From 1c7b5bab5b0ba53ff70ed12d572eaeae9cb3b1ca Mon Sep 17 00:00:00 2001
From: youdie006 <xncb135@korea.ac.kr>
Date: Thu, 13 Aug 2026 12:02:58 +0900
Subject: [PATCH] Strip all leading BOMs, not just the first

(*parser).BOM() removed at most one leading byte-order mark, so a file
that begins with two BOMs (e.g. a tool prepending a BOM to already-BOM'd
content) left the second BOM on the next line. That line no longer began
with [, # or ; and had no key-value delimiter, so the parser aborted with
a misleading "key-value delimiter not found" error on otherwise valid
content.

Loop the BOM detection until no BOM prefix remains.

Fixes #390
---
 parser.go      | 50 ++++++++++++++++++++++++++++----------------------
 parser_test.go |  8 ++++++++
 2 files changed, 36 insertions(+), 22 deletions(-)

diff --git a/parser.go b/parser.go
index 513b19e..ff5e8fc 100644
--- a/parser.go
+++ b/parser.go
@@ -73,36 +73,42 @@ func newParser(r io.Reader, opts parserOptions) *parser {
 // BOM handles header of UTF-8, UTF-16 LE and UTF-16 BE's BOM format.
 // http://en.wikipedia.org/wiki/Byte_order_mark#Representations_of_byte_order_marks_by_encoding
 func (p *parser) BOM() error {
-	mask, err := p.buf.Peek(2)
-	if err != nil && err != io.EOF {
-		return err
-	} else if len(mask) < 2 {
-		return nil
-	}
-
-	switch {
-	case mask[0] == 254 && mask[1] == 255:
-		fallthrough
-	case mask[0] == 255 && mask[1] == 254:
-		_, err = p.buf.Read(mask)
-		if err != nil {
-			return err
-		}
-	case mask[0] == 239 && mask[1] == 187:
-		mask, err := p.buf.Peek(3)
+	// Strip every leading BOM: a file may accidentally carry more than one
+	// (e.g. a tool prepending a BOM to already-BOM'd content). Stopping after
+	// the first one leaves the remaining BOM on the next token and makes the
+	// parser fail with a misleading "key-value delimiter not found" (#390).
+	for {
+		mask, err := p.buf.Peek(2)
 		if err != nil && err != io.EOF {
 			return err
-		} else if len(mask) < 3 {
+		} else if len(mask) < 2 {
 			return nil
 		}
-		if mask[2] == 191 {
-			_, err = p.buf.Read(mask)
-			if err != nil {
+
+		switch {
+		case mask[0] == 254 && mask[1] == 255:
+			fallthrough
+		case mask[0] == 255 && mask[1] == 254:
+			if _, err = p.buf.Read(mask); err != nil {
 				return err
 			}
+		case mask[0] == 239 && mask[1] == 187:
+			mask, err := p.buf.Peek(3)
+			if err != nil && err != io.EOF {
+				return err
+			} else if len(mask) < 3 {
+				return nil
+			}
+			if mask[2] != 191 {
+				return nil
+			}
+			if _, err = p.buf.Read(mask); err != nil {
+				return err
+			}
+		default:
+			return nil
 		}
 	}
-	return nil
 }
 
 func (p *parser) readUntil(delim byte) ([]byte, error) {
diff --git a/parser_test.go b/parser_test.go
index 7016d67..4555e0c 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -39,6 +39,14 @@ func TestBOM(t *testing.T) {
 
 		t.Run("UTF-16-BE-BOM", func(t *testing.T) {
 		})
+
+		t.Run("multiple UTF-8-BOM", func(t *testing.T) {
+			f, err := Load([]byte("\xef\xbb\xbf\xef\xbb\xbf[author]\nE-MAIL = example@email.com"))
+			require.NoError(t, err)
+			require.NotNil(t, f)
+
+			assert.Equal(t, "example@email.com", f.Section("author").Key("E-MAIL").String())
+		})
 	})
 }