WasmFS JS API: Implement truncate

emcc.py

@@ -2320,6 +2320,8 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_close',
         '_wasmfs_rename',
         '_wasmfs_mkdir',
+        '_wasmfs_truncate',
+        '_wasmfs_ftruncate',
         '_wasmfs_unlink',
         '_wasmfs_chdir',
         '_wasmfs_rmdir',

src/library_wasmfs.js

@@ -255,8 +255,21 @@ FS.createPreloadedFile = FS_createPreloadedFile;
     // TDOO: chown
     // TODO: lchown
     // TODO: fchown
-    // TODO: truncate
-    // TODO: ftruncate
+    truncate: (path, len) => {
+      if (len < 0) {
+        throw new FS.ErrnoError({{{ cDefs.EINVAL }}});
+      }
+      return FS.handleError(withStackSave(() => {
+        var pathBuffer = stringToUTF8OnStack(path);
+        return __wasmfs_truncate(pathBuffer, len);
+      }));
+    },
+    ftruncate: (fd, len) => {
+      if (len < 0) {
+        throw new FS.ErrnoError({{{ cDefs.EINVAL }}});
+      }
+      return FS.handleError(__wasmfs_ftruncate(fd, len));
+    },
     // TODO: utime
     findObject: (path) => {
       var result = __wasmfs_identify(path);

system/lib/wasmfs/js_api.cpp

@@ -137,6 +137,22 @@ int _wasmfs_unlink(char* path) {
   return __syscall_unlinkat(AT_FDCWD, (intptr_t)path, 0);
 }
 
+int _wasmfs_truncate(char *path, off_t length) {
+  int err = __syscall_truncate64((intptr_t)path, length);
+  if (err == -1) {
+    return errno;
+  }
+  return err;
+}
+
+int _wasmfs_ftruncate(int fd, off_t size) {
+  int err = __syscall_ftruncate64(fd, size);
+  if (err == -1) {
+    return errno;
+  }
+  return err;
+}
+
 int _wasmfs_chdir(char* path) { return __syscall_chdir((intptr_t)path); }
 
 int _wasmfs_symlink(char* old_path, char* new_path) {

test/fs/test_fs_js_api.c

@@ -1,5 +1,7 @@
 #include <emscripten/emscripten.h>
 #include <stdio.h>
+#include <sys/stat.h>
+#include <assert.h>
 
 int main() {
     /********** test FS.open() **********/
@@ -37,6 +39,84 @@ int main() {
 #endif
     );
 
+    /********** 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');
+#if WASMFS
+        FS.ftruncate(truncateStream, 4);
+#else
+        FS.ftruncate(truncateStream.fd, 4);
+#endif
+    );
+    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 */);
+    );
+
+    EM_ASM(
+        var ex;
+        try {
+            var truncateStream = FS.open('truncatetest', 'w');
+#if WASMFS
+            FS.ftruncate(truncateStream, -10);
+#else
+            FS.ftruncate(truncateStream.fd, -10);
+#endif
+        } catch(err) {
+            ex = err;
+        }
+
+        assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+    );
+
+    EM_ASM(
+        var ex;
+        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 */);
+    );
+
     /********** test FS.rename() **********/
     EM_ASM(
         FS.mkdir('renamedir');
@@ -139,6 +219,7 @@ int main() {
         assert(ex.name === "ErrnoError" && ex.errno === 8 /* EBADF */)
     );
 
+    remove("truncatetest");
     remove("testfile");
     remove("renametestfile");
     remove("readtestfile");