helper/schema: add support for StateFunc

helper/schema/resource_data.go

@@ -28,6 +28,7 @@ const (
 type getResult struct {
 	Value  interface{}
 	Exists bool
+	Schema *Schema
 }
 
 var getResultEmpty getResult
@@ -200,6 +201,10 @@ func (d *ResourceData) diffChange(k string) (interface{}, interface{}, bool) {
 		n.Value = nil
 	}
 
+	if n.Exists && n.Schema.StateFunc != nil {
+		n.Value = n.Schema.StateFunc(n.Value)
+	}
+
 	// Return the old, new, and whether there is a change
 	return o.Value, n.Value, !reflect.DeepEqual(o.Value, n.Value)
 }
@@ -248,7 +253,7 @@ func (d *ResourceData) getSet(
 	schema *Schema,
 	source getSource) getResult {
 	s := &Set{F: schema.Set}
-	result := getResult{Value: s}
+	result := getResult{Schema: schema, Value: s}
 	raw := d.getList(k, nil, schema, source)
 	if !raw.Exists {
 		if len(parts) > 0 {
@@ -394,6 +399,7 @@ func (d *ResourceData) getMap(
 	return getResult{
 		Value:  resultValue,
 		Exists: resultSet,
+		Schema: schema,
 	}
 }
 
@@ -429,6 +435,9 @@ func (d *ResourceData) getObject(
 	return getResult{
 		Value:  result,
 		Exists: true,
+		Schema: &Schema{
+			Elem: schema,
+		},
 	}
 }
 
@@ -469,6 +478,7 @@ func (d *ResourceData) getList(
 	return getResult{
 		Value:  result,
 		Exists: count.Exists,
+		Schema: schema,
 	}
 }
 
@@ -553,6 +563,7 @@ func (d *ResourceData) getPrimitive(
 	return getResult{
 		Value:  resultValue,
 		Exists: resultSet,
+		Schema: schema,
 	}
 }
 

helper/schema/resource_data_test.go

@@ -1430,6 +1430,35 @@ func TestResourceDataState(t *testing.T) {
 			},
 		},
 
+		// Basic primitive with StateFunc set
+		{
+			Schema: map[string]*Schema{
+				"availability_zone": &Schema{
+					Type:      TypeString,
+					Optional:  true,
+					Computed:  true,
+					StateFunc: func(interface{}) string { return "" },
+				},
+			},
+
+			State: nil,
+
+			Diff: &terraform.ResourceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"availability_zone": &terraform.ResourceAttrDiff{
+						Old: "",
+						New: "foo",
+					},
+				},
+			},
+
+			Result: &terraform.ResourceState{
+				Attributes: map[string]string{
+					"availability_zone": "foo",
+				},
+			},
+		},
+
 		// List
 		{
 			Schema: map[string]*Schema{

helper/schema/schema.go

@@ -41,8 +41,14 @@ type Schema struct {
 	//
 	// If ForceNew is true, then a change in this resource necessitates
 	// the creation of a new resource.
+	//
+	// StateFunc is a function called to change the value of this before
+	// storing it in the state (and likewise before comparing for diffs).
+	// The use for this is for example with large strings, you may want
+	// to simply store the hash of it.
 	Computed  bool
 	ForceNew  bool
+	StateFunc SchemaStateFunc
 
 	// The following fields are only set for a TypeList or TypeSet Type.
 	//
@@ -66,7 +72,11 @@ type Schema struct {
 
 // SchemaSetFunc is a function that must return a unique ID for the given
 // element. This unique ID is used to store the element in a hash.
-type SchemaSetFunc func(a interface{}) int
+type SchemaSetFunc func(interface{}) int
+
+// SchemaStateFunc is a function used to convert some type to a string
+// to be stored in the state.
+type SchemaStateFunc func(interface{}) string
 
 func (s *Schema) finalizeDiff(
 	d *terraform.ResourceAttrDiff) *terraform.ResourceAttrDiff {

helper/schema/schema_test.go

@@ -76,6 +76,37 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Err: false,
 		},
 
+		// String with StateFunc
+		{
+			Schema: map[string]*Schema{
+				"availability_zone": &Schema{
+					Type:     TypeString,
+					Optional: true,
+					Computed: true,
+					StateFunc: func(a interface{}) string {
+						return a.(string) + "!"
+					},
+				},
+			},
+
+			State: nil,
+
+			Config: map[string]interface{}{
+				"availability_zone": "foo",
+			},
+
+			Diff: &terraform.ResourceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"availability_zone": &terraform.ResourceAttrDiff{
+						Old: "",
+						New: "foo!",
+					},
+				},
+			},
+
+			Err: false,
+		},
+
 		/*
 		 * Int decode
 		 */