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chunk_reader.go
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chunk_reader.go
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package natshttp
import (
"bytes"
"context"
"errors"
"io"
"github.com/nats-io/nats.go"
)
type ChunkReader struct {
ctx context.Context
sub *nats.Subscription
firstMsg *nats.Msg
remainingMsgs <-chan *nats.Msg
idx int
reader io.Reader
}
func NewChunkReader(
firstMsg *nats.Msg,
sub *nats.Subscription,
ctx context.Context,
) (*ChunkReader, error) {
if sub == nil {
return nil, errors.New("sub cannot be nil")
}
if firstMsg == nil {
return nil, errors.New("firstMsg cannot be nil")
}
if ctx == nil {
// default
ctx = context.Background()
}
return &ChunkReader{
ctx: ctx,
sub: sub,
firstMsg: firstMsg,
}, nil
}
func (c *ChunkReader) Read(p []byte) (n int, err error) {
if c.reader == nil {
// determine next msg
var msg *nats.Msg
if c.idx == 0 {
msg = c.firstMsg
} else {
msg, err = c.sub.NextMsgWithContext(c.ctx)
if err != nil {
return
}
}
// empty data indicates the end of the chunk stream
if len(msg.Data) == 0 {
return 0, io.EOF
}
// otherwise create a new reader for the next chunk
c.reader = bytes.NewReader(msg.Data)
c.idx += 1
}
// read from the current chunk
n, err = c.reader.Read(p)
if err == io.EOF {
// we have exhausted the current chunk
// clear state for next read
err = nil
c.reader = nil
}
return
}
func (c *ChunkReader) Close() error {
return c.sub.Unsubscribe()
}