Introduce TSDB service (#31520)

* Introduce TSDB service

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

Co-authored-by: Erik Sundell <erik.sundell87@gmail.com>
Co-authored-by: Will Browne <will.browne@grafana.com>
Co-authored-by: Torkel Ödegaard <torkel@grafana.org>
Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>
Co-authored-by: Zoltán Bedi <zoltan.bedi@gmail.com>

pkg/plugins/dataframes.go

@@ -0,0 +1,87 @@
+package plugins
+
+import (
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	jsoniter "github.com/json-iterator/go"
+)
+
+// DataFrames is an interface for retrieving encoded and decoded data frames.
+//
+// See NewDecodedDataFrames and NewEncodedDataFrames for more information.
+type DataFrames interface {
+	// Encoded encodes Frames into a slice of []byte.
+	// If an error occurs [][]byte will be nil.
+	// The encoded result, if any, will be cached and returned next time Encoded is called.
+	Encoded() ([][]byte, error)
+
+	// Decoded decodes a slice of Arrow encoded frames to data.Frames ([]*data.Frame).
+	// If an error occurs Frames will be nil.
+	// The decoded result, if any, will be cached and returned next time Decoded is called.
+	Decoded() (data.Frames, error)
+}
+
+type dataFrames struct {
+	decoded data.Frames
+	encoded [][]byte
+}
+
+// NewDecodedDataFrames instantiates DataFrames from decoded frames.
+//
+// This should be the primary function for creating DataFrames if you're implementing a plugin.
+// In a Grafana alerting scenario it needs to operate on decoded frames, which is why this function is
+// preferrable. When encoded data frames are needed, e.g. returned from Grafana HTTP API, it will
+// happen automatically when MarshalJSON() is called.
+func NewDecodedDataFrames(decodedFrames data.Frames) DataFrames {
+	return &dataFrames{
+		decoded: decodedFrames,
+	}
+}
+
+// NewEncodedDataFrames instantiates DataFrames from encoded frames.
+//
+// This one is primarily used for creating DataFrames when receiving encoded data frames from an external
+// plugin or similar. This may allow the encoded data frames to be returned to Grafana UI without any additional
+// decoding/encoding required. In Grafana alerting scenario it needs to operate on decoded data frames why encoded
+// frames needs to be decoded before usage.
+func NewEncodedDataFrames(encodedFrames [][]byte) DataFrames {
+	return &dataFrames{
+		encoded: encodedFrames,
+	}
+}
+
+func (df *dataFrames) Encoded() ([][]byte, error) {
+	if df.encoded == nil {
+		encoded, err := df.decoded.MarshalArrow()
+		if err != nil {
+			return nil, err
+		}
+		df.encoded = encoded
+	}
+
+	return df.encoded, nil
+}
+
+func (df *dataFrames) Decoded() (data.Frames, error) {
+	if df.decoded == nil {
+		decoded, err := data.UnmarshalArrowFrames(df.encoded)
+		if err != nil {
+			return nil, err
+		}
+		df.decoded = decoded
+	}
+
+	return df.decoded, nil
+}
+
+func (df *dataFrames) MarshalJSON() ([]byte, error) {
+	encoded, err := df.Encoded()
+	if err != nil {
+		return nil, err
+	}
+
+	// Use a configuration that's compatible with the standard library
+	// to minimize the risk of introducing bugs. This will make sure
+	// that map keys is ordered.
+	jsonCfg := jsoniter.ConfigCompatibleWithStandardLibrary
+	return jsonCfg.Marshal(encoded)
+}