From b98b107581b2683a2526ba8a9f6a8b3a5b240fc7 Mon Sep 17 00:00:00 2001
From: Parnic <parnic@parnic.com>
Date: Fri, 28 Dec 2018 09:29:36 -0600
Subject: [PATCH] Initial code commit

---
 .gitignore |  3 ++
 main.go    | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 main.go

diff --git a/.gitignore b/.gitignore
index f1c181e..cb7679d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,6 @@
 
 # Output of the go coverage tool, specifically when used with LiteIDE
 *.out
+
+go-journald-monitor
+lastCursor*
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..69c3c0c
--- /dev/null
+++ b/main.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os/exec"
+	"strings"
+)
+
+var (
+	unit = flag.String("unit", "", "specifies a unit to filter the journald output for")
+)
+
+const (
+	cursorPrefix       = "-- cursor: "
+	cursorFilenameBase = "lastCursor"
+)
+
+func main() {
+	flag.Parse()
+
+	parseJournalData(getJournalData())
+}
+
+func getJournalData() (cursorFilename, lastCursor string, output []byte) {
+	cursorFilename, lastCursor = getLastCursor()
+
+	var err error
+	if output, err = getCmd(lastCursor).Output(); err != nil {
+		panic(err)
+	}
+
+	return
+}
+
+func getLastCursor() (cursorFilename, lastCursor string) {
+	cursorFilename = cursorFilenameBase
+	if len(*unit) > 0 {
+		cursorFilename = fmt.Sprintf("%s-%s", cursorFilenameBase, *unit)
+	}
+
+	lastCursorBytes, _ := ioutil.ReadFile(cursorFilename)
+	lastCursor = string(lastCursorBytes)
+
+	return
+}
+
+func getCmd(lastCursor string) (cmd *exec.Cmd) {
+	cmd = exec.Command("journalctl", "--quiet", "--show-cursor", "--no-pager")
+	if len(*unit) > 0 {
+		cmd.Args = append(cmd.Args, []string{
+			"-u",
+			*unit,
+		}...)
+	}
+	if len(lastCursor) > 0 {
+		cmd.Args = append(cmd.Args, fmt.Sprintf("--after-cursor=%s", lastCursor))
+	}
+
+	return
+}
+
+func parseJournalData(cursorFilename, lastCursor string, output []byte) {
+	buf := bytes.NewBuffer(output)
+	scanner := bufio.NewScanner(buf)
+
+	for hasData := true; hasData; hasData = scanner.Scan() {
+		handleLine(scanner.Text(), lastCursor, cursorFilename)
+	}
+}
+
+func handleLine(line, lastCursor, cursorFilename string) {
+	if strings.HasPrefix(line, cursorPrefix) {
+		lastCursor = line[len(cursorPrefix):]
+		ioutil.WriteFile(cursorFilename, []byte(lastCursor), 0664)
+	} else if len(lastCursor) > 0 && len(line) > 0 {
+		fmt.Println(line)
+	}
+}