terraform/helper/schema/field_reader_diff.go

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package schema
import (
"fmt"
"strings"
"github.com/hashicorp/terraform/terraform"
"github.com/mitchellh/mapstructure"
)
// DiffFieldReader reads fields out of a diff structures.
//
// It also requires access to a Reader that reads fields from the structure
// that the diff was derived from. This is usually the state. This is required
// because a diff on its own doesn't have complete data about full objects
// such as maps.
//
// The Source MUST be the data that the diff was derived from. If it isn't,
// the behavior of this struct is undefined.
//
// Reading fields from a DiffFieldReader is identical to reading from
// Source except the diff will be applied to the end result.
//
// The "Exists" field on the result will be set to true if the complete
// field exists whether its from the source, diff, or a combination of both.
// It cannot be determined whether a retrieved value is composed of
// diff elements.
type DiffFieldReader struct {
Diff *terraform.InstanceDiff
Source FieldReader
Schema map[string]*Schema
}
func (r *DiffFieldReader) ReadField(address []string) (FieldReadResult, error) {
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schemaList := addrToSchema(address, r.Schema)
if len(schemaList) == 0 {
return FieldReadResult{}, nil
}
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schema := schemaList[len(schemaList)-1]
switch schema.Type {
case TypeBool, TypeInt, TypeFloat, TypeString:
return r.readPrimitive(address, schema)
case TypeList:
return readListField(r, address, schema)
case TypeMap:
return r.readMap(address, schema)
case TypeSet:
return r.readSet(address, schema)
case typeObject:
return readObjectField(r, address, schema.Elem.(map[string]*Schema))
default:
panic(fmt.Sprintf("Unknown type: %#v", schema.Type))
}
}
func (r *DiffFieldReader) readMap(
address []string, schema *Schema) (FieldReadResult, error) {
result := make(map[string]interface{})
resultSet := false
// First read the map from the underlying source
source, err := r.Source.ReadField(address)
if err != nil {
return FieldReadResult{}, err
}
if source.Exists {
result = source.Value.(map[string]interface{})
resultSet = true
}
// Next, read all the elements we have in our diff, and apply
// the diff to our result.
prefix := strings.Join(address, ".") + "."
for k, v := range r.Diff.Attributes {
if !strings.HasPrefix(k, prefix) {
continue
}
core: Use .% instead of .# for maps in state The flatmapped representation of state prior to this commit encoded maps and lists (and therefore by extension, sets) with a key corresponding to the number of elements, or the unknown variable indicator under a .# key and then individual items. For example, the list ["a", "b", "c"] would have been encoded as: listname.# = 3 listname.0 = "a" listname.1 = "b" listname.2 = "c" And the map {"key1": "value1", "key2", "value2"} would have been encoded as: mapname.# = 2 mapname.key1 = "value1" mapname.key2 = "value2" Sets use the hash code as the key - for example a set with a (fictional) hashcode calculation may look like: setname.# = 2 setname.12312512 = "value1" setname.56345233 = "value2" Prior to the work done to extend the type system, this was sufficient since the internal representation of these was effectively the same. However, following the separation of maps and lists into distinct first-class types, this encoding presents a problem: given a state file, it is impossible to tell the encoding of an empty list and an empty map apart. This presents problems for the type checker during interpolation, as many interpolation functions will operate on only one of these two structures. This commit therefore changes the representation in state of maps to use a "%" as the key for the number of elements. Consequently the map above will now be encoded as: mapname.% = 2 mapname.key1 = "value1" mapname.key2 = "value2" This has the effect of an empty list (or set) now being encoded as: listname.# = 0 And an empty map now being encoded as: mapname.% = 0 Therefore we can eliminate some nasty guessing logic from the resource variable supplier for interpolation, at the cost of having to migrate state up front (to follow in a subsequent commit). In order to reduce the number of potential situations in which resources would be "forced new", we continue to accept "#" as the count key when reading maps via helper/schema. There is no situation under which we can allow "#" as an actual map key in any case, as it would not be distinguishable from a list or set in state.
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if strings.HasPrefix(k, prefix+"%") {
// Ignore the count field
continue
}
resultSet = true
k = k[len(prefix):]
if v.NewRemoved {
delete(result, k)
continue
}
result[k] = v.New
}
err = mapValuesToPrimitive(result, schema)
if err != nil {
return FieldReadResult{}, nil
}
var resultVal interface{}
if resultSet {
resultVal = result
}
return FieldReadResult{
Value: resultVal,
Exists: resultSet,
}, nil
}
func (r *DiffFieldReader) readPrimitive(
address []string, schema *Schema) (FieldReadResult, error) {
result, err := r.Source.ReadField(address)
if err != nil {
return FieldReadResult{}, err
}
attrD, ok := r.Diff.Attributes[strings.Join(address, ".")]
if !ok {
return result, nil
}
var resultVal string
if !attrD.NewComputed {
resultVal = attrD.New
if attrD.NewExtra != nil {
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result.ValueProcessed = resultVal
if err := mapstructure.WeakDecode(attrD.NewExtra, &resultVal); err != nil {
return FieldReadResult{}, err
}
}
}
result.Computed = attrD.NewComputed
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result.Exists = true
result.Value, err = stringToPrimitive(resultVal, false, schema)
if err != nil {
return FieldReadResult{}, err
}
return result, nil
}
func (r *DiffFieldReader) readSet(
address []string, schema *Schema) (FieldReadResult, error) {
prefix := strings.Join(address, ".") + "."
// Create the set that will be our result
set := schema.ZeroValue().(*Set)
// Go through the map and find all the set items
for k, d := range r.Diff.Attributes {
if d.NewRemoved {
// If the field is removed, we always ignore it
continue
}
if !strings.HasPrefix(k, prefix) {
continue
}
if strings.HasSuffix(k, "#") {
// Ignore any count field
continue
}
// Split the key, since it might be a sub-object like "idx.field"
parts := strings.Split(k[len(prefix):], ".")
idx := parts[0]
raw, err := r.ReadField(append(address, idx))
if err != nil {
return FieldReadResult{}, err
}
if !raw.Exists {
// This shouldn't happen because we just verified it does exist
panic("missing field in set: " + k + "." + idx)
}
set.Add(raw.Value)
}
// Determine if the set "exists". It exists if there are items or if
// the diff explicitly wanted it empty.
exists := set.Len() > 0
if !exists {
// We could check if the diff value is "0" here but I think the
// existence of "#" on its own is enough to show it existed. This
// protects us in the future from the zero value changing from
// "0" to "" breaking us (if that were to happen).
if _, ok := r.Diff.Attributes[prefix+"#"]; ok {
exists = true
}
}
if !exists {
result, err := r.Source.ReadField(address)
if err != nil {
return FieldReadResult{}, err
}
if result.Exists {
return result, nil
}
}
return FieldReadResult{
Value: set,
Exists: exists,
}, nil
}