From b994d2086710a6a66cc1491fd9eb91debef37b73 Mon Sep 17 00:00:00 2001
From: Michael Rykov <mrykov@gmail.com>
Date: Thu, 2 Dec 2021 23:41:22 +0800
Subject: [PATCH] encoding: publicly expose identifier.{MIB,Interface}

---
 encoding/ianaindex/ianaindex.go      |  9 +++++++++
 encoding/ianaindex/ianaindex_test.go | 15 +++++++++++++++
 encoding/identifier/identifier.go    | 12 ++++++++++++
 3 files changed, 36 insertions(+)
 create mode 100644 encoding/identifier/identifier.go

diff --git a/encoding/ianaindex/ianaindex.go b/encoding/ianaindex/ianaindex.go
index f4b18875c..4b17b35b1 100644
--- a/encoding/ianaindex/ianaindex.go
+++ b/encoding/ianaindex/ianaindex.go
@@ -104,6 +104,15 @@ func (x *Index) Name(e encoding.Encoding) (string, error) {
 	return x.names(v), nil
 }
 
+// FindMIB searches encoding by MIBenum identifier
+func (x *Index) FindMIB(mib identifier.MIB) (encoding.Encoding, error) {
+	v := findMIB(x.toMIB, mib)
+	if v == -1 {
+		return nil, errUnsupported
+	}
+	return x.enc[v], nil
+}
+
 // TODO: the coverage of this index is rather spotty. Allowing users to set
 // encodings would allow:
 // - users to increase coverage
diff --git a/encoding/ianaindex/ianaindex_test.go b/encoding/ianaindex/ianaindex_test.go
index d545fcf23..49b68fce1 100644
--- a/encoding/ianaindex/ianaindex_test.go
+++ b/encoding/ianaindex/ianaindex_test.go
@@ -105,6 +105,21 @@ func TestEncoding(t *testing.T) {
 		if got, err := tc.index.Name(enc); got != tc.canonical {
 			t.Errorf("%d: Name(Encoding(%q)) = %q; want %q (%v)", i, tc.name, got, tc.canonical, err)
 		}
+
+		id, ok := enc.(identifier.Interface)
+		if !ok {
+			t.Errorf("%d: encoding %q has no ID", i, tc.name)
+		}
+		mib, _ := id.ID()
+		if mib == 0 {
+			t.Errorf("%d: encoding %q returned 0 MIB enum", i, tc.name)
+		}
+		mibEnc, err := tc.index.FindMIB(mib)
+		if err != nil {
+			t.Errorf("%d: FindMIB error %q", i, err)
+		} else if mibEnc != enc {
+			t.Errorf("%d: FindMIB did not match encoding", i)
+		}
 	}
 }
 
diff --git a/encoding/identifier/identifier.go b/encoding/identifier/identifier.go
new file mode 100644
index 000000000..a31413a39
--- /dev/null
+++ b/encoding/identifier/identifier.go
@@ -0,0 +1,12 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package identifier
+
+import (
+	"golang.org/x/text/encoding/internal/identifier"
+)
+
+type Interface = identifier.Interface
+type MIB = identifier.MIB