add NOTICE and OK envelope encoders with marshal/unmarshal support and comprehensive tests

pkg/encoders/envelopes/messages/messages.go

@@ -0,0 +1,54 @@
+// Package messages is a collection of example/common messages and
+// machine-readable prefixes to use with OK and CLOSED envelopes.
+package messages
+
+import (
+	"lukechampine.com/frand"
+)
+
+const (
+	// Duplicate is a machine readable prefix for OK envelopes indicating that the
+	// submitted event is already in the relay,s event store.
+	Duplicate = "duplicate"
+
+	// Pow is a machine readable prefix for OK envelopes indicating that the
+	// eventid.T lacks sufficient zeros at the front.
+	Pow = "pow"
+
+	// Blocked is a machine readable prefix for OK envelopes indicating the event
+	// submission or REQ has been rejected.
+	Blocked = "blocked"
+
+	// RateLimited is a machine readable prefix for CLOSED and OK envelopes
+	// indicating the relay is now slowing down processing of requests from the
+	// client.
+	RateLimited = "rate-limited"
+
+	// Invalid is a machine readable prefix for OK envelopes indicating
+	// that the submitted event or other request is not correctly formatted, and may
+	// mean a signature does not verify.
+	Invalid = "invalid"
+
+	// Error is a machine readable prefix for CLOSED and OK envelopes indicating
+	// there was some kind of error in processing the request.
+	Error = "error"
+)
+
+// Examples are some examples of the use of the prefixes above with appropriate
+// human-readable suffixes.
+var Examples = [][]byte{
+	[]byte("pow: difficulty 25>=24"),
+	[]byte("duplicate: already have this event"),
+	[]byte("blocked: you are banned from posting here"),
+	[]byte("blocked: please register your pubkey at " +
+		"https://my-expensive-relay.example.com"),
+	[]byte("rate-limited: slow down there chief"),
+	[]byte("invalid: event creation date is too far off from the current time"),
+	[]byte("pow: difficulty 26 is less than 30"),
+	[]byte("error: could not connect to the database"),
+}
+
+// RandomMessage generates a random message out of the above list of Examples.
+func RandomMessage() []byte {
+	return Examples[frand.Intn(len(Examples)-1)]
+}