
#!cpp
int read_gzip_file_string(string file, string* result) {
    FILE *infile;
    char cmd[512];
    char buf[4096];

    result->erase();
    sprintf(cmd, "gzip -dcf %s", file.c_str());
    infile = popen(cmd, "r");
    if (infile == NULL) {
        return ERR_FOPEN;
    }

    while( fgets(buf, 4096, infile) != NULL ) {
        result->append(buf);
    }
    result->append("\0");
    if (pclose(infile) != 0) {
        fprintf(stderr, "%s: pclose failed\n", file.c_str());
        return 1;
    }
    return 0;
}
}}}
This will uncompress the file if it is compressed or will read it without modification
if it is not compressed.

== Application-level compression ==
=== Using boinc_zip === #boinc-zip
You can also do compression in your application.
To assist this, BOINC provides a library boinc_zip,
based on the [http://www.info-zip.org Info-Zip] libraries,
but combines both zip & unzip functionality in one library.
Any questions/comments please email Carl Christensen (carlgt1 at yahoo dot com)

This library can "co-exist" with zlib (libz) in case you need that too.

Basically, it will allow you to build a library that you can link
against to provide basic zip/unzip compression functionality.
It should only add a few hundred KB to your app
(basically like distributing `zip` & `unzip` executable binaries for different platforms).

==== Limitations ==== #boinc-zip-limitations
The "unzip" functionality is there,
that is you can unzip a file and it will create all directories & files in the zip file.
The "zip" functionality has some limitations due to the cross-platform nature:
mainly it doesn't provide zipping recursively (i.e. subdirectories);
and wildcard handling is done using the "boinc_filelist" function which will be explained below.

==== Building ==== #boinc-zip-building
For Windows, you can just add the project "boinc_zip" to your Visual Studio "Solution" or "Workspace."
Basically just "Insert Existing Project" from the Visual Studio IDE,
navigate over to the boinc/zip directory, and it should load the appropriate files.
You can then build "Debug" and "Release" versions of the library.
Then just add the appropriate reference to "boinc_zip.lib" (Release build)
or "boinc_zipd.lib" (Debug build) in your app.

For Linux & Mac, you should be able to run "./configure" and then do a "make"
to build the "libboinc_zip.a" lib that you will link against.
In extreme cases, you may need to do an "aclocal && autoconf && automake" first,
to build properly for your platform.

Also, please note that boinc_zip relies on some BOINC functions that you will need
(and will most likely be in your app already since they are handy) --
namely `boinc/lib/filesys.C` and `boinc/lib/util.C`.

==== Using ==== #boinc-zip-using
Basically, you will need to `#include "boinc_zip.h"` in your app
(of course your compiler will need to know where it is, i.e. -I../boinc/zip).

Then you can just call the function `boinc_zip` with the appropriate arguments to zip or unzip.
There are three overloaded boinc_zip's provided:

{{{
#!cpp
int boinc_zip(int bZipType, const std::string szFileZip, const ZipFileList* pvectszFileIn);
int boinc_zip(int bZipType, const std::string szFileZip, const std::string szFileIn);
int boinc_zip(int bZipType, const char* szFileZip, const char* szFileIn);
}}}
`bZipType` is `ZIP_IT` or `UNZIP_IT` (self-explanatory)

`szFileZip` is the name of the zip file to create or extract
(I assume the user will provide it with the .zip extension)

The main differences are in the file parameter.
The zip library used was exhibiting odd behavior when "coexisting" with unzip,
particularly in the wildcard handling.
So a function was made that creates a `ZipFileList` class,
which is basically a vector of filenames.
If you are just compressing a single file,
you can use either the `std::string` or `const char* szFileIn` overrides.

You can also just pass in a `*` or a `*.*` to zip up all files in a directory.

To zip multiple files in a "mix & match" fashion,
you can use the `boinc_filelist` function provided.
Basically, it's a crude pattern matching of files in a directory,
but it has been useful for us on the CPDN project.
Just create a `ZipFileList` instance, and then pass this into `boinc_filelist` as follows:

{{{
#!cpp
bool boinc_filelist(
    const std::string directory,
    const std::string pattern,
    ZipFileList* pList,
    const unsigned char ucSort = SORT_NAME | SORT_DESCENDING,
    const bool bClear = true
);
}}}
if you want to zip up all text (.txt) files in a directory,
just pass in: the directory as a `std::string`, the pattern, i.e. ".txt", `&yourZipList`

The last two flags are the sort order of the file list
(CPDN files need to be in a certain order -- descending filenames, which is why that's the default).
The default is to "clear" your list,
you can set that to `false` to keep adding files to your `ZipFileList`.

When you have created your `ZipFileList` just pass that pointer to `boinc_zip`.
You will be able to add files in other directories this way.

There is a `ziptest` Project for Windows provided to experiment,
which can also be run (the "ziptest.cpp") on Unix & Mac to experiment
with how `boinc_zip` work (just g++ with the `boinc/lib/filesys.C` & `util.C` as described above).

=== Using gzip (zlib) === #gzip
These basic routines may be useful if you want to compress/decompress a file using the zlib library
(usually called "libz.a" and available for most platforms).
Include the header file below (qcn_gzip.h) in your program,
and link against libz, and you will gain two simple to use functions for gzip'ing or gunzip'ing a file.
This is for simple single file or file-by-file compression or decompression
(i.e. one file that is to be compressed into a .gz or decompressed back to it's original uncompressed state).
You can check for boinc client status if you want the ability to quit inside an operation etc.

qcn_gzip.h:

{{{
#!cpp
#ifndef _QCN_GZIP_H_
#define _QCN_GZIP_H_

#include <zlib.h>

int do_gzip(const char* strGZ, const char* strInput);
int do_gunzip(const char* strGZ, const char* strInput, bool bKeep = false);

#endif
}}}
qcn_gzip.cpp:

{{{
#!cpp
#include <stdio.h>
#include "filesys.h"
#include "qcn_gzip.h"

int do_gzip(const char* strGZ, const char* strInput) {
    // take an input file (strInput) and turn it into a compressed file (strGZ)
    // get rid of the input file after
    FILE* fIn = boinc_fopen(strInput, "rb");
    if (!fIn)  return 1; //error
    gzFile fOut = gzopen(strGZ, "wb");
    if (!fOut) return 1; //error
    fseek(fIn, 0, SEEK_SET);  // go to the top of the files
    gzseek(fOut, 0, SEEK_SET);
    unsigned char buf[1024];
    long lRead = 0, lWrite = 0;
    while (!feof(fIn)) { // read 1KB at a time until end of file
        memset(buf, 0x00, 1024);
        lRead = 0;
        lRead = (long) fread(buf, 1, 1024, fIn);
        lWrite = (long) gzwrite(fOut, buf, lRead);
        if (lRead != lWrite) break;
    }
    gzclose(fOut);
    fclose(fIn);
    if (lRead != lWrite) return 1;  //error -- read bytes != written bytes
    // if we made it here, it compressed OK, can erase strInput and leave
    boinc_delete_file(strInput);
    return 0;
}

// CMC - commented out status calls, are they too paranoid?
//      if needed use sm->statusBOINC instead (for quit_request etc)

int do_gunzip(const char* strGZ, const char* strInput, bool bKeep) {
	// take an input file (strInput) and turn it into a compressed file (strGZ)
	// get rid of the input file after
	//s.quit_request = 0;
	//checkBOINCStatus();
	FILE* fIn = boinc_fopen(strInput, "wb");
	if (!fIn)  return 1; //error
	gzFile fOut = gzopen(strGZ, "rb");
	if (!fOut) return 1; //error
	fseek(fIn, 0, SEEK_SET);  // go to the top of the files
	gzseek(fOut, 0, SEEK_SET);
	unsigned char buf[1024];
	long lRead = 0, lWrite = 0;
	while (!gzeof(fOut)) { // read 1KB at a time until end of file
		memset(buf, 0x00, 1024);
		lRead = 0;
		lRead = (long) gzread(fOut,buf,1024);
		lWrite = (long) fwrite(buf, 1, 1024, fIn);
		if (lRead != lWrite) break;
		//boinc_get_status(&s);
		//if (s.quit_request || s.abort_request || s.no_heartbeat) break;
	}
	gzclose(fOut);
	fclose(fIn);
	//checkBOINCStatus();
	if (lRead != lWrite) return 1;  //error -- read bytes != written bytes
	// if we made it here, it compressed OK, can erase strInput and leave
	if (!bKeep) boinc_delete_file(strGZ);
	return 0;
}

}}}