1 files changed, 365 insertions, 0 deletions
diff --git a/header.go b/header.go
new file mode 100644
index 0000000..e185dca
--- /dev/null
+++ b/header.go
@@ -0,0 +1,365 @@
+package cnp
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"sort"
+	"strconv"
+)
+
+const (
+	// IntentOK represents the "ok" response intent.
+	IntentOK = "ok"
+	// IntentNotModified represents the "not_modified" response intent.
+	IntentNotModified = "not_modified"
+	// IntentError represents the "error" response intent.
+	IntentError = "error"
+	// IntentRedirect represents the "redirect" response intent.
+	IntentRedirect = "redirect"
+)
+
+// Header represents a CNP message header
+type Header struct {
+	// VersionMajor is the major CNP version given in the header.
+	VersionMajor int
+	// VersionMinor is the minor CNP version given in the header.
+	VersionMinor int
+	// Intent is the intent string of the message.
+	Intent string
+	// Parameters is a decoded map of the message parameters.
+	Parameters Parameters
+}
+
+// NewHeader creates a new CNP header from an intent and optional parameter
+// map.
+func NewHeader(intent string, params Parameters) Header {
+	if params == nil {
+		params = make(Parameters)
+	}
+	return Header{
+		VersionMajor: VersionMajor,
+		VersionMinor: VersionMinor,
+		Intent:       intent,
+		Parameters:   params,
+	}
+}
+
+// ParseHeader parses a CNP header from a bytestring.
+// The line parameter must be a single line that ends with a line feed.
+func ParseHeader(line []byte) (h Header, err error) {
+	if bytes.IndexByte(line, '\x00') >= 0 {
+		err = ErrorSyntax{"invalid header: NUL byte"}
+		return
+	}
+
+	if !bytes.HasPrefix(line, []byte("cnp/")) {
+		err = ErrorSyntax{"invalid header: no version string"}
+		return
+	}
+	line = line[len("cnp/"):]
+
+	var o int
+
+	h.VersionMajor, o, err = parseHeaderNumber(line)
+	if err != nil {
+		return
+	}
+	line = line[o:]
+
+	if len(line) == 0 || line[0] != '.' {
+		err = ErrorSyntax{"invalid header: invalid version number tuple"}
+		return
+	}
+	line = line[1:]
+	h.VersionMinor, o, err = parseHeaderNumber(line)
+	if err != nil {
+		return
+	}
+	line = line[o:]
+
+	if len(line) == 0 || line[0] != ' ' {
+		err = ErrorSyntax{"invalid header: expected a space"}
+		return
+	}
+	line = line[1:]
+
+	h.Intent, o, err = parseHeaderIntent(line)
+	if err != nil {
+		return
+	}
+	line = line[o:]
+
+	h.Parameters, o, err = parseHeaderParameters(line)
+	if err != nil {
+		return
+	}
+	line = line[o:]
+
+	if len(line) != 1 || line[0] != '\n' {
+		err = ErrorSyntax{"invalid header: expected line feed and end"}
+		return
+	}
+
+	return
+}
+
+func parseHeaderNumber(line []byte) (n int, length int, err error) {
+	i := 0
+	for ; i < len(line); i++ {
+		b := line[i]
+		if '0' <= b && b <= '9' {
+		} else {
+			break
+		}
+	}
+	n, err = strconv.Atoi(string(line[:i]))
+	if err != nil || (i > 1 && line[0] == '0') {
+		err = ErrorSyntax{"invalid header: invalid version number format"}
+		return
+	}
+	length = i
+	return
+}
+
+func parseHeaderIntent(line []byte) (intent string, length int, err error) {
+	p := bytes.IndexAny(line, " \n=\x00")
+	if p < 0 {
+		p = len(line) - 1
+	}
+	if p == 0 {
+		err = ErrorSyntax{"invalid header: empty intent"}
+		return
+	}
+	intent, err = Unescape(line[:p])
+	length = p
+	return
+}
+
+func parseHeaderParameters(line []byte) (params Parameters, length int, err error) {
+	params = make(Parameters)
+
+	for len(line) > 1 {
+		if line[0] == '\n' {
+			break
+		} else if line[0] != ' ' {
+			err = ErrorSyntax{"invalid header: expected a space"}
+			return
+		}
+		line = line[1:]
+		length++
+
+		var k, v string
+		var o int
+		k, v, o, err = parseHeaderParameter(line)
+		if err != nil {
+			return
+		}
+		if _, ok := params[k]; ok {
+			err = ErrorSyntax{"invalid header: duplicate parameter"}
+			return
+		}
+		params[k] = v
+		line = line[o:]
+		length += o
+	}
+
+	return
+}
+
+func parseHeaderParameter(line []byte) (key, value string, length int, err error) {
+	var o int
+	key, o, err = parseHeaderParamString(line)
+	if err != nil {
+		return
+	}
+	line = line[o:]
+	length += o
+
+	if len(line) == 0 || line[0] != '=' {
+		err = ErrorSyntax{"invalid header: expected an equals sign"}
+		return
+	}
+	line = line[1:]
+	length++
+
+	value, o, err = parseHeaderParamString(line)
+	if err != nil {
+		return
+	}
+	length += o
+
+	return
+}
+
+func parseHeaderParamString(line []byte) (s string, length int, err error) {
+	for ; length < len(line); length++ {
+		b := line[length]
+		if b == '\n' || b == ' ' || b == '=' {
+			break
+		}
+	}
+	s, err = Unescape(line[:length])
+	return
+}
+
+// Version returns the message's CNP version as a "cnp/X.Y" string.
+func (h Header) Version() string {
+	return "cnp/" + strconv.Itoa(h.VersionMajor) + "." + strconv.Itoa(h.VersionMinor)
+}
+
+// Write writes the CNP message header line in the wire format.
+// The written line ends with a line feed.
+func (h Header) Write(w io.Writer) (err error) {
+	bw := bufio.NewWriter(w)
+	_, err = bw.WriteString(h.Version())
+	if err != nil {
+		return
+	}
+	err = bw.WriteByte(' ')
+	if err != nil {
+		return
+	}
+	_, err = bw.Write(Escape(h.Intent))
+	if err != nil {
+		return
+	}
+	err = h.Parameters.Write(bw)
+	if err != nil {
+		return
+	}
+	err = bw.WriteByte('\n')
+	if err != nil {
+		return
+	}
+	return bw.Flush()
+}
+
+func (h Header) String() string {
+	var buf bytes.Buffer
+	_ = h.Write(&buf)
+	return buf.String()
+}
+
+// Parameters represents CNP message parameter key=value pairs.
+type Parameters map[string]string
+
+// Write writes the parameters encoded for inclusion in the wire format.
+// Includes a leading space.
+func (p Parameters) Write(w io.Writer) (err error) {
+	bw := bufio.NewWriter(w)
+	keys := []string{}
+	for k := range p {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, k := range keys {
+		err = bw.WriteByte(' ')
+		if err != nil {
+			return
+		}
+		_, err = bw.Write(Escape(k))
+		if err != nil {
+			return
+		}
+		err = bw.WriteByte('=')
+		if err != nil {
+			return
+		}
+		_, err = bw.Write(Escape(p[k]))
+		if err != nil {
+			return
+		}
+	}
+	return
+}
+
+// Escape CNP-escapes the bytestring s.
+func Escape(s string) []byte {
+	el := escapeLength(s)
+	if el == len(s) {
+		return []byte(s)
+	}
+	bs := make([]byte, el)
+	bi := 0
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '\x00':
+			bs[bi] = '\\'
+			bs[bi+1] = '0'
+			bi += 2
+
+		case '\n':
+			bs[bi] = '\\'
+			bs[bi+1] = 'n'
+			bi += 2
+
+		case ' ':
+			bs[bi] = '\\'
+			bs[bi+1] = '_'
+			bi += 2
+
+		case '=':
+			bs[bi] = '\\'
+			bs[bi+1] = '-'
+			bi += 2
+
+		case '\\':
+			bs[bi] = '\\'
+			bs[bi+1] = '\\'
+			bi += 2
+
+		default:
+			bs[bi] = s[i]
+			bi++
+		}
+	}
+	return bs
+}
+
+func escapeLength(s string) (l int) {
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '\x00', '\n', ' ', '=', '\\':
+			l += 2
+		default:
+			l++
+		}
+	}
+	return
+}
+
+// Unescape unescapes the bs from wire format into a bytestring.
+func Unescape(bs []byte) (string, error) {
+	buf := make([]byte, len(bs))
+	bi := 0
+
+	for i := 0; i < len(bs); i++ {
+		switch bs[i] {
+		case '\\':
+			i++
+			if i >= len(bs) {
+				return string(buf[:bi]), ErrorSyntax{"invalid escape sequence: unexpected end of string"}
+			}
+			switch bs[i] {
+			case '0':
+				buf[bi] = '\x00'
+			case 'n':
+				buf[bi] = '\n'
+			case '_':
+				buf[bi] = ' '
+			case '-':
+				buf[bi] = '='
+			case '\\':
+				buf[bi] = '\\'
+			default:
+				return string(buf[:bi]), ErrorSyntax{"invalid escape sequence: undefined sequence"}
+			}
+		default:
+			buf[bi] = bs[i]
+		}
+		bi++
+	}
+
+	return string(buf[:bi]), nil
+}