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<B> Next:</B> <A NAME="tex2html1266"
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<H2><A NAME="SECTION00071000000000000000">
General API</A> |
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</H2> |
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Every program based on libclamav must include the <code>clamav.h</code> header
file: |
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<PRE> |
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#include <clamav.h> |
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</PRE> |
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A first step is to initialize the scanning engine. There are three
functions available: |
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<PRE> |
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int cl_loaddb(const char *filename, struct cl_node **root,
int *virnum);
int cl_loaddbdir(const char *dirname, struct cl_node **root,
int *virnum);
const char *cl_retdbdir(void);
</PRE>
<code>cl_loaddb()</code> loads a particular database, <code>cl_loaddbdir()</code>
loads all <I>.cvd</I> (and older <I>.db</I>, .db2) databases from a
directory <code>dirname</code>. <code>cl_retdbdir()</code> returns a hardcoded
database directory path. Initial internal database (Aho-Corasick tree,
trie; see <A HREF="node75.html#engine">6.3</A>) will be saved under <code>root</code> and a number of
signatures loaded will be <B>added</B> <A NAME="tex2html121"
HREF="footnode.html#foot716"><SUP>8</SUP></A> to <code>virnum</code>. Pointer to the trie
must initially point to NULL. If you don't care about number of signatures
pass NULL as a third argument. <code>cl_loaddb</code> functions return 0 on
success and an other value on failure.
<PRE>
struct cl_node *root = NULL;
int ret;
ret = cl_loaddbdir(cl_retdbdir(), &root, NULL); |
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</PRE> |
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There's an elegant way to print libclamav's error codes: |
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<PRE> |
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const char *cl_strerror(int clerror);
</PRE>
<code>cl_strerror()</code> returns a (statically allocated) string describing
a <code>clerror</code> code:
<PRE>
if(ret) {
printf("cl_loaddbdir() error: %s\n", cl_strerror(ret));
exit(1); |
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}
</PRE> |
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When database is loaded you must build the final trie with:
<PRE>
int cl_buildtrie(struct cl_node *root);
</PRE>
In our example:
<PRE>
if((ret = cl_buildtrie(root)))
printf("cl_buildtrie() error: %s\n", cl_strerror(ret));
</PRE>
Now you can scan a buffer, a descriptor or a file with:
<PRE>
int cl_scanbuff(const char *buffer, unsigned int length,
const char **virname, const struct cl_node *root);
int cl_scandesc(int desc, const char **virname, unsigned
long int *scanned, const struct cl_node *root, const
struct cl_limits *limits, int options);
int cl_scanfile(const char *filename, const char **virname,
unsigned long int *scanned, const struct cl_node *root,
const struct cl_limits *limits, int options);
</PRE>
All the functions save a virus name address under <code>virname</code> pointer.
It points to a name in the trie structure thus it can't be released
directly. <code>cl_scandesc()</code> and <code>cl_scanfile()</code> can
increase the <code>scanned</code> value in <code>CL_COUNT_PRECISION</code> units,
they also support archive limits:
<PRE>
struct cl_limits {
int maxreclevel; /* maximal recursion level */
int maxfiles; /* maximal number of files to be
* scanned within an archive
*/
int maxratio; /* maximal compression ratio */
short archivememlim; /* limit memory usage for bzip2 (0/1) */
long int maxfilesize; /* files in an archive larger than
* this value will not be scanned
*/
};
</PRE>
The last argument in the <code>cl_scan</code> family configures the scan
engine. It supports the following flags:
<UL>
<LI><B>CL_RAW</B>
<BR>
It does nothing. Please use it (alone) if you don't want
to scan any special files.
</LI>
<LI><B>CL_ARCHIVE</B>
<BR>
This flag enables the transparent archive scanning.
</LI>
<LI><B>CL_DISABLERAR</B>
<BR>
Disables the built-in RAR unpacker which is known to cause
memory leaks.
</LI>
<LI><B>CL_ENCRYPTED</B>
<BR>
Marks encrypted archives as viruses (Encrypted.Zip,
Encrypted.RAR).
</LI>
<LI><B>CL_MAIL</B>
<BR>
Required to scan various types of mail files.
</LI>
<LI><B>CL_OLE2</B>
<BR>
Enables support for Microsoft Office document files.
</LI>
</UL>
All functions return 0 (<code>CL_CLEAN</code>) if the file is clean,
<code>CL_VIRUS</code> when virus is detected and an other value on failure.
<PRE>
struct cl_limits limits;
const char *virname;
memset(&limits, 0, sizeof(struct cl_limits));
/* maximal number of files in archive */;
limits.maxfiles = 1000
/* maximal archived file size == 10 MB */
limits.maxfilesize = 10 * 1048576;
/* maximal recursion level */
limits.maxreclevel = 5;
/* maximal compression ratio */
limits.maxratio = 200;
/* disable memory limit for bzip2 scanner */
limits.archivememlim = 0;
if((ret = cl_scanfile("/home/zolw/test", &virname, NULL, root,
&limits, CL_ARCHIVE | CL_MAIL | CL_OLE2)) == CL_VIRUS) {
printf("Detected %s virus.\n", virname);
} else {
printf("No virus detected.\n");
if(ret != CL_CLEAN)
printf("Error: %s\n", cl_strerror(ret));
}
</PRE>
Release the trie if you no longer need it:
<PRE>
void cl_freetrie(struct cl_node *root);
</PRE>
You will find an example scanner in clamav sources (/example). All
programs based on libclamav must be linked against it:
<PRE>
gcc -Wall ex1.c -o ex1 -lclamav
</PRE>
Enjoy ! |
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<ADDRESS>
Tomasz Kojm |
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2004-06-14 |
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