package gomatrix import ( "bytes" "encoding/hex" "fmt" ) const lowerhex = "0123456789abcdef" // encode the given byte using quoted-printable encoding (e.g "=2f") // and writes it to the buffer // See https://golang.org/src/mime/quotedprintable/writer.go func encode(buf *bytes.Buffer, b byte) { buf.WriteByte('=') buf.WriteByte(lowerhex[b>>4]) buf.WriteByte(lowerhex[b&0x0f]) } // escape the given alpha character and writes it to the buffer func escape(buf *bytes.Buffer, b byte) { buf.WriteByte('_') if b == '_' { buf.WriteByte('_') // another _ } else { buf.WriteByte(b + 0x20) // ASCII shift A-Z to a-z } } func shouldEncode(b byte) bool { return b != '-' && b != '.' && b != '_' && !(b >= '0' && b <= '9') && !(b >= 'a' && b <= 'z') && !(b >= 'A' && b <= 'Z') } func shouldEscape(b byte) bool { return (b >= 'A' && b <= 'Z') || b == '_' } func isValidByte(b byte) bool { return isValidEscapedChar(b) || (b >= '0' && b <= '9') || b == '.' || b == '=' || b == '-' } func isValidEscapedChar(b byte) bool { return b == '_' || (b >= 'a' && b <= 'z') } // EncodeUserLocalpart encodes the given string into Matrix-compliant user ID localpart form. // // This returns a string with only the characters "a-z0-9._=-". The uppercase range A-Z // are encoded using leading underscores ("_"). Characters outside the aforementioned ranges // (including literal underscores ("_") and equals ("=")) are encoded as UTF8 code points (NOT NCRs) // and converted to lower-case hex with a leading "=". For example: // Alph@Bet_50up => _alph=40_bet=5f50up func EncodeUserLocalpart(str string) string { strBytes := []byte(str) var outputBuffer bytes.Buffer for _, b := range strBytes { if shouldEncode(b) { encode(&outputBuffer, b) } else if shouldEscape(b) { escape(&outputBuffer, b) } else { outputBuffer.WriteByte(b) } } return outputBuffer.String() } // DecodeUserLocalpart decodes the given string back into the original input string. // Returns an error if the given string is not a valid user ID localpart encoding. // // This decodes quoted-printable bytes back into UTF8, and unescapes casing. For // example: // _alph=40_bet=5f50up => Alph@Bet_50up // Returns an error if the input string contains characters outside the // range "a-z0-9._=-", has an invalid quote-printable byte (e.g. not hex), or has // an invalid _ escaped byte (e.g. "_5"). func DecodeUserLocalpart(str string) (string, error) { strBytes := []byte(str) var outputBuffer bytes.Buffer for i := 0; i < len(strBytes); i++ { b := strBytes[i] if !isValidByte(b) { return "", fmt.Errorf("Byte pos %d: Invalid byte", i) } if b == '_' { // next byte is a-z and should be upper-case or is another _ and should be a literal _ if i+1 >= len(strBytes) { return "", fmt.Errorf("Byte pos %d: expected _[a-z_] encoding but ran out of string", i) } if !isValidEscapedChar(strBytes[i+1]) { // invalid escaping return "", fmt.Errorf("Byte pos %d: expected _[a-z_] encoding", i) } if strBytes[i+1] == '_' { outputBuffer.WriteByte('_') } else { outputBuffer.WriteByte(strBytes[i+1] - 0x20) // ASCII shift a-z to A-Z } i++ // skip next byte since we just handled it } else if b == '=' { // next 2 bytes are hex and should be buffered ready to be read as utf8 if i+2 >= len(strBytes) { return "", fmt.Errorf("Byte pos: %d: expected quote-printable encoding but ran out of string", i) } dst := make([]byte, 1) _, err := hex.Decode(dst, strBytes[i+1:i+3]) if err != nil { return "", err } outputBuffer.WriteByte(dst[0]) i += 2 // skip next 2 bytes since we just handled it } else { // pass through outputBuffer.WriteByte(b) } } return outputBuffer.String(), nil }