Added block interface and memory block implementations.

internal/block/block.go

@@ -0,0 +1,64 @@
+package block
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+// Block represents the buffer which holds the data.
+type Block interface {
+	// Reuse resets the blocks for reuse.
+	Reuse()
+
+	// Size provides the current data size of the block. The capacity of the block
+	// can be >= data_size.
+	Size() int64
+
+	// Write writes the given data to block.
+	Write(bytes []byte) error
+
+	// Reader interface helps in copying the data directly to storage.writer
+	// while uploading to GCS.
+	Reader() io.Reader
+}
+
+// TODO: check if we need offset or just storing end is sufficient. We might need
+// for handling ordered writes. It will be decided after ordered writes design.
+type offset struct {
+	start, end int64
+}
+
+type memoryBlock struct {
+	Block
+	buffer []byte
+	offset offset
+}
+
+func (m *memoryBlock) Reuse() {
+	clear(m.buffer)
+
+	m.offset.end = 0
+	m.offset.start = 0
+}
+
+func (m *memoryBlock) Size() int64 {
+	return m.offset.end - m.offset.start
+}
+func (m *memoryBlock) Write(bytes []byte) error {
+	if m.Size()+int64(len(bytes)) > int64(cap(m.buffer)) {
+		return fmt.Errorf("received data more than capacity of the block")
+	}
+
+	n := copy(m.buffer[m.offset.end:], bytes)
+	if n != len(bytes) {
+		return fmt.Errorf("error in copying the data to block. Expected %d, got %d", len(bytes), n)
+	}
+
+	m.offset.end += int64(len(bytes))
+	return nil
+}
+
+func (m *memoryBlock) Reader() io.Reader {
+	return bytes.NewReader(m.buffer[0:m.offset.end])
+}

internal/block/block_test.go

@@ -0,0 +1,107 @@
+package block
+
+import (
+	"fmt"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/suite"
+)
+
+type MemoryBlockTest struct {
+	suite.Suite
+}
+
+func TestMemoryBlockTestSuite(t *testing.T) {
+	suite.Run(t, new(MemoryBlockTest))
+}
+
+func createBlock(size uint32) Block {
+	mb := memoryBlock{
+		buffer: make([]byte, size),
+		offset: offset{0, 0},
+	}
+
+	return &mb
+}
+
+func (testSuite *MemoryBlockTest) TestMemoryBlockWrite() {
+	mb := createBlock(12)
+	content := []byte("hi")
+	err := mb.Write(content)
+
+	assert.Nil(testSuite.T(), err)
+	output, err := io.ReadAll(mb.Reader())
+	assert.Nil(testSuite.T(), err)
+	assert.Equal(testSuite.T(), content, output)
+	assert.Equal(testSuite.T(), int64(2), mb.Size())
+}
+
+func (testSuite *MemoryBlockTest) TestMemoryBlockWriteWithDataGreaterThanCapacity() {
+	mb := createBlock(1)
+	content := []byte("hi")
+	err := mb.Write(content)
+
+	assert.NotNil(testSuite.T(), err)
+	assert.EqualError(testSuite.T(), err, fmt.Sprintf("received data more than capacity of the block"))
+}
+
+func (testSuite *MemoryBlockTest) TestMemoryBlockWriteWithMultipleWrites() {
+	mb := createBlock(12)
+	err := mb.Write([]byte("hi"))
+	assert.Nil(testSuite.T(), err)
+	err = mb.Write([]byte("hello"))
+	assert.Nil(testSuite.T(), err)
+
+	output, err := io.ReadAll(mb.Reader())
+	assert.Nil(testSuite.T(), err)
+	assert.Equal(testSuite.T(), []byte("hihello"), output)
+	assert.Equal(testSuite.T(), int64(7), mb.Size())
+}
+
+func (testSuite *MemoryBlockTest) TestMemoryBlockWriteWith2ndWriteBeyondCapacity() {
+	mb := createBlock(2)
+	content := []byte("hi")
+	err := mb.Write(content)
+	assert.Nil(testSuite.T(), err)
+	err = mb.Write(content)
+
+	assert.NotNil(testSuite.T(), err)
+	assert.EqualError(testSuite.T(), err, fmt.Sprintf("received data more than capacity of the block"))
+}
+
+func (testSuite *MemoryBlockTest) TestMemoryBlockReuse() {
+	mb := createBlock(12)
+	content := []byte("hi")
+	err := mb.Write(content)
+	assert.Nil(testSuite.T(), err)
+	output, err := io.ReadAll(mb.Reader())
+	assert.Nil(testSuite.T(), err)
+	assert.Equal(testSuite.T(), content, output)
+	assert.Equal(testSuite.T(), int64(2), mb.Size())
+
+	mb.Reuse()
+
+	output, err = io.ReadAll(mb.Reader())
+	assert.Nil(testSuite.T(), err)
+	assert.Empty(testSuite.T(), output)
+	assert.Equal(testSuite.T(), int64(0), mb.Size())
+}
+
+// Other cases for Size are covered as part of write tests.
+func (testSuite *MemoryBlockTest) TestMemoryBlockSizeForEmptyBlock() {
+	mb := createBlock(12)
+
+	assert.Equal(testSuite.T(), int64(0), mb.Size())
+}
+
+// Other cases for reader are covered as part of write tests.
+func (testSuite *MemoryBlockTest) TestMemoryBlockReaderForEmptyBlock() {
+	mb := createBlock(12)
+
+	output, err := io.ReadAll(mb.Reader())
+	assert.Nil(testSuite.T(), err)
+	assert.Empty(testSuite.T(), output)
+	assert.Equal(testSuite.T(), int64(0), mb.Size())
+}