channel: Remove the Sender and Receiver types.

The distinction between sender and receiver is not carrying its weight in the
public API for this package. Move unexported safety-check wrappers into the
top-level package and collapse the methods back into the Channel type.

base.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/creachadair/jrpc2/channel"
 	"github.com/creachadair/jrpc2/code"
 )
 
@@ -389,8 +388,14 @@ func fixID(id json.RawMessage) json.RawMessage {
 	return nil
 }
 
+// sender is the subset of channel.Channel needed to send messages.
+type sender interface{ Send([]byte) error }
+
+// receiver is the subset of channel.Channel needed to receive messages.
+type receiver interface{ Recv() ([]byte, error) }
+
 // encode marshals rsps as JSON and forwards it to the channel.
-func encode(ch channel.Sender, rsps jmessages) (int, error) {
+func encode(ch sender, rsps jmessages) (int, error) {
 	bits, err := rsps.toJSON()
 	if err != nil {
 		return 0, err

channel/channel_test.go

@@ -20,7 +20,7 @@ func newPipe(framing Framing) (client, server Channel) {
 	return
 }
 
-func testSendRecv(t *testing.T, s Sender, r Receiver, msg string) {
+func testSendRecv(t *testing.T, s, r Channel, msg string) {
 	var wg sync.WaitGroup
 	var sendErr, recvErr error
 	var data []byte

channel/doc.go

@@ -33,30 +33,21 @@ package channel
 
 import "strings"
 
-// A Sender represents the ability to transmit a message on a channel.
-type Sender interface {
+// A Channel represents the ability to transmit and receive data records.  A
+// channel does not interpret the contents of a record, but may add and remove
+// framing so that records can be embedded in higher-level protocols.
+//
+// One sender and one receiver may use a Channel concurrently, but the methods
+// of a Channel are not otherwise required to be safe for concurrent use.
+type Channel interface {
 	// Send transmits a record on the channel. Each call to Send transmits one
 	// complete record.
 	Send([]byte) error
-}
 
-// A Receiver represents the ability to receive a message from a channel.
-type Receiver interface {
 	// Recv returns the next available record from the channel.  If no further
 	// messages are available, it returns nil, io.EOF.  Each call to Recv
 	// fetches a single complete record.
 	Recv() ([]byte, error)
-}
-
-// A Channel represents the ability to transmit and receive data records.  A
-// channel does not interpret the contents of a record, but may add and remove
-// framing so that records can be embedded in higher-level protocols.
-//
-// One sender and one receiver may use a Channel concurrently, but the methods
-// of a Channel are not otherwise required to be safe for concurrent use.
-type Channel interface {
-	Sender
-	Receiver
 
 	// Close shuts down the channel, after which no further records may be
 	// sent or received.

client.go

@@ -69,7 +69,7 @@ func NewClient(ch channel.Channel, opts *ClientOptions) *Client {
 // accept receives the next batch of responses from the server.  This may
 // either be a list or a single object, the decoder for jmessages knows how to
 // handle both. The caller must not hold c.mu.
-func (c *Client) accept(ch channel.Receiver) error {
+func (c *Client) accept(ch receiver) error {
 	var in jmessages
 	bits, err := ch.Recv()
 	if err == nil {

server.go

@@ -200,7 +200,7 @@ func (s *Server) waitForBarrier(n int) {
 // completed, to ensure that notifications are processed in a partial order
 // that respects order of receipt. Notifications within a batch are handled
 // concurrently.
-func (s *Server) dispatch(next jmessages, ch channel.Sender) func() error {
+func (s *Server) dispatch(next jmessages, ch sender) func() error {
 	// Resolve all the task handlers or record errors.
 	start := time.Now()
 	tasks := s.checkAndAssign(next)
@@ -240,7 +240,7 @@ func (s *Server) dispatch(next jmessages, ch channel.Sender) func() error {
 
 // deliver cleans up completed responses and arranges their replies (if any) to
 // be sent back to the client.
-func (s *Server) deliver(rsps jmessages, ch channel.Sender, elapsed time.Duration) error {
+func (s *Server) deliver(rsps jmessages, ch sender, elapsed time.Duration) error {
 	if len(rsps) == 0 {
 		return nil
 	}
@@ -563,7 +563,7 @@ func (s *Server) stop(err error) {
 // them to the queue. Decoding errors and message-format problems are handled
 // and reported back to the client directly, so that any message that survives
 // into the request queue is structurally valid.
-func (s *Server) read(ch channel.Receiver) {
+func (s *Server) read(ch receiver) {
 	for {
 		// If the message is not sensible, report an error; otherwise enqueue it
 		// for processing. Errors in individual requests are handled later.