We now peform a total-size preflight pass before committing data to the
wire. This is to eliminate the large superfluous network traffic that
would otherwise happen if the transport enforces internal quotas: we
now instead ask the transport up front whether it's prepared to accept
a given payload size for the package.
From the app's perspective this preflight operation is indistinguishable
from a full-data backup pass. If the app has provided its own full-data
handling in a subclassed backup agent, their usual file-providing code
path will be executed. However, the files named for backup during this
pass are not opened and read; just measured for their total size. As
far as component lifecycles, this measurement pass is simply another
call to the agent, immediately after it is bound, with identical
timeout semantics to the existing full-data backup invocation.
Once the app's file set has been measured the preflight operation
invokes a new method on BackupTransport, called checkFullBackupSize().
This method is called after performFullBackup() (which applies any
overall whitelist/blacklist policy) but before any data is delivered
to the transport via sendBackupData(). The return code from
checkFullBackupSize() is similar to the other transport methods:
TRANSPORT_OK to permit the full backup to proceed; or
TRANSPORT_REJECT_PACKAGE to indicate that the requested payload is
unacceptable; or TRANSPORT_ERROR to report a more serious overall
transport-level problem that prevents a full-data backup operation
from occurring right now.
The estimated payload currently does not include the size of the
source-package metadata (technically, the manifest entry in its
archive payload) or the size of any widget metadata associated with
the package's install. In practice this means the preflighted size
underestimates by 3 to 5 KB. In addition, the preflight API currently
cannot distinguish between payload sizes larger than 2 gigabytes;
any payload estimate larger than that is passed as Integer.MAX_VALUE
to the checkFullBackupSize() query.
Bug 19846750
Change-Id: I44498201e2d4b07482dcb3ca8fa6935dddc467ca
We'd observed a bug in which an unchanged file was nevertheless
being redundantly transmitted for backup on every backup pass.
The underlying issue turns out to have been the FileBackupHelper
base implementation's logic for diffing the prior-state file
set against the current state, in the case when there had been
deletions of prior files. In addition, there was also a
parallel bug in which file checksums were not calculated
properly in some cases, leading to at least one additional
redundant backup of the file in question.
Bug 18694053
Change-Id: Ie0dec06486b5fef4624561737019569c85d6b2a0
