Merge pull request 'Emit slog attributes from every handler' (#21) from fix/handler-attrs into main

Reviewed-on: #21

TODO.md

@@ -27,7 +27,8 @@ files it depends on: .golangci.yml, REPO_POLICIES.md, .editorconfig,
 * 2026-08-10: fixed every handler discarding slog attributes: console,
     JSON and webhook handlers now emit record attributes, accumulate
     WithAttrs without mutating the receiver, and honour WithGroup;
-    slog.Group values nest and LogValuer values are resolved
+    slog.Group values nest and LogValuer values are resolved; console
+    keys and values holding invalid UTF-8 are quoted
 * 2026-08-07: added canonical `.golangci.yml` (v2 schema), pinned the
     `Dockerfile` lint stage to golangci-lint v2.12.2 (tag+digest), and
     fixed all findings the v1→v2 jump surfaced without changing any

attrs.go

@@ -6,6 +6,7 @@ import (
 	"strconv"
 	"strings"
 	"unicode"
+	"unicode/utf8"
 )
 
 // handlerAttrs is the attribute state every handler carries: the attributes
@@ -262,16 +263,20 @@ func appendAttrText(out *strings.Builder, prefix string, attr slog.Attr) {
 	out.WriteString(quoteIfNeeded(value.String()))
 }
 
-// quoteIfNeeded quotes a key or a value only when leaving it bare would make
+// quoteIfNeeded quotes a key or a value, as slog.NewTextHandler does, when
-// the key=value pairs ambiguous, matching how the stdlib text handler reads.
+// leaving it bare would make the key=value pairs ambiguous or would write a
+// control character or invalid UTF-8 to the terminal. Unlike the stdlib, it
+// also quotes DEL (0x7f), which is a control character too.
 func quoteIfNeeded(text string) string {
 	if text == "" {
 		return `""`
 	}
 
+	// Ranging over a string yields utf8.RuneError for each invalid byte;
+	// strconv.Quote then escapes that byte, as in "bad\xffkey".
 	for _, r := range text {
 		if unicode.IsSpace(r) || !unicode.IsPrint(r) ||
-			r == '"' || r == '=' {
+			r == utf8.RuneError || r == '"' || r == '=' {
 			return strconv.Quote(text)
 		}
 	}

attrs_test.go

@@ -400,6 +400,27 @@ func TestConsoleHandlerQuotesKeysNeedingIt(t *testing.T) {
 	}
 }
 
+// TestConsoleHandlerQuotesInvalidUTF8 checks that a key or a value holding
+// invalid UTF-8 is quoted with the bad byte escaped, as slog.NewTextHandler
+// does, so the raw byte never reaches the terminal. Valid non-ASCII stays bare.
+func TestConsoleHandlerQuotesInvalidUTF8(t *testing.T) {
+	output := captureStdout(t, func() {
+		handler := simplelog.NewConsoleHandler()
+		record := testRecord(
+			"casting",
+			slog.String("bad\xffkey", "v"),
+			slog.String("raw", "bad\xffvalue"),
+			slog.String("title", "Amélie"),
+		)
+		handle(t, handler, record)
+	})
+
+	wantContains(t, output, ` "bad\xffkey"=v`)
+	wantContains(t, output, ` raw="bad\xffvalue"`)
+	wantContains(t, output, " title=Amélie")
+	wantNotContains(t, output, "\xff")
+}
+
 func TestConsoleHandlerWithAttrsAccumulates(t *testing.T) {
 	output := captureStdout(t, func() {
 		handler := simplelog.NewConsoleHandler().