init

bbs-go/server/cmd/test/main.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"fmt"
+	"log/slog"
+	"os"
+	"runtime"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+func main() {
+	handler := slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{
+		ReplaceAttr: replaceAttr,
+		AddSource:   true,
+	})
+
+	slog.SetDefault(slog.New(handler))
+
+	if err := f(); err != nil {
+		slog.Info("something went wrong", slog.Any("err", err))
+	}
+}
+
+func f() error {
+	return g()
+}
+
+func g() error {
+	return errors.New("test error")
+}
+
+func replaceAttr(groups []string, a slog.Attr) slog.Attr {
+	switch a.Value.Kind() {
+	// other cases
+
+	case slog.KindAny:
+		switch v := a.Value.Any().(type) {
+		case error:
+			a.Value = fmtErr(v)
+		}
+	}
+
+	return a
+}
+
+// fmtErr returns a slog.GroupValue with keys "msg" and "trace". If the error
+// does not implement interface { StackTrace() errors.StackTrace }, the "trace"
+// key is omitted.
+func fmtErr(err error) slog.Value {
+	var groupValues []slog.Attr
+
+	groupValues = append(groupValues, slog.String("msg", err.Error()))
+
+	type StackTracer interface {
+		StackTrace() errors.StackTrace
+	}
+
+	// Find the trace to the location of the first errors.New,
+	// errors.Wrap, or errors.WithStack call.
+	var st StackTracer
+	for err := err; err != nil; err = errors.Unwrap(err) {
+		if x, ok := err.(StackTracer); ok {
+			st = x
+		}
+	}
+
+	if st != nil {
+		groupValues = append(groupValues,
+			slog.Any("trace", traceLines(st.StackTrace())),
+		)
+	}
+
+	return slog.GroupValue(groupValues...)
+}
+
+func traceLines(frames errors.StackTrace) []string {
+	traceLines := make([]string, len(frames))
+
+	// Iterate in reverse to skip uninteresting, consecutive runtime frames at
+	// the bottom of the trace.
+	var skipped int
+	skipping := true
+	for i := len(frames) - 1; i >= 0; i-- {
+		// Adapted from errors.Frame.MarshalText(), but avoiding repeated
+		// calls to FuncForPC and FileLine.
+		pc := uintptr(frames[i]) - 1
+		fn := runtime.FuncForPC(pc)
+		if fn == nil {
+			traceLines[i] = "unknown"
+			skipping = false
+			continue
+		}
+
+		name := fn.Name()
+
+		if skipping && strings.HasPrefix(name, "runtime.") {
+			skipped++
+			continue
+		} else {
+			skipping = false
+		}
+
+		filename, lineNr := fn.FileLine(pc)
+
+		traceLines[i] = fmt.Sprintf("%s %s:%d", name, filename, lineNr)
+	}
+
+	return traceLines[:len(traceLines)-skipped]
+}