fixes, meaningful error messages and new features

src/go-proxy/error.go

@@ -0,0 +1,194 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+)
+
+type NestedError struct {
+	subject string
+	message string
+	extras  []string
+	inner   *NestedError
+	level   int
+
+	sync.Mutex
+}
+
+type NestedErrorLike interface {
+	Error() string
+	Inner() NestedErrorLike
+	Level() int
+	HasInner() bool
+	HasExtras() bool
+
+	Extra(string) NestedErrorLike
+	Extraf(string, ...any) NestedErrorLike
+	ExtraError(error) NestedErrorLike
+	Subject(string) NestedErrorLike
+	Subjectf(string, ...any) NestedErrorLike
+	With(error) NestedErrorLike
+
+	addLevel(int) NestedErrorLike
+	copy() *NestedError
+}
+
+func NewNestedError(message string) NestedErrorLike {
+	return &NestedError{message: message, extras: make([]string, 0)}
+}
+
+func NewNestedErrorf(format string, args ...any) NestedErrorLike {
+	return NewNestedError(fmt.Sprintf(format, args...))
+}
+
+func NewNestedErrorFrom(err error) NestedErrorLike {
+	if err == nil {
+		panic("cannot convert nil error to NestedError")
+	}
+	return NewNestedError(err.Error())
+}
+
+func (ne *NestedError) Extra(s string) NestedErrorLike {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return ne
+	}
+	ne.Lock()
+	defer ne.Unlock()
+	ne.extras = append(ne.extras, s)
+	return ne
+}
+
+func (ne *NestedError) Extraf(format string, args ...any) NestedErrorLike {
+	return ne.Extra(fmt.Sprintf(format, args...))
+}
+
+func (ne *NestedError) ExtraError(e error) NestedErrorLike {
+	switch t := e.(type) {
+	case NestedErrorLike:
+		extra := t.copy()
+		extra.addLevel(ne.Level() + 1)
+		e = extra
+	}
+	return ne.Extra(e.Error())
+}
+
+func (ne *NestedError) Subject(s string) NestedErrorLike {
+	ne.subject = s
+	return ne
+}
+
+func (ne *NestedError) Subjectf(format string, args ...any) NestedErrorLike {
+	ne.subject = fmt.Sprintf(format, args...)
+	return ne
+}
+
+func (ne *NestedError) Inner() NestedErrorLike {
+	return ne.inner
+}
+
+func (ne *NestedError) Level() int {
+	return ne.level
+}
+
+func (ef *NestedError) Error() string {
+	var buf strings.Builder
+	ef.writeToSB(&buf, "")
+	return buf.String()
+}
+
+func (ef *NestedError) HasInner() bool {
+	return ef.inner != nil
+}
+
+func (ef *NestedError) HasExtras() bool {
+	return len(ef.extras) > 0
+}
+
+func (ef *NestedError) With(inner error) NestedErrorLike {
+	ef.Lock()
+	defer ef.Unlock()
+
+	var in *NestedError
+
+	switch t := inner.(type) {
+	case NestedErrorLike:
+		in = t.copy()
+	default:
+		in = &NestedError{extras: []string{t.Error()}}
+	}
+	if ef.inner == nil {
+		ef.inner = in
+	} else {
+		ef.inner.ExtraError(in)
+	}
+	root := ef
+	for root.inner != nil {
+		root.inner.level = root.level + 1
+		root = root.inner
+	}
+	return ef
+}
+
+func (ef *NestedError) addLevel(level int) NestedErrorLike {
+	ef.level += level
+	if ef.inner != nil {
+		ef.inner.addLevel(level)
+	}
+	return ef
+}
+
+func (ef *NestedError) copy() *NestedError {
+	var inner *NestedError
+	if ef.inner != nil {
+		inner = ef.inner.copy()
+	}
+	return &NestedError{
+		subject: ef.subject,
+		message: ef.message,
+		extras:  ef.extras,
+		inner:   inner,
+		level:   ef.level,
+	}
+}
+
+func (ef *NestedError) writeIndents(sb *strings.Builder, level int) {
+	for i := 0; i < level; i++ {
+		sb.WriteString("  ")
+	}
+}
+
+func (ef *NestedError) writeToSB(sb *strings.Builder, prefix string) {
+	ef.writeIndents(sb, ef.level)
+	sb.WriteString(prefix)
+
+	if ef.subject != "" {
+		sb.WriteRune('"')
+		sb.WriteString(ef.subject)
+		sb.WriteRune('"')
+		if ef.message != "" {
+			sb.WriteString(":\n")
+		} else {
+			sb.WriteRune('\n')
+		}
+	}
+	if ef.message != "" {
+		ef.writeIndents(sb, ef.level)
+		sb.WriteString(ef.message)
+		sb.WriteRune('\n')
+	}
+	for _, l := range ef.extras {
+		l = strings.TrimSpace(l)
+		if l == "" {
+			continue
+		}
+		ef.writeIndents(sb, ef.level)
+		sb.WriteString("- ")
+		sb.WriteString(l)
+		sb.WriteRune('\n')
+	}
+	if ef.inner != nil {
+		ef.inner.writeToSB(sb, "- ")
+	}
+}