gs

type GoogleStorage interface {
	// Exists checks whether given Google Storage file exists.
	Exists(ctx context.Context, path string) (exists bool, err error)

	// Size returns the size in bytes of the given Google Storage file.
	Size(ctx context.Context, path string) (size uint64, exists bool, err error)

	// Copy copies a file at 'src' to 'dst'.
	//
	// Applies ifSourceGenerationMatch and ifGenerationMatch preconditions if
	// srcGen or dstGen are non-negative. See Google Storage docs:
	// https://cloud.google.com/storage/docs/json_api/v1/objects/copy
	Copy(ctx context.Context, dst string, dstGen int64, src string, srcGen int64) error

	// Delete removes a file.
	//
	// Missing file is not an error.
	Delete(ctx context.Context, path string) error

	// Publish implements conditional copy operation with some caveats, making it
	// useful for moving uploaded files from a temporary storage area after they
	// have been verified, ensuring they are not modified during this process.
	//
	// 'src' will be copied to 'dst' only if source generation number matches
	// 'srcGen'. If 'srcGen' is negative, the generation check is not performed.
	// Also assumes 'dst' is ether missing, or already contains data matching
	// 'src' (so 'dst' should usually be a content-addressed path). This allows
	// the conditional move operation to be safely retried even if it failed
	// midway before.
	//
	// Note that it keeps 'src' intact. Use Delete to get rid of it when
	// necessary. Google Storage doesn't have atomic "move" operation.
	Publish(ctx context.Context, dst, src string, srcGen int64) error

	// StartUpload opens a new resumable upload session to a given path.
	//
	// Returns an URL to use in Resumable Upload protocol. It contains uploadId
	// that acts as an authentication token, treat the URL as a secret.
	//
	// The upload protocol is finished by the CIPD client, and so it's not
	// implemented here.
	StartUpload(ctx context.Context, path string) (uploadURL string, err error)

	// CancelUpload cancels a resumable upload session.
	CancelUpload(ctx context.Context, uploadURL string) error

	// Reader returns an io.ReaderAt implementation to read contents of a file at
	// a specific generation (if 'gen' is positive) or at the current live
	// generation (if 'gen' is zero or negative).
	Reader(ctx context.Context, path string, gen int64) (Reader, error)
}

type Reader interface {
	io.ReaderAt

	// Size is the total file size.
	Size() int64
	// Generation is generation number of the content we are reading.
	Generation() int64
}

type RestartUploadError struct {
	Offset int64
}

type Uploader struct {
	Context   context.Context // the context for canceling retries and for logging
	Client    *http.Client    // the client to use for sending anonymous requests
	UploadURL string          // upload URL returned by GoogleStorage.StartUpload
	Offset    int64           // offset in the file to upload to, mutated by Write
	FileSize  int64           // total size of the file being uploaded, required
	// contains filtered or unexported fields
}