restructure package. Change label extraction strategy.

envelope.go

@@ -0,0 +1,77 @@
+// Package envelope provides types and functions for working with Nostr protocol
+// websocket messages. It defines the Envelope type representing a Nostr message
+// and offers utilities for creating, parsing, and validating standardized message
+// formats.
+package envelope
+
+// Envelope represents a Nostr websocket message.
+type Envelope []byte
+
+// GetLabel extracts the message label from an envelope.
+// Returns the label as a byte slice or an error if the envelope is malformed.
+func GetLabel(env Envelope) ([]byte, error) {
+	// begin walking byte slice
+	i, n := 0, len(env)
+
+	// skip whitespace before '['
+	for i < n && isSpace(env[i]) {
+		i++
+	}
+
+	// expect '['
+	if i >= n || env[i] != '[' {
+		return nil, ErrInvalidEnvelope
+	}
+	i++
+
+	// skip whitespace before '"'
+	for i < n && isSpace(env[i]) {
+		i++
+	}
+
+	// expect '"'
+	if i >= n || env[i] != '"' {
+		return nil, ErrInvalidEnvelope
+	}
+	i++
+
+	// scan label: [A-Z]+ terminated by '"'
+	start := i
+	for i < n && env[i] != '"' { // do until end or '"' is reached
+		if env[i] < 'A' || env[i] > 'Z' { // character is not [A-Z]
+			return nil, ErrInvalidEnvelope
+		}
+		i++
+	}
+
+	if i == n || i == start { // a label was not found in the previous loop
+		return nil, ErrInvalidEnvelope
+	}
+
+	return env[start:i], nil
+}
+
+func isSpace(b byte) bool {
+	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
+}
+
+// GetStandardLabels returns a set of standard Nostr websocket message labels
+func GetStandardLabels() map[string]struct{} {
+	return map[string]struct{}{
+		"EVENT":  {},
+		"REQ":    {},
+		"CLOSE":  {},
+		"CLOSED": {},
+		"EOSE":   {},
+		"NOTICE": {},
+		"OK":     {},
+		"AUTH":   {},
+	}
+}
+
+// IsStandardLabel checks if the given label is a standard Nostr websocket message label
+func IsStandardLabel(label string) bool {
+	labels := GetStandardLabels()
+	_, ok := labels[label]
+	return ok
+}