Use Limit Reader instead of fixed 1MB/1GB slice for DQ

Fixes #2243

remote_mapper.go

@@ -4,13 +4,14 @@ import (
 	"bytes"
 	"encoding/json"
 	"errors"
+	"io"
 	"net/http"
 
 	"github.com/influxdb/influxdb/influxql"
 )
 
 const (
-	MAX_MAP_RESPONSE_SIZE = 1024 * 1024
+	MAX_MAP_RESPONSE_SIZE = 1024 * 1024 * 1024
 )
 
 // RemoteMapper implements the influxql.Mapper interface. The engine uses the remote mapper
@@ -21,6 +22,7 @@ type RemoteMapper struct {
 	results   chan interface{}
 	unmarshal influxql.UnmarshalFunc
 	complete  bool
+	decoder   *json.Decoder
 
 	Call            string   `json:",omitempty"`
 	Database        string   `json:",omitempty"`
@@ -83,6 +85,8 @@ func (m *RemoteMapper) Begin(c *influxql.Call, startingTime int64, chunkSize int
 		return err
 	}
 	m.resp = resp
+	lr := io.LimitReader(m.resp.Body, MAX_MAP_RESPONSE_SIZE)
+	m.decoder = json.NewDecoder(lr)
 
 	return nil
 }
@@ -94,19 +98,8 @@ func (m *RemoteMapper) NextInterval() (interface{}, error) {
 		return nil, nil
 	}
 
-	// read the chunk
-	chunk := make([]byte, MAX_MAP_RESPONSE_SIZE, MAX_MAP_RESPONSE_SIZE)
-	n, err := m.resp.Body.Read(chunk)
-	if err != nil {
-		return nil, err
-	}
-	if n == 0 {
-		return nil, nil
-	}
-
-	// marshal the response
 	mr := &MapResponse{}
-	err = json.Unmarshal(chunk[:n], mr)
+	err := m.decoder.Decode(&mr)
 	if err != nil {
 		return nil, err
 	}