Add a test case for WASI file truncation.

crates/test-programs/wasi-tests/src/bin/file_truncation.rs

@@ -0,0 +1,83 @@
+use std::{env, process};
+use wasi_tests::open_scratch_directory;
+
+unsafe fn test_file_truncation(dir_fd: wasi::Fd) {
+    const FILENAME: &str = "test.txt";
+
+    // Open a file for writing
+    let file_fd = wasi::path_open(
+        dir_fd,
+        0,
+        FILENAME,
+        wasi::OFLAGS_CREAT,
+        wasi::RIGHTS_FD_WRITE,
+        0,
+        0,
+    )
+    .expect("creating a file for writing");
+
+    // Write to the file
+    let content = b"this content will be truncated!";
+    let nwritten = wasi::fd_write(
+        file_fd,
+        &[wasi::Ciovec {
+            buf: content.as_ptr() as *const _,
+            buf_len: content.len(),
+        }],
+    )
+    .expect("writing file content");
+    assert_eq!(nwritten, content.len(), "nwritten bytes check");
+
+    wasi::fd_close(file_fd).expect("closing the file");
+
+    // Open the file for truncation
+    let file_fd = wasi::path_open(
+        dir_fd,
+        0,
+        FILENAME,
+        wasi::OFLAGS_CREAT | wasi::OFLAGS_TRUNC,
+        wasi::RIGHTS_FD_WRITE | wasi::RIGHTS_FD_READ,
+        0,
+        0,
+    )
+    .expect("creating a truncated file for reading");
+
+    // Read the file's contents
+    let buffer = &mut [0u8; 100];
+    let nread = wasi::fd_read(
+        file_fd,
+        &[wasi::Iovec {
+            buf: buffer.as_mut_ptr(),
+            buf_len: buffer.len(),
+        }],
+    )
+    .expect("reading file content");
+
+    // The file should be empty due to truncation
+    assert_eq!(nread, 0, "expected an empty file after truncation");
+
+    wasi::fd_close(file_fd).expect("closing the 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_file_truncation(dir_fd) }
+}