lib/telemetry: package for collecting and forwarding metrics

Package telemetry is a library for collecting various Metric, for example
from standard runtime/metrics, and send or write it to one or more
Forwarder.
Each Forwarder has capability to format the Metric before sending or
writing it using Formatter.

1 files changed, 44 insertions, 0 deletions

diff --git a/lib/telemetry/stdout_forwarder.go b/lib/telemetry/stdout_forwarder.go
new file mode 100644
index 00000000..4e84898b
--- /dev/null
+++ b/lib/telemetry/stdout_forwarder.go
@@ -0,0 +1,44 @@
+// Copyright 2023, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package telemetry
+
+import (
+	"fmt"
+	"os"
+)
+
+// StdoutForwarder write the metrics to os.Stdout.
+// This type is used as example and to provide wrapper for os.Stdout, since
+// user should not call Close on os.Stdout.
+type StdoutForwarder struct {
+	formatter Formatter
+}
+
+// NewStdoutForwarder create new StdoutForwarder using f as Formatter.
+func NewStdoutForwarder(f Formatter) *StdoutForwarder {
+	return &StdoutForwarder{
+		formatter: f,
+	}
+}
+
+// Close on StdoutForwarder sync the Stdout.
+func (stdout *StdoutForwarder) Close() error {
+	os.Stdout.Sync()
+	return nil
+}
+
+// Formatter return the Formatter used by this StdoutForwarder.
+func (stdout *StdoutForwarder) Formatter() Formatter {
+	return stdout.formatter
+}
+
+// Write the raw metrics to stdout.
+func (stdout *StdoutForwarder) Write(wire []byte) (n int, err error) {
+	n, err = os.Stdout.Write(wire)
+	if err != nil {
+		return n, fmt.Errorf(`StdoutForwarder.Forward: %w`, err)
+	}
+	return n, nil
+}