Add an optional offset to File.readBytes().

src/module/io.c

@@ -228,12 +228,13 @@ static void fileReadBytesCallback(uv_fs_t* request)
 
   FileRequestData* data = (FileRequestData*)request->data;
   uv_buf_t buffer = data->buffer;
+  size_t count = request->result;
 
   // TODO: Having to copy the bytes here is a drag. It would be good if Wren's
   // embedding API supported a way to *give* it bytes that were previously
   // allocated using Wren's own allocator.
   schedulerResume(freeRequest(request), true);
-  wrenSetSlotBytes(getVM(), 2, buffer.base, buffer.len);
+  wrenSetSlotBytes(getVM(), 2, buffer.base, count);
   schedulerFinishResume();
 
   // TODO: Likewise, freeing this after we resume is lame.
@@ -242,19 +243,20 @@ static void fileReadBytesCallback(uv_fs_t* request)
 
 void fileReadBytes(WrenVM* vm)
 {
-  uv_fs_t* request = createRequest(wrenGetSlotValue(vm, 2));
+  uv_fs_t* request = createRequest(wrenGetSlotValue(vm, 3));
 
   int fd = *(int*)wrenGetSlotForeign(vm, 0);
   // TODO: Assert fd != -1.
 
   FileRequestData* data = (FileRequestData*)request->data;
   size_t length = (size_t)wrenGetSlotDouble(vm, 1);
+  size_t offset = (size_t)wrenGetSlotDouble(vm, 2);
 
   data->buffer.len = length;
   data->buffer.base = (char*)malloc(length);
 
-  // TODO: Allow passing in offset.
-  uv_fs_read(getLoop(), request, fd, &data->buffer, 1, 0, fileReadBytesCallback);
+  uv_fs_read(getLoop(), request, fd, &data->buffer, 1, offset,
+             fileReadBytesCallback);
 }
 
 void fileSize(WrenVM* vm)

src/module/io.wren

@@ -62,13 +62,19 @@ foreign class File {
     return Scheduler.runNextScheduled_()
   }
 
-  readBytes(count) {
+  readBytes(count) { readBytes(count, 0) }
+
+  readBytes(count, offset) {
     if (!isOpen) Fiber.abort("File is not open.")
     if (!(count is Num)) Fiber.abort("Count must be an integer.")
     if (!count.isInteger) Fiber.abort("Count must be an integer.")
     if (count < 0) Fiber.abort("Count cannot be negative.")
 
-    readBytes_(count, Fiber.current)
+    if (!(offset is Num)) Fiber.abort("Offset must be an integer.")
+    if (!offset.isInteger) Fiber.abort("Offset must be an integer.")
+    if (offset < 0) Fiber.abort("Offset cannot be negative.")
+
+    readBytes_(count, offset, Fiber.current)
     return Scheduler.runNextScheduled_()
   }
 
@@ -76,7 +82,7 @@ foreign class File {
   foreign static sizePath_(path, fiber)
 
   foreign close_(fiber)
-  foreign readBytes_(count, fiber)
+  foreign readBytes_(count, start, fiber)
   foreign size_(fiber)
 }
 

src/module/io.wren.inc

@@ -53,6 +53,8 @@ static const char* ioModuleSource =
 "    Scheduler.runNextScheduled_()\n"
 "  }\n"
 "\n"
+"  foreign descriptor\n"
+"\n"
 "  isOpen { descriptor != -1 }\n"
 "\n"
 "  size {\n"
@@ -62,13 +64,19 @@ static const char* ioModuleSource =
 "    return Scheduler.runNextScheduled_()\n"
 "  }\n"
 "\n"
-"  readBytes(count) {\n"
+"  readBytes(count) { readBytes(count, 0) }\n"
+"\n"
+"  readBytes(count, offset) {\n"
 "    if (!isOpen) Fiber.abort(\"File is not open.\")\n"
 "    if (!(count is Num)) Fiber.abort(\"Count must be an integer.\")\n"
 "    if (!count.isInteger) Fiber.abort(\"Count must be an integer.\")\n"
 "    if (count < 0) Fiber.abort(\"Count cannot be negative.\")\n"
 "\n"
-"    readBytes_(count, Fiber.current)\n"
+"    if (!(offset is Num)) Fiber.abort(\"Offset must be an integer.\")\n"
+"    if (!offset.isInteger) Fiber.abort(\"Offset must be an integer.\")\n"
+"    if (offset < 0) Fiber.abort(\"Offset cannot be negative.\")\n"
+"\n"
+"    readBytes_(count, offset, Fiber.current)\n"
 "    return Scheduler.runNextScheduled_()\n"
 "  }\n"
 "\n"
@@ -76,8 +84,7 @@ static const char* ioModuleSource =
 "  foreign static sizePath_(path, fiber)\n"
 "\n"
 "  foreign close_(fiber)\n"
-"  foreign descriptor\n"
-"  foreign readBytes_(count, fiber)\n"
+"  foreign readBytes_(count, start, fiber)\n"
 "  foreign size_(fiber)\n"
 "}\n"
 "\n"