Support for json encoding

[AshKash]

When *roaring.Bitmap is part of a struct that is serialized to JSON, it is empty {} and everything silently fails. Could this patch be included:

@@ -9,6 +9,7 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"io"
 	"strconv"
@@ -124,6 +125,14 @@ func (rb *Bitmap) MarshalBinary() ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
+func (rb *Bitmap) MarshalJSON() ([]byte, error) {
+	b, err := rb.MarshalBinary()
+	if err != nil {
+		return nil, err
+	}
+	return json.Marshal(b)
+}
+
 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface for the bitmap
 func (rb *Bitmap) UnmarshalBinary(data []byte) error {
 	var buf bytes.Buffer
@@ -136,6 +145,15 @@ func (rb *Bitmap) UnmarshalBinary(data []byte) error {
 	return err
 }
 
+func (rb *Bitmap) UnmarshalJSON(data []byte) error {
+	var b []byte
+	err := json.Unmarshal(data, &b)
+	if err != nil {
+		return err
+	}
+	return rb.UnmarshalBinary(b)
+}
+
 // NewBitmap creates a new empty Bitmap (see also New)
 func NewBitmap() *Bitmap {
 	return &Bitmap{}

[lemire]

Help needed to review this.

cc @maciej and others.

[maciej]

@AshKash what would be the serialisation format? Would the bitmap be serialised to a JSON Array of numbers?

[AshKash]

@maciej Go's JSON encoder serializes []byte to base64 encoded strings. This should be identical to calling rb.ToBas64() and encoding as string. This should be more compact than storing array of ints.

[lemire]

It does not look harmful. I honestly did not know about the Go JSON encoder, but it looks sensible.

Can you create a pull request or do you want us to apply the patch...? We will need some tests.

[maciej]

I agree. If that's what users would expect – I'm in favour.

[lemire]

Ok... waiting for the pull request.

[AshKash]

Opened PR #205

[abusizhishen]

It does not look harmful. I honestly did not know about the Go JSON encoder, but it looks sensible.

Can you create a pull request or do you want us to apply the patch...? We will need some tests.

i need this support,because i need to serialize bitmap to save it in redis

[lemire]

@abusizhishen Do you want to help out with the PR? The code has been written, but we won't merge it until someone has written tests for it.

Regarding Redis, there is a Roaring module for it... https://github.com/aviggiano/redis-roaring

[maciej]

@abusizhishen you can use any of the existing serialisation: the default binary format (with https://godoc.org/github.com/RoaringBitmap/roaring#Bitmap.ToBytes) or base64 (https://godoc.org/github.com/RoaringBitmap/roaring#Bitmap.ToBase64). Redis accepts binary data.

[lemire]

To add to what @maciej wrote, performance is going to be better if you ingest binary data. Going through JSON is almost surely slower.

(Though you can parse JSON very quickly, I doubt that Redis uses such optimizations.)