move replication package to project root (independent of cmd package)
This commit is contained in:
Christian Schwarz
@@ -0,0 +1,384 @@
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// Package replication implements replication of filesystems with existing
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// versions (snapshots) from a sender to a receiver.
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package replication
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import (
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"context"
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"errors"
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"fmt"
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"math/bits"
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"sync"
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"time"
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"github.com/zrepl/zrepl/replication/pdu"
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"github.com/zrepl/zrepl/replication/fsrep"
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. "github.com/zrepl/zrepl/replication/internal/queue"
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. "github.com/zrepl/zrepl/replication/internal/diff"
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)
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//go:generate stringer -type=State
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type State uint
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const (
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Planning State = 1 << iota
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PlanningError
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Working
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WorkingWait
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Completed
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ContextDone
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)
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func (s State) rsf() state {
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idx := bits.TrailingZeros(uint(s))
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if idx == bits.UintSize {
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panic(s) // invalid value
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}
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m := []state{
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statePlanning,
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statePlanningError,
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stateWorking,
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stateWorkingWait,
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nil,
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nil,
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}
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return m[idx]
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}
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// Replication implements the replication of multiple file systems from a Sender to a Receiver.
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//
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// It is a state machine that is driven by the Drive method
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// and provides asynchronous reporting via the Report method (i.e. from another goroutine).
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type Replication struct {
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// lock protects all fields of this struct (but not the fields behind pointers!)
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lock sync.Mutex
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state State
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// Working, WorkingWait, Completed, ContextDone
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queue *ReplicationQueue
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completed []*fsrep.Replication
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active *ReplicationQueueItemHandle
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// PlanningError
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planningError error
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// ContextDone
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contextError error
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// PlanningError, WorkingWait
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sleepUntil time.Time
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}
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type Report struct {
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Status string
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Problem string
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Completed []*fsrep.Report
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Pending []*fsrep.Report
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Active *fsrep.Report
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}
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func NewReplication() *Replication {
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r := Replication{
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state: Planning,
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}
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return &r
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}
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type Endpoint interface {
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// Does not include placeholder filesystems
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ListFilesystems(ctx context.Context) ([]*pdu.Filesystem, error)
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ListFilesystemVersions(ctx context.Context, fs string) ([]*pdu.FilesystemVersion, error) // fix depS
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}
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type Sender interface {
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Endpoint
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fsrep.Sender
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}
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type Receiver interface {
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Endpoint
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fsrep.Receiver
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}
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type FilteredError struct{ fs string }
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func NewFilteredError(fs string) *FilteredError {
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return &FilteredError{fs}
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}
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func (f FilteredError) Error() string { return "endpoint does not allow access to filesystem " + f.fs }
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type updater func(func(*Replication)) (newState State)
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type state func(ctx context.Context, sender Sender, receiver Receiver, u updater) state
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// Drive starts the state machine and returns only after replication has finished (with or without errors).
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// The Logger in ctx is used for both debug and error logging, but is not guaranteed to be stable
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// or end-user friendly.
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// User-facing replication progress reports and can be obtained using the Report method,
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// whose output will not change after Drive returns.
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//
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// FIXME: Drive may be only called once per instance of Replication
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func (r *Replication) Drive(ctx context.Context, sender Sender, receiver Receiver) {
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var u updater = func(f func(*Replication)) State {
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r.lock.Lock()
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defer r.lock.Unlock()
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if f != nil {
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f(r)
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}
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return r.state
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}
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var s state = statePlanning
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var pre, post State
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for s != nil {
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preTime := time.Now()
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pre = u(nil)
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s = s(ctx, sender, receiver, u)
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delta := time.Now().Sub(preTime)
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post = u(nil)
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getLogger(ctx).
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WithField("transition", fmt.Sprintf("%s => %s", pre, post)).
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WithField("duration", delta).
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Debug("main state transition")
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}
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getLogger(ctx).
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WithField("final_state", post).
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Debug("main final state")
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}
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func resolveConflict(conflict error) (path []*pdu.FilesystemVersion, msg string) {
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if noCommonAncestor, ok := conflict.(*ConflictNoCommonAncestor); ok {
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if len(noCommonAncestor.SortedReceiverVersions) == 0 {
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// FIXME hard-coded replication policy: most recent
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// snapshot as source
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var mostRecentSnap *pdu.FilesystemVersion
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for n := len(noCommonAncestor.SortedSenderVersions) - 1; n >= 0; n-- {
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if noCommonAncestor.SortedSenderVersions[n].Type == pdu.FilesystemVersion_Snapshot {
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mostRecentSnap = noCommonAncestor.SortedSenderVersions[n]
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break
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}
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}
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if mostRecentSnap == nil {
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return nil, "no snapshots available on sender side"
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}
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return []*pdu.FilesystemVersion{mostRecentSnap}, fmt.Sprintf("start replication at most recent snapshot %s", mostRecentSnap.RelName())
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}
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}
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return nil, "no automated way to handle conflict type"
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}
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func statePlanning(ctx context.Context, sender Sender, receiver Receiver, u updater) state {
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log := getLogger(ctx)
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handlePlanningError := func(err error) state {
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return u(func(r *Replication) {
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r.planningError = err
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r.state = PlanningError
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}).rsf()
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}
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sfss, err := sender.ListFilesystems(ctx)
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if err != nil {
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log.WithError(err).Error("error listing sender filesystems")
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return handlePlanningError(err)
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}
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rfss, err := receiver.ListFilesystems(ctx)
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if err != nil {
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log.WithError(err).Error("error listing receiver filesystems")
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return handlePlanningError(err)
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}
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q := NewReplicationQueue()
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mainlog := log
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for _, fs := range sfss {
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log := mainlog.WithField("filesystem", fs.Path)
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log.Info("assessing filesystem")
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sfsvs, err := sender.ListFilesystemVersions(ctx, fs.Path)
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if err != nil {
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log.WithError(err).Error("cannot get remote filesystem versions")
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return handlePlanningError(err)
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}
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if len(sfsvs) <= 1 {
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err := errors.New("sender does not have any versions")
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log.Error(err.Error())
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q.Add(fsrep.NewReplicationWithPermanentError(fs.Path, err))
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continue
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}
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receiverFSExists := false
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for _, rfs := range rfss {
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if rfs.Path == fs.Path {
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receiverFSExists = true
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}
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}
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var rfsvs []*pdu.FilesystemVersion
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if receiverFSExists {
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rfsvs, err = receiver.ListFilesystemVersions(ctx, fs.Path)
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if err != nil {
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if _, ok := err.(*FilteredError); ok {
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log.Info("receiver ignores filesystem")
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continue
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}
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log.WithError(err).Error("receiver error")
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return handlePlanningError(err)
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}
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} else {
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rfsvs = []*pdu.FilesystemVersion{}
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}
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path, conflict := IncrementalPath(rfsvs, sfsvs)
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if conflict != nil {
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var msg string
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path, msg = resolveConflict(conflict) // no shadowing allowed!
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if path != nil {
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log.WithField("conflict", conflict).Info("conflict")
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log.WithField("resolution", msg).Info("automatically resolved")
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} else {
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log.WithField("conflict", conflict).Error("conflict")
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log.WithField("problem", msg).Error("cannot resolve conflict")
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}
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}
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if path == nil {
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q.Add(fsrep.NewReplicationWithPermanentError(fs.Path, conflict))
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continue
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}
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fsrfsm := fsrep.BuildReplication(fs.Path)
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if len(path) == 1 {
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fsrfsm.AddStep(nil, path[0])
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} else {
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for i := 0; i < len(path)-1; i++ {
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fsrfsm.AddStep(path[i], path[i+1])
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}
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}
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qitem := fsrfsm.Done()
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q.Add(qitem)
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}
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return u(func(r *Replication) {
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r.completed = nil
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r.queue = q
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r.planningError = nil
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r.state = Working
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}).rsf()
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}
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func statePlanningError(ctx context.Context, sender Sender, receiver Receiver, u updater) state {
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sleepTime := 10 * time.Second
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u(func(r *Replication) {
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r.sleepUntil = time.Now().Add(sleepTime)
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})
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t := time.NewTimer(sleepTime) // FIXME make constant onfigurable
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defer t.Stop()
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select {
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case <-ctx.Done():
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return u(func(r *Replication) {
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r.state = ContextDone
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r.contextError = ctx.Err()
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}).rsf()
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case <-t.C:
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return u(func(r *Replication) {
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r.state = Planning
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}).rsf()
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}
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}
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func stateWorking(ctx context.Context, sender Sender, receiver Receiver, u updater) state {
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var active *ReplicationQueueItemHandle
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rsfNext := u(func(r *Replication) {
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done, next := r.queue.GetNext()
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r.completed = append(r.completed, done...)
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if next == nil {
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r.state = Completed
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}
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r.active = next
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active = next
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}).rsf()
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if active == nil {
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return rsfNext
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}
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state, nextStepDate := active.GetFSReplication().TakeStep(ctx, sender, receiver)
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return u(func(r *Replication) {
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active.Update(state, nextStepDate)
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r.active = nil
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}).rsf()
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}
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func stateWorkingWait(ctx context.Context, sender Sender, receiver Receiver, u updater) state {
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sleepTime := 10 * time.Second
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u(func(r *Replication) {
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r.sleepUntil = time.Now().Add(sleepTime)
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})
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t := time.NewTimer(sleepTime)
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defer t.Stop()
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select {
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case <-ctx.Done():
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return u(func(r *Replication) {
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r.state = ContextDone
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r.contextError = ctx.Err()
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}).rsf()
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case <-t.C:
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return u(func(r *Replication) {
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r.state = Working
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}).rsf()
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}
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}
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// Report provides a summary of the progress of the Replication,
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// i.e., a condensed dump of the internal state machine.
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// Report is safe to be called asynchronously while Drive is running.
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func (r *Replication) Report() *Report {
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r.lock.Lock()
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defer r.lock.Unlock()
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rep := Report{
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Status: r.state.String(),
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}
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if r.state&(Planning|PlanningError|ContextDone) != 0 {
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switch r.state {
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case PlanningError:
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rep.Problem = r.planningError.Error()
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case ContextDone:
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rep.Problem = r.contextError.Error()
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}
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return &rep
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}
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rep.Pending = make([]*fsrep.Report, 0, r.queue.Len())
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rep.Completed = make([]*fsrep.Report, 0, len(r.completed)) // room for active (potentially)
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var active *fsrep.Replication
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if r.active != nil {
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active = r.active.GetFSReplication()
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rep.Active = active.Report()
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}
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r.queue.Foreach(func(h *ReplicationQueueItemHandle) {
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fsr := h.GetFSReplication()
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if active != fsr {
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rep.Pending = append(rep.Pending, fsr.Report())
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}
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})
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for _, fsr := range r.completed {
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rep.Completed = append(rep.Completed, fsr.Report())
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}
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return &rep
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}
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