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Add really basic "OrderedMap" implementation for round-tripping JSON …
…maps in a defined order
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| package om | ||
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| // https://github.com/golang/go/issues/27179 | ||
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| import ( | ||
| "bytes" | ||
| "encoding/json" | ||
| "fmt" | ||
| ) | ||
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| // only supports string keys because JSON is the intended use case (and the JSON spec says only string keys are allowed) | ||
| type OrderedMap[T any] struct { | ||
| m map[string]T | ||
| keys []string | ||
| } | ||
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| func (m OrderedMap[T]) Keys() []string { | ||
| return append([]string{}, m.keys...) | ||
| } | ||
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| func (m OrderedMap[T]) Get(key string) T { | ||
| return m.m[key] | ||
| } | ||
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| // TODO Has()? two-return form of Get? (we don't need either right now) | ||
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| func (m *OrderedMap[T]) Set(key string, val T) { // TODO make this variadic so it can take an arbitrary number of pairs? (would be useful for tests, but we don't need something like that right now) | ||
| if m.m == nil || m.keys == nil { | ||
| m.m = map[string]T{} | ||
| m.keys = []string{} | ||
| } | ||
| if _, ok := m.m[key]; !ok { | ||
| m.keys = append(m.keys, key) | ||
| } | ||
| m.m[key] = val | ||
| } | ||
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| func (m *OrderedMap[T]) UnmarshalJSON(b []byte) error { | ||
| dec := json.NewDecoder(bytes.NewReader(b)) | ||
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| // read opening { | ||
| if tok, err := dec.Token(); err != nil { | ||
| return err | ||
| } else if tok != json.Delim('{') { | ||
| return fmt.Errorf("expected '{', got %T: %#v", tok, tok) | ||
| } | ||
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| for { | ||
| tok, err := dec.Token() | ||
| if err != nil { | ||
| return err | ||
| } | ||
| if tok == json.Delim('}') { | ||
| break | ||
| } | ||
| key, ok := tok.(string) | ||
| if !ok { | ||
| return fmt.Errorf("expected string key, got %T: %#v", tok, tok) | ||
| } | ||
| var val T | ||
| err = dec.Decode(&val) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| m.Set(key, val) | ||
| } | ||
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| if dec.More() { | ||
| return fmt.Errorf("unexpected extra content after closing '}'") | ||
| } | ||
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| return nil | ||
| } | ||
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| func (m OrderedMap[T]) MarshalJSON() ([]byte, error) { | ||
| var buf bytes.Buffer | ||
| enc := json.NewEncoder(&buf) | ||
| if err := buf.WriteByte('{'); err != nil { | ||
| return nil, err | ||
| } | ||
| for i, key := range m.keys { | ||
| if i > 0 { | ||
| buf.WriteByte(',') | ||
| } | ||
| if err := enc.Encode(key); err != nil { | ||
| return nil, err | ||
| } | ||
| buf.WriteByte(':') | ||
| if err := enc.Encode(m.m[key]); err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
| if err := buf.WriteByte('}'); err != nil { | ||
| return nil, err | ||
| } | ||
| return buf.Bytes(), nil | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| package om_test | ||
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| import ( | ||
| "encoding/json" | ||
| "testing" | ||
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| "github.com/docker-library/meta-scripts/om" | ||
| ) | ||
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| func assert[V comparable](t *testing.T, v V, expected V) { | ||
| t.Helper() | ||
| if v != expected { | ||
| t.Fatalf("expected %v, got %v", expected, v) | ||
| } | ||
| } | ||
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| func assertJSON[V any](t *testing.T, v V, expected string) { | ||
| t.Helper() | ||
| b, err := json.Marshal(v) | ||
| assert(t, err, nil) | ||
| assert(t, string(b), expected) | ||
| } | ||
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| func TestOrderedMapSet(t *testing.T) { | ||
| var m om.OrderedMap[string] | ||
| assertJSON(t, m, `{}`) | ||
| m.Set("c", "a") | ||
| assert(t, m.Get("c"), "a") | ||
| assert(t, m.Get("b"), "") | ||
| assertJSON(t, m, `{"c":"a"}`) | ||
| m.Set("b", "b") | ||
| assertJSON(t, m, `{"c":"a","b":"b"}`) | ||
| m.Set("a", "c") | ||
| assertJSON(t, m, `{"c":"a","b":"b","a":"c"}`) | ||
| m.Set("c", "d") | ||
| assert(t, m.Get("c"), "d") | ||
| assertJSON(t, m, `{"c":"d","b":"b","a":"c"}`) | ||
| keys := m.Keys() | ||
| assert(t, len(keys), 3) | ||
| assert(t, keys[0], "c") | ||
| assert(t, keys[1], "b") | ||
| assert(t, keys[2], "a") | ||
| keys[0] = "d" // make sure the result of .Keys cannot modify the original | ||
| keys = m.Keys() | ||
| assert(t, keys[0], "c") | ||
| } | ||
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| func TestOrderedMapUnmarshal(t *testing.T) { | ||
| var m om.OrderedMap[string] | ||
| assert(t, json.Unmarshal([]byte(`{}`), &m), nil) | ||
| assertJSON(t, m, `{}`) | ||
| assert(t, json.Unmarshal([]byte(`{ "foo" : "bar" }`), &m), nil) | ||
| assertJSON(t, m, `{"foo":"bar"}`) | ||
| assert(t, json.Unmarshal([]byte(`{ "baz" : "buzz" }`), &m), nil) | ||
| assertJSON(t, m, `{"foo":"bar","baz":"buzz"}`) | ||
| assert(t, json.Unmarshal([]byte(`{ "foo" : "foo" }`), &m), nil) | ||
| assertJSON(t, m, `{"foo":"foo","baz":"buzz"}`) | ||
| } | ||
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| func TestOrderedMapUnmarshalDupes(t *testing.T) { | ||
| var m om.OrderedMap[string] | ||
| assert(t, json.Unmarshal([]byte(`{ "foo":"foo", "bar":"bar", "foo":"baz" }`), &m), nil) | ||
| assertJSON(t, m, `{"foo":"baz","bar":"bar"}`) | ||
| } |