Add command-line tool to manually subscribe to an event stream. (#8015)

This tool is an aid to debugging, and demonstrates the API of the eventstream
helper package. It subscribes to the event stream of a running node with the
ADR 075 event log enabled, and writes matching events to stdout as JSON.

scripts/estream/estream.go

@@ -0,0 +1,81 @@
+// Program estream is a manual testing tool for polling the event stream
+// of a running Tendermint consensus node.
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"path/filepath"
+
+	"github.com/tendermint/tendermint/rpc/client/eventstream"
+	rpcclient "github.com/tendermint/tendermint/rpc/client/http"
+	"github.com/tendermint/tendermint/rpc/coretypes"
+)
+
+var (
+	query      = flag.String("query", "", "Filter query")
+	batchSize  = flag.Int("batch", 0, "Batch size")
+	resumeFrom = flag.String("resume", "", "Resume cursor")
+	numItems   = flag.Int("count", 0, "Number of items to read (0 to stream)")
+	waitTime   = flag.Duration("poll", 0, "Long poll interval")
+	rpcAddr    = flag.String("addr", "http://localhost:26657", "RPC service address")
+)
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, `Usage: %[1]s [options]
+
+Connect to the Tendermint node whose RPC service is at -addr, and poll for events
+matching the specified -query. If no query is given, all events are fetched.
+The resulting event data are written to stdout as JSON.
+
+Use -resume to pick up polling from a previously-reported event cursor.
+Use -count to stop polling after a certain number of events has been reported.
+Use -batch to override the default request batch size.
+Use -poll to override the default long-polling interval.
+
+Options:
+`, filepath.Base(os.Args[0]))
+		flag.PrintDefaults()
+	}
+}
+
+func main() {
+	flag.Parse()
+
+	cli, err := rpcclient.New(*rpcAddr)
+	if err != nil {
+		log.Fatalf("RPC client: %v", err)
+	}
+	stream := eventstream.New(cli, *query, &eventstream.StreamOptions{
+		BatchSize:  *batchSize,
+		ResumeFrom: *resumeFrom,
+		WaitTime:   *waitTime,
+	})
+
+	// Shut down cleanly on SIGINT.  Don't attempt clean shutdown for other
+	// fatal signals.
+	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
+	defer cancel()
+
+	var nr int
+	if err := stream.Run(ctx, func(itm *coretypes.EventItem) error {
+		nr++
+		bits, err := json.Marshal(itm)
+		if err != nil {
+			return err
+		}
+		fmt.Println(string(bits))
+		if *numItems > 0 && nr >= *numItems {
+			return eventstream.ErrStopRunning
+		}
+		return nil
+	}); err != nil {
+		log.Fatalf("Stream failed: %v", err)
+	}
+}