Open MMKV File Failing Due to Lack of Write Permission in iOS Keyboard Extension

[mfbx9da4]

The language of MMKV

Objective-C & Swift

The version of MMKV

1.2.14

The platform of MMKV

iOS

The installation of MMKV

Cocoapods

What's the issue?

I am building an iOS Keyboard Extension. The keyboard does not require OpenAccess, meaning the app extension does not have write capabilities. Initialization of MMKV is failing because it opens the file with read & write. Is it possible to configure a read-only mode?

[I] <MMKV.cpp:207::initializeMMKV> root dir: /var/mobile/Containers/Data/PluginKitPlugin/348876A7-DA00-425D-A17A-927902D2B39C/Documents/mmkv
[I] <libMMKV.mm:115::+[MMKV initializeMMKV:groupDir:logLevel:]> 
groupDir: 
/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv
[D] <libMMKV.mm:721::+[MMKV mmapKeyWithMMapID:rootPath:]> mmapKey: 893c7e6db2d602f7ff1df4cf29ac1b50
[I] <MMKV.cpp:234::mmkvWithID> prepare to load default.mmkv (id 893c7e6db2d602f7ff1df4cf29ac1b50) from rootPath /private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv
[E] <MemoryFile.cpp:94::open> fail to open [/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv], 1(Operation not permitted)
[E] <MemoryFile.cpp:94::open> fail to open [/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv], 1(Operation not permitted)
[E] <MemoryFile.cpp:208::reloadFromFile> fail to open:/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv, Undefined error: 0
[E] <MemoryFile.cpp:94::open> fail to open [/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv.crc], 1(Operation not permitted)
[E] <MemoryFile.cpp:94::open> fail to open [/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv.crc], 1(Operation not permitted)
[E] <MemoryFile.cpp:208::reloadFromFile> fail to open:/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv.crc, Undefined error: 0
[E] <MemoryFile.cpp:94::open> fail to open [/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv], 1(Operation not permitted)
[E] <MemoryFile.cpp:208::reloadFromFile> fail to open:/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv, Undefined error: 0
[E] <MMKV_IO.cpp:74::loadFromFile> file [/private/var/mobile/Containers/Shared/AppGroup/307129F1-4DB2-4AC3-B519-4D29E8FA9F3C/mmkv/default.mmkv] not valid

I've "fixed" this by changing MemoryFile.cpp:94 from

m_fd = ::open(m_path.c_str(), OpenFlag2NativeFlag(m_flag), S_IRWXU);

to

m_fd = ::open(m_path.c_str(), O_RDONLY);

and MemoryFile.cpp:188 from

m_ptr = (char *) ::mmap(m_ptr, m_size, PROT_READ | PROT_WRITE, MAP_SHARED, m_diskFile.m_fd, 0);

to

m_ptr = (char *) ::mmap(m_ptr, m_size, PROT_READ, MAP_SHARED, m_diskFile.m_fd, 0);

[lingol]

Why would you create a read-only MMKV instance? It provides little functionality.

[mfbx9da4]

A read-only MMKV instance is needed if you would like to display data from the main app in the keyboard extension.

For example, the user has logged in and created some todo items in the main app. The keyboard extension may want to display that the user is logged in or is required to log in and list those todo items.