fs: add ftruncate() function

Trunates the file referenced by a file descriptor

Signed-off-by: Felix Fietkau <[email protected]>

lib/fs.c

@@ -738,6 +738,46 @@ uc_fs_seek(uc_vm_t *vm, size_t nargs)
 	return ucv_boolean_new(true);
 }
 
+/**
+ * Truncate file to a given size
+ *
+ * Returns `true` if the file was successfully truncated.
+ *
+ * Returns `null` if an error occurred.
+ *
+ * @function module:fs.file#truncate
+ *
+ * @param {number} [fd]
+ * The file descriptor.
+ *
+ * @param {number} [offset=0]
+ * The offset in bytes.
+ *
+ * @returns {?boolean}
+ */
+static uc_value_t *
+uc_fs_ftruncate(uc_vm_t *vm, size_t nargs)
+{
+	uc_value_t *fd = uc_fn_arg(0);
+	uc_value_t *ofs = uc_fn_arg(1);
+	off_t offset;
+
+	if (ucv_type(fd) != UC_INTEGER)
+		err_return(EINVAL);
+
+	if (!ofs)
+		offset = 0;
+	else if (ucv_type(ofs) != UC_INTEGER)
+		err_return(EINVAL);
+	else
+		offset = (off_t)ucv_int64_get(ofs);
+
+	if (ftruncate(ucv_int64_get(fd), offset) < 0)
+		err_return(errno);
+
+	return ucv_boolean_new(true);
+}
+
 /**
  * Obtain current read position.
  *
@@ -2609,6 +2649,7 @@ static const uc_function_list_t global_fns[] = {
 	{ "writefile",	uc_fs_writefile },
 	{ "realpath",	uc_fs_realpath },
 	{ "pipe",		uc_fs_pipe },
+	{ "ftruncate",	uc_fs_ftruncate },
 };