LIBDAR

APPLICATION INTERFACE

TUTORIAL

  for API version 3.0.x


Presentation

The Libdar library has been built from source code originally located directly in the dar command line application. Libdar provides a complete abstraction for handling Disk ARchive (dar)'s archives. The general operations provided are:

Note that Disk ARchive and libdar have been released under the Gnu General Public License (GPL). All code linked to libdar (statically or dynamically), must also be covered by the GPL.

This tutorial will show you how to use the libdar API. As dar now also uses this API, looking at it's code may also provide a good illustration. The file dar_suite/dar.cpp is the primary consumer.

The sample code provided here is solely illustrative and is not guaranteed to compile. More detailed API documentation is contained in the source code and can be compiled to the doc/html directory using Doxygen. The API reference is also available online.


Let's Start

Conventions

Language

Dar and libdar are written in C++, and so is the libdar API. While written in C++, libdar is easily usable with both C and C++ code. Access from other languages can be provided by specific bindings. I would only say that you are welcome to provide the necessary bindings yourself. :-)

Libdar namespace

All libdar symbols are defined under the libdar namespace. You can either add the using namespace libdar; line at the beginning of your source files:

using namespace libdar;

get_version(....);

 or, as shown below, you can explicitly use the namespace in front of libdar objects :


libdar::get_version(....);

Exceptions or no Exceptions

The library can be used with or without exceptions. For each example we will see sample code for both methods. To the left is with exceptions, to the right without:


example code using exceptions
example code not using exceptions

All exceptions used by libdar inherit from the pure virtual class Egeneric. The only method you will need to know about for any exception is the get_message() call, which returns a message string describing the message (in human language). The type of the error is defined by the class of the exception. The possible exception types follow:

class libdar::Egeneric
 the parent class of all exceptions (a pure virtual class)
class libdar::Ememory
 memory has been exhausted
class libdar::Ebug
 signals a bug, which is triggered when reaching some code that should never be reached
class libdar::Einfinint
 arithmetic error detected when operating on infinint
class libdar::Elimitint
 a limitint overflow is detected, indicating the maximum value of the limitint has been exceeded
class libdar::Erange
 signals a range error
class libdar::Edeci
 signals conversion problem between infinint and string (decimal representation)
class libdar::Efeature
 a requested feature is not (yet) implemented
class libdar::Ehardware
 hardware problem is found
class libdar::Euser_abort
 signals that the user has aborted the operation
class libdar::Edata
 an error concerning the treated data has been encountered
class libdar::Escript
 the script executed between slices returned an error code
class libdar::Elibcall
 signals an error in the arguments given to a libdar call of the API
class libdar::Ecompilation
 a requested feature has not been activated at compilation time




 1 - First we *must* check the libdar version


  
    // we'll want to display some messages
#include <io.h>

    // we include this header to access lidbar API
#include <dar/libdar.h>

    // all sample code shown will be inside this
    // function for simplicity's sake
void my_sample_function()
{
   try
   {
      libdar::U_I maj, med, min;

        // first we MUST call get_version()

      libdar::get_version(maj, med, min);

      if(maj != libdar::LIBDAR_COMPILE_TIME_MAJOR ||
         med < libdar::LIBDAR_COMPILE_TIME_MEDIUM)
        throw libdar::Erange("initialization",
        "we are linking against a wrong libdar");
   }
   catch(libdar::Egeneric & e)
   {
      std::cout << e.get_message() << std::endl;
   }
}

  
  
    // we'll want to display some messages
#include <io.h>

    // we include this header to access lidbar API
#include <dar/libdar.h>

    // all sample code shown will be inside this
    // function for simplicity's sake
void my_sample_function()
{

   libdar::U_I maj, med, min;
   libdar::U_16 excode;
   std::string msg;

    // first we MUST call get_version()

   libdar::get_version_noexcept(maj, med, min,
                                excode, msg);

   if(excode != LIBDAR_NOEXCEPT)
   {
      std::cout << msg << endl;
      return;
   }
 
   if(maj != LIBDAR_COMPILE_TIME_MAJOR ||
      med < libdar::LIBDAR_COMPILE_TIME_MEDIUM)
   {
      std::cout << "we are linking against wrong libdar" << std::endl;
      return;
    }

The get_version* family function must be called for several reasons :

2 - Let's see the available features

once we have called a function of the get_version* function it is possible to access the features activated at compilation time:



void my_sample_function()
{
        // let's continue in the same function

    bool ea;
    bool largefile;
    bool nodump;
    bool special_alloc;
    libdar::U_I bits;
    bool thread_safe;
    bool libz;
    bool libbz2;
    bool libcrypto;

    libdar::get_compile_time_features(ea,
                                      largefile,
                                      nodump,
                                      special_alloc,
                                      bits,
                                      thread_safe,
                                      libz,
                                      libbz2,
                                      libcrypto);

}

 // here there is no difference because no exceptions
 // are thrown by the get_compile_time_feature()
 // function


You can do what you want with the resulting values. It's possible to display the available libdar features or to terminate if you don't find a desired feature. However, verifying that features are available is not strictly necesary because libdar will tell you if an operation you call requires a feature that has not been activated by throwing an Ecompile exception or returning the LIBDAR_ECOMPILATION error code.


3 -User interaction

The generic user_interaction class

To be able to report messages to the user and prompt for feedback a special class called user_interaction has been introduced. Simply put, user_interaction is a virtual class which you can derive to provide user interaction (a GUI's graphical interaction, for example). There are four methods whose prototypes you must override:

void pause (const std::string &message);
this method is called by libdar when the library needs a yes or no ("continue" or "kill") answer to a question, which is provided by the string message. The question posed by pause() must be answered by returning "true" or throwing a Euser_abort exception if the user refused the proposition. Don't worry about throwing an exception in your code; it will be trapped by libdar if you don't want to manage exceptions, and are using libdar in the "no exception" method. (NOTE: Unfortunately there is currently no way to send + back a cancel signal without throwing an exception. For next API version a new method called pause2() will allow you to answer "true" or "false" and thus avoid using exceptions)


void warning (const std::string &message);
libdar calls this method to display an informational message to the user. It is not always a warning as the name suggests, but sometimes just normal information.

std::string get_string (const std::string &message, bool echo);
This call is used to get a arbitrary answer from the user. This is mainly used to get a password from the user (when no password has been supplied for an encrypted archive), the echo argument indicates if the user response should be displayed on the screen (again, very useful for handling password input). If echo is set to "false" the implementation of get_string() should hide the characters typed by the user.

 user_interaction * clone () const;
A deep copy operation must be implemented here. This is because libdar stores the reference to the user_interaction class as a pointer but may want to keep a complete internal copy at some point. A simple implementation of this method should be something like this (even if you don't want to use exceptions):


user_interaction *my_own_class::clone() const
{
    my_own_class *ret = new my_own_class(*this);
    if(ret == NULL)
        throw Ememory("user_interaction_callback::clone");
    else
        return ret;
}

The callback interaction class

An inherited class from user_interaction called user_interaction_callback provides an implementation of the user interaction based on callback functions. This allows you to replace the three interactions methods (pause, warning and get_string) by three normal functions of your choice, which must be given to the user_interaction_callback's constructor. The clone() method is implemented internally, leaving only the three callback functions to be implemented. Look at dar's command line code for a practical example. dar's user interaction code is implemented using an instance of user_interaction_callback and three static functions in the module dar_suite/shell_interaction.cpp

Pay attention to the contextual value present in the arguments of theses callback functions :
 
 
  // our own callback functions.
  // for the illustration of what theses 'context' arguments
  // can be used for we will imagine the situation where
  // multiple windows or multiple threads may each one use
  // libdar. But all share the same callback functions
 
typedef class t_window_type t_win;

  // this is an arbitrary type that here we will say
  // points to a graphical window object wrapped in a C++
  // class.
  // Note that the method show() wait_for_click() and so on
  // attributed to the t_win class are absolutely
  // imaginary. Any link to an existing class is a pure
  // coincidence...

void warning_callback(const std::string &x, void *context)
{
    (t_win *)(context)->show(x);
}
 
bool answer_callback(const std::string &x, void *context)
{
    click_type ret;

    (t_win *)(context)->show(x);
    ret = (t_win *)(context)->wait_for_click();

    return ret == click_OK;
}

std::string string_callback(const std::string &x, bool echo, void *context)
{
    (t_win *)(context)->show(x);
    if(!echo)
      (t_win *)(context)->set_hide_typed_char();
    (t_win *)(context)->wait_for_click();
    return (t_win *)(context)->read_text();
}

---------8<-------8<-------8<-------

  // So now each window can have its user_interaction object based on the same
  // user_interaction_callback object pointing to the same functions.
  // user_interaction_callback objects can be shared among different window objects

libdar::user_interaction_callback dialog =
        libdar::user_interaction_callback(&warning_callback, &answer_callback, &string_callback,
                                          (void *)get_current_windows_id());

  // just the "context" argument changes, and will be passed as is from the constructor to the callback
  // functions


4 - Masks

Mask are used to define which files will be considered and which will not. Libdar implements masks as several classes that all inherit from a virtual class that defines the way masks are used. This root class is the class mask and provides the is_covered() method which libdar uses to determine which files are considered. There are many different basic masks classes you can use to build fairly complex masks:


class libdar::mask
 the generic class, parent of all masks (a pure virtual class)
class libdar::bool_mask
 boolean mask, either always true or false, it matches either all files or no files at all
class libdar::simple_mask
 matches as done by the shell on the command lines (see "man 7 glob")
class libdar::regular_mask
 matches regular expressions (see "man 7 regex")
class libdar::not_mask
 negation of another mask
class libdar::et_mask
 makes an *AND* operator between two or more masks
class libdar::ou_mask
 makes the *OR* operator between  two or more masks
class lbdar::simple_path_mask

string matches if it is subdirectory of mask or is a directory that contains the specified path itself
class libdar::same_path_mask
 matches if the string is exactly the given mask (no wild card expression)
class libdar::exclude_dir_mask
 matches if string is the given string or a sub directory of it

Let's play with some masks :



      // all files will be elected by this mask
  libdar::bool_mask m1 = true;   

      // all file that match the glob expession "A*~" will match.
      // the second argument of the constructor tell if the match is case sensitive so here
      // any file beginning by 'A' or by 'a' and ending by '~' will be selected by this mask
  libdar::simple_mask m2 = libdar::simple_mask(std::string("A*~"), false);

      // m3 is the negation if m2. This mask will thus match
      // any file that does not begin by 'A' or 'a' and also finish by '~'
  libdar::not_mask m3 = m2;

      // this mask matches any file that is a subdirectory of "/home/joe"
      // and any directory that contains /home/joe, meaning
      // "/", "/home", "/jome/joe" and any subdirectory are matched.
      // here, the second argument is also case sensitivity (so
      //  "/HoMe" will not be selected by this mask.
  libdar::simple_path_mask m4 = simple_path_mask("/home/joe", true);

      // now let's do some more complex things:
      // m5 will now match only files that are selected by both m2 AND m4
  libdar::et_mask m5;
  m5.add_mask(m2);
  m5.add_mask(m4);
     
      // we can make more silly things like this, where m5 will select files
      // that match m2 AND m4 AND m3. But m3 = not m2 so now m5 will never
      // match any file...
  m5.add_mask(m3);

      // but we could do the same with an "ou_mask" and would get a silly
      // counterpart of m1 (a mask that matches any files)
  libdar::ou_mask m6;
  m6.add_mask(m2);
  m6.add_mask(m4);
  m6.add_mask(m3);

      // lastly, the NOT, AND and OR operation can be used recursively.
      // Frankly, it's possible to have masks reference each other!
  libdar::not_mask m7 = m6;
  m6.add_mask(m7);

Now that you've seen the power of these masks, you should know that in libdar there are two masks that are required:

5 - Let's create a simple archive

Now that we have seen masks and exceptions let's start the real thing:
 

  // creating an archive is simple; it is just
  // a matter of calling the "create" constructor
  // of the archive class. It may be used for full or
  // differential archives. We'll see an example of
  // of differential archives later.

  // note that while this example uses a pointer to store
  // my_arch, it is perhaps better practice to use a plain
  // stack object. In your code, use an object instead of
  // a pointer to an object under normal circumstances.

libdar::user_interaction_callback dialog = libdar::user_interaction_callback(ptr1, ptr2, ptr3);
  // where ptr1, ptr2 and ptr3 are three callback
  // functions.
libdar::statistics ret;
  // we will see this structure a bit further

libdar::archive *my_arch =
     new libdar::archive(dialog,
     "/home",  // saving all under this "root"
     "/tmp",   // where the slices will go
     NULL,     // we do a full backup for now
     libdar::not_mask(simple_mask("*~", true)),
            // we don't save the files ending with
            // '~' this does not concern directories
     libdar::bool_mask(true),
            // all directories and files not rejected
            // by the previous mask are saved
     "my_archive", 
            // the basename of the slices
     "dar", // dar's slice extensions
     true,  // we allow slice overwriting
     true,  // but ask to be warned in such occurrence
     false, // we don't want a verbose output
     false, // nor do we want to pause between slices
     true,  // rejected directories will be saved as
            // empty (no directory is rejected so
            // here there is no importance for that
            // parameter)
     libdar::gzip // the archive will be compressed
            // using gzip
     9,     // at maximum compression level
     0,     // no slicing is done,
     0,     // so the first slice size must also be
            // set to zero
     true,  // root EA will be saved if present
     true,  // user EA too
     "",    // no script will be executed between
            // slices (as there is no slicing)
     libdar::crypto_blowfish,
            // the blowfish strong encryption
            // will be used
     "",    // as the password is not given here   
            // (empty string is not a valid password)
            // it will be queried interactively
            // through the dialog
            // user_interaction object
     20480, // the block of encryption will be
            // 20 kbytes
     libdar::not_mask(libdar::simple_mask("*gz")),
            // all files will be compressed except
            // those ending with "gz"
     800,   // files whose sized is below 800 bytes
            // will not be compressed
     false, // all files will be saved regardless of
            // the nodump flag value
     false, // as we're making a full backup this
            // "ignore_owner" parameter is useless
      0,    // hourshift is useless here as we're making
            // a full backup
     false, // we will make a real archive not a
            // dry-run operation
     true,  // dar will set back the access time of
            // file it opens, which will change the
            // ctime date of theses files
     false, // we may cross to other filesystems if
            // necessary
     ret);  // this value is returned by libdar

    // creating an archive is simple; it is just
  // a matter of calling the "create" constructor
  // of the archive class. It may be used for full or
  // differential archives. We'll see an example of
  // of differential archives later.

  // note that while this example uses a pointer to store
  // my_arch, it is perhaps better practice to use a plain
  // stack object. In your code, use an object instead of
  // a pointer to an object under normal circumstances.

libdar::user_interaction_callback dialog = libdar::user_interaction_callback(ptr1, ptr2, ptr3);
  // where ptr1, ptr2 and ptr3 are three callback
  // functions.
libdar::statistics ret;
  // we will see this structure a bit further

U_16 exception,
std::string except_msg;

libdar::archive *my_arch =    
     libdar::create_archive_noexcept(dialog, 
     "/home",  // saving all under this "root"
     "/tmp",   // where the slices will go
     NULL,     // we do a full backup for now
     libdar::not_mask(simple_mask("*~", true)),
            // we don't save the files ending with
            // '~' this does not concern directories
     libdar::bool_mask(true),
            // all directories and files not rejected
            // by the previous mask are saved
     "my_archive", 
            // the basename of the slices
     "dar", // dar's slice extensions
     true,  // we allow slice overwriting
     true,  // but ask to be warned in such occurrence
     false, // we don't want a verbose output
     false, // nor do we want to pause between slices
     true,  // rejected directories will be saved as
            // empty (no directory is rejected so
            // here there is no importance for that
            // parameter)
     libdar::gzip // the archive will be compressed
            // using gzip
     9,     // at maximum compression level
     0,     // no slicing is done,
     0,     // so the first slice size must also be
            // set to zero
     true,  // root EA will be saved if present
     true,  // user EA too
     "",    // no script will be executed between
            // slices (as there is no slicing)
     libdar::crypto_blowfish,
            // the blowfish strong encryption
            // will be used
     "",    // as the password is not given here   
            // (empty string is not a valid password)
            // it will be queried interactively
            // through the dialog
            // user_interaction object
     20480, // the block of encryption will be
            // 20 kbytes
     libdar::not_mask(libdar::simple_mask("*gz")),
            // all files will be compressed except
            // those ending with "gz"
     800,   // files whose size is below 800 bytes
            // will not be compressed
     false, // all files will be saved regardless of
            // the nodump flag value
     false, // as we're making a full backup this
            // "ignore_owner" parameter is useless
      0,    // hourshift is useless here as we're making
            // a full backup
     false, // we will make a real archive not a
            // dry-run operation
     true,  // dar will set back the access time of
            // file it opens, which will change the
            // ctime date of theses files
     false, // we may cross to other filesystems if
            // necessary
     ret,   // this value is returned by libdar
     exception, // this gives the status of the call
     except_msg); // and in case of error the cause.

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;


When creating an archive, the created archive object can be used only as reference for an isolation or for differential backups. You cannot use it for restoration, listing, or comparison, because the underlying file descriptors are opened in write only mode. An implementation which uses file descriptors in read-write access is not possible and is not a good idea anyway. Why? Because, for example, if you want to test the newly created archive, using the newly created object would make the test rely on information stored in virtual memory (the archive contents, the data location of a file, etc.), not on the file archive itself. If some corruption occurred in the file you would not notice it.

So to totally complete the archive creation we must destroy the archive object we have just created, which will also close any file descriptors used by the object :



     delete my_arch;
libdar::close_archive_noexcept(my_arch, exception,
                        except_msg);

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;

6 - Testing the archive we have created

So, as explained previously, we must create a new archive object but this time with the "read" constructor:

my_arch = new libdar::archive(dialog,     
        "/tmp",  // where is the archive
        "my_archive", // slice name
        "dar",   // dar's archive extensions
        libdar::crypto_blowfish,
        "",
        20480, // theses last three are for encryptions
        "",    // not used as we didn't gave "-" as
        "",    // slice name
        "",    // no command executed for now
        false); // no verbose output
my_arch = libdar::open_archive_noexcept(dialog,     
        "/tmp",  // where is the archive
        "my_archive", // slice name
        "dar",   // dar's archive extensions
        libdar::crypto_blowfish,
        "",
        20480, // theses last three are for encryptions
        "",    // not used as we didn't gave "-" as
        "",    // slice name
        "",    // no command executed for now
        false, // no verbose output
       exception,// this gives the status of the call
       except_msg); // and in case of error the
                    // cause of the error

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;


Now that we have opened the archive we can perform any operation on it. Let's thus start by testing the archive coherence:



ret = my_arch->op_test(dialog,
             libdar::bool_mask(true),
                        // all files are tested
             libdar::bool_mask(true),
                        //no directory is prune
             false);    // no verbose output    

 
ret = libdar::op_test_noexcept(dialog,
       my_arch,         // the archive to test
       libdar::bool_mask(true),
                 // all files are tested
       libdar::bool_mask(true),
                 //no directory is prune
       false,    // no verbose output
       exception,// this gives the status of the call
       except_msg); // and in case of error the
                    // cause of the error

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;

We have tested the archive, but have not yet seen the libdar::statistics variable. It can be used when creating an archive as well as when testing it.  This structure reports the number of files treated, as well as the number files with errors and the type of error. You can have a look at the API reference guide for more information about the uses of different fields. Here is an example, which relies on the class deci to display the value of an infinint variable:

     
     // we need the class deci to display the value of an infinint:
#include "deci.hpp"

 std::cout << std::string("Number of file treated :") << libdar::deci(ret.treated).human() << std::endl;

    // or much simpler (but totally equivalent):
 std::cout << std::string("Number of file treated :") libdar::<< ret.treated << std::endl;

Note that the use of the class deci may throw exceptions (in case of lack of memory, for example), and there is actually no wrapper available to trap the exceptions that may be thrown by the class deci. So you have to protect the code using a try {} catch {}  statement.

7 - listing archive contents

The simple way:


my_arch->op_listing(dialog,
             false, // not a verbose output
             false, // not using the tar-like format
             bool_mask(true),
                    // all filenames are listed
             false);// do not filter unsaved files 

 
libdar::op_test_listing(dialog,
      false, // not a verbose output
      false, // not using the tar-like format
      bool_mask(true),
             // all filenames are listed
       false,// do not filter unsaved files
       exception,// this gives the status of the call
       except_msg); // and in case of error the
                    // cause of the error

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << endl;

By default the library will complete the listing by calling the warning() method of the dialog object one time for each file listed. The warning text will consist of a string for each file with the relevant information in columns that would need to be parsed if individual information was desired. This may not be appropriate for you and as such there is another way to get listing information. This requires a simple reimplementation of the user_interaction object.

The user_interaction class has a listing() method which provides separate arguments for each piece of information that can be displayed:


Technical note: You may notice that file type is not explicitly given as a parameter in the listing method. File type is available as the first byte of the permissions string. This is standard POSIX stuff except for an extension: "h" for files hard linked several times. See man 2 stat for more information. Note however that in the last arguments of this call, you may easily know whether a file is a directory or not and whether it is empty or not.

In the user_interaction class (a virtual class), the listing() method is not a pure virtual method, so you are not obliged to overwrite it, but it has just an empty implementation so it does nothing. You understand now that, by default, this method is not used. To activate it, you must call  set_use_listing(true) protected method and of course you will have to overwrite the listing() method to have a less silly behavior:


    // here follows the definition of our own implementation of
    // of a user_interaction class

class my_user_interaction : public user_interaction
{
public :
     // the inherited pure virtual methods we must define
     // as seen at the beginning of this tutorial:
       void pause(const std::string & message);
       void warning(const std::string & message);
       std::string get_string(const std::string & message, bool echo);
       user_interaction *clone() const;

    // we can overwrite this method to have splitted fields for listing:
        void listing(const std::string & flag,
                            const std::string & perm,
                            const std::string & uid,
                            const std::string & gid,
                            const std::string & size,
                            const std::string & date,
                            const std::string & filename,
                            bool is_dir,
                            bool has_children);

     // but it will not get used by libdar unless we call the protected method set_use_listing()
     // for example this can be done in the class constructor :

     my_user_interaction() { set_use_listing(true); };
};

Now assuming we have implemented the listing() method in  my_user_interaction class, calling op_listing() exactly as we did before, only replacing the dialog object by one of the my_user_interaction class. Then this listing() method will be called for each file to be listed, in place of the warning() method.

As seen at the beginning of this tutorial, there is a child class of user_interaction based on callback functions which is called user_interaction_callback. The listing() method must also be activated here. This is done automatically when you give a callback function to the object, thanks to the set_listing_callback() method :

 
  // our mandatory callback functions:

void warning_callback(const std::string &x, void *context)
{
    ....
}
 
bool answer_callback(const std::string &x, void *context)
{
    ....
}

std::string string_callback(const std::string &x, bool echo, void *context)
{
    ....
}

  // let's build a user_interaction_callback object:

libdar::user_interaction_callback dialog =
        libdar::user_interaction_callback(&warning_callback, &answer_callback, &string_callback, NULL);

   // at this point our dialog object is perfectly operational for listing
   // but libdar will call the warning_callback function to list the archive
   // contents

   // a new callback function for listing :

void listing_callback(const std::string & flag,
                      const std::string & perm,
                      const std::string & uid,
                      const std::string & gid,
                      const std::string & size,
                      const std::string & date,
                      const std::string & filename,
                      bool is_dir,
                      bool has_children,
                      void *context)
{
    ....
}

dialog.set_listing_callback(&listing_callback);

   // now libdar will call the listing_callback function when we
   // use this dialog object for listing the archive contents.


8 - comparing with filesystem

We can compare file in an archive with the filesystem by calling the op_diff method of the class archive.


     ret = my_arch->op_diff(dialog,
                 "/home", // what directory to take
                          // as root we shall
                          // compare the archive
                          // contents to
                 libdar::bool_mask(true),
                 libdar::bool_mask(true),
                 false,   // no verbose output
                 true,    // comparing root EA
                 true,    // comparing user EA
                 false,   // do not ignore ownership
                          // differences
                 false);  // do not set back atime
                          // of read files





 		           
  ret = libdar::op_diff_noexcept(dialog,
                 my_arch, // the archive to use
                 "/home", // what directory to take
                          // as root we shall
                          // compare the archive
                          // contents to
                 libdar::bool_mask(true),
                 libdar::bool_mask(true),
                 false,   // no verbose output
                 true,    // comparing root EA
                 true,    // comparing user EA
                 false,   // do not ignore ownership
                          // differences
                 false,   // do not set back atime
                          // of read    
                 filesexception, // this gives the
                          // status of the call
                 except_msg); // and in case of
                          // error the cause of the
                          // error

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;

Simple, no?

9 - restoring files

Restoration of files is done by calling the  op_extract method of class archive.


ret = my_arch->op_extract(dialog,
             "/tmp",   // where to restore files to
             libdar::bool_mask(true),
                       // restore any filename
            libdar::simple_path_mask("denis/.tcshrc",
                               true),
                            // but only restore
                            // this file or directory
             false,// overwriting not allowed
             true, // warn before overwriting
                   // useless here, not overwritting
             true, // verbose output
             true, // remove files marked as deleted
                   // useless here too, as verwriting
                   // has been disabled
             false,// restore even if a file is more
                   // recent, (useless here too)
             true, // restore root EA  
             true, // restore user EA
             false,// restore directory structure   
             false,// restore ownership
             false,// don't warn if a file to be
                   // removed has a type that does
                   // the type of the orginal file  
             0,   // no daylight saving consideration
             false); // not a dry-run execution

  
ret = libdar::op_extract_noexcept(dialog,
       my_arch,         // the archive to test
       "/tmp",   // where to restore files to
       libdar::bool_mask(true),
                // restore any filename
       libdar::simple_path_mask("denis/.tcshrc",
                                true),
                        // but only restore
                        // this file or directory
       false,// overwriting not allowed
       true, // warn before overwriting
             // useless here, not overwritting
       true, // verbose output
       true, // remove files marked as deleted
             // useless here too, as verwriting
             // has been disabled
       false,// restore even if a file is more
             // recent, (useless here too)
       true, // restore root EA  
       true, // restore user EA
       false,// restore directory structure   
       false,// restore ownership
       false,// don't warn if a file to be
             // removed has a type that does
             // the type of the orginal file  
        0,   // no daylight saving consideration
       false,// not a dry-run execution
       exception,// this gives the status of the call
       except_msg); // and in case of error the
                    // cause of the error

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;

10 - isolating the catalogue

OK, I know, catalogue is not an English word (one would rather write catalog), but that's the name of the C++ class used in libdar, so we will keep using it here. Note that you don't have to directly access this class (if you really don't like French).

Isolating the catalogue creates a new archive that only contains the list of files and their attributes (ownership, dates, size, etc.), but no data and no EA are stored in it. It is very similar to the same archive one gets if one makes a differential backup of a filesystem that has not changed since the creation of a reference archive. The usage is very similar to the archive creation, but it uses a different constructor that has less arguments :



libdar::archive *my_cat = new libdar::archive(dialog,
                "/tmp",  // where the extracted
                         // catalogue is saved
                my_arch, // the archive of reference
                         // is the one we have been
                         // playing with previously
                "my_catalogue", // slice name
                "dar",   // file extension
                true,    // allow slice overwriting
                true,    // but warn before
                true,    // verbose output
                true,    // pause between slices
                libdar::bzip2, // compression
                9,       // max compression level
                3000, // cut in slices of 3000 Bytes
                3000, // first slice size is the same
                "echo slice %p/%b.%n.%e created",
                      // the script to run after
                      // slice creation
                libdar::crypto_none, // no encryption
                "",    // unused password
                0,     // unused crypto size
                false); // not a dry-run execution
      

           
libdar::archive *my_cat =
    libdar::op_isolate_noexcept(dialog,
               "/tmp",   // where is saved the
                         // extracted catalogue
                my_arch, // the archive of reference
                         // is the one we have been
                         // playing with previously
                "my_catalogue", // slice name
                "dar",   // file extension
                true,    // allow slice overwriting
                true,    // but warn before
                true,    // verbose output
                true,    // pause between slices
                libdar::bzip2, // compression
                9,       // max compression level
                3000, // cut in slices of 3000 Bytes
                3000, // first slice size is the same
                "echo slice %p/%b.%n.%e created",
                      // the script to run after
                      // slice creation
                libdar::crypto_none, // no encryption
                "",    // unused password
                0,     // unused crypto size
                false, // not a dry-run execution
                exception,
                       // this gives the status
                       // of the call
                except_msg);
                       // and in case of error the
                       // cause of the error

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;


Now we have two archive objects. my_arch is a read-only object created by the "read" constructor. You can do any operations with it, like file restoration, file comparison, archive testing, as we have done in the previous sections. The second archive object is my_cat which is a write only object. It can only be used as a reference for another backup (a differential backup) or as a reference for a subsequent catalogue isolation (which would just clone the already isolated catalogue object here).

Note that, if desired, an isolated catalogue can be tested, compared with the filesystem, and you can even try to restore files from it. But as there is no data associated with the files contents, dar will not restore any files from it, of course. So for now we will just destroy the extracted catalogue object, so that all its file descriptors are closed:



delete my_cat;   


close_archive_noexcept (my_cat, exception,
                        except_msg);

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;


and we keep the my_arch object for our last operation:

11 - creating a differential backup

This operation is the same as the first one we did (archive creation). Perhaps you have noted that an argument was set to NULL. Here we will pass it my_arch which means that my_arch will become the reference archive for the archive we will create. If we had not destroyed my_cat above, we could have used it in place of my_arch for exactly the same result.


 
libdar::archive *my_other_arch =
     new libdar::archive(dialog,
     "/home",  // saving all under this "root"
     "/tmp",   // where the slices will go
     my_arch,  // differential backup
     not_mask(simple_mask("*~", true)),
            // we don't save the files ending with
            // '~' this does not concern directories
     bool_mask(true),
            // all directories and files not rejected
            // by the previous mask are saved
     "my_archive", 
            // the basename of the slices
     "dar", // dar's slice extensions
     true,  // we allow slice overwriting
     true,  // but ask to be warned in such occurrence
     false, // we don't want a verbose output
     false, // nor we want to pause between slices
     true,  // rejected directory will be saved as
            // empty (no directory is rejected so
            // here there is no importance for that
            // parameter)
     libdar::gzip // the archive will be compressed
            // using gzip
     9,     // at maximum compression level
     0,     // no slicing is done,
     0,     // so the first slice size must also be
            // set to zero
     true,  // root EA will be saved if present
     true,  // user EA too
     "",    // no script will be executed between
            // slices (as there is no slicing)
     libdar::crypto_blowfish,
            // the blowfish strong encryption
            // will be used
     "",    // as the password is not given here   
            // (empty string is not a valid password)
            // it will be asked interactively to the
            // user through the dialog
            // user_interaction object
     20480, // the block of encryption will be
            // 20 kbytes
     not_mask(simple_mask("*gz")),
            // all files will be compressed except
            // those ending by "gz"
     800,   // file which size is below 800 bytes
            // will not be compressed
     false, // all files will be saved whatever is
            // the nodump flag value
     false, // as we make a full backup this
            // "ignore_owner" parameter is useless
      0,    // hourshift is useless here as we make
            // a full backup
     false, // we will make a real archive not a
            // dry-run operation
     true,  // dar will set back the access time of
            // file it opens, which will change the
            // ctime date of theses files
     false, // we may change of filesystem if
            // necessary
     ret);  // this value is returned by libdar
libdar::archive *my_other_arch =    
     libdar::create_archive_noexcept(dialog, 
     "/home",  // saving all under this "root"
     "/tmp",   // where the slices will go
     my_arch,  // differential backup
     not_mask(simple_mask("*~", true)),
            // we don't save the files ending with
            // '~' this does not concern directories
     bool_mask(true),
            // all directories and files not rejected
            // by the previous mask are saved
     "my_archive", 
            // the basename of the slices
     "dar", // dar's slice extensions
     true,  // we allow slice overwriting
     true,  // but ask to be warned in such occurrence
     false, // we don't want a verbose output
     false, // nor we want to pause between slices
     true,  // rejected directory will be saved as
            // empty (no directory is rejected so
            // here there is no importance for that
            // parameter)
     libdar::gzip // the archive will be compressed
            // using gzip
     9,     // at maximum compression level
     0,     // no slicing is done,
     0,     // so the first slice size must also be
            // set to zero
     true,  // root EA will be saved if present
     true,  // user EA too
     "",    // no script will be executed between
            // slices (as there is no slicing)
     libdar::crypto_blowfish,
            // the blowfish strong encryption
            // will be used
     "",    // as the password is not given here   
            // (empty string is not a valid password)
            // it will be asked interactively to the
            // user through the dialog
            // user_interaction object
     20480, // the block of encryption will be
            // 20 kbytes
     not_mask(simple_mask("*gz")),
            // all files will be compressed except
            // those ending by "gz"
     800,   // file which size is below 800 bytes
            // will not be compressed
     false, // all files will be saved whatever is
            // the nodump flag value
     false, // as we make a full backup this
            // "ignore_owner" parameter is useless
      0,    // hourshift is useless here as we make
            // a full backup
     false, // we will make a real archive not a
            // dry-run operation
     true,  // dar will set back the access time of
            // file it opens, which will change the
            // ctime date of theses files
     false, // we may change of filesystem if
            // necessary
     ret,   // this value is returned by libdar
     exception, // thisgives the status of the call
     except_msg); // and in case of error the cause.

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;

As previously, my_other_arch is a write only object that we won't need anymore. So we destroy it:


     delete my_other_arch;
libdar::close_archive_noexcept(my_other_arch,
                        exception,
                        except_msg);

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;



So, we are at the end of the tutorial. We still have an object we need to destroy to cleanly release the memory used:



     delete my_arch;
libdar::close_archive_noexcept(my_arch, exception,
                        except_msg);

if(exception != LIBDAR_NOEXCEPT)
  std::cout << "an error occurred: " << except_msg
            << std::endl;


For more detailed information about the API you can build the API documentation from the source code using Doxygen.


12 - Compilation & Linking

Compilation

All the symbols found in the libdar API are defined via <dar/libdar.h> so you should only need to include this header.



> cat my_prog.cpp
#include <dar/libdar.h>

main()
{
   libdar::get_version(...);
   ...
}
> gcc -c my_prog.cpp


Linking

Of course, you need to link your program with libdar. This is done by adding -ldar :


 
> gcc -ldar my_prog.o -o my_prog


Libdar's different flavors

Well, all the compilation and linking steps described above assume you have a "full" libdar library. Beside the full (alias infinint) libdar flavor, libdar also comes in 32 and 64 bits versions. In theses last ones, in place of internally relying on a special type (which is a C++ class called infinint) to handle arbitrary large integers, libdar32 relies on 32 bits integers and libdar64 relies on 64 bits integers (there are limitations which are described in doc/LIMITATIONS). But all theses libdar version (infinint, 32bits, 64bits) have the same interface and must be used the same way, except for compilation and linking.

Theses different libdar versions can coexist on the same system, they share the same include files. But the MODE macro must be set to 32 or 64 when compiling for linking with libdar32 or libdar64 respectively. The MODE macro defines the way the "class infinint" type is implemented in libdar, and thus changes the way the libdar headers files are interpreted by the compiler.

> cat my_prog.cpp
#include <dar/libdar.h>

main()
{
   libdar::get_version(...);
   ...
}
> gcc -c -DMODE=32 my_prog.cpp


> gcc -ldar32 my_prog.o -o my_prog

and replace 32 by 64 to link with libdar64.

Thanks

I would like to thank Wesley Leggette for having given his feedback and having done grammar corrections to this document.

Regards,
Denis Corbin.