fix(types): Extensions conversion with storage (#948)

This change ensures that we can construct a working extension array from the underlying storage.
Specifically, there should be no difference between the array constructed from storage & the one constructed from the extension builder.
Additionally, the constructed array should be intact (so that it son't panic if the underlying storage doesn't).

Author: candiduslynx

types/extensions_test.go

@@ -100,3 +100,46 @@ func TestValueStrRoundTrip(t *testing.T) {
 		})
 	}
 }
+
+func TestStorageArrayConv(t *testing.T) {
+	const amount = 100
+	cases := []arrow.ExtensionType{ExtensionTypes.UUID, ExtensionTypes.MAC, ExtensionTypes.JSON, ExtensionTypes.Inet}
+	for _, dt := range cases {
+		t.Run(dt.String(), func(t *testing.T) {
+			storageBuilder := array.NewBuilder(memory.DefaultAllocator, dt.StorageType())
+			defer storageBuilder.Release()
+			builder := array.NewBuilder(memory.DefaultAllocator, dt)
+			defer builder.Release()
+
+			for i := 0; i < amount; i++ {
+				if i%2 == 0 {
+					storageBuilder.AppendNull()
+					builder.AppendNull()
+					continue
+				}
+				storageBuilder.AppendEmptyValue()
+				builder.AppendEmptyValue()
+			}
+
+			storage := storageBuilder.NewArray()
+			defer storage.Release()
+			arr := builder.NewArray().(array.ExtensionArray)
+			defer arr.Release()
+
+			// check matching
+			assert.True(t, array.Equal(storage, arr.Storage()))
+
+			// check that creating extension from storage matches
+			fromStorage := array.NewExtensionArrayWithStorage(dt, storage)
+			defer fromStorage.Release()
+
+			assert.True(t, array.Equal(arr, fromStorage))
+
+			// assert that no issues are in the fromStorage array
+			for i := 0; i < fromStorage.Len(); i++ {
+				assert.NotPanics(t, func() { fromStorage.ValueStr(i) })
+				assert.Equal(t, arr.ValueStr(i), fromStorage.ValueStr(i))
+			}
+		})
+	}
+}

types/inet.go

@@ -20,11 +20,6 @@ func NewInetBuilder(builder *array.ExtensionBuilder) *InetBuilder {
 	return &InetBuilder{ExtensionBuilder: builder}
 }
 
-func (b *InetBuilder) AppendEmptyValue() {
-	const zeroIPNet = "0.0.0.0/0"
-	b.ExtensionBuilder.Builder.(*array.BinaryBuilder).Append([]byte(zeroIPNet))
-}
-
 func (b *InetBuilder) Append(v *net.IPNet) {
 	if v == nil {
 		b.AppendNull()
@@ -154,7 +149,14 @@ func (a *InetArray) Value(i int) *net.IPNet {
 	if a.IsNull(i) {
 		return nil
 	}
-	_, ipnet, err := net.ParseCIDR(string(a.Storage().(*array.Binary).Value(i)))
+	cidr := string(a.Storage().(*array.Binary).Value(i))
+	if len(cidr) == 0 {
+		return &net.IPNet{
+			IP:   net.IPv4zero,
+			Mask: make(net.IPMask, len(net.IPv4zero)),
+		}
+	}
+	_, ipnet, err := net.ParseCIDR(cidr)
 	if err != nil {
 		panic(fmt.Errorf("invalid ip+net: %w", err))
 	}

types/mac.go

@@ -20,10 +20,6 @@ func NewMACBuilder(builder *array.ExtensionBuilder) *MACBuilder {
 	return &MACBuilder{ExtensionBuilder: builder}
 }
 
-func (b *MACBuilder) AppendEmptyValue() {
-	b.Append(make(net.HardwareAddr, 6))
-}
-
 func (b *MACBuilder) Append(v net.HardwareAddr) {
 	b.ExtensionBuilder.Builder.(*array.BinaryBuilder).Append(v[:])
 }
@@ -147,7 +143,13 @@ func (a *MACArray) Value(i int) net.HardwareAddr {
 	if a.IsNull(i) {
 		return nil
 	}
-	return net.HardwareAddr(a.Storage().(*array.Binary).Value(i))
+	b := a.Storage().(*array.Binary).Value(i)
+	if len(b) == 0 {
+		const minMACLen = 6
+		return make(net.HardwareAddr, minMACLen)
+	}
+
+	return net.HardwareAddr(b)
 }
 
 func (a *MACArray) ValueStr(i int) string {