Convert return value to optional where appropriate

Now that we have compressed APEX, some of the field in ApexFile no
longer have values in them. We turned their getters to optional.

Bug: 172911820
Test: atest ApexTestCases
Change-Id: Ib502bc0c0c84fcb65e7995af5fa106ecdee1cf0c

apexd/apex_file.cpp

diff --git a/apexd/apex_file.cpp b/apexd/apex_file.cpp
index 269fd3d..b645e76 100644
--- a/apexd/apex_file.cpp
+++ b/apexd/apex_file.cpp
@@ -75,11 +75,11 @@
 }  // namespace
 
 Result<ApexFile> ApexFile::Open(const std::string& path) {
-  int32_t image_offset;
-  size_t image_size;
+  std::optional<int32_t> image_offset;
+  std::optional<size_t> image_size;
   std::string manifest_content;
   std::string pubkey;
-  Result<std::string> fs_type;
+  std::optional<std::string> fs_type;
   ZipEntry entry;
 
   unique_fd fd(open(path.c_str(), O_RDONLY | O_BINARY | O_CLOEXEC));
@@ -114,11 +114,12 @@
     image_offset = entry.offset;
     image_size = entry.uncompressed_length;
 
-    fs_type = RetrieveFsType(fd, image_offset);
-    if (!fs_type.ok()) {
+    auto fs_type_result = RetrieveFsType(fd, image_offset.value());
+    if (!fs_type_result.ok()) {
       return Error() << "Failed to retrieve filesystem type for " << path
-                     << ": " << fs_type.error();
+                     << ": " << fs_type_result.error();
     }
+    fs_type = std::move(*fs_type_result);
   }
 
   ret = FindEntry(handle, kManifestFilenamePb, &entry);
@@ -155,7 +156,7 @@
   }
 
   return ApexFile(path, image_offset, image_size, std::move(*manifest), pubkey,
-                  *fs_type, is_compressed);
+                  fs_type, is_compressed);
 }
 
 // AVB-related code.
@@ -195,7 +196,11 @@
   auto footer = std::make_unique<AvbFooter>();
 
   // The AVB footer is located in the last part of the image
-  off_t offset = apex.GetImageSize() + apex.GetImageOffset() - AVB_FOOTER_SIZE;
+  if (!apex.GetImageOffset() || !apex.GetImageSize()) {
+    return Error() << "Cannot check avb footer without image offset and size";
+  }
+  off_t offset = apex.GetImageSize().value() + apex.GetImageOffset().value() -
+                 AVB_FOOTER_SIZE;
   int ret = lseek(fd, offset, SEEK_SET);
   if (ret == -1) {
     return ErrnoError() << "Couldn't seek to AVB footer";
@@ -259,7 +264,11 @@
     return Errorf("VbMeta size in footer exceeds kVbMetaMaxSize.");
   }
 
-  off_t offset = apex.GetImageOffset() + footer.vbmeta_offset;
+  if (!apex.GetImageOffset()) {
+    return Error() << "Cannot check VbMeta size without image offset";
+  }
+
+  off_t offset = apex.GetImageOffset().value() + footer.vbmeta_offset;
   std::unique_ptr<uint8_t[]> vbmeta_buf(new uint8_t[footer.vbmeta_size]);
 
   if (!ReadFullyAtOffset(fd, vbmeta_buf.get(), footer.vbmeta_size, offset)) {