From 18bd1fb12dd62f0fbc53f0bbef6593dbd8aeb481 Mon Sep 17 00:00:00 2001
From: "Alexander \"Arav\" Andreev" <me@arav.su>
Date: Sun, 1 Oct 2023 03:34:16 +0400
Subject: [PATCH] Implementation of a simple OGG tag reader.

---
 pkg/oggtag/oggtag.go      | 23 +++++++++++++++++++++++
 pkg/oggtag/oggtag_test.go | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 pkg/oggtag/oggtag.go
 create mode 100644 pkg/oggtag/oggtag_test.go

diff --git a/pkg/oggtag/oggtag.go b/pkg/oggtag/oggtag.go
new file mode 100644
index 0000000..7fcf8aa
--- /dev/null
+++ b/pkg/oggtag/oggtag.go
@@ -0,0 +1,23 @@
+package oggtag
+
+/* oggtag is a naive implementation of OGG tag's reader that is just looking
+for certain tag names ending with an = character, e.g. artist= and title=.
+*/
+
+import (
+	"bytes"
+)
+
+// OggGetTag is searching for a certain tag in a given buffer buf and returns
+// its value.
+//
+// It is a simple implementation that doesn't parse a header and instead just
+// looking for a certain tag preceded with three zero bytes and ends with
+// an = character.
+func OggGetTag(buf []byte, tag string) string {
+	tagIdx := bytes.Index(buf, append([]byte{0, 0, 0}, (tag+"=")...)) + 3
+	tagNameLen := len(tag) + 1
+	valStart := tagIdx + tagNameLen
+	valLen := int(buf[tagIdx-4]) - tagNameLen
+	return string(buf[valStart : valStart+valLen])
+}
diff --git a/pkg/oggtag/oggtag_test.go b/pkg/oggtag/oggtag_test.go
new file mode 100644
index 0000000..a98c23f
--- /dev/null
+++ b/pkg/oggtag/oggtag_test.go
@@ -0,0 +1,35 @@
+package oggtag
+
+import (
+	"os"
+	"testing"
+)
+
+const bufferSize = 4096
+const sampleSong = "/mnt/data/appdata/radio/fallback.ogg"
+const sampleArtist = "breskina"
+const sampleTitle = "Песня про мечты"
+
+func TestOggGetTag(t *testing.T) {
+	f, _ := os.Open(sampleSong)
+	buf := make([]byte, bufferSize)
+	f.Read(buf)
+	tag := OggGetTag(buf, "artist")
+	if tag != sampleArtist {
+		t.Error(tag, "!=", sampleArtist)
+	}
+	tag = OggGetTag(buf, "title")
+	if tag != sampleTitle {
+		t.Error(tag, "!=", sampleTitle)
+	}
+}
+
+func BenchmarkOggGetTag(b *testing.B) {
+	f, _ := os.Open(sampleSong)
+	buf := make([]byte, bufferSize)
+	f.Read(buf)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		OggGetTag(buf, "artist")
+	}
+}