From 9eaf85b974eeb4754d9c5226a9de91798d89936a Mon Sep 17 00:00:00 2001
From: Jonathan Hall <flimzy@flimzy.com>
Date: Tue, 25 Jun 2019 12:18:44 +0200
Subject: [PATCH] Convert RevsDiff to a stream producer

---
 db.go            | 20 +++++++++++++-------
 db_test.go       | 32 ++++++++++++++++++++------------
 driver/driver.go |  4 +++-
 mock/db.go       |  4 ++--
 4 files changed, 38 insertions(+), 22 deletions(-)

diff --git a/db.go b/db.go
index 8bb7b98d8..3ed27efee 100644
--- a/db.go
+++ b/db.go
@@ -661,18 +661,24 @@ type Diffs map[string]RevDiff
 // and is normally never needed otherwise.  revMap must marshal to the expected
 // format.
 //
+// Uses Rows.ScanValue to access each element in the returned list. The
+// value will be of the JSON format:
+//
+//     {
+//         "{doc_id}": {
+//             "missing": ["rev1",...],
+//             "possible_ancestors": ["revA",...]
+//         }
+//     }
+//
 // See http://docs.couchdb.org/en/stable/api/database/misc.html#db-revs-diff
-func (db *DB) RevsDiff(ctx context.Context, revMap interface{}) (Diffs, error) {
+func (db *DB) RevsDiff(ctx context.Context, revMap interface{}) (*Rows, error) {
 	if rd, ok := db.driverDB.(driver.RevsDiffer); ok {
-		result, err := rd.RevsDiff(ctx, revMap)
+		rowsi, err := rd.RevsDiff(ctx, revMap)
 		if err != nil {
 			return nil, err
 		}
-		diffs := make(Diffs, len(result))
-		for k, v := range result {
-			diffs[k] = RevDiff(v)
-		}
-		return diffs, nil
+		return newRows(ctx, rowsi), nil
 	}
 	return nil, &Error{HTTPStatus: http.StatusNotImplemented, Message: "kivik: _revs_diff not supported by driver"}
 }
diff --git a/db_test.go b/db_test.go
index adec6cc8e..46b01a561 100644
--- a/db_test.go
+++ b/db_test.go
@@ -1964,10 +1964,11 @@ func TestClientClose(t *testing.T) {
 
 func TestRevsDiff(t *testing.T) {
 	type tt struct {
-		db     *DB
-		revMap interface{}
-		status int
-		err    string
+		db       *DB
+		revMap   interface{}
+		status   int
+		err      string
+		expected interface{}
 	}
 	tests := testy.NewTable()
 	tests.Add("non-DBReplicator", tt{
@@ -1977,7 +1978,7 @@ func TestRevsDiff(t *testing.T) {
 	})
 	tests.Add("network error", tt{
 		db: &DB{driverDB: &mock.RevsDiffer{
-			RevsDiffFunc: func(_ context.Context, revMap interface{}) (map[string]driver.RevDiff, error) {
+			RevsDiffFunc: func(_ context.Context, revMap interface{}) (driver.Rows, error) {
 				return nil, errors.New("net error")
 			},
 		}},
@@ -1986,19 +1987,26 @@ func TestRevsDiff(t *testing.T) {
 	})
 	tests.Add("success", tt{
 		db: &DB{driverDB: &mock.RevsDiffer{
-			RevsDiffFunc: func(_ context.Context, revMap interface{}) (map[string]driver.RevDiff, error) {
-				return map[string]driver.RevDiff{
-					"foo": {Missing: []string{"1", "2"}},
-					"bar": {PossibleAncestors: []string{"3", "4"}},
-				}, nil
+			RevsDiffFunc: func(_ context.Context, revMap interface{}) (driver.Rows, error) {
+				return &mock.Rows{ID: "a"}, nil
 			},
 		}},
+		expected: &Rows{
+			iter: &iter{
+				feed: &rowsIterator{
+					Rows: &mock.Rows{ID: "a"},
+				},
+				curVal: &driver.Row{},
+			},
+			rowsi: &mock.Rows{ID: "a"},
+		},
 	})
 
 	tests.Run(t, func(t *testing.T, tt tt) {
-		result, err := tt.db.RevsDiff(context.Background(), tt.revMap)
+		rows, err := tt.db.RevsDiff(context.Background(), tt.revMap)
 		testy.StatusError(t, tt.err, tt.status, err)
-		if d := diff.AsJSON(&diff.File{Path: "testdata/" + testy.Stub(t)}, result); d != nil {
+		rows.cancel = nil // Determinism
+		if d := diff.Interface(tt.expected, rows); d != nil {
 			t.Error(d)
 		}
 	})
diff --git a/driver/driver.go b/driver/driver.go
index 301d890a0..bba8f93b7 100644
--- a/driver/driver.go
+++ b/driver/driver.go
@@ -403,5 +403,7 @@ type RevDiff struct {
 
 // RevsDiffer is an optional interface that may be implemented by a DB.
 type RevsDiffer interface {
-	RevsDiff(ctx context.Context, revMap interface{}) (map[string]RevDiff, error)
+	// RevsDiff returns a Rows iterator, which should populate the Value
+	// field, and nothing else.
+	RevsDiff(ctx context.Context, revMap interface{}) (Rows, error)
 }
diff --git a/mock/db.go b/mock/db.go
index 01ff12e9e..b4f65dff8 100644
--- a/mock/db.go
+++ b/mock/db.go
@@ -267,12 +267,12 @@ func (db *DBCloser) Close(ctx context.Context) error {
 // RevsDiffer mocks a driver.DB and driver.RevsDiffer.
 type RevsDiffer struct {
 	*BulkDocer
-	RevsDiffFunc func(context.Context, interface{}) (map[string]driver.RevDiff, error)
+	RevsDiffFunc func(context.Context, interface{}) (driver.Rows, error)
 }
 
 var _ driver.RevsDiffer = &RevsDiffer{}
 
 // RevsDiff calls db.RevsDiffFunc
-func (db *RevsDiffer) RevsDiff(ctx context.Context, revMap interface{}) (map[string]driver.RevDiff, error) {
+func (db *RevsDiffer) RevsDiff(ctx context.Context, revMap interface{}) (driver.Rows, error) {
 	return db.RevsDiffFunc(ctx, revMap)
 }