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Alexey Palazhchenko
February 05, 2022
Programming
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Fuzzy generics
Alexey Palazhchenko
February 05, 2022
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Transcript
Fuzzy generics Several months of using 1.18 features Alexey Palazhchenko
FOSDEM 2022-02-05
None
Why Go 1.18?
Why Go 1.18? Generics
Why Go 1.18? Generics Fuzzing
Why Go 1.18? Generics Fuzzing
Generics
Generics • Generics do not work there; let's go back
to interfaces
Generics • Generics do not work there; let's go back
to interfaces • Let me extract a small example for a talk
Generics • Generics do not work there; let's go back
to interfaces • Let me extract a small example for a talk • Hm, that's not that bad
BSON Document
BSON Document • Ordered map
BSON Document • Ordered map • Keys – string, values
– any BSON value, including other documents
BSON Document • Ordered map • Keys – string, values
– any BSON value, including other documents • The central data structure in FerretDB
Interfaces type BSONType interface { bsontype() // sealed } type
Int int func (Int) bsontype() {} type String string func (String) bsontype() {}
Interfaces type BSONType interface { bsontype() // sealed } type
Int int func (Int) bsontype() {} type String string func (String) bsontype() {} type Document struct { m map[string]BSONType keys []string } func (*Document) bsontype() {}
Interfaces func (d *Document) Set(key String, value BSONType) { if
_, ok := d.m[key]; !ok { d.keys = append(d.keys, key) } d.m[key] = value }
Interfaces d.Set("foo", Int(42))
Interfaces d.Set("foo", Int(42)) d.Set("qux", nil)
Generics type BSONType interface { int | string | *Document
}
Generics type BSONType interface { int | string | *Document
} type Document struct { m map[string]any keys []string }
Generics func (d *Document) Set[T BSONType](key string, value T) {
if _, ok := d.m[key]; !ok { d.keys = append(d.keys, key) } d.m[key] = value }
Generics func (d *Document) Set[T BSONType](key string, value T) {
if _, ok := d.m[key]; !ok { d.keys = append(d.keys, key) } d.m[key] = value } syntax error: method must have no type parameters
Generics func DocumentSet[T BSONType](d *Document, key string, value T) {
if _, ok := d.m[key]; !ok { d.keys = append(d.keys, key) } d.m[key] = value }
Generics DocumentSet(d, "foo", 42)
Generics DocumentSet(d, "foo", 42) // DocumentSet(d, "qux", nil)
Interfaces func MakeDocument(pairs ...BSONType) (*Document, error) { l := len(pairs)
if l%2 != 0 { return nil, fmt.Errorf("%d arguments", l)
Interfaces
Interfaces MakeDocument( String("foo"), Int(42), String("bar"), String("baz"), )
Interfaces MakeDocument( String("foo"), Int(42), String("bar"), String("baz"), ) MakeDocument(String("invalid number of
arguments"))
Interfaces MakeDocument( String("foo"), Int(42), String("bar"), String("baz"), ) MakeDocument(String("invalid number of
arguments")) MakeDocument(Int(42), String("invalid key type"))
Generics
Generics func MakeDocument[T BSONType](key string, value T) *Document
Generics func MakeDocument[T BSONType](key string, value T) *Document func MakeDocument2[T1,
T2 BSONType](key1 string, value1 T1, key2 string, value2 T2) *Document
Generics func MakeDocument[T BSONType](key string, value T) *Document func MakeDocument2[T1,
T2 BSONType](key1 string, value1 T1, key2 string, value2 T2) *Document func MakeDocument3[T1, T2, T3 BSONType](key1 string, value1 T1, key2 string, value2 T2, key3 string, value3 T3) *Document
Interfaces
Interfaces func (d *Document) Get(key String) BSONType { return d.m[key]
}
Interfaces func (d *Document) Get(key String) BSONType { return d.m[key]
} assert.Equal(t, Int(42), d.Get("foo")) assert.Equal(t, nil, d.Get("baz"))
Generics
Generics func DocumentGet[T BSONType](d *Document, key string) T { v,
_ := d.m[key].(T) return v }
Generics func DocumentGet[T BSONType](d *Document, key string) T { v,
_ := d.m[key].(T) return v } assert.Equal(t, 42, DocumentGet[int](d, "foo")) assert.Equal(t, "", DocumentGet[string](d, "foo"))
Generics vs Interfaces
Generics vs Interfaces • Better in some aspects
Generics vs Interfaces • Better in some aspects • Worse
in others
Generics vs Interfaces • Better in some aspects • Worse
in others
Fuzzing
Fuzzing • testing/quick on steroids
Fuzzing • testing/quick on steroids • MongoDB binary protocol parsing
packages
Fuzzing • testing/quick on steroids • MongoDB binary protocol parsing
packages • FerretDB had fuzzing tests even before unit tests
Table-driven tests type testCase struct { name string b []byte
v bsontype err error }
Table-driven tests type testCase struct { name string b []byte
v bsontype err error } • Unmarshal b to (v2, err2) • compare with v or err • Marshal v2 to b2 • compare with b
Table-driven tests func TestDocument(t *testing.T) { for _, tc :=
range testCases { tc := tc t.Run(tc.name, func(t *testing.T) {
Fuzzing func FuzzDocument(f *testing.F) { for _, tc := range
testCases { f.Add(tc.b) } f.Fuzz(func(t *testing.T, b []byte) {
When b2 != b
When b2 != b • b might be larger than
needed
When b2 != b • b might be larger than
needed • The unread portion of b should be removed
When b2 != b • b might be larger than
needed • The unread portion of b should be removed • Some bytes might be insigni fi cant
When b2 != b • b might be larger than
needed • The unread portion of b should be removed • Some bytes might be insigni fi cant • Use canonization (json.Compact, etc)
Fuzzing issues
Fuzzing issues • No subtests (testing.F.Run)
Fuzzing issues • No subtests (testing.F.Run) • Unnamed seed values
Fuzzing issues • No subtests (testing.F.Run) • Unnamed seed values
• Hanging detection is unreliable with unset GOMAXPROCS
Fuzzing
Fuzzing • Found a few bugs in `go test -fuzz`
Fuzzing • Found a few bugs in `go test -fuzz`
• Found many many bugs in FerretDB
Fuzzing • Found a few bugs in `go test -fuzz`
• Found many many bugs in FerretDB • De fi nitely use it for parsing
Links • https://github.com/AlekSi/ generics-vs-interfaces • https://github.com/akutz/ go-generics-the-hard-way • https://go.dev/doc/tutorial/ •
https://go.dev/doc/fuzz/ • https://www.ferretdb.io • https://github.com/FerretDB ⭐ • https://github.com/AlekSi • @paaleksey