Class AsyncWriterConnection (2.18.0)

An interface to asynchronously perform resumable uploads.

The client library uses the google.storage.v2.StorageService.BidiWriteObject RPC to perform asynchronous resumable uploads to Google Cloud Storage. As the name implies, this is a bi-directional RPC. The messages sent via this RPC are google.storage.v2.BidiWriteObjectRequest and google.storage.v2.BidiWriteObjectResponse.

The BidiWriteObjectRequest messages upload the object data.
The last BidiWriteObjectRequest message in an upload must include a finalize attribute. These messages result in a BidiWriteObjectResponse message, which includes the metadata of the GCS object created by the upload.
BidiWriteObjectRequest messages may include a flush attribute. Such messages result in a BidiReadObjectResponse message, which includes how much of the uploaded data has been persisted.

This interface uses different member functions to write messages with and without the finalize attribute. The functions have different return types reflecting the absence of response messages for BidiWriteObjectRequest messages that do not finalize an upload.

This interface does not provide a member function to create BidiWriteObjectRequest messages with a flush attribute.

This interface can be used to mock the behavior of these bidirectional streaming RPCs. Applications may use these mocks in their own tests.

Warning: We expect most applications will use this class in mocks or via the AsyncWriter wrapper, and do not recommend its use outside mocks. If using this class directly keep in mind the following restrictions: - Never destroy an AsyncWriterConnection object while any calls to Write() or Finalize() are pending. - Have at most one call to Write() pending. - Do not issue any Finalize() calls while a Write() call is pending. - Only issue one Finalize() call.

Functions

Cancel()

Cancels the streaming RPC, terminating any pending operations.

Returns
Type	Description
`void`

UploadId() const

Returns the upload id. Used to checkpoint the state and resume uploads.

Returns
Type	Description
`std::string`

PersistedState() const

Returns the last known state of the upload.

Updated during initialization and by a successful Finalize() request.

Returns
Type	Description
`absl::variant< std::int64_t, storage::ObjectMetadata >`

Write(WritePayload)

Uploads some data to the service.

Parameter
Name	Description
`payload`	`WritePayload`

Returns
Type	Description
`future< Status >`

Finalize(WritePayload)

Finalizes an upload.

Parameter
Name	Description
	`WritePayload`

Returns
Type	Description
`future< StatusOr< storage::ObjectMetadata > >`