rpc: make stdio usable over custom channels (#19046)

rpc/stdio.go

@@ -19,26 +19,38 @@ package rpc
 import (
 	"context"
 	"errors"
+	"io"
 	"net"
 	"os"
 	"time"
 )
 
 // DialStdIO creates a client on stdin/stdout.
 func DialStdIO(ctx context.Context) (*Client, error) {
+	return DialIO(ctx, os.Stdin, os.Stdout)
+}
+
+// DialIO creates a client which uses the given IO channels
+func DialIO(ctx context.Context, in io.Reader, out io.Writer) (*Client, error) {
 	return newClient(ctx, func(_ context.Context) (ServerCodec, error) {
-		return NewJSONCodec(stdioConn{}), nil
+		return NewJSONCodec(stdioConn{
+			in:  in,
+			out: out,
+		}), nil
 	})
 }
 
-type stdioConn struct{}
+type stdioConn struct {
+	in  io.Reader
+	out io.Writer
+}
 
 func (io stdioConn) Read(b []byte) (n int, err error) {
-	return os.Stdin.Read(b)
+	return io.in.Read(b)
 }
 
 func (io stdioConn) Write(b []byte) (n int, err error) {
-	return os.Stdout.Write(b)
+	return io.out.Write(b)
 }
 
 func (io stdioConn) Close() error {