replacer: {file.*} global placeholder strips trailing newline (#6411)

Co-authored-by: Kanashimia <chad@redpilled.dev>

caddytest/integration/testdata/foo_with_multiple_trailing_newlines.txt

@@ -0,0 +1,2 @@
+foo
+

caddytest/integration/testdata/foo_with_trailing_newline.txt

@@ -0,0 +1 @@
+foo

replacer.go

@@ -15,6 +15,7 @@
 package caddy
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"net/http"
@@ -354,6 +355,8 @@ func (f fileReplacementProvider) replace(key string) (any, bool) {
 			zap.Error(err))
 		return nil, true
 	}
+	body = bytes.TrimSuffix(body, []byte("\n"))
+	body = bytes.TrimSuffix(body, []byte("\r"))
 	return string(body), true
 }
 

replacer_test.go

@@ -431,6 +431,14 @@ func TestReplacerNew(t *testing.T) {
 			variable: "file.caddytest/integration/testdata/foo.txt",
 			value:    "foo",
 		},
+		{
+			variable: "file.caddytest/integration/testdata/foo_with_trailing_newline.txt",
+			value:    "foo",
+		},
+		{
+			variable: "file.caddytest/integration/testdata/foo_with_multiple_trailing_newlines.txt",
+			value:    "foo" + getEOL(),
+		},
 	} {
 		if val, ok := repl.providers[1].replace(tc.variable); ok {
 			if val != tc.value {
@@ -442,6 +450,13 @@ func TestReplacerNew(t *testing.T) {
 	}
 }
 
+func getEOL() string {
+	if os.PathSeparator == '\\' {
+		return "\r\n" // Windows EOL
+	}
+	return "\n" // Unix and modern macOS EOL
+}
+
 func TestReplacerNewWithoutFile(t *testing.T) {
 	repl := NewReplacer().WithoutFile()