feat: add SentryStreamHandler as drop-in log.Handler

Creates a custom SentryStremHandler that functions analgously to a
log.StreamHandler, with the exception that any LvlError logs or higher
are posted to Sentry. It also leverages the existing go-ethereum logging
formatters, specifically JSONFormat, to post any additional log context
items as a JSON blob via extra data.

go/batch-submitter/go.mod

@@ -4,6 +4,7 @@ go 1.16
 
 require (
 	github.com/ethereum/go-ethereum v1.10.8
+	github.com/getsentry/sentry-go v0.11.0
 	github.com/stretchr/testify v1.7.0
 	github.com/urfave/cli v1.22.5
 )

go/batch-submitter/sentry_log.go

+package batchsubmitter
+
+import (
+	"errors"
+	"io"
+
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/getsentry/sentry-go"
+)
+
+var jsonFmt = log.JSONFormat()
+
+// SentryStreamHandler creates a log.Handler that behaves similarly to
+// log.StreamHandler, however it writes any log levels greater than or equal to
+// LvlError to Sentry. In that case, the passed log.Record is encoded using JSON
+// rather than the default terminal output, so that it can be captured for
+// debugging in the Sentry dashboard.
+func SentryStreamHandler(wr io.Writer, fmtr log.Format) log.Handler {
+	h := log.FuncHandler(func(r *log.Record) error {
+		_, err := wr.Write(fmtr.Format(r))
+		// If this record is LvlError or higher, serialize the record
+		// using JSON and write it to Sentry. We also capture the error
+		// message separately so that it's easy to parse what the error
+		// is in the dashboard.
+		if r.Lvl >= log.LvlError {
+			sentry.WithScope(func(scope *sentry.Scope) {
+				scope.SetExtra("context", jsonFmt.Format(r))
+				sentry.CaptureException(errors.New(r.Msg))
+			})
+		}
+		return err
+	})
+	return log.LazyHandler(log.SyncHandler(h))
+}