channelmsg/channelmsg.go

package channelmsg

import (
	"errors"
	"fmt"
	"log"
	"strings"
	"unicode"
)

var (
	ChannelMarkerPrefix        = "ch"
	LogDebugOutput             = false
	XmlAttributeEnclosingQuote = "\""
)

func TryLogDebugOutput(format string, v ...any) {
	if LogDebugOutput {
		log.Printf(format, v...)
	}
}

func StringHasAngleBrackets(s string) bool {
	return strings.HasPrefix(s, "<") && strings.HasSuffix(s, ">")
}

func StringHasMatchingEnclosingQuotes(s string) bool {
	return ((strings.HasPrefix(s, "'") && strings.HasSuffix(s, "'")) || (strings.HasPrefix(s, "\"") && strings.HasSuffix(s, "\"")))
}

type token struct {
	Dialect       string
	Channel       string
	Attributes    map[string]string
	Message       string
	ClosesMessage bool
	ClosesChannel bool
}

func newToken() token {
	return token{Attributes: make(map[string]string)}
}

var (
	ErrEmptyString     = errors.New("empty string is not a valid token")
	ErrNoAngleBrackets = errors.New("token does not have angle brackets")
	ErrMalformedToken  = errors.New("token is malformed")
)

func ContainsInvalidXmlElementNameChars(s string) bool {
	for _, r := range s {
		if !(unicode.IsLetter(r) || unicode.IsNumber(r) || r == '.' || r == '_' || r == '-') {
			return true
		}
	}
	return false
}

func IsValidXmlElementName(s string) bool {
	if len(s) == 0 || len(s) > 1024 || !(s[0] == '_' || unicode.IsLetter(rune(s[0]))) || strings.HasPrefix(strings.ToLower(s), "xml") {
		return false
	}
	return !ContainsInvalidXmlElementNameChars(s)
}

func parseToken(s string) (token, error) {
	results := newToken()
	if s = strings.TrimSpace(s); len(s) == 0 {
		return token{}, ErrEmptyString
	} else if !StringHasAngleBrackets(s) {
		return token{}, ErrNoAngleBrackets
	}
	s = strings.TrimSpace(s[1 : len(s)-1])
	if strings.HasPrefix(s, "/") {
		results.ClosesMessage = true
		s = strings.TrimSpace(s[1:])
	}
	if strings.HasSuffix(s, "/") {
		results.ClosesMessage = true
		results.ClosesChannel = true
		s = strings.TrimSpace(s[:len(s)-1])
	}
	// dialect
	fields := strings.Fields(s)
	if len(fields) == 0 {
		return token{}, fmt.Errorf("%w: empty after removing angle brackets", ErrMalformedToken)
	}
	field := fields[0]
	if !IsValidXmlElementName(field) {
		return token{}, fmt.Errorf("%w: invalid XmlElementName '%s'", ErrMalformedToken, field)
	}
	results.Dialect = fields[0]
	// parse attributes
	for position := 1; position < len(fields); position++ {
		field := fields[position]
		i := strings.Index(field, "=")
		if i == -1 {
			return token{}, fmt.Errorf("%w: malformed attribute %s found - missing delimiter '='", ErrMalformedToken, field)
		}
		key, value := strings.TrimSpace(field[:i]), strings.TrimSpace(field[i+1:])
		if !StringHasMatchingEnclosingQuotes(value) {
			for position = position + 1; position < len(fields) && !StringHasMatchingEnclosingQuotes(value); position++ {
				value = fmt.Sprintf("%s %s", value, fields[position])
			}
		}
		if !StringHasMatchingEnclosingQuotes(value) {
			return token{}, fmt.Errorf("%w: malformed attribute found - missing quotes", ErrMalformedToken)
		}
		value = strings.TrimSpace(value[1 : len(value)-1])
		if key == ChannelMarkerPrefix {
			results.Channel = value
		} else {
			results.Attributes[key] = value
		}

	}
	return results, nil

}

type Message struct {
	Dialect       string
	Channel       string
	Attributes    map[string]string
	Message       string
	ClosesChannel bool
}

func (m *Message) String() string {
	if m.Chatter() {
		return m.Message
	}
	var builder strings.Builder
	builder.WriteString(fmt.Sprintf("<%s", m.Dialect))
	if !m.Anonymous() {
		builder.WriteString(fmt.Sprintf(" %s=%s%s%s", ChannelMarkerPrefix, XmlAttributeEnclosingQuote, m.Channel, XmlAttributeEnclosingQuote))
	}
	for k, v := range m.Attributes {
		builder.WriteString(fmt.Sprintf(" %s=%s%s%s", k, XmlAttributeEnclosingQuote, v, XmlAttributeEnclosingQuote))
	}
	if m.ClosesChannel {
		if len(m.Message) > 0 {
			panic("channelmsg.go Message::String error: cannot close the channel and send a message at the same time")
		}
		builder.WriteString(" />")
		return builder.String()
	}
	builder.WriteString(fmt.Sprintf(">%s</%s>", m.Message, m.Dialect))
	return builder.String()
}

func (m *Message) IsEqual(rhs Message) bool {
	attributesMatch := func() bool {
		if want, got := len(m.Attributes), len(rhs.Attributes); want != got {
			return false
		}
		for k, v := range m.Attributes {
			if want, got := v, rhs.Attributes[k]; want != got {
				return false
			}
		}
		return true
	}
	return (m.Dialect == rhs.Dialect &&
		m.Channel == rhs.Channel &&
		m.Message == rhs.Message &&
		m.ClosesChannel == rhs.ClosesChannel &&
		attributesMatch())
}

func (m *Message) Anonymous() bool {
	return len(m.Channel) == 0
}

func (m *Message) Chatter() bool {
	return m.Anonymous() && len(m.Dialect) == 0
}

func New() Message {
	return Message{Attributes: make(map[string]string)}
}

func Parse(s string) Message {
	results := New()
	if s = strings.TrimSpace(s); len(s) == 0 {
		TryLogDebugOutput("channelmsg.go Parse error: empty string\n")
		return results
	} else if !StringHasAngleBrackets(s) {
		TryLogDebugOutput("channelmsg.go Parse error: missing enclosing angle brackets\n")
		results.Message = s
		return results
	}

	// could be a valid channelmsg
	headerEnd := strings.Index(s, ">")
	headerToken, err := parseToken(s[:headerEnd+1])
	if err != nil {
		TryLogDebugOutput("channelmsg.go Parse error parsing headerToken: %v\n", err)
		results.Message = s
		return results
	}
	if headerEnd == len(s)-1 {
		if !headerToken.ClosesMessage {
			TryLogDebugOutput("channelmsg.go Parse error: single-token message did not close the message/channel\n")
			results.Message = s
			return results
		}
		results.Dialect = headerToken.Dialect
		results.Channel = headerToken.Channel
		results.ClosesChannel = headerToken.ClosesChannel
		results.Message = headerToken.Message
		results.Attributes = headerToken.Attributes
		return results
	}
	// parse the footer token
	footerStart := strings.LastIndex(s, "<")
	if footerStart <= 0 {
		TryLogDebugOutput("channelmsg.go Parse error: cannot find footerToken start\n")
		results.Message = s
		return results
	}
	footerToken, err := parseToken(s[footerStart:])
	if err != nil || footerToken.Dialect != headerToken.Dialect || !footerToken.ClosesMessage || len(footerToken.Attributes) > 0 {
		TryLogDebugOutput("channelmsg.go Parse error: footerToken %+v malformed\n", footerToken)
		results.Message = s
		return results
	}
	// cool.
	results.Dialect = headerToken.Dialect
	results.Channel = headerToken.Channel
	results.ClosesChannel = footerToken.ClosesChannel
	results.Message = footerToken.Message
	results.Attributes = headerToken.Attributes
	results.Message = strings.TrimSpace(s[headerEnd+1 : footerStart])
	return results
}