The Fiber Polyfill library

The project provides polyfill implementation of wasi_unstable and wasi_snapshot_preview1 functions using Fiber Syscall API.

Usage

The intended use is to add this library as a dependency to your rust project. And then run wasi2fx on the produced Wasm binary.

In your project you would need to call the init function. It makes sure the linker does not remove the functions and can be used to initialize the random seed and define some environment variables.

Example:

    init(&[12,3,54,1], &[("PATH", "/usr/bin"), ("UID", "1028"), ("HOME", "/home/user")]);

Supported WASI functions (wasi_unstable, wasi_snapshot_preview1)

Status	Description
Supported	Function is fully supported.
Not implemented	Empty implementation that does nothing but can be called without issues.
Not implemented	Function is not yet implemented - calling it causes the application to panic.
Not supported	Function is not planned to be implemented - calling it causes the application to panic.

WASI function	Status
args_get	Not implemented
args_sizes_get	Not implemented
clock_res_get	Not implemented
clock_time_get	Not implemented
environ_get	Not implemented
environ_sizes_get	Not implemented
fd_advise	Not implemented
fd_allocate	Not implemented
fd_close	Not implemented
fd_datasync	Not implemented
fd_fdstat_get	Not implemented
fd_fdstat_set_flags	Not implemented
fd_fdstat_set_rights	Not implemented
fd_filestat_get	Not implemented
fd_filestat_set_size	Not implemented
fd_filestat_set_times	Not implemented
fd_pread	Not implemented
fd_prestat_dir_name	Not implemented
fd_prestat_get	Not implemented
fd_pwrite	Not implemented
fd_read	Not implemented
fd_readdir	Not implemented
fd_renumber	Not implemented
fd_seek	Not implemented
fd_sync	Not implemented
fd_tell	Not implemented
fd_write	Not implemented
path_create_directory	Not implemented
path_filestat_get	Not implemented
path_filestat_set_times	Not implemented
path_link	Supported1
path_open	Supported1
path_readlink	Not implemented
path_remove_directory	Not implemented
path_rename	Not implemented
path_symlink	Not implemented
path_unlink_file	Not implemented
poll_oneoff	Not implemented
proc_exit	Not implemented
proc_raise	Not implemented
random_get	Supported2
sched_yield	Not implemented
sock_accept	Not supported
sock_recv	Not supported
sock_send	Not supported
sock_shutdown	Not supported

¹ - Currently symlinks are not supported by the file system, this affects a few path_ functions, the flags ("follow symlink") parameter is currently ignored.

² - The random_get function utilizes a synchronous pseudo-random number generator.

Additional library functions

Function	Description
init(seed: &[u8], env_pairs: &[(&str, &str)])	Initialization call.
raw_init(seed: *const u8, len: usize)	Similar to init, but has simpler parameters for calling from C or C++.
init_seed(seed: &[u8])	Convenience method to explicitly re-initialize the random seed.
raw_init_seed(seed: *const u8, len: usize)	Similar to init_seed, but has simpler parameters for calling from C or C++.
init_with_memory(seed: &[u8], env_pairs: &[(&str, &str)]), memory: Memory)	Initialization on top of custom memory provided by user.
init_with_memory_manager(seed: &[u8], env_pairs: &[(&str, &str)]), memory_manager: &MemoryManager, memory_index_range: Range<u8>)	Initialization with the provided memory manager and a range of memory indices to be used by the stable storage.

Project features

The polyfill library's behavior can be configured using the following Cargo features:

• transient use the transient file system implementation. This works faster but does not take the advantage of keeping the file system's state in stable memory (and the ability to keep FS state between canister upgrades).
• report_wasi_calls outputs statistical information of the called polyfill functions.
• skip_unimplemented_functions rather than throw exception on calling the unimplemented function, its implementation will be missing in the compilation. This can be useful if you want to provide custom implementations for those functions.