From 9de82c2af2a67ab991c3aac687020bb0759c4ab8 Mon Sep 17 00:00:00 2001
From: TheRodzz <81969589+TheRodzz@users.noreply.github.com>
Date: Wed, 5 Aug 2026 09:47:49 +0530
Subject: [PATCH 1/2] embed: return fs.ErrInvalid for invalid Seek whence

This commit addresses an inconsistency in the behavior of the Seek method
implemented by embed.FS compared to os.File. Previously, when an invalid
whence value was provided to Seek on an embedded file, the method would
silently ignore the error and perform no operation.

To align the behavior with the standard io.Seeker interface and os.File,
we now explicitly validate the whence parameter. If the provided whence
is not one of io.SeekStart, io.SeekCurrent, or io.SeekEnd, the method
will return an fs.ErrInvalid error. A regression test has also been added
to ensure this behavior remains correct.

Fixes #80696
---
 src/embed/embed.go                         |  2 ++
 src/embed/internal/embedtest/embed_test.go | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/src/embed/embed.go b/src/embed/embed.go
index 4d5e418c9024b3..d5d436d3ce0d0f 100644
--- a/src/embed/embed.go
+++ b/src/embed/embed.go
@@ -365,6 +365,8 @@ func (f *openFile) Seek(offset int64, whence int) (int64, error) {
 		offset += f.offset
 	case 2:
 		offset += int64(len(f.f.data))
+	default:
+		return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid}
 	}
 	if offset < 0 || offset > int64(len(f.f.data)) {
 		return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid}
diff --git a/src/embed/internal/embedtest/embed_test.go b/src/embed/internal/embedtest/embed_test.go
index 875265556f0940..2af4f7438a1668 100644
--- a/src/embed/internal/embedtest/embed_test.go
+++ b/src/embed/internal/embedtest/embed_test.go
@@ -6,7 +6,9 @@ package embedtest
 
 import (
 	"embed"
+	"errors"
 	"io"
+	"io/fs"
 	"reflect"
 	"slices"
 	"testing"
@@ -220,6 +222,15 @@ func TestOffset(t *testing.T) {
 		t.Fatal("Seek:", off)
 	}
 
+	// Use Seek with an invalid whence.
+	_, err = seeker.Seek(0, 3)
+	if err == nil {
+		t.Fatal("Seek: expected error for invalid whence")
+	}
+	if !errors.Is(err, fs.ErrInvalid) {
+		t.Fatalf("Seek: expected fs.ErrInvalid, got %v", err)
+	}
+
 	// Use ReadAt to read the entire file, ignoring the offset.
 	at := file.(io.ReaderAt)
 	got = make([]byte, len(want))

From a9f28f4f5cc28a5b662aa5452939c5c8e39ccbca Mon Sep 17 00:00:00 2001
From: TheRodzz <81969589+TheRodzz@users.noreply.github.com>
Date: Thu, 6 Aug 2026 11:35:32 +0530
Subject: [PATCH 2/2] embed: use io.Seek constants in Seek whence switch and
 tests

Use io.SeekStart, io.SeekCurrent, and io.SeekEnd constants in
openFile.Seek instead of raw numeric literals. Also update the invalid
whence test to use io.SeekEnd+5.
---
 src/embed/embed.go                         | 6 +++---
 src/embed/internal/embedtest/embed_test.go | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/embed/embed.go b/src/embed/embed.go
index d5d436d3ce0d0f..5b99c5e69a6526 100644
--- a/src/embed/embed.go
+++ b/src/embed/embed.go
@@ -359,11 +359,11 @@ func (f *openFile) Read(b []byte) (int, error) {
 
 func (f *openFile) Seek(offset int64, whence int) (int64, error) {
 	switch whence {
-	case 0:
+	case io.SeekStart:
 		// offset += 0
-	case 1:
+	case io.SeekCurrent:
 		offset += f.offset
-	case 2:
+	case io.SeekEnd:
 		offset += int64(len(f.f.data))
 	default:
 		return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid}
diff --git a/src/embed/internal/embedtest/embed_test.go b/src/embed/internal/embedtest/embed_test.go
index 2af4f7438a1668..3c69cce21f9059 100644
--- a/src/embed/internal/embedtest/embed_test.go
+++ b/src/embed/internal/embedtest/embed_test.go
@@ -223,7 +223,7 @@ func TestOffset(t *testing.T) {
 	}
 
 	// Use Seek with an invalid whence.
-	_, err = seeker.Seek(0, 3)
+	_, err = seeker.Seek(0, io.SeekEnd+5)
 	if err == nil {
 		t.Fatal("Seek: expected error for invalid whence")
 	}