Library
Module
Module type
Parameter
Class
Class type
Loopback implementation of the FS signature.
type write_error = [
| Mirage_kv.write_error
| `Storage_error of Mirage_kv.Key.t * string
| `Key_exists of Mirage_kv.Key.t
]
include Mirage_kv.RW
with type error := error
and type write_error := write_error
The functions set
and remove
will cause a flush in the underlying storage layer every time, which can degrade performance.
include Mirage_kv.RO with type error := error
val pp_error : error Fmt.t
pp_error
is the pretty-printer for errors.
Disconnect from the key-value store. While this might take some time to complete, it can never result in an error.
type key = Mirage_kv.Key.t
The type for keys.
exists t k
is Some `Value
if k
is bound to a value in t
, Some `Dictionary
if k
is a prefix of a valid key in t
and None
if no key with that prefix exists in t
.
exists
answers two questions: does the key exist and is it referring to a value or a dictionary.
An error occurs when the underlying storage layer fails.
get t k
is the value bound to k
in t
.
The result is Error (`Value_expected k)
if k
refers to a dictionary in t
.
val get_partial :
t ->
key ->
offset:Optint.Int63.t ->
length:int ->
(string, error) Stdlib.result Lwt.t
get_partial t k ~offset ~length
is the length
bytes wide value bound at offset
of k
in t
.
If the size of k
is less than offset
, get_partial
returns an empty string. If the size of k
is less than offset
+length
, get_partial
returns a short string. The result is Error (`Value_expected k)
if k
refers to a dictionary in t
.
list t k
is the list of entries and their types in the dictionary referenced by k
in t
. The returned keys are all absolute (i.e. Key.add k entry
).
The result is Error (`Dictionary_expected k)
if k
refers to a value in t
.
last_modified t k
is the last time the value bound to k
in t
has been modified.
When the value bound to k
is a dictionary, the implementation is free to decide how to compute a last modified timestamp, or return Error
(`Value_expected _)
.
digest t k
is the unique digest of the value bound to k
in t
.
When the value bound to k
is a dictionary, the implementation is allowed to return Error (`Value_expected _)
. Otherwise, the digest
is a unique and deterministic digest of its entries.
val pp_write_error : write_error Fmt.t
The pretty-printer for pp_write_error
.
val allocate :
t ->
key ->
?last_modified:Ptime.t ->
Optint.Int63.t ->
(unit, write_error) Stdlib.result Lwt.t
allocate t key ~last_modified size
allocates space for key
in t
with the provided size
and last_modified
. This is useful for e.g. append-only backends that could still use set_partial
. The data will be filled with 0. If key
already exists, Error (`Already_present key)
is returned. If there's not enough space, Error `No_space
is returned.
val set : t -> key -> string -> (unit, write_error) Stdlib.result Lwt.t
set t k v
replaces the binding k -> v
in t
.
Durability is guaranteed.
val set_partial :
t ->
key ->
offset:Optint.Int63.t ->
string ->
(unit, write_error) Stdlib.result Lwt.t
set_partial t k offset v
attempts to write v
at offset
in the value bound to k
in t
. If k
contains directories that do not exist, set_partial
will attempt to create them. If the size of k
is less than offset
, set_partial
appends v
at the end of k
. If the size of k
is greater than offset
+length of v
, set_partial
leaves the last bytes of k
unchanged.
The result is Error (`Value_expected k)
if k
refers to a dictionary in t
.
val remove : t -> key -> (unit, write_error) Stdlib.result Lwt.t
remove t k
removes any binding of k
in t
. If k
was bound to a dictionary, the full dictionary will be removed.
Durability is guaranteed.
val rename :
t ->
source:key ->
dest:key ->
(unit, write_error) Stdlib.result Lwt.t
rename t source dest
rename source
to dest
in t
. If source
and dest
are both bound to values in t
, dest
is removed and the binding of source
is moved to dest
. If dest
is bound to a dictionary in t
, source
is moved inside dest
. If source
is bound to a dictionary, the full dictionary is moved.
The result is Error (`Not_found source)
if source
does not exists in t
. The result is Error (`Value_expected source)
if source
is bound to a dictionary in t
and dest
is bound to a value in t
. The result id Error (`Rename_source_prefix (source, dest))
if source
is a prefix of dest
, and source
is a directory.