fix: unescape quoted logfmt values (#4844)

Co-authored-by: Claude <noreply@anthropic.com>

internal/container/logfmt.go

@@ -2,6 +2,8 @@ package container
 
 import (
 	"errors"
+	"strconv"
+	"strings"
 
 	orderedmap "github.com/wk8/go-ordered-map/v2"
 )
@@ -36,7 +38,7 @@ func ParseLogFmt(log string) (*orderedmap.OrderedMap[string, string], error) {
 				} else if char == '\\' {
 					escaping = true
 				} else if char == '"' {
-					value = log[start:i]
+					value = unescapeQuoted(log[start-1 : i+1])
 					result.Set(key, value)
 					inQuotes = false
 					isKey = true
@@ -77,3 +79,19 @@ func ParseLogFmt(log string) (*orderedmap.OrderedMap[string, string], error) {
 
 	return result, nil
 }
+
+// unescapeQuoted decodes a quoted logfmt value (including the surrounding
+// quotes) so escape sequences like \" and \\ produced by logfmt encoders
+// (logrus, go-kit, go-logfmt) yield the original text instead of leaking
+// backslashes into the parsed value. If the sequence is not decodable, the
+// raw content between the quotes is returned unchanged.
+func unescapeQuoted(quoted string) string {
+	raw := quoted[1 : len(quoted)-1]
+	if !strings.ContainsRune(raw, '\\') {
+		return raw
+	}
+	if unquoted, err := strconv.Unquote(quoted); err == nil {
+		return unquoted
+	}
+	return raw
+}

internal/container/logfmt_test.go

@@ -67,6 +67,28 @@ func TestParseLog(t *testing.T) {
 			),
 			wantErr: false,
 		},
+		{
+			name: "Escaped quotes and backslashes in quoted values",
+			log:  `level=info msg="failed to open \"config.yml\"" path="C:\\temp"`,
+			want: orderedmap.New[string, string](
+				orderedmap.WithInitialData(
+					orderedmap.Pair[string, string]{Key: "level", Value: "info"},
+					orderedmap.Pair[string, string]{Key: "msg", Value: `failed to open "config.yml"`},
+					orderedmap.Pair[string, string]{Key: "path", Value: `C:\temp`},
+				),
+			),
+			wantErr: false,
+		},
+		{
+			name: "Quoted value with undecodable escape is kept as-is",
+			log:  `msg="foo \q bar"`,
+			want: orderedmap.New[string, string](
+				orderedmap.WithInitialData(
+					orderedmap.Pair[string, string]{Key: "msg", Value: `foo \q bar`},
+				),
+			),
+			wantErr: false,
+		},
 		{
 			name:    "Broken format with unexpected quotes",
 			log:     `key1=value"1"= key2="value2"`,