Improve std file read/write ergonomics (#1365)

- make `pos` and `len` arguments optional
- accept strings in file.write()

Author: bnoordhuis

docs/docs/stdlib.md

@@ -566,15 +566,15 @@ Return true if there was an error.
 
 Clear the error indication.
 
-#### `read(buffer, position, length)`
+#### `read(buffer, position = 0, length = buffer.length)`
 
 Read `length` bytes from the file to the ArrayBuffer `buffer` at byte
-position `position` (wrapper to the libc `fread`).
+position `position`. Wrapper to the libc function `fread`.
 
-#### `write(buffer, position, length)`
+#### `write(buffer, position = 0, length = buffer.length)`
 
-Write `length` bytes to the file from the ArrayBuffer `buffer` at byte
-position `position` (wrapper to the libc `fwrite`).
+Write `length` bytes to the file from the ArrayBuffer or string `buffer`
+at byte position `position`. Wrapper to the libc function `fwrite`.
 
 #### `getline()`
 

quickjs-libc.c

@@ -1519,25 +1519,41 @@ static JSValue js_std_file_read_write(JSContext *ctx, JSValueConst this_val,
                                       int argc, JSValueConst *argv, int magic)
 {
     FILE *f = js_std_file_get(ctx, this_val);
+    bool is_write = (magic != 0);
     uint64_t pos, len;
     size_t size, ret;
+    const char *str;
     uint8_t *buf;
 
     if (!f)
         return JS_EXCEPTION;
-    if (JS_ToIndex(ctx, &pos, argv[1]))
+    pos = 0;
+    if (argc > 1 && JS_ToIndex(ctx, &pos, argv[1]))
         return JS_EXCEPTION;
-    if (JS_ToIndex(ctx, &len, argv[2]))
+    len = 0;
+    if (argc > 2 && JS_ToIndex(ctx, &len, argv[2]))
         return JS_EXCEPTION;
-    buf = JS_GetArrayBuffer(ctx, &size, argv[0]);
+    if (is_write && JS_IsString(argv[0])) {
+        str = JS_ToCStringLen(ctx, &size, argv[0]);
+        buf = (void *)str;
+    } else {
+        str = NULL;
+        buf = JS_GetArrayBuffer(ctx, &size, argv[0]);
+    }
     if (!buf)
         return JS_EXCEPTION;
+    if (pos > size)
+        pos = size;
+    if (argc < 3)
+        len = size - pos;
     if (pos + len > size)
-        return JS_ThrowRangeError(ctx, "read/write array buffer overflow");
-    if (magic)
+        len = size - pos;
+    if (is_write) {
         ret = fwrite(buf + pos, 1, len, f);
-    else
+    } else {
         ret = fread(buf + pos, 1, len, f);
+    }
+    JS_FreeCString(ctx, str);
     return JS_NewInt64(ctx, ret);
 }
 
@@ -1909,8 +1925,8 @@ static const JSCFunctionListEntry js_std_file_proto_funcs[] = {
     JS_CFUNC_DEF("fileno", 0, js_std_file_fileno ),
     JS_CFUNC_DEF("error", 0, js_std_file_error ),
     JS_CFUNC_DEF("clearerr", 0, js_std_file_clearerr ),
-    JS_CFUNC_MAGIC_DEF("read", 3, js_std_file_read_write, 0 ),
-    JS_CFUNC_MAGIC_DEF("write", 3, js_std_file_read_write, 1 ),
+    JS_CFUNC_MAGIC_DEF("read", 1, js_std_file_read_write, 0 ),
+    JS_CFUNC_MAGIC_DEF("write", 1, js_std_file_read_write, 1 ),
     JS_CFUNC_DEF("getline", 0, js_std_file_getline ),
     JS_CFUNC_MAGIC_DEF("readAsArrayBuffer", 0, js_std_file_readAs, 0 ),
     JS_CFUNC_MAGIC_DEF("readAsString", 0, js_std_file_readAs, 1 ),

tests/test_std.js

@@ -223,7 +223,18 @@ function test_os()
         [fpath, fd] = os.mkstemp(`${fdir}/XXXXXX`);
         assert(fdir.startsWith(`${fdir}`));
         assert(fd >= 0);
-        os.close(fd);
+
+        const f = std.fdopen(fd, "w+");
+        f.write("xyzzy");
+        f.flush();
+        const b = new Uint8Array(5);
+        f.seek(0, std.SEEK_SET);
+        assert(5, f.read(b.buffer));
+        const s = [...b].map(c => String.fromCharCode(c)).join("");
+        assert(s, "xyzzy");
+        f.seek(0, std.SEEK_SET);
+        assert(0, f.read(b.buffer, 5, 42));
+        f.close();
 
         assert(os.remove(fpath), 0);
         assert(os.remove(fdir), 0);