Add std.file.readAsArrayBuffer() (#835)

Like std.file.readAsString(), except it returns an ArrayBuffer and
doesn't assume anything about the file's character encoding.

Author: bnoordhuis

docs/docs/stdlib.md

@@ -538,11 +538,16 @@ position `position` (wrapper to the libc `fwrite`).
 Return the next line from the file, assuming UTF-8 encoding, excluding
 the trailing line feed.
 
+#### `readAsArrayBuffer(max_size = undefined)`
+
+Read `max_size` bytes from the file and return them as an ArrayBuffer.
+If `max_size` is not present, the file is read until its end.
+
 #### `readAsString(max_size = undefined)`
 
 Read `max_size` bytes from the file and return them as a string
 assuming UTF-8 encoding. If `max_size` is not present, the file
-is read up its end.
+is read until its end.
 
 #### `getByte()`
 

quickjs-libc.c

@@ -1365,8 +1365,8 @@ static JSValue js_std_file_getline(JSContext *ctx, JSValue this_val,
 }
 
 /* XXX: could use less memory and go faster */
-static JSValue js_std_file_readAsString(JSContext *ctx, JSValue this_val,
-                                        int argc, JSValue *argv)
+static JSValue js_std_file_readAs(JSContext *ctx, JSValue this_val,
+                                  int argc, JSValue *argv, int magic)
 {
     FILE *f = js_std_file_get(ctx, this_val);
     int c;
@@ -1402,7 +1402,11 @@ static JSValue js_std_file_readAsString(JSContext *ctx, JSValue this_val,
         }
         max_size--;
     }
-    obj = JS_NewStringLen(ctx, (const char *)dbuf.buf, dbuf.size);
+    if (magic) {
+        obj = JS_NewStringLen(ctx, (const char *)dbuf.buf, dbuf.size);
+    } else {
+        obj = JS_NewArrayBufferCopy(ctx, dbuf.buf, dbuf.size);
+    }
     dbuf_free(&dbuf);
     return obj;
 }
@@ -1694,7 +1698,8 @@ static const JSCFunctionListEntry js_std_file_proto_funcs[] = {
     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_DEF("getline", 0, js_std_file_getline ),
-    JS_CFUNC_DEF("readAsString", 0, js_std_file_readAsString ),
+    JS_CFUNC_MAGIC_DEF("readAsArrayBuffer", 0, js_std_file_readAs, 0 ),
+    JS_CFUNC_MAGIC_DEF("readAsString", 0, js_std_file_readAs, 1 ),
     JS_CFUNC_DEF("getByte", 0, js_std_file_getByte ),
     JS_CFUNC_DEF("putByte", 1, js_std_file_putByte ),
     /* setvbuf, ...  */

tests/test_std.js

@@ -19,12 +19,16 @@ function test_printf()
 
 function test_file1()
 {
-    var f, len, str, size, buf, ret, i, str1;
+    var f, len, str, size, buf, ret, i, str1, ab;
 
     f = std.tmpfile();
     str = "hello world\n";
     f.puts(str);
 
+    f.seek(0, std.SEEK_SET);
+    ab = f.readAsArrayBuffer();
+    assert([...new Uint8Array(ab)], str.split("").map(c => c.charCodeAt(0)));
+
     f.seek(0, std.SEEK_SET);
     str1 = f.readAsString();
     assert(str1, str);