Fix PackageCollection.Update to detect conflicts and skip updates when it's not necessary.

debian/package.go

@@ -205,14 +205,18 @@ func (p *Package) Key() []byte {
 	return []byte("P" + p.Architecture + " " + p.Name + " " + p.Version)
 }
 
-// Encode does msgpack encoding of Package
+// Internal buffer reused by all Package.Encode operations
-func (p *Package) Encode() []byte {
+var encodeBuf bytes.Buffer
-	var buf bytes.Buffer
 
-	encoder := codec.NewEncoder(&buf, &codec.MsgpackHandle{})
+// Encode does msgpack encoding of Package, []byte should be copied, as buffer would
+// be used for the next call to Encode
+func (p *Package) Encode() []byte {
+	encodeBuf.Reset()
+
+	encoder := codec.NewEncoder(&encodeBuf, &codec.MsgpackHandle{})
 	encoder.Encode(p)
 
-	return buf.Bytes()
+	return encodeBuf.Bytes()
 }
 
 // Decode decodes msgpack representation into Package
@@ -499,6 +503,33 @@ func (collection *PackageCollection) ByKey(key []byte) (*Package, error) {
 
 // Update adds or updates information about package in DB
 func (collection *PackageCollection) Update(p *Package) error {
+	existing, err := collection.ByKey(p.Key())
+	if err == nil {
+		// check for conflict
+		if existing.Equals(p) {
+			// packages are the same, no need to update
+			return nil
+		}
+
+		// if .Files is different, consider to be conflict
+		if len(p.Files) != len(existing.Files) {
+			return fmt.Errorf("unable to save: %s, conflict with existing packge", p)
+		}
+
+		for i, f := range p.Files {
+			if existing.Files[i] != f {
+				return fmt.Errorf("unable to save: %s, conflict with existing packge", p)
+			}
+		}
+
+		// ok, .Files are the same, but some meta-data is different, proceed to saving
+	} else {
+		if err != database.ErrNotFound {
+			return err
+		}
+		// ok, package doesn't exist yet
+	}
+
 	return collection.db.Put(p.Key(), p.Encode())
 }
 

debian/package_test.go

@@ -306,7 +306,45 @@ func (s *PackageCollectionSuite) TearDownTest(c *C) {
 	s.db.Close()
 }
 
-func (s *PackageCollectionSuite) TestUpdateByKey(c *C) {
+func (s *PackageCollectionSuite) TestUpdate(c *C) {
+	// package doesn't exist, update ok
+	err := s.collection.Update(s.p)
+	c.Assert(err, IsNil)
+	res, err := s.collection.ByKey(s.p.Key())
+	c.Assert(err, IsNil)
+	c.Assert(res.Equals(s.p), Equals, true)
+
+	// same package, ok
+	p2 := NewPackageFromControlFile(packageStanza.Copy())
+	err = s.collection.Update(p2)
+	c.Assert(err, IsNil)
+	res, err = s.collection.ByKey(p2.Key())
+	c.Assert(err, IsNil)
+	c.Assert(res.Equals(s.p), Equals, true)
+
+	// change some metadata
+	p2.Source = "lala"
+	err = s.collection.Update(p2)
+	c.Assert(err, IsNil)
+	res, err = s.collection.ByKey(p2.Key())
+	c.Assert(err, IsNil)
+	c.Assert(res.Equals(s.p), Equals, false)
+	c.Assert(res.Equals(p2), Equals, true)
+
+	// change file info
+	p2 = NewPackageFromControlFile(packageStanza.Copy())
+	p2.Files = nil
+	res, err = s.collection.ByKey(p2.Key())
+	err = s.collection.Update(p2)
+	c.Assert(err, ErrorMatches, ".*conflict with existing packge")
+	p2 = NewPackageFromControlFile(packageStanza.Copy())
+	p2.Files[0].Checksums.MD5 = "abcdef"
+	res, err = s.collection.ByKey(p2.Key())
+	err = s.collection.Update(p2)
+	c.Assert(err, ErrorMatches, ".*conflict with existing packge")
+}
+
+func (s *PackageCollectionSuite) TestByKey(c *C) {
 	err := s.collection.Update(s.p)
 	c.Assert(err, IsNil)