vfs-host 0.2.5

Host trait implementation for VFS adapter - enables multiple applications to share a single VFS instance
Documentation 
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// WASI Filesystem Preopens Host Implementation
//
// Implements wasi:filesystem/preopens interface using fs-core directly

use super::{FsDescriptorWrapper, VfsHostState};
use wasmtime::component::Resource;

impl wasmtime_wasi::p2::bindings::sync::filesystem::preopens::Host for VfsHostState {
    fn get_directories(
        &mut self,
    ) -> Result<
        Vec<(
            Resource<wasmtime_wasi::p2::bindings::filesystem::types::Descriptor>,
            String,
        )>,
        wasmtime::Error,
    > {
        log::debug!("[VFS-HOST] get_directories() called");

        // Open root directory using fs-core directly (no external lock needed)
        // O_RDONLY | O_DIRECTORY flags
        const O_RDONLY: u32 = 0;
        const O_DIRECTORY: u32 = 0x10000;

        let fd = self
            .shared_vfs
            .open_path_with_flags("/", O_RDONLY | O_DIRECTORY)
            .map_err(|e| wasmtime::format_err!("Failed to open root directory: {:?}", e))?;

        log::debug!("[VFS-HOST] Opened root directory with fd={}", fd);

        // Create wrapper with directory path for relative path resolution
        let wrapper = FsDescriptorWrapper {
            fd,
            path: Some("/".to_string()),
        };

        // Push to ResourceTable
        let wrapper_resource: Resource<FsDescriptorWrapper> = self.table.push(wrapper)?;

        // Transmute Resource<FsDescriptorWrapper> to Resource<Descriptor>
        // SAFETY: Resource<T> is a transparent u32 wrapper, so transmute is safe
        // Compile-time checks ensure size and alignment match
        const _: () = {
            use std::mem::{align_of, size_of};
            assert!(
                size_of::<Resource<FsDescriptorWrapper>>()
                    == size_of::<
                        Resource<wasmtime_wasi::p2::bindings::filesystem::types::Descriptor>,
                    >()
            );
            assert!(
                align_of::<Resource<FsDescriptorWrapper>>()
                    == align_of::<
                        Resource<wasmtime_wasi::p2::bindings::filesystem::types::Descriptor>,
                    >()
            );
        };
        let host_descriptor = unsafe {
            std::mem::transmute::<
                Resource<FsDescriptorWrapper>,
                Resource<wasmtime_wasi::p2::bindings::filesystem::types::Descriptor>,
            >(wrapper_resource)
        };

        log::debug!("[VFS-HOST] Returning preopened root directory");
        Ok(vec![(host_descriptor, "/".to_string())])
    }
}