diff --git a/src/cmd/tusd/chunk.go b/src/cmd/tusd/chunk.go
new file mode 100644
index 0000000..f350ccc
--- /dev/null
+++ b/src/cmd/tusd/chunk.go
@@ -0,0 +1,66 @@
+package main
+
+import (
+	"sort"
+)
+
+// chunk holds the offsets for a partial piece of data
+type chunk struct {
+	Start int64 `json:"start"`
+	End   int64 `json:"end"`
+}
+
+// Size returns the number of bytes between Start and End.
+func (c chunk) Size() int64 {
+	return c.End - c.Start + 1
+}
+
+// chunkSet holds a set of chunks and helps with adding/merging new chunks into
+// set set.
+type chunkSet []chunk
+
+// Add merges a newChunk into a chunkSet. This may lead to the chunk being
+// combined with one or more adjecent chunks, possibly shrinking the chunkSet
+// down to a single member.
+func (c *chunkSet) Add(newChunk chunk) {
+	if newChunk.Size() <= 0 {
+		return
+	}
+
+	*c = append(*c, newChunk)
+	sort.Sort(c)
+
+	// merge chunks that can be combined
+	for i := 0; i < len(*c)-1; i++ {
+		current := (*c)[i]
+		next := (*c)[i+1]
+
+		if current.End+1 < next.Start {
+			continue
+		}
+
+		*c = append((*c)[0:i], (*c)[i+1:]...)
+
+		if current.End > next.End {
+			(*c)[i].End = current.End
+		}
+
+		if current.Start < next.Start {
+			(*c)[i].Start = current.Start
+		}
+
+		i--
+	}
+}
+
+func (c chunkSet) Len() int {
+	return len(c)
+}
+
+func (c chunkSet) Less(i, j int) bool {
+	return c[i].Start < c[j].Start
+}
+
+func (c chunkSet) Swap(i, j int) {
+	c[i], c[j] = c[j], c[i]
+}
diff --git a/src/cmd/tusd/chunk_test.go b/src/cmd/tusd/chunk_test.go
new file mode 100644
index 0000000..59eecc1
--- /dev/null
+++ b/src/cmd/tusd/chunk_test.go
@@ -0,0 +1,99 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+)
+
+var chunkSet_AddTests = []struct {
+	Name   string
+	Add    []chunk
+	Expect []chunk
+}{
+	{
+		Name:   "add one",
+		Add:    []chunk{{Start: 1, End: 5}},
+		Expect: []chunk{{Start: 1, End: 5}},
+	},
+	{
+		Name:   "add twice",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 1, End: 5}},
+		Expect: []chunk{{Start: 1, End: 5}},
+	},
+	{
+		Name:   "append",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 7, End: 10}},
+		Expect: []chunk{{Start: 1, End: 5}, {Start: 7, End: 10}},
+	},
+	{
+		Name:   "insert",
+		Add:    []chunk{{Start: 0, End: 5}, {Start: 12, End: 15}, {Start: 7, End: 10}},
+		Expect: []chunk{{Start: 0, End: 5}, {Start: 7, End: 10}, {Start: 12, End: 15}},
+	},
+	{
+		Name:   "prepend",
+		Add:    []chunk{{Start: 5, End: 10}, {Start: 1, End: 3}},
+		Expect: []chunk{{Start: 1, End: 3}, {Start: 5, End: 10}},
+	},
+	{
+		Name:   "grow start",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 0, End: 5}},
+		Expect: []chunk{{Start: 0, End: 5}},
+	},
+	{
+		Name:   "grow end",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 1, End: 6}},
+		Expect: []chunk{{Start: 1, End: 6}},
+	},
+	{
+		Name:   "grow end with multiple items",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 7, End: 10}, {Start: 8, End: 15}},
+		Expect: []chunk{{Start: 1, End: 5}, {Start: 7, End: 15}},
+	},
+	{
+		Name:   "grow exact end match",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 6, End: 6}},
+		Expect: []chunk{{Start: 1, End: 6}},
+	},
+	{
+		Name:   "sink",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 2, End: 3}},
+		Expect: []chunk{{Start: 1, End: 5}},
+	},
+	{
+		Name:   "swallow",
+		Add:    []chunk{{Start: 1, End: 5}, {Start: 6, End: 10}, {Start: 0, End: 11}},
+		Expect: []chunk{{Start: 0, End: 11}},
+	},
+	{
+		Name:   "ignore 0 byte chunks",
+		Add:    []chunk{{Start: 0, End: -1}},
+		Expect: []chunk{},
+	},
+	{
+		Name:   "ignore invalid chunks",
+		Add:    []chunk{{Start: 0, End: -2}},
+		Expect: []chunk{},
+	},
+}
+
+func Test_chunkSet_Add(t *testing.T) {
+	for _, test := range chunkSet_AddTests {
+		var chunks chunkSet
+		for _, chunk := range test.Add {
+			chunks.Add(chunk)
+		}
+
+		expected := fmt.Sprintf("%+v", test.Expect)
+		got := fmt.Sprintf("%+v", chunks)
+
+		if got != expected {
+			t.Errorf(
+				"Failed test '%s':\nexpected: %s\ngot: %s",
+				test.Name,
+				expected,
+				got,
+			)
+		}
+	}
+}