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Commit cf962601 authored by Christopher Tate's avatar Christopher Tate
Browse files

Don't write widget metadata to backup unless it's new/changed 

Redundant backup traffic is bad.  Don't commit the widget metadata payload
(or the deletion operation for it) unless the widget state of the app has
actually changed since the last backup.

Bug 19003911

Change-Id: I93819173c0e2357b030d9e2b3d2ee57f2410bb57
parent faf92d72

services/backup/java/com/android/server/backup/BackupManagerService.java

+80 −11
Original line number Diff line number Diff line
@@ -130,6 +130,7 @@ import java.util.Iterator; 
import java.util.List;

import java.util.Map;

import java.util.Map.Entry;

import java.util.Objects;

import java.util.Random;

import java.util.Set;

import java.util.TreeMap;
@@ -2695,6 +2696,84 @@ public class BackupManagerService { 
            }

        }



        // SHA-1 a byte array and return the result in hex

        private String SHA1Checksum(byte[] input) {

            final byte[] checksum;

            try {

                MessageDigest md = MessageDigest.getInstance("SHA-1");

                checksum = md.digest(input);

            } catch (NoSuchAlgorithmException e) {

                Slog.e(TAG, "Unable to use SHA-1!");

                return "00";

            }



            StringBuffer sb = new StringBuffer(checksum.length * 2);

            for (int i = 0; i < checksum.length; i++) {

                sb.append(Integer.toHexString(checksum[i]));

            }

            return sb.toString();

        }



        private void writeWidgetPayloadIfAppropriate(FileDescriptor fd, String pkgName)

                throws IOException {

            byte[] widgetState = AppWidgetBackupBridge.getWidgetState(pkgName,

                    UserHandle.USER_OWNER);

            // has the widget state changed since last time?

            final File widgetFile = new File(mStateDir, pkgName + "_widget");

            final boolean priorStateExists = widgetFile.exists();



            if (MORE_DEBUG) {

                if (priorStateExists || widgetState != null) {

                    Slog.i(TAG, "Checking widget update: state=" + (widgetState != null)

                            + " prior=" + priorStateExists);

                }

            }



            if (!priorStateExists && widgetState == null) {

                // no prior state, no new state => nothing to do

                return;

            }



            // if the new state is not null, we might need to compare checksums to

            // determine whether to update the widget blob in the archive.  If the

            // widget state *is* null, we know a priori at this point that we simply

            // need to commit a deletion for it.

            String newChecksum = null;

            if (widgetState != null) {

                newChecksum = SHA1Checksum(widgetState);

                if (priorStateExists) {

                    final String priorChecksum;

                    try (

                        FileInputStream fin = new FileInputStream(widgetFile);

                        DataInputStream in = new DataInputStream(fin)

                    ) {

                        priorChecksum = in.readUTF();

                    }

                    if (Objects.equals(newChecksum, priorChecksum)) {

                        // Same checksum => no state change => don't rewrite the widget data

                        return;

                    }

                }

            } // else widget state *became* empty, so we need to commit a deletion



            BackupDataOutput out = new BackupDataOutput(fd);

            if (widgetState != null) {

                try (

                    FileOutputStream fout = new FileOutputStream(widgetFile);

                    DataOutputStream stateOut = new DataOutputStream(fout)

                ) {

                    stateOut.writeUTF(newChecksum);

                }



                out.writeEntityHeader(KEY_WIDGET_STATE, widgetState.length);

                out.writeEntityData(widgetState, widgetState.length);

            } else {

                // Widget state for this app has been removed; commit a deletion

                out.writeEntityHeader(KEY_WIDGET_STATE, -1);

                widgetFile.delete();

            }

        }



        @Override

        public void operationComplete() {

            // Okay, the agent successfully reported back to us!
@@ -2733,17 +2812,7 @@ public class BackupManagerService { 
                }



                // Piggyback the widget state payload, if any

                BackupDataOutput out = new BackupDataOutput(fd);

                byte[] widgetState = AppWidgetBackupBridge.getWidgetState(pkgName,

                        UserHandle.USER_OWNER);

                if (widgetState != null) {

                    out.writeEntityHeader(KEY_WIDGET_STATE, widgetState.length);

                    out.writeEntityData(widgetState, widgetState.length);

                } else {

                    // No widget state for this app, but push a 'delete' operation for it

                    // in case they're trying to play games with the payload.

                    out.writeEntityHeader(KEY_WIDGET_STATE, -1);

                }

                writeWidgetPayloadIfAppropriate(fd, pkgName);

            } catch (IOException e) {

                // Hard disk error; recovery/failure policy TBD.  For now roll back,

                // but we may want to consider this a transport-level failure (i.e.