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decoder.go
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decoder.go
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package v2
import (
"context"
"encoding/json"
"fmt"
"io"
"github.com/Azure/azure-kusto-go/kusto/data/table"
"github.com/Azure/azure-kusto-go/kusto/data/errors"
"github.com/Azure/azure-kusto-go/kusto/internal/frames"
)
// Decoder impolements frames.Decoder on the REST v2 frames.
type Decoder struct {
columns table.Columns
dec *json.Decoder
op errors.Op
}
// Decode implements frames.Decoder.Decode(). This is not thread safe.
func (d *Decoder) Decode(ctx context.Context, r io.ReadCloser, op errors.Op) chan frames.Frame {
d.columns = nil
d.dec = json.NewDecoder(r)
d.dec.UseNumber()
d.op = op
ch := make(chan frames.Frame, 1) // Channel is sized to 1. We read from the channel faster than we put on the channel.
go func() {
defer r.Close()
defer close(ch)
// We should receive a '[' indicating the start of the JSON list of Frames.
t, err := d.dec.Token()
if err == io.EOF {
return
}
if err != nil {
frames.Errorf(ctx, ch, err.Error())
return
}
if t != json.Delim('[') {
frames.Errorf(ctx, ch, "Expected '[' delimiter")
return
}
// Extract the initial Frame, a dataSetHeader.
dsh, err := d.dataSetHeader(ctx)
if err != nil {
frames.Errorf(ctx, ch, "first frame had error: %s", err)
return
}
ch <- dsh
// Start decoding the rest of the frames.
d.decodeFrames(ctx, ch)
}()
return ch
}
// dataSetHeader decodes the byte stream into a DataSetHeader.
func (d *Decoder) dataSetHeader(ctx context.Context) (DataSetHeader, error) {
dsh := DataSetHeader{Op: d.op}
err := d.dec.Decode(&dsh)
return dsh, err
}
// decodeFrames is used to decode incoming frames after the DataSetHeader has been received.
func (d *Decoder) decodeFrames(ctx context.Context, ch chan frames.Frame) {
for d.dec.More() {
if err := d.decodetoMap(ctx, ch); err != nil {
frames.Errorf(ctx, ch, err.Error())
return
}
}
// Expect to recieve the end of our JSON list of frames, marked by the ']' delimiter.
t, err := d.dec.Token()
if err != nil {
frames.Errorf(ctx, ch, err.Error())
return
}
if t != json.Delim(']') {
frames.Errorf(ctx, ch, "Expected ']' delimiter")
return
}
}
func (d *Decoder) decodetoMap(ctx context.Context, ch chan frames.Frame) error {
if ctx.Err() != nil {
return ctx.Err()
}
m := frames.Pool.Get().(map[string]interface{})
defer func() {
select {
case frames.PoolCh <- m:
default:
}
}()
err := d.dec.Decode(&m)
if err != nil {
return err
}
if _, ok := m[frames.FieldFrameType]; !ok {
return fmt.Errorf("incoming frame did not have .FrameType")
}
if _, ok := m[frames.FieldFrameType].(string); !ok {
return fmt.Errorf("incoming frame had FrameType that was not a string, was %T", m[frames.FieldFrameType])
}
switch ft := m[frames.FieldFrameType].(string); ft {
case frames.TypeDataTable:
dt := DataTable{}
if err := dt.Unmarshal(m); err != nil {
return err
}
dt.Op = d.op
ch <- dt
case frames.TypeDataSetCompletion:
dc := DataSetCompletion{}
if err := dc.Unmarshal(m); err != nil {
return err
}
dc.Op = d.op
ch <- dc
case frames.TypeTableHeader:
th := TableHeader{}
if err := th.Unmarshal(m); err != nil {
return err
}
th.Op = d.op
d.columns = th.Columns
ch <- th
case frames.TypeTableFragment:
tf := TableFragment{Columns: d.columns}
if err := tf.Unmarshal(m); err != nil {
return err
}
tf.Op = d.op
ch <- tf
case frames.TypeTableProgress:
tp := TableProgress{}
if err := tp.Unmarshal(m); err != nil {
return err
}
tp.Op = d.op
ch <- tp
case frames.TypeTableCompletion:
tc := TableCompletion{}
if err := tc.Unmarshal(m); err != nil {
return err
}
tc.Op = d.op
d.columns = nil
ch <- tc
default:
return fmt.Errorf("received FrameType %s, which we did not expect", ft)
}
return nil
}