Tcp buffer bug fix (#79)

* start working on tracking down tcp buffer bug

* mtu refactor

* modularize test

* more precise testing

* tests fail, but is it the failure we are looking for?

* fix typo in espradio link (#76)

* implement a new backoff abstraction (#75)

* rewrite backoff api

* rewrite tcp.Conn.Write

* keep fixing small things

* much better Conn.Read implementation

* fix critical overflow bug in internal.ConnRWBackoff

---------

Co-authored-by: Joel Wetzell <jwetzell@yahoo.com>

backoff.go

@@ -0,0 +1,36 @@
+package lneto
+
+import (
+	"runtime"
+	"time"
+)
+
+// Flag return values for a BackoffStrategy.
+const (
+	BackoffFlagGosched = time.Duration(-1)
+	BackoffFlagNop     = time.Duration(-2)
+)
+
+// BackoffStrategy is the abstraction of a backoff strategy for retrying an operation.
+// It returns the amount of time to sleep for or a flag value:
+//   - Returns [BackoffFlagNop]: Signal no yielding function should be called.
+//     Useful for when the BackoffStrategy implements its own yield.
+//   - Returns [BackoffFlagGosched]: Signal [runtime.Gosched] should be called.
+//
+// consecutiveBackoffs starts at 1 and increments by 1 every time the operation is retried.
+// See internal/backoff.go for a implementation example.
+type BackoffStrategy func(consecutiveBackoffs int) (sleepOrFlag time.Duration)
+
+// Do applies the backoff strategy by calling backoff(consecutiveBackoffs)
+// and then the corresponding yield function for the returned value. See [BackoffStrategy].
+func (backoff BackoffStrategy) Do(consecutiveBackoffs int) {
+	sleep := backoff(consecutiveBackoffs)
+	switch sleep {
+	case BackoffFlagNop:
+		// No yield. Yield implemented by backoff.
+	case BackoffFlagGosched:
+		runtime.Gosched()
+	default:
+		time.Sleep(sleep)
+	}
+}