Add test case for path_link syscall (#559)

This commit adds a relatively complete test case for the `path_link`
syscall. This commit should serve as some prep work for implementing
`path_link` on Windows (which will follow in a subsequent PR).

crates/wasi-common/build.rs

@@ -180,6 +180,7 @@ mod wasm_tests {
                         "path_rename_trailing_slashes" => true,
                         "fd_readdir" => true,
                         "poll_oneoff" => true,
+                        "path_link" => true,
                         _ => false,
                     }
                 } else {

crates/wasi-common/wasi-misc-tests/src/bin/path_link.rs

@@ -0,0 +1,271 @@
+use more_asserts::assert_gt;
+use std::{env, process};
+use wasi::wasi_unstable;
+use wasi_misc_tests::open_scratch_directory;
+use wasi_misc_tests::utils::{cleanup_dir, cleanup_file, create_dir, create_file};
+use wasi_misc_tests::wasi_wrappers::{
+    wasi_fd_fdstat_get, wasi_fd_filestat_get, wasi_path_link, wasi_path_open, wasi_path_symlink,
+};
+
+unsafe fn create_or_open(
+    dir_fd: wasi_unstable::Fd,
+    name: &str,
+    flags: wasi_unstable::OFlags,
+) -> wasi_unstable::Fd {
+    let mut file_fd = wasi_unstable::Fd::max_value() - 1;
+    let mut status = wasi_path_open(dir_fd, 0, name, flags, 0, 0, 0, &mut file_fd);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "opening '{}'",
+        name
+    );
+    assert_gt!(
+        file_fd,
+        libc::STDERR_FILENO as wasi_unstable::Fd,
+        "file descriptor range check",
+    );
+    file_fd
+}
+
+unsafe fn open_link(dir_fd: wasi_unstable::Fd, name: &str) -> wasi_unstable::Fd {
+    let mut file_fd = wasi_unstable::Fd::max_value() - 1;
+    let mut status = wasi_path_open(dir_fd, 0, name, 0, 0, 0, 0, &mut file_fd);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "opening a link '{}'",
+        name
+    );
+    assert_gt!(
+        file_fd,
+        libc::STDERR_FILENO as wasi_unstable::Fd,
+        "file descriptor range check",
+    );
+    file_fd
+}
+
+unsafe fn check_rights(orig_fd: wasi_unstable::Fd, link_fd: wasi_unstable::Fd) {
+    use std::mem::MaybeUninit;
+
+    // Compare FileStats
+    let mut orig_filestat: wasi_unstable::FileStat = MaybeUninit::zeroed().assume_init();
+    let mut link_filestat: wasi_unstable::FileStat = MaybeUninit::zeroed().assume_init();
+    let mut status = wasi_fd_filestat_get(orig_fd, &mut orig_filestat);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "reading filestat of the source"
+    );
+    status = wasi_fd_filestat_get(link_fd, &mut link_filestat);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "reading filestat of the link"
+    );
+    assert_eq!(orig_filestat, link_filestat, "filestats should match");
+
+    // Compare FdStats
+    let mut orig_fdstat: wasi_unstable::FdStat = MaybeUninit::zeroed().assume_init();
+    let mut link_fdstat: wasi_unstable::FdStat = MaybeUninit::zeroed().assume_init();
+    status = wasi_fd_fdstat_get(orig_fd, &mut orig_fdstat);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "reading fdstat of the source"
+    );
+    status = wasi_fd_fdstat_get(link_fd, &mut link_fdstat);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "reading fdstat of the link"
+    );
+    assert_eq!(orig_fdstat, link_fdstat, "fdstats should match");
+}
+
+unsafe fn test_path_link(dir_fd: wasi_unstable::Fd) {
+    // Create a file
+    let file_fd = create_or_open(dir_fd, "file", wasi_unstable::O_CREAT);
+
+    // Create a link in the same directory and compare rights
+    assert!(
+        wasi_path_link(dir_fd, 0, "file", dir_fd, "link").is_ok(),
+        "creating a link in the same directory"
+    );
+    let mut link_fd = open_link(dir_fd, "link");
+    check_rights(file_fd, link_fd);
+    cleanup_file(dir_fd, "link");
+
+    // Create a link in a different directory and compare rights
+    create_dir(dir_fd, "subdir");
+    let subdir_fd = create_or_open(dir_fd, "subdir", wasi_unstable::O_DIRECTORY);
+    assert!(
+        wasi_path_link(dir_fd, 0, "file", subdir_fd, "link").is_ok(),
+        "creating a link in subdirectory"
+    );
+    link_fd = open_link(subdir_fd, "link");
+    check_rights(file_fd, link_fd);
+    cleanup_file(subdir_fd, "link");
+    cleanup_dir(dir_fd, "subdir");
+
+    // Create a link to a path that already exists
+    create_file(dir_fd, "link");
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "file", dir_fd, "link"),
+        Err(wasi_unstable::EEXIST),
+        "creating a link to existing path"
+    );
+    cleanup_file(dir_fd, "link");
+
+    // Create a link to itself
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "file", dir_fd, "file"),
+        Err(wasi_unstable::EEXIST),
+        "creating a link to itself"
+    );
+
+    // Create a link where target is a directory
+    create_dir(dir_fd, "link");
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "file", dir_fd, "link"),
+        Err(wasi_unstable::EEXIST),
+        "creating a link where target is a directory"
+    );
+    cleanup_dir(dir_fd, "link");
+
+    // Create a link to a directory
+    create_dir(dir_fd, "subdir");
+    let subdir_fd = create_or_open(dir_fd, "subdir", wasi_unstable::O_DIRECTORY);
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "subdir", dir_fd, "link"),
+        Err(wasi_unstable::EPERM),
+        "creating a link to a directory"
+    );
+    cleanup_dir(dir_fd, "subdir");
+
+    // Create a link to a file with trailing slash
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "file", dir_fd, "link/"),
+        Err(wasi_unstable::ENOENT),
+        "creating a link to a file with trailing slash"
+    );
+
+    // Create a link to a dangling symlink
+    assert!(
+        wasi_path_symlink("target", dir_fd, "symlink").is_ok(),
+        "creating a dangling symlink"
+    );
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "symlink", dir_fd, "link"),
+        Err(wasi_unstable::ENOENT),
+        "creating a link to a dangling symlink"
+    );
+    cleanup_file(dir_fd, "symlink");
+
+    // Create a link to a symlink loop
+    assert!(
+        wasi_path_symlink("symlink", dir_fd, "symlink").is_ok(),
+        "creating a symlink loop"
+    );
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "symlink", dir_fd, "link"),
+        Err(wasi_unstable::ELOOP),
+        "creating a link to a symlink loop"
+    );
+    cleanup_file(dir_fd, "symlink");
+
+    // Create a link where target is a dangling symlink
+    assert!(
+        wasi_path_symlink("target", dir_fd, "symlink").is_ok(),
+        "creating a dangling symlink"
+    );
+    assert_eq!(
+        wasi_path_link(dir_fd, 0, "file", dir_fd, "symlink"),
+        Err(wasi_unstable::EEXIST),
+        "creating a link where target is a dangling symlink"
+    );
+    cleanup_file(dir_fd, "symlink");
+
+    // Create a link to a file following symlinks
+    assert!(
+        wasi_path_symlink("file", dir_fd, "symlink").is_ok(),
+        "creating a valid symlink"
+    );
+    assert!(
+        wasi_path_link(
+            dir_fd,
+            wasi_unstable::LOOKUP_SYMLINK_FOLLOW,
+            "symlink",
+            dir_fd,
+            "link"
+        )
+        .is_ok(),
+        "creating a link to a file following symlinks",
+    );
+    link_fd = open_link(dir_fd, "link");
+    check_rights(file_fd, link_fd);
+    cleanup_file(dir_fd, "link");
+    cleanup_file(dir_fd, "symlink");
+
+    // Create a link where target is a dangling symlink following symlinks
+    assert!(
+        wasi_path_symlink("target", dir_fd, "symlink").is_ok(),
+        "creating a dangling symlink"
+    );
+    assert_eq!(
+        wasi_path_link(
+            dir_fd,
+            wasi_unstable::LOOKUP_SYMLINK_FOLLOW,
+            "symlink",
+            dir_fd,
+            "link"
+        ),
+        Err(wasi_unstable::ENOENT),
+        "creating a link where target is a dangling symlink following symlinks"
+    );
+    cleanup_file(dir_fd, "symlink");
+
+    // Create a link to a symlink loop following symlinks
+    assert!(
+        wasi_path_symlink("symlink", dir_fd, "symlink").is_ok(),
+        "creating a symlink loop"
+    );
+    assert_eq!(
+        wasi_path_link(
+            dir_fd,
+            wasi_unstable::LOOKUP_SYMLINK_FOLLOW,
+            "symlink",
+            dir_fd,
+            "link"
+        ),
+        Err(wasi_unstable::ELOOP),
+        "creating a link to a symlink loop following symlinks"
+    );
+    cleanup_file(dir_fd, "symlink");
+
+    // Clean up.
+    cleanup_file(dir_fd, "file");
+}
+
+fn main() {
+    let mut args = env::args();
+    let prog = args.next().unwrap();
+    let arg = if let Some(arg) = args.next() {
+        arg
+    } else {
+        eprintln!("usage: {} <scratch directory>", prog);
+        process::exit(1);
+    };
+
+    // Open scratch directory
+    let dir_fd = match open_scratch_directory(&arg) {
+        Ok(dir_fd) => dir_fd,
+        Err(err) => {
+            eprintln!("{}", err);
+            process::exit(1)
+        }
+    };
+
+    // Run the tests.
+    unsafe { test_path_link(dir_fd) }
+}

crates/wasi-common/wasi-misc-tests/src/wasi_wrappers.rs

@@ -61,6 +61,22 @@ pub unsafe fn wasi_path_symlink(
     wasi_unstable::path_symlink(old_path.as_bytes(), dirfd, new_path.as_bytes())
 }
 
+pub unsafe fn wasi_path_link(
+    old_fd: wasi_unstable::Fd,
+    old_flags: wasi_unstable::LookupFlags,
+    old_path: &str,
+    new_fd: wasi_unstable::Fd,
+    new_path: &str,
+) -> Result<(), wasi_unstable::Error> {
+    wasi_unstable::path_link(
+        old_fd,
+        old_flags,
+        old_path.as_bytes(),
+        new_fd,
+        new_path.as_bytes(),
+    )
+}
+
 pub unsafe fn wasi_path_readlink(
     dirfd: wasi_unstable::Fd,
     path: &str,