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replication.go
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replication.go
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package couch
import (
"errors"
"fmt"
"net/url"
"strings"
)
// A replication from a source to a target
type Replication struct {
source *Database
target *Database
continuous bool
sessionID string
}
// A bidirectional replication
type Sync struct {
replA2B *Replication
replB2A *Replication
}
// CouchDB request for replication
type replRequest struct {
CreateTarget bool `json:"create_target"`
Source string `json:"source"`
Target string `json:"target"`
Continuous bool `json:"continuous"`
Cancel bool `json:"cancel,omitempty"`
}
// CouchDB response to replication request
type replResponse struct {
Ok bool `json:"ok"`
ReplIDVersion int `json:"replication_id_version"`
SessionID string `json:"session_id"`
SourceLastSeq int `json:"source_last_seq"`
}
// Replicates given database to a target database. If the target database
// does not exist it will be created. The target database may be on a different host.
func (db *Database) ReplicateTo(target *Database, continuously bool) (*Replication, error) {
var resp replResponse
req := replRequest{CreateTarget: true, Source: db.URL(), Target: target.urlWithCredentials(), Continuous: continuously}
_, err := Do(db.replicationURL(), "POST", db.Cred(), req, &resp)
if err != nil {
return nil, err
}
repl := &Replication{source: db, target: target, continuous: continuously, sessionID: resp.SessionID}
return repl, err
}
// IsReplication returns true if a task represents a replication.
func (t Task) IsReplication() bool {
return t["type"] == "replication"
}
// HasReplicationID returns true if a task has a given replication id.
func (t Task) HasReplicationID(id string) bool {
s, _ := t["replication_id"].(string)
return strings.HasPrefix(s, id)
}
// func (t Task) Replication(relativeTo *Server) *Replication {
// var r *Replication
// if t.isReplication() {
// sourceURL, _ := url.Parse(t["source"])
// sourceURL.Path
// //sourceDB :=
// //targetDB :=
// r = &Replication{
// sessionID: t["replication_id"],
// continuous: t["continuous"],
// }
// }
// return r
// }
// IsRunning returns whether a replication is currently active or not.
func (repl *Replication) IsActive() (bool, error) {
tasks, err := repl.Source().Server().ActiveTasks()
if err != nil {
return false, err
}
for _, task := range tasks {
if task.HasReplicationID(repl.SessionID()) {
return true, nil
}
}
return false, nil
}
// IsActive returns whether a sync is active or not. A sync process consists of
// two replications. If one is active and the other isn't, you get an error message.
func (sync *Sync) IsActive() (bool, error) {
a2bIsActive, err := sync.replA2B.IsActive()
if err != nil {
return false, err
}
b2aIsActive, err := sync.replA2B.IsActive()
if err != nil {
return false, err
}
if a2bIsActive != b2aIsActive {
return false, errors.New("corrupt sync, only one replication active instead of two")
}
return a2bIsActive && b2aIsActive, nil
}
// // ActiveReplications returns all currently active replications on a server
// func (s *Server) ActiveReplications() ([]*Replication, error) {
// var repls []*Replication
// err := s.ActiveTasks(func(t Task) {
// repl := t.Replication(s)
// if repl != nil {
// repls = append(repls, repl)
// }
// })
// return repls, err
// }
// Cancel a continuously running replication
func (repl *Replication) Cancel() error {
req := replRequest{CreateTarget: true, Source: repl.source.URL(), Target: repl.target.URL(), Continuous: repl.continuous, Cancel: true}
_, err := Do(repl.Source().replicationURL(), "POST", repl.source.Cred(), req, nil)
return err
}
// Returns replication source
func (repl *Replication) Source() *Database {
return repl.source
}
// Returns replication target
func (repl *Replication) Target() *Database {
return repl.target
}
// Returns whether replication is running continuously or not
func (repl *Replication) Continuous() bool {
return repl.continuous
}
func (repl *Replication) SessionID() string {
return repl.sessionID
}
// Synchronizes two databases by setting up two replications, one from given database
// to target and from target to given database. If the target database does not exist it will be created.
// The target database may be on a different host.
//
// This method may be convenient but note that it is not atomic: Sync means that this method will first
// replicate db to target and then target to db. If the first one fails, both fail. If the first one works but
// the second doesn't, the first one will have executed nonetheless. If the sync has been set up to be continuous,
// the first continuous replication will be cancelled if the second one fails.
func (db *Database) SyncWith(target *Database, continuously bool) (*Sync, error) {
replA2B, err := db.ReplicateTo(target, continuously)
if err != nil {
return nil, err
}
replB2A, err := target.ReplicateTo(db, continuously)
if err != nil {
replA2B.Cancel()
return nil, err
}
sync := &Sync{replA2B, replB2A}
return sync, nil
}
// Cancel a continuously running sync
func (sync *Sync) Cancel() error {
// Call cancel directly on both replications, if replA2B.Cancel() leads to
// an error we might still be able to cancel replB2A. Errors will be combined later.
errA2B := sync.replA2B.Cancel()
errB2A := sync.replB2A.Cancel()
var err error
if errA2B != nil || errB2A != nil {
err = fmt.Errorf("can't cancel sync: a->b: %v, b->a: %v", errA2B, errB2A)
}
return err
}
// Not safe, only used body of replication request
func (db *Database) urlWithCredentials() string {
result, _ := url.Parse(db.URL())
cred := db.Cred()
if cred != nil {
result.User = url.UserPassword(db.server.cred.user, db.server.cred.password)
}
return result.String()
}
func (db *Database) replicationURL() string {
return db.server.url + "/_replicate"
}