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Name

DAV_LOCK , DAV_UNLOCK , DAV_IS_LOCKED , DAV_LIST_LOCKS — Operations on locks of DAV collections and resources

Synopsis

integer DAV_LOCK ( in path varchar ,
  in locktype varchar ,
  in scope varchar ,
  in token varchar ,
  in owner_name varchar ,
  in owned_tokens varchar ,
  in depth varchar ,
  in timeout_sec integer ,
  in auth_uname varchar ,
  in auth_pwd varchar );
 
any DAV_UNLOCK ( in path varchar ,
  in token varchar ,
  in auth_uname varchar ,
  in auth_pwd varchar );
 
integer DAV_IS_LOCKED ( in id any ,
  in type char(1) ,
  in owned_tokens any := 1 );
 
integer DAV_LIST_LOCKS ( in id any ,
  in type char(1) );
 

Description

DAV_LOCK sets a new lock or refresh an existing lock or creates a lock object.

DAV_UNLOCK releases a lock.

DAV_IS_LOCKED reports whether the resource or collection is locked.

DAV_LIST_LOCKS returns a full list of all locks on a resource or collection.

It is strongly recommended to carefully study DAV standards before using these functions in applications. Improper use of DAV locks may result in subtle application errors that are hard to debug.

Parameters

path

Resource or collection path. As usual, collection names must end with '/' and both sorts of path strings should begin with '/'. If the path specifies a non-existing resource in an existing collection then a lock object is created and only lock owner can create a resource with this name in future.

locktype

The type of lock. Current set of DAV standards specifies only one type of locks, called 'D:write'; the parameter value is stored 'as is' and never used, so the recommended value is an empty string.

scope

The scope of lock as a single-char string: 'S' for shared lock, 'X' for exclusive.

token

The token to update. Empty string or NULL means creation of a new lock, not an update of the existing one.

owner_name

Lock owner name as it will be displayed to other users that will query for existing locks. It is strongly recommended to provide commonly used names such as e-mails to let users ask each other to remove forgotten locks.

owned_tokens

String of tokens owned by a user, to let user ignore his own tokens. The string should match syntax of DAV HTTP 'If' parameter. This can be also an integer, this will work as empty list of tokens.

depth

This specifies the recursive depth of the lock. The string can be '0' to lock the specified collection only, '1' to lock the collection and its subcollections, 'infinity' to lock the whole subtree. When the lock is added to a resource, the value '0' is used, for obvious reason. If NULL is passed to the function then the effective value is 'infinity' for collection lock or '0' for resource lock.

timeout_sec

Expiration interval for the lock, in seconds. If 0 or NULL is passed then HTTP DAV default is used that is equal to 604800 seconds (one week).

auth_uname

DAV user name to authenticate access. Lock, Lock refresh and unlock operations on existing resource or collection require write permission. To create a lock object in a collection, user should have write permission on that collection. This may cause problem when user first locks a resource and then loose write permission for some reason: the user is unable to remove his own lock. Default is NULL that means public access.

auth_pwd

User password. Default is NULL.

id

Internal identifier of a resource or collection as returned by DAV_SEARCH_ID().

Examples

Example 24.78. Two concurrent users

The following example shows how two users can prevent each other from undesired operations.

The sample function DAV_LOCK_DEMO() uses a function DUMP_VEC() that print the content of vector in Virtuoso/PL syntax. Yon can find the implementation of this function as one of examples for vector() Virtuoso/PL function. 

create procedure DAV_LOCK_DEMO (in dav_passwd varchar := 'dav')
{
  declare ACTION, RETVAL, token_s1, token_s2, token_x varchar;
  result_names (ACTION, RETVAL);
  result ('Adding group lock_demo_grp:',
    DAV_ADD_GROUP ('lock_demo_grp', 'dav', dav_passwd) );
  result ('Adding user lock_u1:',
    DAV_ADD_USER ('lock_u1', 'lock_u1_pwd', 'lock_demo_grp', '110110000T', 0, '/DAV/lock_demo_u1_home/', 'First User of lock demo', 'lock_u1@localhost', 'dav', dav_passwd) );
  result ('Adding user lock_u2:',
    DAV_ADD_USER ('lock_u2', 'lock_u2_pwd', 'lock_demo_grp', '110110000T', 0, '/DAV/lock_demo_u2_home/', 'Second User of lock demo', 'lock_u2@localhost', 'dav', dav_passwd) );
  result ('Adding a collection:',
    DAV_COL_CREATE ('/DAV/lock_demo/', '110110000R', 'lock_u1', 'lock_demo_grp', 'dav', dav_passwd) );
  result ('Uploading /DAV/lock_demo/sample.htm:',
    DAV_RES_UPLOAD ('/DAV/lock_demo/sample.htm', '<html><body>This is /DAV/lock_demo/sample.htm</body></html>', 'text/plain', '110110000R', 'lock_u1', 'lock_demo_grp', 'lock_u1', 'lock_u1_pwd') );
  token_s1 := DAV_LOCK ('/DAV/lock_demo/sample.htm', '', 'S', NULL, 'user1@example.com', '', '0', NULL, 'lock_u1', 'lock_u1_pwd');
  result ('First user set a shared lock:', token_s1);
  token_s2 := DAV_LOCK ('/DAV/lock_demo/sample.htm', '', 'S', NULL, 'user2@example.com', '', '0', NULL, 'lock_u2', 'lock_u2_pwd');
  result ('Second user set a shared lock:', token_s2);
  token_x := DAV_LOCK ('/DAV/lock_demo/sample.htm', '', 'X', NULL, 'user1@example.com', token_s1, '0', NULL, 'lock_u1', 'lock_u1_pwd');
  result ('Lock dump',
    DUMP_VEC (DAV_LIST_LOCKS (DAV_SEARCH_ID ('/DAV/lock_demo/sample.htm', 'R'), 'R')) );
  result ('First user tries to set an exclusive lock:', token_x);
  result ('Second user releases his lock:',
    DAV_UNLOCK ('/DAV/lock_demo/sample.htm', token_s2, 'lock_u2', 'lock_u2_pwd') );
  token_x := DAV_LOCK ('/DAV/lock_demo/sample.htm', '', 'X', NULL, 'user1@example.com', token_s1, '0', NULL, 'lock_u1', 'lock_u1_pwd');
  result ('First user sets an exclusive lock:', token_x);
  result ('First user releases his lock:',
    DAV_UNLOCK ('/DAV/lock_demo/sample.htm', token_s1, 'lock_u1', 'lock_u1_pwd') );
  token_x := DAV_LOCK ('/DAV/lock_demo/sample.htm', '', 'X', NULL, 'user1@example.com', token_s1, '0', NULL, 'lock_u1', 'lock_u1_pwd');
  result ('First user sets an exclusive lock:', token_x);
  result ('Second user tries to add a property to the resource:',
    DAV_PROP_SET ('/DAV/lock_demo/sample.htm', 'sample_prop', 'sample value', 'lock_u2', 'lock_u2_pwd') );
  result ('First user releases his shared:',
    DAV_UNLOCK ('/DAV/lock_demo/sample.htm', token_x, 'lock_u1', 'lock_u1_pwd') );
  result ('Second user adds a property to the resource:',
    DAV_PROP_SET ('/DAV/lock_demo/sample.htm', 'sample_prop', 'sample value', 'lock_u2', 'lock_u2_pwd') );
}

DAV_LOCK_DEMO ();
ACTION   RETVAL
VARCHAR  VARCHAR
_______________________________________________________________________________

Adding group lock_demo_grp:  107
Adding user lock_u1:  108
Adding user lock_u2:  109
Adding a collection:  171
Uploading /DAV/lock_demo/sample.htm:  1103
First user set a shared lock:  1545ce54-3599-11da-8697-8f3efbd86ef2
Second user set a shared lock:  15460590-3599-11da-8697-8f3efbd86ef2
Lock dump  
vector (
vector ('', 'S', '1545ce54-3599-11da-8697-8f3efbd86ef2', 604800, 108, 'user1@example.com'), 
vector ('', 'S', '15460590-3599-11da-8697-8f3efbd86ef2', 604800, 109, 'user2@example.com'))
First user tries to set an exclusive lock:  -8
Second user releases his lock:  15460590-3599-11da-8697-8f3efbd86ef2
First user sets an exclusive lock:  -8
First user releases his lock:  1545ce54-3599-11da-8697-8f3efbd86ef2
First user sets an exclusive lock:  1547251a-3599-11da-8697-8f3efbd86ef2
Second user tries to add a property to the resource:  -8
First user releases his shared:  1547251a-3599-11da-8697-8f3efbd86ef2
Second user adds a property to the resource:  1321

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