From fa6426f803b8a4f8559519db82596613d36e8575 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Wed, 2 May 2018 21:26:56 +0200
Subject: [PATCH] WIP: zfs: hacky resume token parsing

---
 zfs/resume_token.go      | 105 +++++++++++++++++++++++++++++++++++++++
 zfs/resume_token_test.go |  64 ++++++++++++++++++++++++
 2 files changed, 169 insertions(+)
 create mode 100644 zfs/resume_token.go
 create mode 100644 zfs/resume_token_test.go

diff --git a/zfs/resume_token.go b/zfs/resume_token.go
new file mode 100644
index 0000000..4423626
--- /dev/null
+++ b/zfs/resume_token.go
@@ -0,0 +1,105 @@
+package zfs
+
+import (
+	"context"
+	"errors"
+	"os/exec"
+	"regexp"
+	"strconv"
+	"time"
+)
+
+type ResumeToken struct {
+	HasFromGUID, HasToGUID bool
+	FromGUID, ToGUID       uint64
+	// no support for other fields
+}
+
+var resumeTokenNVListRE = regexp.MustCompile(`\t(\S+) = (.*)`)
+var resumeTokenContentsRE = regexp.MustCompile(`resume token contents:\nnvlist version: 0`)
+var resumeTokenIsCorruptRE = regexp.MustCompile(`resume token is corrupt`)
+
+var ResumeTokenCorruptError = errors.New("resume token is corrupt")
+var ResumeTokenDecodingNotSupported = errors.New("zfs binary does not allow decoding resume token or zrepl cannot scrape zfs output")
+var ResumeTokenParsingError = errors.New("zrepl cannot parse resume token values")
+
+// Abuse 'zfs send' to decode the resume token
+//
+// FIXME: implement nvlist unpacking in Go and read through libzfs_sendrecv.c
+func ParseResumeToken(ctx context.Context, token string) (*ResumeToken, error) {
+
+	// Example resume tokens:
+	//
+	// From a non-incremental send
+	// 1-bf31b879a-b8-789c636064000310a500c4ec50360710e72765a5269740f80cd8e4d3d28a534b18e00024cf86249f5459925acc802a8facbf243fbd3433858161f5ddb9ab1ae7c7466a20c97382e5f312735319180af2f3730cf58166953824c2cc0200cde81651
+
+	// From an incremental send
+	// 1-c49b979a2-e0-789c636064000310a501c49c50360710a715e5e7a69766a63040c1eabb735735ce8f8d5400b2d991d4e52765a5269740f82080219f96569c5ac2000720793624f9a4ca92d46206547964fd25f91057f09e37babb88c9bf5503499e132c9f97989bcac050909f9f63a80f34abc421096616007c881d4c
+
+	// Resulting output of zfs send -nvt <token>
+	//
+	//resume token contents:
+	//nvlist version: 0
+	//	fromguid = 0x595d9f81aa9dddab
+	//	object = 0x1
+	//	offset = 0x0
+	//	bytes = 0x0
+	//	toguid = 0x854f02a2dd32cf0d
+	//	toname = pool1/test@b
+	//cannot resume send: 'pool1/test@b' used in the initial send no longer exists
+
+	ctx, _ = context.WithTimeout(ctx, 500*time.Millisecond)
+	cmd := exec.CommandContext(ctx, ZFS_BINARY, "send", "-nvt", string(token))
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			if !exitErr.Exited() {
+				return nil, err
+			}
+			// we abuse zfs send for decoding, the exit error may be due to
+			// a) the token being from a third machine
+			// b) it no longer exists on the machine where
+		} else {
+			return nil, err
+		}
+	}
+
+	if !resumeTokenContentsRE.Match(output) {
+		if resumeTokenIsCorruptRE.Match(output) {
+			return nil, ResumeTokenCorruptError
+		}
+		return nil, ResumeTokenDecodingNotSupported
+	}
+
+	matches := resumeTokenNVListRE.FindAllStringSubmatch(string(output), -1)
+	if matches == nil {
+		return nil, ResumeTokenDecodingNotSupported
+	}
+
+	rt := &ResumeToken{}
+
+	for _, m := range matches {
+		attr, val := m[1], m[2]
+		switch attr {
+		case "fromguid":
+			rt.FromGUID, err = strconv.ParseUint(val, 0, 64)
+			if err != nil {
+				return nil, ResumeTokenParsingError
+			}
+			rt.HasFromGUID = true
+		case "toguid":
+			rt.ToGUID, err = strconv.ParseUint(val, 0, 64)
+			if err != nil {
+				return nil, ResumeTokenParsingError
+			}
+			rt.HasToGUID = true
+		}
+	}
+
+	if !rt.HasToGUID {
+		return nil, ResumeTokenDecodingNotSupported
+	}
+
+	return rt, nil
+
+}
diff --git a/zfs/resume_token_test.go b/zfs/resume_token_test.go
new file mode 100644
index 0000000..33f560a
--- /dev/null
+++ b/zfs/resume_token_test.go
@@ -0,0 +1,64 @@
+package zfs_test
+
+import (
+	"context"
+	"github.com/stretchr/testify/assert"
+	"github.com/zrepl/zrepl/zfs"
+	"testing"
+)
+
+type ResumeTokenTest struct {
+	Msg         string
+	Token       string
+	ExpectToken *zfs.ResumeToken
+	ExpectError error
+}
+
+func (rtt *ResumeTokenTest) Test(t *testing.T) {
+	t.Log(rtt.Msg)
+	res, err := zfs.ParseResumeToken(context.TODO(), rtt.Token)
+
+	if rtt.ExpectError != nil {
+		assert.EqualValues(t, rtt.ExpectError, err)
+		return
+	}
+	if rtt.ExpectToken != nil {
+		assert.Nil(t, err)
+		assert.EqualValues(t, rtt.ExpectToken, res)
+		return
+	}
+}
+
+func TestParseResumeToken(t *testing.T) {
+
+	tbl := []ResumeTokenTest{
+		{
+			Msg:   "normal send (non-incremental)",
+			Token: `1-bf31b879a-b8-789c636064000310a500c4ec50360710e72765a5269740f80cd8e4d3d28a534b18e00024cf86249f5459925acc802a8facbf243fbd3433858161f5ddb9ab1ae7c7466a20c97382e5f312735319180af2f3730cf58166953824c2cc0200cde81651`,
+			ExpectToken: &zfs.ResumeToken{
+				HasToGUID: true,
+				ToGUID:    0x595d9f81aa9dddab,
+			},
+		},
+		{
+			Msg:   "normal send (incremental)",
+			Token: `1-c49b979a2-e0-789c636064000310a501c49c50360710a715e5e7a69766a63040c1eabb735735ce8f8d5400b2d991d4e52765a5269740f82080219f96569c5ac2000720793624f9a4ca92d46206547964fd25f91057f09e37babb88c9bf5503499e132c9f97989bcac050909f9f63a80f34abc421096616007c881d4c`,
+			ExpectToken: &zfs.ResumeToken{
+				HasToGUID:   true,
+				ToGUID:      0x854f02a2dd32cf0d,
+				HasFromGUID: true,
+				FromGUID:    0x595d9f81aa9dddab,
+			},
+		},
+		{
+			Msg:         "corrupted token",
+			Token:       `1-bf31b879a-b8-789c636064000310a500c4ec50360710e72765a5269740f80cd8e4d3d28a534b18e00024cf86249f5459925acc802a8facbf243fbd3433858161f5ddb9ab1ae7c7466a20c97382e5f312735319180af2f3730cf58166953824c2cc0200cd12345`,
+			ExpectError: zfs.ResumeTokenCorruptError,
+		},
+	}
+
+	for _, test := range tbl {
+		test.Test(t)
+	}
+
+}