feat: add roots helper function (#270)

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## Overview

close [#249](#249)

## Changes

 Add helper function and unit test for new function

---------

Co-authored-by: Rootul Patel <[email protected]>

datasquare_test.go

@@ -188,9 +188,9 @@ func TestInvalidSquareExtension(t *testing.T) {
 	}
 }
 
-// TestRoots verifies that the row roots and column roots are equal for a 1x1
+// Test_getRoots verifies that the row roots and column roots are equal for a 1x1
 // square.
-func TestRoots(t *testing.T) {
+func Test_getRoots(t *testing.T) {
 	result, err := newDataSquare([][]byte{{1, 2}}, NewDefaultTree, 2)
 	assert.NoError(t, err)
 

extendeddatasquare.go

@@ -322,6 +322,24 @@ func (eds *ExtendedDataSquare) Equals(other *ExtendedDataSquare) bool {
 	return true
 }
 
+// Roots returns a byte slice with this eds's RowRoots and ColRoots
+// concatenated.
+func (eds *ExtendedDataSquare) Roots() (roots [][]byte, err error) {
+	rowRoots, err := eds.RowRoots()
+	if err != nil {
+		return nil, err
+	}
+	colRoots, err := eds.ColRoots()
+	if err != nil {
+		return nil, err
+	}
+
+	roots = make([][]byte, 0, len(rowRoots)+len(colRoots))
+	roots = append(roots, rowRoots...)
+	roots = append(roots, colRoots...)
+	return roots, nil
+}
+
 // validateEdsWidth returns an error if edsWidth is not a valid width for an
 // extended data square.
 func validateEdsWidth(edsWidth uint) error {

extendeddatasquare_test.go

@@ -426,6 +426,49 @@ func TestEquals(t *testing.T) {
 	})
 }
 
+func TestRoots(t *testing.T) {
+	t.Run("returns roots for a 4x4 EDS", func(t *testing.T) {
+		eds, err := ComputeExtendedDataSquare([][]byte{
+			ones, twos,
+			threes, fours,
+		}, NewLeoRSCodec(), NewDefaultTree)
+		require.NoError(t, err)
+
+		roots, err := eds.Roots()
+		require.NoError(t, err)
+		assert.Len(t, roots, 8)
+
+		rowRoots, err := eds.RowRoots()
+		require.NoError(t, err)
+
+		colRoots, err := eds.ColRoots()
+		require.NoError(t, err)
+
+		assert.Equal(t, roots[0], rowRoots[0])
+		assert.Equal(t, roots[1], rowRoots[1])
+		assert.Equal(t, roots[2], rowRoots[2])
+		assert.Equal(t, roots[3], rowRoots[3])
+		assert.Equal(t, roots[4], colRoots[0])
+		assert.Equal(t, roots[5], colRoots[1])
+		assert.Equal(t, roots[6], colRoots[2])
+		assert.Equal(t, roots[7], colRoots[3])
+	})
+
+	t.Run("returns an error for an incomplete EDS", func(t *testing.T) {
+		eds, err := ComputeExtendedDataSquare([][]byte{
+			ones, twos,
+			threes, fours,
+		}, NewLeoRSCodec(), NewDefaultTree)
+		require.NoError(t, err)
+
+		// set a cell to nil to make the EDS incomplete
+		eds.setCell(0, 0, nil)
+
+		_, err = eds.Roots()
+		assert.Error(t, err)
+	})
+}
+
 func createExampleEds(t *testing.T, chunkSize int) (eds *ExtendedDataSquare) {
 	ones := bytes.Repeat([]byte{1}, chunkSize)
 	twos := bytes.Repeat([]byte{2}, chunkSize)