WasmFS JS API: Implement truncate (#19543)

Author: jameshu15869

emcc.py

@@ -2338,6 +2338,8 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_read',
         '_wasmfs_pread',
         '_wasmfs_symlink',
+        '_wasmfs_truncate',
+        '_wasmfs_ftruncate',
         '_wasmfs_stat',
         '_wasmfs_lstat',
         '_wasmfs_chmod',

src/library_wasmfs.js

@@ -279,8 +279,12 @@ FS.createPreloadedFile = FS_createPreloadedFile;
     // TDOO: chown
     // TODO: lchown
     // TODO: fchown
-    // TODO: truncate
-    // TODO: ftruncate
+    truncate: (path, len) => {
+      return FS.handleError(withStackSave(() => (__wasmfs_truncate(stringToUTF8OnStack(path), {{{ splitI64('len') }}}))));
+    },
+    ftruncate: (fd, len) => {
+      return FS.handleError(__wasmfs_ftruncate(fd, {{{ splitI64('len') }}}));
+    },
     // TODO: utime
     findObject: (path) => {
       var result = __wasmfs_identify(path);

system/lib/wasmfs/js_api.cpp

@@ -220,6 +220,14 @@ int _wasmfs_pread(int fd, void *buf, size_t count, off_t offset) {
   return numBytes;
 }
 
+int _wasmfs_truncate(char* path, off_t length) {
+  return __syscall_truncate64((intptr_t)path, length);
+}
+
+int _wasmfs_ftruncate(int fd, off_t length) {
+  return __syscall_ftruncate64(fd, length);
+}
+
 int _wasmfs_close(int fd) {
   return __wasi_fd_close(fd);
 }

test/fs/test_fs_js_api.c

@@ -4,6 +4,70 @@
 #include <assert.h>
 #include <fcntl.h>
 
+void test_fs_truncate() {
+    EM_ASM(
+        FS.writeFile('truncatetest', 'a=1\nb=2\n');
+    );
+
+    struct stat s;
+    stat("truncatetest", &s);
+    assert(s.st_size == 8);
+
+    EM_ASM(
+        FS.truncate('truncatetest', 2);
+    );
+    stat("truncatetest", &s);
+    assert(s.st_size == 2);
+
+    EM_ASM(
+        FS.truncate('truncatetest', 10);
+    );
+    stat("truncatetest", &s);
+    assert(s.st_size == 10);
+
+    EM_ASM(
+        var truncateStream = FS.open('truncatetest', 'w');
+        FS.ftruncate(truncateStream.fd, 4);
+    );
+    stat("truncatetest", &s);
+    assert(s.st_size == 4);
+
+    EM_ASM(
+        var ex;
+        try {
+            FS.truncate('truncatetest', -10);
+        } catch(err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+
+        try {
+            var truncateStream = FS.open('truncatetest', 'w');
+            FS.ftruncate(truncateStream.fd, -10);
+        } catch(err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+
+        try {
+            FS.truncate('nonexistent', 10);
+        } catch(err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 44 /* ENOENT */);
+
+        var ex;
+        try {
+            FS.ftruncate(99, 10);
+        } catch(err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 8 /* EBADF */);
+    );
+
+    remove("truncatetest");
+}
+
 int main() {
     /********** test FS.open() **********/
     EM_ASM(
@@ -201,6 +265,8 @@ int main() {
     assert(S_ISREG(stats.st_mode));
     assert(stats.st_mode & 0400);
 
+    test_fs_truncate();
+
     remove("mknodtest");
     remove("createtest");
     remove("testfile");