idmap2: replace std::pair<bool, T> with Result<T>
Introduce a new type Result<T> to indicate if an operation succeeded or
not, and if it did, to hold the return value of the operation. This is
the same as how std::pair<bool, T> is already used in the codebase, so
replace all instances with Result<T> to improve clarity.
Result<T> is simply an alias for std::optional<T>. The difference is
semantic: use Result<T> as the return value for functions that can fail,
use std::optional<T> when values are truly optional. This is modelled
after Rust's std::result and std::option.
A future change may graduate Result<T> to a proper class which can hold
additional details on why an operation failed, such as a string or an
error code. As a special case, continue to use std::unique_ptr<T>
instead of Result<std::unique_ptr<T>> for now: the latter would increase
code complexity without added benefit.
Test: make idmap2_tests
Change-Id: I2a8355107ed2b6485409e5e655a84cf1e20b9911
diff --git a/cmds/idmap2/libidmap2/Idmap.cpp b/cmds/idmap2/libidmap2/Idmap.cpp
index 5a47e30..1ef3267 100644
--- a/cmds/idmap2/libidmap2/Idmap.cpp
+++ b/cmds/idmap2/libidmap2/Idmap.cpp
@@ -33,6 +33,7 @@
#include "idmap2/Idmap.h"
#include "idmap2/ResourceUtils.h"
+#include "idmap2/Result.h"
#include "idmap2/ZipFile.h"
namespace android {
@@ -143,18 +144,16 @@
return false;
}
- bool status;
- uint32_t target_crc;
- std::tie(status, target_crc) = target_zip->Crc("resources.arsc");
- if (!status) {
+ Result<uint32_t> target_crc = target_zip->Crc("resources.arsc");
+ if (!target_crc) {
out_error << "error: failed to get target crc" << std::endl;
return false;
}
- if (target_crc_ != target_crc) {
+ if (target_crc_ != *target_crc) {
out_error << base::StringPrintf(
"error: bad target crc: idmap version 0x%08x, file system version 0x%08x",
- target_crc_, target_crc)
+ target_crc_, *target_crc)
<< std::endl;
return false;
}
@@ -165,17 +164,16 @@
return false;
}
- uint32_t overlay_crc;
- std::tie(status, overlay_crc) = overlay_zip->Crc("resources.arsc");
- if (!status) {
+ Result<uint32_t> overlay_crc = overlay_zip->Crc("resources.arsc");
+ if (!overlay_crc) {
out_error << "error: failed to get overlay crc" << std::endl;
return false;
}
- if (overlay_crc_ != overlay_crc) {
+ if (overlay_crc_ != *overlay_crc) {
out_error << base::StringPrintf(
"error: bad overlay crc: idmap version 0x%08x, file system version 0x%08x",
- overlay_crc_, overlay_crc)
+ overlay_crc_, *overlay_crc)
<< std::endl;
return false;
}
@@ -322,17 +320,20 @@
std::unique_ptr<IdmapHeader> header(new IdmapHeader());
header->magic_ = kIdmapMagic;
header->version_ = kIdmapCurrentVersion;
- bool crc_status;
- std::tie(crc_status, header->target_crc_) = target_zip->Crc("resources.arsc");
- if (!crc_status) {
+
+ Result<uint32_t> crc = target_zip->Crc("resources.arsc");
+ if (!crc) {
out_error << "error: failed to get zip crc for target" << std::endl;
return nullptr;
}
- std::tie(crc_status, header->overlay_crc_) = overlay_zip->Crc("resources.arsc");
- if (!crc_status) {
+ header->target_crc_ = *crc;
+
+ crc = overlay_zip->Crc("resources.arsc");
+ if (!crc) {
out_error << "error: failed to get zip crc for overlay" << std::endl;
return nullptr;
}
+ header->overlay_crc_ = *crc;
if (target_apk_path.size() > sizeof(header->target_path_)) {
out_error << "error: target apk path \"" << target_apk_path << "\" longer that maximum size "
@@ -358,15 +359,14 @@
const auto end = overlay_pkg->end();
for (auto iter = overlay_pkg->begin(); iter != end; ++iter) {
const ResourceId overlay_resid = *iter;
- bool lookup_ok;
- std::string name;
- std::tie(lookup_ok, name) = utils::ResToTypeEntryName(overlay_asset_manager, overlay_resid);
- if (!lookup_ok) {
+ Result<std::string> name = utils::ResToTypeEntryName(overlay_asset_manager, overlay_resid);
+ if (!name) {
continue;
}
// prepend "<package>:" to turn name into "<package>:<type>/<name>"
- name = base::StringPrintf("%s:%s", target_pkg->GetPackageName().c_str(), name.c_str());
- const ResourceId target_resid = NameToResid(target_asset_manager, name);
+ const std::string full_name =
+ base::StringPrintf("%s:%s", target_pkg->GetPackageName().c_str(), name->c_str());
+ const ResourceId target_resid = NameToResid(target_asset_manager, full_name);
if (target_resid == 0) {
continue;
}