1 files changed, 91 insertions, 0 deletions
diff --git a/internal/journal/fuzz_test.go b/internal/journal/fuzz_test.go
new file mode 100644
index 0000000..0090d5c
--- /dev/null
+++ b/internal/journal/fuzz_test.go
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package journal
+
+import (
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// FuzzEscapeRoundTrip: escape never yields a tab or a newline, which would
+// split a log line, and unescape returns exactly the bytes escaped - for
+// any string, invalid UTF-8 included. Undo reads every path back through
+// this pair.
+func FuzzEscapeRoundTrip(f *testing.F) {
+	for _, s := range []string{"plain.pdf", "tab\there", "new\nline", `back\slash`, `\x41`, "\xff\xfe", `\\n`, "zażółć gęślą jaźń", "\x00\x1b[2K"} {
+		f.Add(s)
+	}
+	f.Fuzz(func(t *testing.T, s string) {
+		e := escape(s)
+		if strings.ContainsAny(e, "\t\n") {
+			t.Fatalf("escape(%q) = %q holds a tab or a newline", s, e)
+		}
+		if got := unescape(e); got != s {
+			t.Fatalf("unescape(escape(%q)) = %q", s, got)
+		}
+	})
+}
+
+// FuzzParseLine: a log line of any content is rejected or parsed, never a
+// panic - the log is a file a crash can truncate or a person can edit.
+func FuzzParseLine(f *testing.F) {
+	f.Add("2026-09-11T10:02:03+02:00\tR\tdl\ta.pdf\t1\tmove\tok\tacme\t/a\t/b\t3\t2026-09-11T10:02:03+02:00\t")
+	f.Add("\t\t\t\t\t\t\t\t\t\t\t\t")
+	f.Add("")
+	f.Add("2026-09-11T10:02:03+02:00\tR\tdl\t\\x\t99999999999999999999\tmove")
+	f.Fuzz(func(t *testing.T, line string) {
+		parseLine(line)
+	})
+}
+
+// FuzzEntryRoundTrip: a step written with Append comes back from Entries
+// field for field, whatever its file name, rule, paths and detail hold.
+func FuzzEntryRoundTrip(f *testing.F) {
+	f.Add("a.pdf", "acme", "/dl/a.pdf", "/w/a.pdf", "")
+	f.Add("new\nline\t.pdf", "r", `/dl/\x`, "", "bad\xffbyte")
+	f.Fuzz(func(t *testing.T, file, rule, src, dst, detail string) {
+		path := filepath.Join(t.TempDir(), "krino.log")
+		w, err := Open(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		at := time.Date(2026, 9, 11, 10, 2, 3, 0, time.FixedZone("CEST", 2*3600))
+		want := Entry{Time: at, Run: "R", Dir: "dl", File: file, Step: 1, Action: "move", Status: "ok",
+			Rule: rule, Src: src, Dst: dst, Size: 3, ModTime: at, Detail: detail}
+		for _, e := range []Entry{
+			{Time: at, Run: "R", Action: "run-start", Status: "ok"},
+			want,
+			{Time: at, Run: "R", Action: "run-end", Status: "ok"},
+		} {
+			if err := w.Append(e); err != nil {
+				t.Fatal(err)
+			}
+		}
+		if err := w.Close(); err != nil {
+			t.Fatal(err)
+		}
+		entries, err := Entries(path, "R")
+		if err != nil {
+			t.Fatal(err)
+		}
+		var got []Entry
+		for _, e := range entries {
+			if e.Action == "move" {
+				got = append(got, e)
+			}
+		}
+		if len(got) != 1 {
+			t.Fatalf("read back %d move entries, want 1: %+v", len(got), entries)
+		}
+		g := got[0]
+		if !g.Time.Equal(want.Time) || !g.ModTime.Equal(want.ModTime) {
+			t.Fatalf("times changed: %v %v", g.Time, g.ModTime)
+		}
+		g.Time, g.ModTime = want.Time, want.ModTime
+		if g != want {
+			t.Fatalf("read back\n%+v\nwant\n%+v", g, want)
+		}
+	})
+}