chicken-lmdb

Chicken Scheme bindings for the Lightning Memory-Mapped Database Manager (LMDB) (http://symas.com/mdb/doc/index.html) database management library.

Library procedures

(db-open filename [key: enckey] [mapsize: size]) Opens or creates LMDB database with optional encryption key and map size.

(db-close db) Closes LMDB database handle.

(db-begin db [dbname: dbname] [flags: 0]) Begins LMDB transaction with optional database name and flags returned by db-flags. Commits and ends LMDB transaction.

(db-flags flag-name ...) Returns a bit mask that represents LMDB environment flags. The flag name is one of the following keywords:

• #:fixed-map : mmap at a fixed address
• #:no-subdirectory : no environment directory
• #:read-only : read only
• #:write-map : use writable mmap
• #:no-meta-sync : don't fsync metapage after commit
• #:no-sync : don't fsync after commit
• #:map-async : use asynchronous sync with #:write-map is used
• #:no-lock : don't do locking
• #:no-read-ahead : don't do readahead

(db-abort db) Aborts LMDB transaction.

(db-delete db key) Removes a key from the database.

(db-delete-database dbname) Deletes LMDB database.

(db-ref db key) Looks up key in database.

(db-set! db key value) Sets a key-value pair in the database.

(db-count db) Returns number of key-value pairs in database.

(db-keys db) Returns a list of database keys.

(db-values db) Returns a list of database values.

(db-key-len m) Returns the length of the current key.

(db-value-len m) Returns the length of the current value.

(db-key m buf) Copies the current key to the specified blob.

(db-value m buf) Copies the current value to the specified blob.

(db-fold f init db) Fold over the keys and values in the database.

(db-for-each f db) Iterate over the keys and values in the database.

(hash-table->db t dbfile [enckey]) Saves SRFI-69 hash table to database.

(db->hash-table dbfile [enckey]) Load database into SRFI-69 hash table.

Examples

;; lmdb encrypted key-value creation and lookup

(let* ((fname (make-pathname "." "mydb.mdb"))
       (keys (list "k1" 'k2 '(k3)))
       (values (list 'one 2 "three"))
       (cryptokey (string->blob "1234"))
       (mm (db-open fname key: cryptokey)))
  (db-begin mm)
  (let loop ((ks keys) (vs values))
    (if (> (length ks) 0) 
        (begin
          (db-set! mm (string->blob (->string (car ks))) (string->blob (->string (car vs))))
          (loop (cdr ks) (cdr vs)))))
  (db-end mm)
  (db-begin mm)
  (let ((res (let loop ((ks keys) (vs values))
               (if (= (length ks) 0) #t
                   (let ((v (db-ref mm (string->blob (->string (car ks))))))
                     (if (not (equal? (string->blob (->string (car vs))) v))  #f
                         (loop (cdr ks) (cdr vs)))))))
        )
    (db-end mm)
    (db-close mm)
    res)
  )

;; lmdb readonly test

(let* ((fname (make-pathname "." "unittest.mdb")))
       (db-delete-database fname)
  (let ((mm (db-open fname maxdbs: 2)))
       (db-begin mm)
		;; set foo
		(db-set! mm (string->blob "foo") (string->blob "one"))
		(db-end mm)
        ;; reopen as readonly
		(db-begin mm flags: (db-flags #:read-only))
		;; foo is still set
		(test (string->blob "one")
		      (db-ref mm (string->blob "foo")))
		;; cannot set bar
		(test 'unknown
		      (condition-case (db-set! mm (string->blob "bar") (string->blob "two"))
			((exn lmdb unknown) 'unknown)))
                (db-close mm)))