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reduce number of allocations in ScanForLinks #24

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merged 2 commits into from
Jul 3, 2020
Merged

reduce number of allocations in ScanForLinks #24

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4acf0cf
reduce number of allocations in ScanForLinks
whyrusleeping Jul 3, 2020
201ee87
add a benchmark for scan links
whyrusleeping Jul 3, 2020
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27 changes: 27 additions & 0 deletions testing/bench_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,9 @@ import (
"reflect"
"testing"
"testing/quick"

"github.com/ipfs/go-cid"
cbg "github.com/whyrusleeping/cbor-gen"
)

func BenchmarkMarshaling(b *testing.B) {
Expand Down Expand Up @@ -51,3 +54,27 @@ func BenchmarkUnmarshaling(b *testing.B) {
}

}

func BenchmarkLinkScan(b *testing.B) {
r := rand.New(rand.NewSource(123456))
val, ok := quick.Value(reflect.TypeOf(SimpleTypeTwo{}), r)
if !ok {
b.Fatal("failed to construct type")
}

tt := val.Interface().(SimpleTypeTwo)

buf := new(bytes.Buffer)
if err := tt.MarshalCBOR(buf); err != nil {
b.Fatal(err)
}

b.ReportAllocs()
b.ReportAllocs()

for i := 0; i < b.N; i++ {
if err := cbg.ScanForLinks(bytes.NewReader(buf.Bytes()), func(cid.Cid) {}); err != nil {
b.Fatal(err)
}
}
}
40 changes: 25 additions & 15 deletions utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -13,19 +13,15 @@ import (
cid "github.com/ipfs/go-cid"
)

func ScanForLinks(br io.Reader) ([]cid.Cid, error) {
var out []cid.Cid
if err := scanForLinksRec(br, func(c cid.Cid) {
out = append(out, c)
}); err != nil {
return nil, err
}
const maxCidLength = 100
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Will this apply to embedded identity multihash links?

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@ianopolous yes, though only if youre using this method. Is that an issue? I guess we can make it a var instead of a const so you can tweak it in your own applications

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We only interact over the http api. So hopefully that doesn't affect us then? I can't think of a use case where it actually matters unless pinning could end up calling this to get links and then error?

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It looks like this library is used in go-ipfs indirectly through go-ipld-cbor: https://github.com/ipfs/go-ipld-cbor/blob/master/go.mod#L12


return out, nil
func ScanForLinks(br io.Reader, cb func(cid.Cid)) error {
buf := make([]byte, maxCidLength)
return scanForLinksRec(br, cb, buf)
}

func scanForLinksRec(br io.Reader, cb func(cid.Cid)) error {
maj, extra, err := CborReadHeader(br)
func scanForLinksRec(br io.Reader, cb func(cid.Cid), scratch []byte) error {
maj, extra, err := CborReadHeaderBuf(br, scratch)
if err != nil {
return err
}
Expand All @@ -39,29 +35,43 @@ func scanForLinksRec(br io.Reader, cb func(cid.Cid)) error {
}
case MajTag:
if extra == 42 {
buf, err := ReadByteArray(br, 1000)
maj, extra, err = CborReadHeaderBuf(br, scratch)
if err != nil {
return err
}
c, err := cid.Cast(buf[1:])

if maj != MajByteString {
return fmt.Errorf("expected cbor type 'byte string' in input")
}

if extra > maxCidLength {
return fmt.Errorf("string in cbor input too long")
}

if _, err := io.ReadAtLeast(br, scratch, int(extra)); err != nil {
return err
}

c, err := cid.Cast(scratch[1:extra])
if err != nil {
return err
}
cb(c)

} else {
if err := scanForLinksRec(br, cb); err != nil {
if err := scanForLinksRec(br, cb, scratch); err != nil {
return err
}
}
case MajArray:
for i := 0; i < int(extra); i++ {
if err := scanForLinksRec(br, cb); err != nil {
if err := scanForLinksRec(br, cb, scratch); err != nil {
return err
}
}
case MajMap:
for i := 0; i < int(extra*2); i++ {
if err := scanForLinksRec(br, cb); err != nil {
if err := scanForLinksRec(br, cb, scratch); err != nil {
return err
}
}
Expand Down