Leave overflow logic to go-msgio

It seems as though go-msgio now implements the message length limit
(currently 8MB), so the logic in secio reader can be simplified.

License: MIT
Signed-off-by: Randall Leeds <randall@bleeds.info>

p2p/crypto/secio/rw.go

@@ -15,10 +15,6 @@ import (
 	context "github.com/ipfs/go-ipfs/Godeps/_workspace/src/golang.org/x/net/context"
 )
 
-const MaxMsgSize = 8 * 1024 * 1024
-
-var ErrMaxMessageSize = errors.New("attempted to read message larger than max size")
-
 // ErrMACInvalid signals that a MAC verification failed
 var ErrMACInvalid = errors.New("MAC verification failed")
 
@@ -105,66 +101,27 @@ func (r *etmReader) NextMsgLen() (int, error) {
 	return r.msg.NextMsgLen()
 }
 
-func (r *etmReader) drainBuf(buf []byte) int {
-	if r.buf == nil {
-		return 0
-	}
-
-	n := copy(buf, r.buf)
-	r.buf = r.buf[n:]
-	return n
-}
-
 func (r *etmReader) Read(buf []byte) (int, error) {
 	r.Lock()
 	defer r.Unlock()
 
-	// first, check if we have anything in the buffer
-	copied := r.drainBuf(buf)
-	buf = buf[copied:]
-	if copied > 0 {
-		return copied, nil
-		// return here to avoid complicating the rest...
-		// user can call io.ReadFull.
-	}
-
-	// check the buffer has enough space for the next msg
-	fullLen, err := r.msg.NextMsgLen()
-	if err != nil {
-		return 0, err
-	}
-
-	if fullLen > MaxMsgSize {
-		return 0, ErrMaxMessageSize
-	}
+	if len(r.buf) == 0 {
+		msg, err := r.msg.ReadMsg()
+		if err != nil {
+			return 0, err
+		}
 
-	buf2 := buf
-	changed := false
-	// if not enough space, allocate a new buffer.
-	if cap(buf) < fullLen {
-		buf2 = make([]byte, fullLen)
-		changed = true
-	}
-	buf2 = buf2[:fullLen]
+		m, err := r.macCheckThenDecrypt(msg)
+		if err != nil {
+			return 0, err
+		}
 
-	n, err := io.ReadFull(r.msg, buf2)
-	if err != nil {
-		return n, err
+		r.buf = msg[:m]
 	}
 
-	m, err := r.macCheckThenDecrypt(buf2)
-	if err != nil {
-		return 0, err
-	}
-	buf2 = buf2[:m]
-	if !changed {
-		return m, nil
-	}
-
-	n = copy(buf, buf2)
-	if len(buf2) > len(buf) {
-		r.buf = buf2[len(buf):] // had some left over? save it.
-	}
+	n := copy(buf, r.buf)
+	buf = buf[:n]
+	r.buf = r.buf[n:]
 	return n, nil
 }