-)
-
-type BlockWriter interface {
- // WriteBlock reads all data from r, writes it to a backing
- // store as "loc", and returns the number of bytes written.
- WriteBlock(ctx context.Context, loc string, r io.Reader) error
-}
-
-type BlockReader interface {
- // ReadBlock retrieves data previously stored as "loc" and
- // writes it to w.
- ReadBlock(ctx context.Context, loc string, w io.Writer) error
-}
-
-// A Volume is an interface representing a Keep back-end storage unit:
-// for example, a single mounted disk, a RAID array, an Amazon S3 volume,
-// etc.
-type Volume interface {
- // Volume type as specified in config file. Examples: "S3",
- // "Directory".
- Type() string
-
- // Do whatever private setup tasks and configuration checks
- // are needed. Return non-nil if the volume is unusable (e.g.,
- // invalid config).
- Start() error
-
- // Get a block: copy the block data into buf, and return the
- // number of bytes copied.
- //
- // loc is guaranteed to consist of 32 or more lowercase hex
- // digits.
- //
- // Get should not verify the integrity of the data: it should
- // just return whatever was found in its backing
- // store. (Integrity checking is the caller's responsibility.)
- //
- // If an error is encountered that prevents it from
- // retrieving the data, that error should be returned so the
- // caller can log (and send to the client) a more useful
- // message.
- //
- // If the error is "not found", and there's no particular
- // reason to expect the block to be found (other than that a
- // caller is asking for it), the returned error should satisfy
- // os.IsNotExist(err): this is a normal condition and will not
- // be logged as an error (except that a 404 will appear in the
- // access log if the block is not found on any other volumes
- // either).
- //
- // If the data in the backing store is bigger than len(buf),
- // then Get is permitted to return an error without reading
- // any of the data.
- //
- // len(buf) will not exceed BlockSize.
- Get(ctx context.Context, loc string, buf []byte) (int, error)
-
- // Compare the given data with the stored data (i.e., what Get
- // would return). If equal, return nil. If not, return
- // CollisionError or DiskHashError (depending on whether the
- // data on disk matches the expected hash), or whatever error
- // was encountered opening/reading the stored data.
- Compare(ctx context.Context, loc string, data []byte) error
-
- // Put writes a block to an underlying storage device.
- //
- // loc is as described in Get.
- //
- // len(block) is guaranteed to be between 0 and BlockSize.
- //
- // If a block is already stored under the same name (loc) with
- // different content, Put must either overwrite the existing
- // data with the new data or return a non-nil error. When
- // overwriting existing data, it must never leave the storage
- // device in an inconsistent state: a subsequent call to Get
- // must return either the entire old block, the entire new
- // block, or an error. (An implementation that cannot peform
- // atomic updates must leave the old data alone and return an
- // error.)
- //
- // Put also sets the timestamp for the given locator to the
- // current time.
- //
- // Put must return a non-nil error unless it can guarantee
- // that the entire block has been written and flushed to
- // persistent storage, and that its timestamp is current. Of
- // course, this guarantee is only as good as the underlying
- // storage device, but it is Put's responsibility to at least
- // get whatever guarantee is offered by the storage device.
- //
- // Put should not verify that loc==hash(block): this is the
- // caller's responsibility.
- Put(ctx context.Context, loc string, block []byte) error