Implement record roundtrip tests (matthewstevenson88#53)

* draft code

* finished write impl.

* fixed record, added tests

* fixed tests

* fixed writing to buffer

* fixed merge conflicts with master

* added comments

* fixed some pr issues, fixed comments, added new methods and tests

* added constants

* added comments, fixed var names

* compeletely removed hex notation

* fixed pr issues, still working on tests

* fixed all tests except for read multiple records, impl create record with plaintext len 0

* fixed pr issues, all tests pass, added exceed maxPayloadLength test

* fixed constant definitions, pr issues

* split plaintext test passes, organized code

* added comments

* removed unusedBuf allocation

* fixed split record exceeding maxlength test

* added test max payload for all ciphersuites

* fixed return value to only be plaintext bytes, fixed pr issues.

* fixed comments, test descriptions, pr issues

* changed error bytes written calculation, removed error check in tests

* fixed multiple record writing to buffer

* removed min from totalNumOfrecordBytes, added tests for re-allocate buffer

* added test comments, moved constants, fixed pr issues

* fixed small comment

* added round trip tests

* fixed test error messages

* added different traffic secret test

* added more tests

* expanded conversation test

* fixed error msg

* removed TODO

* fixed read implementation and tests

* removed excess space

* added helper function, fixed pr issues

* fixed tests

* fixed roundtrip test

security/s2a/internal/record/record.go

@@ -515,11 +515,11 @@ func (p *conn) readFullRecord() (fullRecord []byte, err error) {
 	// Keep reading from the wire until we have a complete record.
 	for len(fullRecord) == 0 {
 		if len(p.unusedBuf) == cap(p.unusedBuf) {
-			tmp := make([]byte, len(p.unusedBuf), cap(p.unusedBuf)+tlsRecordMaxPayloadSize)
+			tmp := make([]byte, len(p.unusedBuf), cap(p.unusedBuf)+tlsRecordMaxSize)
 			copy(tmp, p.unusedBuf)
 			p.unusedBuf = tmp
 		}
-		n, err := p.Conn.Read(p.unusedBuf[len(p.unusedBuf):min(cap(p.unusedBuf), len(p.unusedBuf)+tlsRecordMaxPayloadSize)])
+		n, err := p.Conn.Read(p.unusedBuf[len(p.unusedBuf):min(cap(p.unusedBuf), len(p.unusedBuf)+tlsRecordMaxSize)])
 		if err != nil {
 			return nil, err
 		}