Clean up req and xreq. Add common errors package.

The goal here is to clean up these protocol packages a bit,
so they use more common names.  Also, we're now exporting a
NewProtocol() and Info() fields, which should make using these
in other packages easier.

errors.go

@@ -15,34 +15,32 @@
 package mangos
 
 import (
-	"errors"
+	"nanomsg.org/go/mangos/v2/errors"
 )
 
 // Various error codes.
-var (
-	ErrBadAddr     = errors.New("invalid address")
-	ErrBadHeader   = errors.New("invalid header received")
-	ErrBadVersion  = errors.New("invalid protocol version")
-	ErrTooShort    = errors.New("message is too short")
-	ErrTooLong     = errors.New("message is too long")
-	ErrClosed      = errors.New("connection closed")
-	ErrConnRefused = errors.New("connection refused")
-	ErrSendTimeout = errors.New("send time out")
-	ErrRecvTimeout = errors.New("receive time out")
-	ErrProtoState  = errors.New("incorrect protocol state")
-	ErrProtoOp     = errors.New("invalid operation for protocol")
-	ErrBadTran     = errors.New("invalid or unsupported transport")
-	ErrBadProto    = errors.New("invalid or unsupported protocol")
-	ErrPipeFull    = errors.New("pipe full")
-	ErrPipeEmpty   = errors.New("pipe empty")
-	ErrBadOption   = errors.New("invalid or unsupported option")
-	ErrBadValue    = errors.New("invalid option value")
-	ErrGarbled     = errors.New("message garbled")
-	ErrAddrInUse   = errors.New("address in use")
-	ErrBadProperty = errors.New("invalid property name")
-	ErrTLSNoConfig = errors.New("missing TLS configuration")
-	ErrTLSNoCert   = errors.New("missing TLS certificates")
-	ErrNotRaw      = errors.New("socket not raw")
-	ErrCanceled    = errors.New("operation canceled")
-	ErrNoContext   = errors.New("protocol does not support contexts")
+const (
+	ErrBadAddr     = errors.ErrBadAddr
+	ErrBadHeader   = errors.ErrBadHeader
+	ErrBadVersion  = errors.ErrBadVersion
+	ErrTooShort    = errors.ErrTooShort
+	ErrTooLong     = errors.ErrTooLong
+	ErrClosed      = errors.ErrClosed
+	ErrConnRefused = errors.ErrConnRefused
+	ErrSendTimeout = errors.ErrSendTimeout
+	ErrRecvTimeout = errors.ErrRecvTimeout
+	ErrProtoState  = errors.ErrProtoState
+	ErrProtoOp     = errors.ErrProtoOp
+	ErrBadTran     = errors.ErrBadTran
+	ErrBadProto    = errors.ErrBadProto
+	ErrBadOption   = errors.ErrBadOption
+	ErrBadValue    = errors.ErrBadValue
+	ErrGarbled     = errors.ErrGarbled
+	ErrAddrInUse   = errors.ErrAddrInUse
+	ErrBadProperty = errors.ErrBadProperty
+	ErrTLSNoConfig = errors.ErrTLSNoConfig
+	ErrTLSNoCert   = errors.ErrTLSNoCert
+	ErrNotRaw      = errors.ErrNotRaw
+	ErrCanceled    = errors.ErrCanceled
+	ErrNoContext   = errors.ErrNoContext
 )

errors/errors.go

@@ -0,0 +1,52 @@
+// Copyright 2018 The Mangos Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use file except in compliance with the License.
+// You may obtain a copy of the license at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package errors just defines some constant error codes, and is intended
+// to be directly imported.  It is safe to import using ".", so that
+// short names can be used without concern about unrelated namespace
+// pollution.
+package errors
+
+type err string
+
+func (e err) Error() string {
+	return string(e)
+}
+
+// Predefined error values.
+const (
+	ErrBadAddr     = err("invalid address")
+	ErrBadHeader   = err("invalid header received")
+	ErrBadVersion  = err("invalid protocol version")
+	ErrTooShort    = err("message is too short")
+	ErrTooLong     = err("message is too long")
+	ErrClosed      = err("object closed")
+	ErrConnRefused = err("connection refused")
+	ErrSendTimeout = err("send time out")
+	ErrRecvTimeout = err("receive time out")
+	ErrProtoState  = err("incorrect protocol state")
+	ErrProtoOp     = err("invalid operation for protocol")
+	ErrBadTran     = err("invalid or unsupported transport")
+	ErrBadProto    = err("invalid or unsupported protocol")
+	ErrBadOption   = err("invalid or unsupported option")
+	ErrBadValue    = err("invalid option value")
+	ErrGarbled     = err("message garbled")
+	ErrAddrInUse   = err("address in use")
+	ErrBadProperty = err("invalid property name")
+	ErrTLSNoConfig = err("missing TLS configuration")
+	ErrTLSNoCert   = err("missing TLS certificates")
+	ErrNotRaw      = err("socket not raw")
+	ErrCanceled    = err("operation canceled")
+	ErrNoContext   = err("protocol does not support contexts")
+)