Use stream helpers from top-level package

2 files changed, 107 insertions, 0 deletions

diff --git a/streamio/stream.go b/streamio/stream.go
new file mode 100644
index 000000000..dafade8fb
--- /dev/null
+++ b/streamio/stream.go
@@ -0,0 +1,44 @@
+package streamio
+
+import (
+	"io"
+)
+
+// NewReader turns receiver into an io.Reader. Errors from the receiver
+// function are passed on unmodified. This means receiver should emit
+// io.EOF when done.
+func NewReader(receiver func() ([]byte, error)) io.Reader {
+	return &receiveReader{receiver: receiver}
+}
+
+type receiveReader struct {
+	receiver func() ([]byte, error)
+	data     []byte
+	err      error
+}
+
+func (rr *receiveReader) Read(p []byte) (int, error) {
+	if len(rr.data) == 0 {
+		rr.data, rr.err = rr.receiver()
+	}
+	n := copy(p, rr.data)
+	rr.data = rr.data[n:]
+	if len(rr.data) == 0 {
+		return n, rr.err
+	}
+	return n, nil
+}
+
+// NewWriter turns sender into an io.Writer. The number of 'bytes
+// written' reported back is always len(p).
+func NewWriter(sender func(p []byte) error) io.Writer {
+	return &sendWriter{sender: sender}
+}
+
+type sendWriter struct {
+	sender func([]byte) error
+}
+
+func (sw *sendWriter) Write(p []byte) (int, error) {
+	return len(p), sw.sender(p)
+}
diff --git a/streamio/stream_test.go b/streamio/stream_test.go
new file mode 100644
index 000000000..456d17e80
--- /dev/null
+++ b/streamio/stream_test.go
@@ -0,0 +1,63 @@
+package streamio
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"strings"
+	"testing"
+	"testing/iotest"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestReceiveSources(t *testing.T) {
+	testData := "Hello this is the test data that will be received"
+	testCases := []struct {
+		desc string
+		r    io.Reader
+	}{
+		{desc: "base", r: strings.NewReader(testData)},
+		{desc: "dataerr", r: iotest.DataErrReader(strings.NewReader(testData))},
+		{desc: "onebyte", r: iotest.OneByteReader(strings.NewReader(testData))},
+		{desc: "dataerr(onebyte)", r: iotest.DataErrReader(iotest.OneByteReader(strings.NewReader(testData)))},
+	}
+
+	for _, tc := range testCases {
+		data, err := ioutil.ReadAll(NewReader(receiverFromReader(tc.r)))
+		require.NoError(t, err, tc.desc)
+		require.Equal(t, testData, string(data), tc.desc)
+	}
+}
+
+func TestReadSizes(t *testing.T) {
+	testData := "Hello this is the test data that will be received. It goes on for a while bla bla bla."
+	for n := 1; n < 100; n *= 3 {
+		desc := fmt.Sprintf("reads of size %d", n)
+		buffer := make([]byte, n)
+		result := &bytes.Buffer{}
+		reader := &opaqueReader{NewReader(receiverFromReader(strings.NewReader(testData)))}
+		_, err := io.CopyBuffer(&opaqueWriter{result}, reader, buffer)
+		require.NoError(t, err, desc)
+		require.Equal(t, testData, result.String())
+	}
+}
+
+func receiverFromReader(r io.Reader) func() ([]byte, error) {
+	return func() ([]byte, error) {
+		data := make([]byte, 10)
+		n, err := r.Read(data)
+		return data[:n], err
+	}
+}
+
+// Hide io.WriteTo if it exists
+type opaqueReader struct {
+	io.Reader
+}
+
+// Hide io.ReadFrom if it exists
+type opaqueWriter struct {
+	io.Writer
+}