Initial sketch of qrep scripting, mechanism should work for cdc too

Needs to address error handling, maybe run inside errgroup as a long way to cancel incoming stream

Also need to implement __newindex on LuaRow to allow mutating value

flow/activities/flowable_core.go

@@ -6,11 +6,13 @@ import (
 	"fmt"
 	"log/slog"
 	"reflect"
+	"strings"
 	"sync/atomic"
 	"time"
 
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/yuin/gopher-lua"
 	"go.temporal.io/sdk/activity"
 	"go.temporal.io/sdk/log"
 	"go.temporal.io/sdk/temporal"
@@ -23,6 +25,7 @@ import (
 	"github.com/PeerDB-io/peer-flow/generated/protos"
 	"github.com/PeerDB-io/peer-flow/model"
 	"github.com/PeerDB-io/peer-flow/peerdbenv"
+	"github.com/PeerDB-io/peer-flow/pua"
 	"github.com/PeerDB-io/peer-flow/shared"
 )
 
@@ -343,10 +346,35 @@ func (a *FlowableActivity) replicateQRepPartition(ctx context.Context,
 	})
 	defer shutdown()
 
-	var rowsSynced int
 	bufferSize := shared.FetchAndChannelSize
-	errGroup, errCtx := errgroup.WithContext(ctx)
 	stream := model.NewQRecordStream(bufferSize)
+	outstream := stream
+	if config.Script != "" {
+		ls, err := utils.LoadScript(ctx, config.Script, func(ls *lua.LState) int {
+			top := ls.GetTop()
+			ss := make([]string, top)
+			for i := range top {
+				ss[i] = ls.ToStringMeta(ls.Get(i + 1)).String()
+			}
+			a.Alerter.LogFlowInfo(ctx, config.FlowJobName, strings.Join(ss, "\t"))
+			return 0
+		})
+		if err != nil {
+			a.Alerter.LogFlowError(ctx, config.FlowJobName, err)
+			return err
+		}
+		lfn := ls.Env.RawGetString("transformRow")
+		fn, ok := lfn.(*lua.LFunction)
+		if !ok {
+			err := fmt.Errorf("script should define `transformRow` as function, not %s", lfn)
+			a.Alerter.LogFlowError(ctx, config.FlowJobName, err)
+			return err
+		}
+		outstream = pua.AttachToStream(ls, fn, stream)
+	}
+
+	var rowsSynced int
+	errGroup, errCtx := errgroup.WithContext(ctx)
 	errGroup.Go(func() error {
 		tmp, err := srcConn.PullQRepRecords(errCtx, config, partition, stream)
 		if err != nil {
@@ -363,7 +391,7 @@ func (a *FlowableActivity) replicateQRepPartition(ctx context.Context,
 	})
 
 	errGroup.Go(func() error {
-		rowsSynced, err = dstConn.SyncQRepRecords(errCtx, config, partition, stream)
+		rowsSynced, err = dstConn.SyncQRepRecords(errCtx, config, partition, outstream)
 		if err != nil {
 			a.Alerter.LogFlowError(ctx, config.FlowJobName, err)
 			return fmt.Errorf("failed to sync records: %w", err)

flow/pua/stream_adapter.go

@@ -0,0 +1,32 @@
+package pua
+
+import (
+	"github.com/yuin/gopher-lua"
+
+	"github.com/PeerDB-io/peer-flow/model"
+)
+
+func AttachToStream(ls *lua.LState, lfn *lua.LFunction, stream *model.QRecordStream) *model.QRecordStream {
+	output := model.NewQRecordStream(0)
+	go func() {
+		schema := stream.Schema()
+		output.SetSchema(schema)
+		for record := range stream.Records {
+			row := model.NewRecordItems(len(record))
+			for i, qv := range record {
+				row.AddColumn(schema.Fields[i].Name, qv)
+			}
+			ls.Push(lfn)
+			ls.Push(LuaRow.New(ls, row))
+			if err := ls.PCall(1, 0, nil); err != nil {
+				panic(err.Error()) // TODO error handling
+			}
+			for i, field := range schema.Fields {
+				record[i] = row.GetColumnValue(field.Name)
+			}
+			output.Records <- record
+		}
+		output.Close(stream.Err())
+	}()
+	return output
+}

protos/flow.proto

@@ -297,6 +297,7 @@ message QRepConfig {
   string soft_delete_col_name = 17;
 
   TypeSystem system = 18;
+  string script = 19;
 }
 
 message QRepPartition {