add a Size field to Query's Result

Rational is that some datastore can easilty get the size of a value when
listing only keys, so we might as well have a way to pass that. One way this
could be useful is when implementing a cache for Has/GetSize.

Author: MichaelMure

basic_ds.go

@@ -61,7 +61,7 @@ func (d *MapDatastore) Delete(key Key) (err error) {
 func (d *MapDatastore) Query(q dsq.Query) (dsq.Results, error) {
 	re := make([]dsq.Entry, 0, len(d.values))
 	for k, v := range d.values {
-		e := dsq.Entry{Key: k.String()}
+		e := dsq.Entry{Key: k.String(), Size: len(v)}
 		if !q.KeysOnly {
 			e.Value = v
 		}

namespace/namespace_test.go

@@ -101,9 +101,9 @@ func (ks *DSSuite) TestQuery(c *C) {
 	c.Check(err, Equals, nil)
 
 	expect := []dsq.Entry{
-		{Key: "/bar", Value: []byte("/foo/bar")},
-		{Key: "/bar/baz", Value: []byte("/foo/bar/baz")},
-		{Key: "/baz/abc", Value: []byte("/foo/baz/abc")},
+		{Key: "/bar", Size: len([]byte("/foo/bar")), Value: []byte("/foo/bar")},
+		{Key: "/bar/baz", Size: len([]byte("/foo/bar/baz")), Value: []byte("/foo/bar/baz")},
+		{Key: "/baz/abc", Size: len([]byte("/foo/baz/abc")), Value: []byte("/foo/baz/abc")},
 	}
 
 	results, err := qres.Rest()
@@ -122,8 +122,8 @@ func (ks *DSSuite) TestQuery(c *C) {
 	c.Check(err, Equals, nil)
 
 	expect = []dsq.Entry{
-		{Key: "/bar", Value: []byte("/foo/bar")},
-		{Key: "/bar/baz", Value: []byte("/foo/bar/baz")},
+		{Key: "/bar", Size: len([]byte("/foo/bar")), Value: []byte("/foo/bar")},
+		{Key: "/bar/baz", Size: len([]byte("/foo/bar/baz")), Value: []byte("/foo/bar/baz")},
 	}
 
 	results, err = qres.Rest()

query/query.go

@@ -70,6 +70,7 @@ type Query struct {
 // Entry is a query result entry.
 type Entry struct {
 	Key        string    // cant be ds.Key because circular imports ...!!!
+	Size       int       // Might be zero if the datastore doesn't support listing the size with KeysOnly
 	Value      []byte    // Will be nil if KeysOnly has been passed.
 	Expiration time.Time // Entry expiration timestamp if requested and supported (see TTLDatastore).
 }

query/query_impl.go

@@ -136,7 +136,7 @@ func NaiveQueryApply(q Query, qr Results) Results {
 func ResultEntriesFrom(keys []string, vals [][]byte) []Entry {
 	re := make([]Entry, len(keys))
 	for i, k := range keys {
-		re[i] = Entry{Key: k, Value: vals[i]}
+		re[i] = Entry{Key: k, Size: len(vals[i]), Value: vals[i]}
 	}
 	return re
 }

test/basic_tests.go

@@ -267,6 +267,7 @@ func subtestQuery(t *testing.T, ds dstore.Datastore, q dsq.Query, check func(t *
 		value := randValue()
 		input = append(input, dsq.Entry{
 			Key:   key,
+			Size:  len(value),
 			Value: value,
 		})
 	}