acpi: implement memory-based reader for AML byte-code streams

src/gopheros/device/acpi/aml/stream_reader.go

@@ -0,0 +1,84 @@
+package aml
+
+import (
+	"errors"
+	"io"
+	"reflect"
+	"unsafe"
+)
+
+var (
+	errInvalidUnreadByte = errors.New("amlStreamReader: invalid use of UnreadByte")
+)
+
+type amlStreamReader struct {
+	offset uint32
+	data   []byte
+}
+
+// Init sets up the reader so it can read up to dataLen bytes from the virtual
+// memory address dataAddr. If a non-zero initialOffset is specified, it will
+// be used as the current offset in the stream.
+func (r *amlStreamReader) Init(dataAddr uintptr, dataLen, initialOffset uint32) {
+	// Overlay a byte slice on top of the memory block to be accessed.
+	r.data = *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
+		Len:  int(dataLen),
+		Cap:  int(dataLen),
+		Data: dataAddr,
+	}))
+
+	r.SetOffset(initialOffset)
+}
+
+// EOF returns true if the end of the stream has been reached.
+func (r *amlStreamReader) EOF() bool {
+	return r.offset == uint32(len(r.data))
+}
+
+// ReadByte returns the next byte from the stream.
+func (r *amlStreamReader) ReadByte() (byte, error) {
+	if r.EOF() {
+		return 0, io.EOF
+	}
+
+	r.offset++
+	return r.data[r.offset-1], nil
+}
+
+// PeekByte returns the next byte from the stream without advancing the read pointer.
+func (r *amlStreamReader) PeekByte() (byte, error) {
+	if r.EOF() {
+		return 0, io.EOF
+	}
+
+	return r.data[r.offset], nil
+}
+
+// LastByte returns the last byte read off the stream
+func (r *amlStreamReader) LastByte() (byte, error) {
+	if r.offset == 0 {
+		return 0, io.EOF
+	}
+
+	return r.data[r.offset-1], nil
+}
+
+// UnreadByte moves back the read pointer by one byte.
+func (r *amlStreamReader) UnreadByte() error {
+	if r.offset == 0 {
+		return errInvalidUnreadByte
+	}
+
+	r.offset--
+	return nil
+}
+
+// Offset returns the current offset.
+func (r *amlStreamReader) Offset() uint32 {
+	return r.offset
+}
+
+// SetOffset sets the reader offset to the supplied value.
+func (r *amlStreamReader) SetOffset(off uint32) {
+	r.offset = off
+}

src/gopheros/device/acpi/aml/stream_reader_test.go

@@ -0,0 +1,97 @@
+package aml
+
+import (
+	"io"
+	"testing"
+	"unsafe"
+)
+
+func TestAMLStreamReader(t *testing.T) {
+	buf := make([]byte, 16)
+	for i := 0; i < len(buf); i++ {
+		buf[i] = byte(i)
+	}
+
+	t.Run("without offset", func(t *testing.T) {
+		var r amlStreamReader
+		r.Init(
+			uintptr(unsafe.Pointer(&buf[0])),
+			uint32(len(buf)),
+			0,
+		)
+
+		if r.EOF() {
+			t.Fatal("unexpected EOF")
+		}
+
+		if err := r.UnreadByte(); err != errInvalidUnreadByte {
+			t.Fatalf("expected errInvalidUnreadByte; got %v", err)
+		}
+
+		if _, err := r.LastByte(); err != io.EOF {
+			t.Fatalf("unexpected error: %v", err)
+		}
+
+		for i := 0; i < len(buf); i++ {
+			exp := byte(i)
+
+			next, err := r.PeekByte()
+			if err != nil {
+				t.Fatal(err)
+			}
+			if next != exp {
+				t.Fatalf("expected PeekByte to return %d; got %d", exp, next)
+			}
+
+			next, err = r.ReadByte()
+			if err != nil {
+				t.Fatal(err)
+			}
+			if next != exp {
+				t.Fatalf("expected ReadByte to return %d; got %d", exp, next)
+			}
+
+			last, err := r.LastByte()
+			if err != nil {
+				t.Fatal(err)
+			}
+			if last != exp {
+				t.Fatalf("expected LastByte to return %d; got %d", exp, last)
+			}
+		}
+
+		if _, err := r.PeekByte(); err != io.EOF {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if _, err := r.ReadByte(); err != io.EOF {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		exp := byte(len(buf) - 1)
+		if last, _ := r.LastByte(); last != exp {
+			t.Fatalf("expected LastByte to return %d; got %d", exp, last)
+		}
+
+	})
+
+	t.Run("with offset", func(t *testing.T) {
+		var r amlStreamReader
+		r.Init(
+			uintptr(unsafe.Pointer(&buf[0])),
+			uint32(len(buf)),
+			8,
+		)
+
+		if r.EOF() {
+			t.Fatal("unexpected EOF")
+		}
+
+		if exp, got := uint32(8), r.Offset(); got != exp {
+			t.Fatalf("expected Offset() to return %d; got %d", exp, got)
+		}
+
+		exp := byte(8)
+		if next, _ := r.ReadByte(); next != exp {
+			t.Fatalf("expected ReadByte to return %d; got %d", exp, next)
+		}
+	})
+}