dbus: implement dbus_parse_address

This parses D-Bus addresses according to spec. It does significantly fewer copies than dbus_parse_address.

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 186 insertions, 0 deletions

diff --git a/dbus/address.go b/dbus/address.go
new file mode 100644
index 00000000..bec49e62
--- /dev/null
+++ b/dbus/address.go
@@ -0,0 +1,186 @@
+package dbus
+
+import (
+	"bytes"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"slices"
+)
+
+type AddrEntry struct {
+	Method string      `json:"method"`
+	Values [][2]string `json:"values"`
+}
+
+// Parse parses D-Bus address according to
+// https://dbus.freedesktop.org/doc/dbus-specification.html#addresses
+func Parse(addr []byte) ([]AddrEntry, error) {
+	// Look for a semicolon
+	address := bytes.Split(bytes.TrimSuffix(addr, []byte{';'}), []byte{';'})
+
+	// Allocate for entries
+	v := make([]AddrEntry, len(address))
+
+	for i, s := range address {
+		var pairs [][]byte
+
+		// Look for the colon :
+		if method, list, ok := bytes.Cut(s, []byte{':'}); !ok {
+			return v, &BadAddressError{ErrNoColon, i, s, -1, nil}
+		} else {
+			pairs = bytes.Split(list, []byte{','})
+			v[i].Method = string(method)
+			v[i].Values = make([][2]string, len(pairs))
+		}
+
+		for j, pair := range pairs {
+			key, value, ok := bytes.Cut(pair, []byte{'='})
+			if !ok {
+				return v, &BadAddressError{ErrBadPairSep, i, s, j, pair}
+			}
+			if len(key) == 0 {
+				return v, &BadAddressError{ErrBadPairKey, i, s, j, pair}
+			}
+			if len(value) == 0 {
+				return v, &BadAddressError{ErrBadPairVal, i, s, j, pair}
+			}
+			v[i].Values[j][0] = string(key)
+
+			if val, errno := unescapeValue(value); errno != errSuccess {
+				return v, &BadAddressError{errno, i, s, j, pair}
+			} else {
+				v[i].Values[j][1] = string(val)
+			}
+		}
+	}
+
+	return v, nil
+}
+
+func unescapeValue(v []byte) (val []byte, errno ParseError) {
+	if l := len(v) - (bytes.Count(v, []byte{'%'}) * 2); l < 0 {
+		errno = ErrBadValLength
+		return
+	} else {
+		val = make([]byte, l)
+	}
+
+	var i, skip int
+	for iu, b := range v {
+		if skip > 0 {
+			skip--
+			continue
+		}
+
+		if ib := bytes.IndexByte([]byte("-_/.\\*"), b); ib != -1 { // - // _/.\*
+			goto opt
+		} else if b >= '0' && b <= '9' { // 0-9
+			goto opt
+		} else if b >= 'A' && b <= 'Z' { // A-Z
+			goto opt
+		} else if b >= 'a' && b <= 'z' { // a-z
+			goto opt
+		}
+
+		if b != '%' {
+			errno = ErrBadValByte
+			break
+		}
+
+		skip += 2
+		if iu+2 >= len(v) {
+			errno = ErrBadValHexLength
+			break
+		}
+		if c, err := hex.Decode(val[i:i+1], v[iu+1:iu+3]); err != nil {
+			if errors.As(err, new(hex.InvalidByteError)) {
+				errno = ErrBadValHexByte
+				break
+			}
+			// unreachable
+			panic(err.Error())
+		} else if c != 1 {
+			// unreachable
+			panic(fmt.Sprintf("invalid decode length %d", c))
+		}
+		i++
+		continue
+
+	opt:
+		val[i] = b
+		i++
+	}
+
+	return
+}
+
+type ParseError uint8
+
+func (e ParseError) Error() string {
+	switch e {
+	case errSuccess:
+		panic("attempted to return success as error")
+	case ErrNoColon:
+		return "address does not contain a colon"
+	case ErrBadPairSep:
+		return "'=' character not found"
+	case ErrBadPairKey:
+		return "'=' character has no key preceding it"
+	case ErrBadPairVal:
+		return "'=' character has no value following it"
+	case ErrBadValLength:
+		return "unescaped value has impossible length"
+	case ErrBadValByte:
+		return "in D-Bus address, characters other than [-0-9A-Za-z_/.\\*] should have been escaped"
+	case ErrBadValHexLength:
+		return "in D-Bus address, percent character was not followed by two hex digits"
+	case ErrBadValHexByte:
+		return "in D-Bus address, percent character was followed by characters other than hex digits"
+
+	default:
+		return fmt.Sprintf("parse error %d", e)
+	}
+}
+
+const (
+	errSuccess ParseError = iota
+	ErrNoColon
+	ErrBadPairSep
+	ErrBadPairKey
+	ErrBadPairVal
+	ErrBadValLength
+	ErrBadValByte
+	ErrBadValHexLength
+	ErrBadValHexByte
+)
+
+type BadAddressError struct {
+	// error type
+	Type ParseError
+
+	// bad entry position
+	EntryPos int
+	// bad entry value
+	EntryVal []byte
+
+	// bad pair position
+	PairPos int
+	// bad pair value
+	PairVal []byte
+}
+
+func (a *BadAddressError) Is(err error) bool {
+	var b *BadAddressError
+	return errors.As(err, &b) && a.Type == b.Type &&
+		a.EntryPos == b.EntryPos && slices.Equal(a.EntryVal, b.EntryVal) &&
+		a.PairPos == b.PairPos && slices.Equal(a.PairVal, b.PairVal)
+}
+
+func (a *BadAddressError) Error() string {
+	return a.Type.Error()
+}
+
+func (a *BadAddressError) Unwrap() error {
+	return a.Type
+}