Implement the C++ class to write the backed up file data.
diff --git a/libs/utils/backup_data.cpp b/libs/utils/backup_data.cpp
new file mode 100644
index 0000000..c7f1fdb
--- /dev/null
+++ b/libs/utils/backup_data.cpp
@@ -0,0 +1,236 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <utils/backup_helpers.h>
+#include <utils/ByteOrder.h>
+
+#include <stdio.h>
+#include <unistd.h>
+
+namespace android {
+
+/*
+ * File Format (v1):
+ *
+ * All ints are stored little-endian.
+ *
+ * - An app_header_v1 struct.
+ * - The name of the package, utf-8, null terminated, padded to 4-byte boundary.
+ * - A sequence of zero or more key/value paires (entities), each with
+ * - A entity_header_v1 struct
+ * - The key, utf-8, null terminated, padded to 4-byte boundary.
+ * - The value, padded to 4 byte boundary
+ */
+
+#define APP_MAGIC_V1 0x31707041 // App1 (little endian)
+#define ENTITY_MAGIC_V1 0x61746144 // Data (little endian)
+#define FOOTER_MAGIC_V1 0x746f6f46 // Foot (little endian)
+
+typedef struct {
+ int type; // == APP_MAGIC_V1
+ int packageLen; // length of the name of the package that follows, not including the null.
+} app_header_v1;
+
+typedef struct {
+ int type; // ENTITY_MAGIC_V1
+ int keyLen; // length of the key name, not including the null terminator
+ int dataSize; // size of the data, not including the padding
+} entity_header_v1;
+
+typedef struct {
+ int type; // FOOTER_MAGIC_V1
+ int entityCount; // the number of entities that were written
+} app_footer_v1;
+
+const static int ROUND_UP[4] = { 0, 3, 2, 1 };
+
+static inline size_t
+round_up(size_t n)
+{
+ return n + ROUND_UP[n % 4];
+}
+
+static inline size_t
+padding_extra(size_t n)
+{
+ return ROUND_UP[n % 4];
+}
+
+BackupDataWriter::BackupDataWriter(int fd)
+ :m_fd(fd),
+ m_status(NO_ERROR),
+ m_pos(0),
+ m_entityCount(0)
+{
+}
+
+BackupDataWriter::~BackupDataWriter()
+{
+}
+
+// Pad out anything they've previously written to the next 4 byte boundary.
+status_t
+BackupDataWriter::write_padding_for(int n)
+{
+ ssize_t amt;
+ ssize_t paddingSize;
+
+ paddingSize = padding_extra(n);
+ if (paddingSize > 0) {
+ uint32_t padding = 0xbcbcbcbc;
+ amt = write(m_fd, &padding, paddingSize);
+ if (amt != paddingSize) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+ }
+ return NO_ERROR;
+}
+
+status_t
+BackupDataWriter::WriteAppHeader(const String8& packageName)
+{
+ if (m_status != NO_ERROR) {
+ return m_status;
+ }
+
+ ssize_t amt;
+
+ amt = write_padding_for(m_pos);
+ if (amt != 0) {
+ return amt;
+ }
+
+ app_header_v1 header;
+ ssize_t nameLen;
+
+ nameLen = packageName.length();
+
+ header.type = tolel(APP_MAGIC_V1);
+ header.packageLen = tolel(nameLen);
+
+ amt = write(m_fd, &header, sizeof(app_header_v1));
+ if (amt != sizeof(app_header_v1)) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+
+ amt = write(m_fd, packageName.string(), nameLen+1);
+ if (amt != nameLen+1) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+
+ return NO_ERROR;
+}
+
+status_t
+BackupDataWriter::WriteEntityHeader(const String8& key, size_t dataSize)
+{
+ if (m_status != NO_ERROR) {
+ return m_status;
+ }
+
+ ssize_t amt;
+
+ amt = write_padding_for(m_pos);
+ if (amt != 0) {
+ return amt;
+ }
+
+ entity_header_v1 header;
+ ssize_t keyLen;
+
+ keyLen = key.length();
+
+ header.type = tolel(ENTITY_MAGIC_V1);
+ header.keyLen = tolel(keyLen);
+ header.dataSize = tolel(dataSize);
+
+ amt = write(m_fd, &header, sizeof(entity_header_v1));
+ if (amt != sizeof(entity_header_v1)) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+
+ amt = write(m_fd, key.string(), keyLen+1);
+ if (amt != keyLen+1) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+
+ amt = write_padding_for(keyLen+1);
+
+ m_entityCount++;
+
+ return amt;
+}
+
+status_t
+BackupDataWriter::WriteEntityData(const void* data, size_t size)
+{
+ if (m_status != NO_ERROR) {
+ return m_status;
+ }
+
+ // We don't write padding here, because they're allowed to call this several
+ // times with smaller buffers. We write it at the end of WriteEntityHeader
+ // instead.
+ ssize_t amt = write(m_fd, data, size);
+ if (amt != (ssize_t)size) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+ return NO_ERROR;
+}
+
+status_t
+BackupDataWriter::WriteAppFooter()
+{
+ if (m_status != NO_ERROR) {
+ return m_status;
+ }
+
+ ssize_t amt;
+
+ amt = write_padding_for(m_pos);
+ if (amt != 0) {
+ return amt;
+ }
+
+ app_footer_v1 footer;
+ ssize_t nameLen;
+
+ footer.type = tolel(FOOTER_MAGIC_V1);
+ footer.entityCount = tolel(m_entityCount);
+
+ amt = write(m_fd, &footer, sizeof(app_footer_v1));
+ if (amt != sizeof(app_footer_v1)) {
+ m_status = errno;
+ return m_status;
+ }
+ m_pos += amt;
+
+ return NO_ERROR;
+}
+
+} // namespace android