From d908678b16ec8b741cda6c0e54b1df0847380dc3 Mon Sep 17 00:00:00 2001
From: Evgeniy Kosov <ekosov@gmail.com>
Date: Sat, 19 Oct 2019 19:42:44 +0200
Subject: [PATCH] Add support for MARC file format

Magic number: First five octets: ASCII digits
              Octets 20-23: 4500

Reference:
https://en.wikipedia.org/wiki/MARC_standards
https://www.loc.gov/marc/specifications/specrecstruc.html
---
 internal/matchers/binary.go | 27 +++++++++++++++++++++++++++
 mime_test.go                |  1 +
 supported_mimes.md          |  3 ++-
 testdata/mrc.mrc            |  1 +
 tree.go                     |  3 ++-
 5 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 testdata/mrc.mrc

diff --git a/internal/matchers/binary.go b/internal/matchers/binary.go
index 8a4e4e90..0494277d 100644
--- a/internal/matchers/binary.go
+++ b/internal/matchers/binary.go
@@ -108,3 +108,30 @@ func Dcm(in []byte) bool {
 func Nes(in []byte) bool {
 	return bytes.HasPrefix(in, []byte{0x4E, 0x45, 0x53, 0x1A})
 }
+
+// Marc matches a MARC21 (MAchine-Readable Cataloging) file.
+func Marc(in []byte) bool {
+	// File is at least 24 bytes ("leader" field size)
+	if len(in) < 24 {
+		return false
+	}
+
+	// Fixed bytes at offset 20
+	if !bytes.Equal(in[20:24], []byte("4500")) {
+		return false
+	}
+
+	// First 5 bytes are ASCII digits
+	for i := 0; i < 5; i++ {
+		if in[i] < '0' || in[i] > '9' {
+			return false
+		}
+	}
+
+	// Field terminator is present
+	if !bytes.Contains(in, []byte{0x1E}) {
+		return false
+	}
+
+	return true
+}
diff --git a/mime_test.go b/mime_test.go
index 00164f3c..cf37a9ae 100644
--- a/mime_test.go
+++ b/mime_test.go
@@ -132,6 +132,7 @@ var files = map[string]*node{
 	"o.o":         elfObj,
 	"dcm.dcm":     dcm,
 	"mach.o":      macho,
+	"mrc.mrc":     mrc,
 
 	// fonts
 	"woff.woff":   woff,
diff --git a/supported_mimes.md b/supported_mimes.md
index 51d96161..2c58f29e 100644
--- a/supported_mimes.md
+++ b/supported_mimes.md
@@ -1,4 +1,4 @@
-## 125 Supported MIME types
+## 126 Supported MIME types
 This file is automatically generated when running tests. Do not edit manually.
 
 Extension | MIME type
@@ -128,3 +128,4 @@ Extension | MIME type
 **nes** | application/vnd.nintendo.snes.rom
 **macho** | application/x-mach-binary
 **qcp** | audio/qcelp
+**mrc** | application/marc
diff --git a/testdata/mrc.mrc b/testdata/mrc.mrc
new file mode 100644
index 00000000..6b997df9
--- /dev/null
+++ b/testdata/mrc.mrc
@@ -0,0 +1 @@
+00057     2200037   450024500190000001aTest MARC file
\ No newline at end of file
diff --git a/tree.go b/tree.go
index 28d63357..ad6f4613 100644
--- a/tree.go
+++ b/tree.go
@@ -11,7 +11,7 @@ var root = newNode("application/octet-stream", "", matchers.True,
 	wav, aiff, au, mpeg, quickTime, mqv, mp4, webM, threeGP, threeG2, avi, flv,
 	mkv, asf, aac, voc, aMp4, m4a, txt, gzip, class, swf, crx, woff, woff2, otf,
 	eot, wasm, shx, dbf, dcm, rar, djvu, mobi, lit, bpg, sqlite3, dwg, nes, macho,
-	qcp,
+	qcp, mrc,
 )
 
 // The list of nodes appended to the root node
@@ -140,4 +140,5 @@ var (
 	nes       = newNode("application/vnd.nintendo.snes.rom", "nes", matchers.Nes)
 	macho     = newNode("application/x-mach-binary", "macho", matchers.MachO)
 	qcp       = newNode("audio/qcelp", "qcp", matchers.Qcp)
+	mrc       = newNode("application/marc", "mrc", matchers.Marc)
 )