taildrop: merge taildrop and feature/taildrop packages together

Fixes #15812

Change-Id: I3bf0666bf9e7a9caea5f0f99fdb0eb2812157608
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/taildrop/resume_test.go

@@ -0,0 +1,74 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package taildrop
+
+import (
+	"bytes"
+	"io"
+	"math/rand"
+	"os"
+	"testing"
+	"testing/iotest"
+
+	"tailscale.com/util/must"
+)
+
+func TestResume(t *testing.T) {
+	oldBlockSize := blockSize
+	defer func() { blockSize = oldBlockSize }()
+	blockSize = 256
+
+	m := managerOptions{Logf: t.Logf, Dir: t.TempDir()}.New()
+	defer m.Shutdown()
+
+	rn := rand.New(rand.NewSource(0))
+	want := make([]byte, 12345)
+	must.Get(io.ReadFull(rn, want))
+
+	t.Run("resume-noexist", func(t *testing.T) {
+		r := io.Reader(bytes.NewReader(want))
+
+		next, close, err := m.HashPartialFile("", "foo")
+		must.Do(err)
+		defer close()
+		offset, r, err := resumeReader(r, next)
+		must.Do(err)
+		must.Do(close()) // Windows wants the file handle to be closed to rename it.
+
+		must.Get(m.PutFile("", "foo", r, offset, -1))
+		got := must.Get(os.ReadFile(must.Get(joinDir(m.opts.Dir, "foo"))))
+		if !bytes.Equal(got, want) {
+			t.Errorf("content mismatches")
+		}
+	})
+
+	t.Run("resume-retry", func(t *testing.T) {
+		rn := rand.New(rand.NewSource(0))
+		for i := 0; true; i++ {
+			r := io.Reader(bytes.NewReader(want))
+
+			next, close, err := m.HashPartialFile("", "bar")
+			must.Do(err)
+			defer close()
+			offset, r, err := resumeReader(r, next)
+			must.Do(err)
+			must.Do(close()) // Windows wants the file handle to be closed to rename it.
+
+			numWant := rn.Int63n(min(int64(len(want))-offset, 1000) + 1)
+			if offset < int64(len(want)) {
+				r = io.MultiReader(io.LimitReader(r, numWant), iotest.ErrReader(io.ErrClosedPipe))
+			}
+			if _, err := m.PutFile("", "bar", r, offset, -1); err == nil {
+				break
+			}
+			if i > 1000 {
+				t.Fatalf("too many iterations to complete the test")
+			}
+		}
+		got := must.Get(os.ReadFile(must.Get(joinDir(m.opts.Dir, "bar"))))
+		if !bytes.Equal(got, want) {
+			t.Errorf("content mismatches")
+		}
+	})
+}