Snapshot difference algorithm.

debian/list.go

@@ -376,3 +376,100 @@ func (l *PackageRefList) ForEach(handler func([]byte) error) error {
 	}
 	return err
 }
+
+// PackageDiff is a difference between two packages in a list.
+//
+// If left & right are present, difference is in package version
+// If left is nil, package is present only in right
+// If right is nil, package is present only in left
+type PackageDiff struct {
+	Left, Right *Package
+}
+
+// PackageDiffs is a list of PackageDiff records
+type PackageDiffs []PackageDiff
+
+// Diff calculates difference between two reflists
+func (l *PackageRefList) Diff(r *PackageRefList, packageCollection *PackageCollection) (result PackageDiffs, err error) {
+	result = make(PackageDiffs, 0, 128)
+
+	// pointer to left and right reflists
+	il, ir := 0, 0
+	// length of reflists
+	ll, lr := l.Len(), r.Len()
+	// cached loaded packages on the left & right
+	pl, pr := (*Package)(nil), (*Package)(nil)
+
+	// until we reached end of both lists
+	for il < ll || ir < lr {
+		// if we've exhausted left list, pull the rest from the right
+		if il == ll {
+			pr, err = packageCollection.ByKey(r.Refs[ir])
+			if err != nil {
+				return nil, err
+			}
+			result = append(result, PackageDiff{Left: nil, Right: pr})
+			ir++
+			continue
+		}
+		// if we've exhausted right list, pull the rest from the left
+		if ir == lr {
+			pl, err = packageCollection.ByKey(l.Refs[il])
+			if err != nil {
+				return nil, err
+			}
+			result = append(result, PackageDiff{Left: pl, Right: nil})
+			il++
+			continue
+		}
+
+		// refs on both sides are present, load them
+		rl, rr := l.Refs[il], r.Refs[ir]
+		// compare refs
+		rel := bytes.Compare(rl, rr)
+
+		if rel == 0 {
+			// refs are identical, so are packages, advance pointer
+			il++
+			ir++
+			pl, pr = nil, nil
+		} else {
+			// load pl & pr if they haven't been loaded before
+			if pl == nil {
+				pl, err = packageCollection.ByKey(rl)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			if pr == nil {
+				pr, err = packageCollection.ByKey(rr)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			// is pl & pr the same package, but different version?
+			if pl.Name == pr.Name && pl.Architecture == pr.Architecture {
+				result = append(result, PackageDiff{Left: pl, Right: pr})
+				il++
+				ir++
+				pl, pr = nil, nil
+			} else {
+				// otherwise pl or pr is missing on one of the sides
+				if rel < 0 {
+					result = append(result, PackageDiff{Left: pl, Right: nil})
+					il++
+					pl = nil
+				} else {
+					result = append(result, PackageDiff{Left: nil, Right: pr})
+					ir++
+					pr = nil
+				}
+			}
+
+		}
+	}
+
+	return
+}

debian/list_test.go

@@ -322,3 +322,75 @@ func (s *PackageListSuite) TestPackageRefListForeach(c *C) {
 
 	c.Check(err, Equals, e)
 }
+
+func (s *PackageListSuite) TestDiff(c *C) {
+	db, _ := database.OpenDB(c.MkDir())
+	coll := NewPackageCollection(db)
+
+	packages := []*Package{
+		&Package{Name: "lib", Version: "1.0", Architecture: "i386"},      //0
+		&Package{Name: "dpkg", Version: "1.7", Architecture: "i386"},     //1
+		&Package{Name: "data", Version: "1.1~bp1", Architecture: "all"},  //2
+		&Package{Name: "app", Version: "1.1~bp1", Architecture: "i386"},  //3
+		&Package{Name: "app", Version: "1.1~bp2", Architecture: "i386"},  //4
+		&Package{Name: "app", Version: "1.1~bp2", Architecture: "amd64"}, //5
+		&Package{Name: "xyz", Version: "3.0", Architecture: "sparc"},     //6
+	}
+
+	for _, p := range packages {
+		coll.Update(p)
+	}
+
+	listA := NewPackageList()
+	listA.Add(packages[0])
+	listA.Add(packages[1])
+	listA.Add(packages[2])
+	listA.Add(packages[3])
+	listA.Add(packages[6])
+
+	listB := NewPackageList()
+	listB.Add(packages[0])
+	listB.Add(packages[2])
+	listB.Add(packages[4])
+	listB.Add(packages[5])
+
+	reflistA := NewPackageRefListFromPackageList(listA)
+	reflistB := NewPackageRefListFromPackageList(listB)
+
+	diffAA, err := reflistA.Diff(reflistA, coll)
+	c.Check(err, IsNil)
+	c.Check(diffAA, HasLen, 0)
+
+	diffAB, err := reflistA.Diff(reflistB, coll)
+	c.Check(err, IsNil)
+	c.Check(diffAB, HasLen, 4)
+
+	c.Check(diffAB[0].Left, IsNil)
+	c.Check(diffAB[0].Right.String(), Equals, "app-1.1~bp2_amd64")
+
+	c.Check(diffAB[1].Left.String(), Equals, "app-1.1~bp1_i386")
+	c.Check(diffAB[1].Right.String(), Equals, "app-1.1~bp2_i386")
+
+	c.Check(diffAB[2].Left.String(), Equals, "dpkg-1.7_i386")
+	c.Check(diffAB[2].Right, IsNil)
+
+	c.Check(diffAB[3].Left.String(), Equals, "xyz-3.0_sparc")
+	c.Check(diffAB[3].Right, IsNil)
+
+	diffBA, err := reflistB.Diff(reflistA, coll)
+	c.Check(err, IsNil)
+	c.Check(diffBA, HasLen, 4)
+
+	c.Check(diffBA[0].Right, IsNil)
+	c.Check(diffBA[0].Left.String(), Equals, "app-1.1~bp2_amd64")
+
+	c.Check(diffBA[1].Right.String(), Equals, "app-1.1~bp1_i386")
+	c.Check(diffBA[1].Left.String(), Equals, "app-1.1~bp2_i386")
+
+	c.Check(diffBA[2].Right.String(), Equals, "dpkg-1.7_i386")
+	c.Check(diffBA[2].Left, IsNil)
+
+	c.Check(diffBA[3].Right.String(), Equals, "xyz-3.0_sparc")
+	c.Check(diffBA[3].Left, IsNil)
+
+}