Create a FuseDataProvider base class

The fuse data provider for adb/sdcard shares common code and structures.
This cl creates a FuseDataProvider base class and provides
implementations for adb and sdcard.

In the follow cls, we can kill the provider_vtab struct; and also add
another implementation to parse a block map file and provides data.

Test: unit tests pass, sideload a package, apply a package from sdcard
Change-Id: If8311666a52a2e3c0fbae0ee9688fa6d01e4ad09

fuse_sideload/fuse_provider.cpp

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2019 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 "fuse_provider.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <functional>
+
+#include <android-base/file.h>
+
+#include "fuse_sideload.h"
+
+FuseFileDataProvider::FuseFileDataProvider(const std::string& path, uint32_t block_size) {
+  struct stat sb;
+  if (stat(path.c_str(), &sb) == -1) {
+    fprintf(stderr, "failed to stat %s: %s\n", path.c_str(), strerror(errno));
+    return;
+  }
+
+  fd_.reset(open(path.c_str(), O_RDONLY));
+  if (fd_ == -1) {
+    fprintf(stderr, "failed to open %s: %s\n", path.c_str(), strerror(errno));
+    return;
+  }
+  file_size_ = sb.st_size;
+  fuse_block_size_ = block_size;
+}
+
+bool FuseFileDataProvider::ReadBlockAlignedData(uint8_t* buffer, uint32_t fetch_size,
+                                                uint32_t start_block) const {
+  uint64_t offset = static_cast<uint64_t>(start_block) * fuse_block_size_;
+  if (fetch_size > file_size_ || offset > file_size_ - fetch_size) {
+    fprintf(stderr,
+            "Out of bound read, start block: %" PRIu32 ", fetch size: %" PRIu32
+            ", file size %" PRIu64 "\n",
+            start_block, fetch_size, file_size_);
+    return false;
+  }
+
+  if (!android::base::ReadFullyAtOffset(fd_, buffer, fetch_size, offset)) {
+    fprintf(stderr, "Failed to read fetch size: %" PRIu32 " bytes data at offset %" PRIu64 ": %s\n",
+            fetch_size, offset, strerror(errno));
+    return false;
+  }
+
+  return true;
+}
+
+void FuseFileDataProvider::Close() {
+  fd_.reset();
+}