client

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 Go to latest Published: Feb 17, 2016 License: Apache-2.0 Imports: 22 Imported by: 0

README

etcd/client

etcd/client is the Go client library for etcd.

GoDoc

Install

go get github.com/coreos/etcd/client

Usage

package main

import (
	"log"
	"time"

	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
	"github.com/coreos/etcd/client"
)

func main() {
	cfg := client.Config{
		Endpoints:               []string{"http://127.0.0.1:2379"},
		Transport:               client.DefaultTransport,
		// set timeout per request to fail fast when the target endpoint is unavailable
		HeaderTimeoutPerRequest: time.Second,
	}
	c, err := client.New(cfg)
	if err != nil {
		log.Fatal(err)
	}
	kapi := client.NewKeysAPI(c)
	// set "/foo" key with "bar" value
	log.Print("Setting '/foo' key with 'bar' value")
	resp, err := kapi.Set(context.Background(), "/foo", "bar", nil)
	if err != nil {
		log.Fatal(err)
	} else {
		// print common key info
		log.Printf("Set is done. Metadata is %q\n", resp)
	}
	// get "/foo" key's value
	log.Print("Getting '/foo' key value")
	resp, err = kapi.Get(context.Background(), "/foo", nil)
	if err != nil {
		log.Fatal(err)
	} else {
		// print common key info
		log.Printf("Get is done. Metadata is %q\n", resp)
		// print value
		log.Printf("%q key has %q value\n", resp.Node.Key, resp.Node.Value)
	}
}

Error Handling

etcd client might return three types of errors.

  • context error

Each API call has its first parameter as context. A context can be canceled or have an attached deadline. If the context is canceled or reaches its deadline, the responding context error will be returned no matter what internal errors the API call has already encountered.

  • cluster error

Each API call tries to send request to the cluster endpoints one by one until it successfully gets a response. If a requests to an endpoint fails, due to exceeding per request timeout or connection issues, the error will be added into a list of errors. If all possible endpoints fail, a cluster error that includes all encountered errors will be returned.

  • response error

If the response gets from the cluster is invalid, a plain string error will be returned. For example, it might be a invalid JSON error.

Here is the example code to handle client errors:

cfg := client.Config{Endpoints: []string{"http://etcd1:2379","http://etcd2:2379","http://etcd3:2379"}}
c, err := client.New(cfg)
if err != nil {
	log.Fatal(err)
}

kapi := client.NewKeysAPI(c)
resp, err := kapi.Set(ctx, "test", "bar", nil)
if err != nil {
	if err == context.Canceled {
		// ctx is canceled by another routine
	} else if err == context.DeadlineExceeded {
		// ctx is attached with a deadline and it exceeded
	} else if cerr, ok := err.(*client.ClusterError); ok {
		// process (cerr.Errors)
	} else {
		// bad cluster endpoints, which are not etcd servers
	}
}

Caveat

  1. etcd/client prefers to use the same endpoint as long as the endpoint continues to work well. This saves socket resources, and improves efficiency for both client and server side. This preference doesn't remove consistency from the data consumed by the client because data replicated to each etcd member has already passed through the consensus process.

  2. etcd/client does round-robin rotation on other available endpoints if the preferred endpoint isn't functioning properly. For example, if the member that etcd/client connects to is hard killed, etcd/client will fail on the first attempt with the killed member, and succeed on the second attempt with another member. If it fails to talk to all available endpoints, it will return all errors happened.

  3. Default etcd/client cannot handle the case that the remote server is SIGSTOPed now. TCP keepalive mechanism doesn't help in this scenario because operating system may still send TCP keep-alive packets. Over time we'd like to improve this functionality, but solving this issue isn't high priority because a real-life case in which a server is stopped, but the connection is kept alive, hasn't been brought to our attention.

  4. etcd/client cannot detect whether the member in use is healthy when doing read requests. If the member is isolated from the cluster, etcd/client may retrieve outdated data. As a workaround, users could monitor experimental /health endpoint for member healthy information. We are improving it at #3265.

Documentation

Overview

Package client provides bindings for the etcd APIs.

Create a Config and exchange it for a Client: 

import (
	"net/http"

	"github.com/coreos/etcd/client"
	"golang.org/x/net/context"
)

cfg := client.Config{
	Endpoints: []string{"http://127.0.0.1:2379"},
	Transport: DefaultTransport,
}

c, err := client.New(cfg)
if err != nil {
	// handle error
}

Create a KeysAPI using the Client, then use it to interact with etcd: 

kAPI := client.NewKeysAPI(c)

// create a new key /foo with the value "bar"
_, err = kAPI.Create(context.Background(), "/foo", "bar")
if err != nil {
	// handle error
}

// delete the newly created key only if the value is still "bar"
_, err = kAPI.Delete(context.Background(), "/foo", &DeleteOptions{PrevValue: "bar"})
if err != nil {
	// handle error
}

Use a custom context to set timeouts on your operations: 

import "time"

ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

// set a new key, ignoring it's previous state
_, err := kAPI.Set(ctx, "/ping", "pong", nil)
if err != nil {
	if err == context.DeadlineExceeded {
		// request took longer than 5s
	} else {
		// handle error
	}
}

Index

Constants

View Source 
const (
	ErrorCodeKeyNotFound  = 100
	ErrorCodeTestFailed   = 101
	ErrorCodeNotFile      = 102
	ErrorCodeNotDir       = 104
	ErrorCodeNodeExist    = 105
	ErrorCodeRootROnly    = 107
	ErrorCodeDirNotEmpty  = 108
	ErrorCodeUnauthorized = 110

	ErrorCodePrevValueRequired = 201
	ErrorCodeTTLNaN            = 202
	ErrorCodeIndexNaN          = 203
	ErrorCodeInvalidField      = 209
	ErrorCodeInvalidForm       = 210

	ErrorCodeRaftInternal = 300
	ErrorCodeLeaderElect  = 301

	ErrorCodeWatcherCleared    = 400
	ErrorCodeEventIndexCleared = 401
)
View Source 
const (
	PrevIgnore  = PrevExistType("")
	PrevExist   = PrevExistType("true")
	PrevNoExist = PrevExistType("false")
)

Variables

View Source 
var (
	ErrNoEndpoints        = errors.New("client: no endpoints available")
	ErrTooManyRedirects   = errors.New("client: too many redirects")
	ErrClusterUnavailable = errors.New("client: etcd cluster is unavailable or misconfigured")
	ErrNoLeaderEndpoint   = errors.New("client: no leader endpoint available")
)
View Source 
var (
	ErrInvalidJSON = errors.New("client: response is invalid json. The endpoint is probably not valid etcd cluster endpoint.")
	ErrEmptyBody   = errors.New("client: response body is empty")
)
View Source 
var DefaultRequestTimeout = 5 * time.Second

Functions

func DisablecURLDebug 

func DisablecURLDebug()

func EnablecURLDebug 

func EnablecURLDebug()

func IsKeyNotFound 

func IsKeyNotFound(err error) bool

IsKeyNotFound returns true if the error code is ErrorCodeKeyNotFound.

Types

type AuthAPI 

type AuthAPI interface {
	// Enable auth.
	Enable(ctx context.Context) error

	// Disable auth.
	Disable(ctx context.Context) error
}

func NewAuthAPI 

func NewAuthAPI(c Client) AuthAPI

NewAuthAPI constructs a new AuthAPI that uses HTTP to interact with etcd's general auth features.

type AuthRoleAPI 

type AuthRoleAPI interface {
	// Add a role.
	AddRole(ctx context.Context, role string) error

	// Remove a role.
	RemoveRole(ctx context.Context, role string) error

	// Get role details.
	GetRole(ctx context.Context, role string) (*Role, error)

	// Grant a role some permission prefixes for the KV store.
	GrantRoleKV(ctx context.Context, role string, prefixes []string, permType PermissionType) (*Role, error)

	// Revoke some some permission prefixes for a role on the KV store.
	RevokeRoleKV(ctx context.Context, role string, prefixes []string, permType PermissionType) (*Role, error)

	// List roles.
	ListRoles(ctx context.Context) ([]string, error)
}

func NewAuthRoleAPI 

func NewAuthRoleAPI(c Client) AuthRoleAPI

NewAuthRoleAPI constructs a new AuthRoleAPI that uses HTTP to interact with etcd's role creation and modification features.

type AuthUserAPI 

type AuthUserAPI interface {
	// Add a user.
	AddUser(ctx context.Context, username string, password string) error

	// Remove a user.
	RemoveUser(ctx context.Context, username string) error

	// Get user details.
	GetUser(ctx context.Context, username string) (*User, error)

	// Grant a user some permission roles.
	GrantUser(ctx context.Context, username string, roles []string) (*User, error)

	// Revoke some permission roles from a user.
	RevokeUser(ctx context.Context, username string, roles []string) (*User, error)

	// Change the user's password.
	ChangePassword(ctx context.Context, username string, password string) (*User, error)

	// List users.
	ListUsers(ctx context.Context) ([]string, error)
}

func NewAuthUserAPI 

func NewAuthUserAPI(c Client) AuthUserAPI

NewAuthUserAPI constructs a new AuthUserAPI that uses HTTP to interact with etcd's user creation and modification features.

type CancelableTransport 

type CancelableTransport interface {
	http.RoundTripper
	CancelRequest(req *http.Request)
}

CancelableTransport mimics net/http.Transport, but requires that the object also support request cancellation. 

var DefaultTransport CancelableTransport = &http.Transport{
	Proxy: http.ProxyFromEnvironment,
	Dial: (&net.Dialer{
		Timeout:   30 * time.Second,
		KeepAlive: 30 * time.Second,
	}).Dial,
	TLSHandshakeTimeout: 10 * time.Second,
}

type CheckRedirectFunc 

type CheckRedirectFunc func(via int) error
var DefaultCheckRedirect CheckRedirectFunc = func(via int) error {
	if via > 10 {
		return ErrTooManyRedirects
	}
	return nil
}

DefaultCheckRedirect follows up to 10 redirects, but no more.

type Client 

type Client interface {
	// Sync updates the internal cache of the etcd cluster's membership.
	Sync(context.Context) error

	// AutoSync periodically calls Sync() every given interval.
	// The recommended sync interval is 10 seconds to 1 minute, which does
	// not bring too much overhead to server and makes client catch up the
	// cluster change in time.
	//
	// The example to use it:
	//
	//  for {
	//      err := client.AutoSync(ctx, 10*time.Second)
	//      if err == context.DeadlineExceeded || err == context.Canceled {
	//          break
	//      }
	//      log.Print(err)
	//  }
	AutoSync(context.Context, time.Duration) error

	// Endpoints returns a copy of the current set of API endpoints used
	// by Client to resolve HTTP requests. If Sync has ever been called,
	// this may differ from the initial Endpoints provided in the Config.
	Endpoints() []string

	// SetEndpoints sets the set of API endpoints used by Client to resolve
	// HTTP requests. If the given endpoints are not valid, an error will be
	// returned
	SetEndpoints(eps []string) error
	// contains filtered or unexported methods
}

func New 

func New(cfg Config) (Client, error)

type ClusterError 

type ClusterError struct {
	Errors []error
}

func (*ClusterError) Detail 

func (ce *ClusterError) Detail() string

func (*ClusterError) Error 

func (ce *ClusterError) Error() string

type Config 

type Config struct {
	// Endpoints defines a set of URLs (schemes, hosts and ports only)
	// that can be used to communicate with a logical etcd cluster. For
	// example, a three-node cluster could be provided like so:
	//
	// 	Endpoints: []string{
	//		"http://node1.example.com:2379",
	//		"http://node2.example.com:2379",
	//		"http://node3.example.com:2379",
	//	}
	//
	// If multiple endpoints are provided, the Client will attempt to
	// use them all in the event that one or more of them are unusable.
	//
	// If Client.Sync is ever called, the Client may cache an alternate
	// set of endpoints to continue operation.
	Endpoints []string

	// Transport is used by the Client to drive HTTP requests. If not
	// provided, DefaultTransport will be used.
	Transport CancelableTransport

	// CheckRedirect specifies the policy for handling HTTP redirects.
	// If CheckRedirect is not nil, the Client calls it before
	// following an HTTP redirect. The sole argument is the number of
	// requests that have already been made. If CheckRedirect returns
	// an error, Client.Do will not make any further requests and return
	// the error back it to the caller.
	//
	// If CheckRedirect is nil, the Client uses its default policy,
	// which is to stop after 10 consecutive requests.
	CheckRedirect CheckRedirectFunc

	// Username specifies the user credential to add as an authorization header
	Username string

	// Password is the password for the specified user to add as an authorization header
	// to the request.
	Password string

	// HeaderTimeoutPerRequest specifies the time limit to wait for response
	// header in a single request made by the Client. The timeout includes
	// connection time, any redirects, and header wait time.
	//
	// For non-watch GET request, server returns the response body immediately.
	// For PUT/POST/DELETE request, server will attempt to commit request
	// before responding, which is expected to take `100ms + 2 * RTT`.
	// For watch request, server returns the header immediately to notify Client
	// watch start. But if server is behind some kind of proxy, the response
	// header may be cached at proxy, and Client cannot rely on this behavior.
	//
	// Especially, wait request will ignore this timeout.
	//
	// One API call may send multiple requests to different etcd servers until it
	// succeeds. Use context of the API to specify the overall timeout.
	//
	// A HeaderTimeoutPerRequest of zero means no timeout.
	HeaderTimeoutPerRequest time.Duration

	// SelectionMode is an EndpointSelectionMode enum that specifies the
	// policy for choosing the etcd cluster node to which requests are sent.
	SelectionMode EndpointSelectionMode
}

type CreateInOrderOptions 

type CreateInOrderOptions struct {
	// TTL defines a period of time after-which the Node should
	// expire and no longer exist. Values <= 0 are ignored. Given
	// that the zero-value is ignored, TTL cannot be used to set
	// a TTL of 0.
	TTL time.Duration
}

type DeleteOptions 

type DeleteOptions struct {
	// PrevValue specifies what the current value of the Node must
	// be in order for the Delete operation to succeed.
	//
	// Leaving this field empty means that the caller wishes to
	// ignore the current value of the Node. This cannot be used
	// to compare the Node's current value to an empty string.
	PrevValue string

	// PrevIndex indicates what the current ModifiedIndex of the
	// Node must be in order for the Delete operation to succeed.
	//
	// If PrevIndex is set to 0 (default), no comparison is made.
	PrevIndex uint64

	// Recursive defines whether or not all children of the Node
	// should be deleted. If set to true, all children of the Node
	// identified by the given key will be deleted. If left unset
	// or explicitly set to false, only a single Node will be
	// deleted.
	Recursive bool

	// Dir specifies whether or not this Node should be removed as a directory.
	Dir bool
}

type Discoverer 

type Discoverer interface {
	// Discover looks up the etcd servers for the domain.
	Discover(domain string) ([]string, error)
}

Discoverer is an interface that wraps the Discover method.

func NewSRVDiscover 

func NewSRVDiscover() Discoverer

NewSRVDiscover constructs a new Discoverer that uses the stdlib to lookup SRV records.

type EndpointSelectionMode 

type EndpointSelectionMode int
const (
	// EndpointSelectionRandom is the default value of the 'SelectionMode'.
	// As the name implies, the client object will pick a node from the members
	// of the cluster in a random fashion. If the cluster has three members, A, B,
	// and C, the client picks any node from its three members as its request
	// destination.
	EndpointSelectionRandom EndpointSelectionMode = iota

	// If 'SelectionMode' is set to 'EndpointSelectionPrioritizeLeader',
	// requests are sent directly to the cluster leader. This reduces
	// forwarding roundtrips compared to making requests to etcd followers
	// who then forward them to the cluster leader. In the event of a leader
	// failure, however, clients configured this way cannot prioritize among
	// the remaining etcd followers. Therefore, when a client sets 'SelectionMode'
	// to 'EndpointSelectionPrioritizeLeader', it must use 'client.AutoSync()' to
	// maintain its knowledge of current cluster state.
	//
	// This mode should be used with Client.AutoSync().
	EndpointSelectionPrioritizeLeader
)

type Error 

type Error struct {
	Code    int    `json:"errorCode"`
	Message string `json:"message"`
	Cause   string `json:"cause"`
	Index   uint64 `json:"index"`
}

func (Error) Error 

func (e Error) Error() string

type GetOptions 

type GetOptions struct {
	// Recursive defines whether or not all children of the Node
	// should be returned.
	Recursive bool

	// Sort instructs the server whether or not to sort the Nodes.
	// If true, the Nodes are sorted alphabetically by key in
	// ascending order (A to z). If false (default), the Nodes will
	// not be sorted and the ordering used should not be considered
	// predictable.
	Sort bool

	// Quorum specifies whether it gets the latest committed value that
	// has been applied in quorum of members, which ensures external
	// consistency (or linearizability).
	Quorum bool
}

type KeysAPI 

type KeysAPI interface {
	// Get retrieves a set of Nodes from etcd
	Get(ctx context.Context, key string, opts *GetOptions) (*Response, error)

	// Set assigns a new value to a Node identified by a given key. The caller
	// may define a set of conditions in the SetOptions. If SetOptions.Dir=true
	// then value is ignored.
	Set(ctx context.Context, key, value string, opts *SetOptions) (*Response, error)

	// Delete removes a Node identified by the given key, optionally destroying
	// all of its children as well. The caller may define a set of required
	// conditions in an DeleteOptions object.
	Delete(ctx context.Context, key string, opts *DeleteOptions) (*Response, error)

	// Create is an alias for Set w/ PrevExist=false
	Create(ctx context.Context, key, value string) (*Response, error)

	// CreateInOrder is used to atomically create in-order keys within the given directory.
	CreateInOrder(ctx context.Context, dir, value string, opts *CreateInOrderOptions) (*Response, error)

	// Update is an alias for Set w/ PrevExist=true
	Update(ctx context.Context, key, value string) (*Response, error)

	// Watcher builds a new Watcher targeted at a specific Node identified
	// by the given key. The Watcher may be configured at creation time
	// through a WatcherOptions object. The returned Watcher is designed
	// to emit events that happen to a Node, and optionally to its children.
	Watcher(key string, opts *WatcherOptions) Watcher
}

func NewKeysAPI 

func NewKeysAPI(c Client) KeysAPI

NewKeysAPI builds a KeysAPI that interacts with etcd's key-value API over HTTP.

func NewKeysAPIWithPrefix 

func NewKeysAPIWithPrefix(c Client, p string) KeysAPI

NewKeysAPIWithPrefix acts like NewKeysAPI, but allows the caller to provide a custom base URL path. This should only be used in very rare cases.

type Member 

type Member struct {
	// ID is the unique identifier of this Member.
	ID string `json:"id"`

	// Name is a human-readable, non-unique identifier of this Member.
	Name string `json:"name"`

	// PeerURLs represents the HTTP(S) endpoints this Member uses to
	// participate in etcd's consensus protocol.
	PeerURLs []string `json:"peerURLs"`

	// ClientURLs represents the HTTP(S) endpoints on which this Member
	// serves it's client-facing APIs.
	ClientURLs []string `json:"clientURLs"`
}

type MembersAPI 

type MembersAPI interface {
	// List enumerates the current cluster membership.
	List(ctx context.Context) ([]Member, error)

	// Add instructs etcd to accept a new Member into the cluster.
	Add(ctx context.Context, peerURL string) (*Member, error)

	// Remove demotes an existing Member out of the cluster.
	Remove(ctx context.Context, mID string) error

	// Update instructs etcd to update an existing Member in the cluster.
	Update(ctx context.Context, mID string, peerURLs []string) error

	// Leader gets current leader of the cluster
	Leader(ctx context.Context) (*Member, error)
}

func NewMembersAPI 

func NewMembersAPI(c Client) MembersAPI

NewMembersAPI constructs a new MembersAPI that uses HTTP to interact with etcd's membership API.

type Node 

type Node struct {
	// Key represents the unique location of this Node (e.g. "/foo/bar").
	Key string `json:"key"`

	// Dir reports whether node describes a directory.
	Dir bool `json:"dir,omitempty"`

	// Value is the current data stored on this Node. If this Node
	// is a directory, Value will be empty.
	Value string `json:"value"`

	// Nodes holds the children of this Node, only if this Node is a directory.
	// This slice of will be arbitrarily deep (children, grandchildren, great-
	// grandchildren, etc.) if a recursive Get or Watch request were made.
	Nodes Nodes `json:"nodes"`

	// CreatedIndex is the etcd index at-which this Node was created.
	CreatedIndex uint64 `json:"createdIndex"`

	// ModifiedIndex is the etcd index at-which this Node was last modified.
	ModifiedIndex uint64 `json:"modifiedIndex"`

	// Expiration is the server side expiration time of the key.
	Expiration *time.Time `json:"expiration,omitempty"`

	// TTL is the time to live of the key in second.
	TTL int64 `json:"ttl,omitempty"`
}

func (*Node) CodecDecodeSelf 

func (x *Node) CodecDecodeSelf(d *codec1978.Decoder)

func (*Node) CodecEncodeSelf 

func (x *Node) CodecEncodeSelf(e *codec1978.Encoder)

func (*Node) String 

func (n *Node) String() string

func (*Node) TTLDuration 

func (n *Node) TTLDuration() time.Duration

TTLDuration returns the Node's TTL as a time.Duration object

type Nodes 

type Nodes []*Node

func (*Nodes) CodecDecodeSelf 

func (x *Nodes) CodecDecodeSelf(d *codec1978.Decoder)

func (Nodes) CodecEncodeSelf 

func (x Nodes) CodecEncodeSelf(e *codec1978.Encoder)

func (Nodes) Len 

func (ns Nodes) Len() int

interfaces for sorting

func (Nodes) Less 

func (ns Nodes) Less(i, j int) bool

func (Nodes) Swap 

func (ns Nodes) Swap(i, j int)

type PermissionType 

type PermissionType int
const (
	ReadPermission PermissionType = iota
	WritePermission
	ReadWritePermission
)

type Permissions 

type Permissions struct {
	KV rwPermission `json:"kv"`
}

type PrevExistType 

type PrevExistType string

PrevExistType is used to define an existence condition when setting or deleting Nodes.

type Response 

type Response struct {
	// Action is the name of the operation that occurred. Possible values
	// include get, set, delete, update, create, compareAndSwap,
	// compareAndDelete and expire.
	Action string `json:"action"`

	// Node represents the state of the relevant etcd Node.
	Node *Node `json:"node"`

	// PrevNode represents the previous state of the Node. PrevNode is non-nil
	// only if the Node existed before the action occurred and the action
	// caused a change to the Node.
	PrevNode *Node `json:"prevNode"`

	// Index holds the cluster-level index at the time the Response was generated.
	// This index is not tied to the Node(s) contained in this Response.
	Index uint64 `json:"-"`
}

func (*Response) CodecDecodeSelf 

func (x *Response) CodecDecodeSelf(d *codec1978.Decoder)

func (*Response) CodecEncodeSelf 

func (x *Response) CodecEncodeSelf(e *codec1978.Encoder)

type Role 

type Role struct {
	Role        string       `json:"role"`
	Permissions Permissions  `json:"permissions"`
	Grant       *Permissions `json:"grant,omitempty"`
	Revoke      *Permissions `json:"revoke,omitempty"`
}

type SetOptions 

type SetOptions struct {
	// PrevValue specifies what the current value of the Node must
	// be in order for the Set operation to succeed.
	//
	// Leaving this field empty means that the caller wishes to
	// ignore the current value of the Node. This cannot be used
	// to compare the Node's current value to an empty string.
	//
	// PrevValue is ignored if Dir=true
	PrevValue string

	// PrevIndex indicates what the current ModifiedIndex of the
	// Node must be in order for the Set operation to succeed.
	//
	// If PrevIndex is set to 0 (default), no comparison is made.
	PrevIndex uint64

	// PrevExist specifies whether the Node must currently exist
	// (PrevExist) or not (PrevNoExist). If the caller does not
	// care about existence, set PrevExist to PrevIgnore, or simply
	// leave it unset.
	PrevExist PrevExistType

	// TTL defines a period of time after-which the Node should
	// expire and no longer exist. Values <= 0 are ignored. Given
	// that the zero-value is ignored, TTL cannot be used to set
	// a TTL of 0.
	TTL time.Duration

	// When refresh is set to true a TTL value can be updated
	// without firing a watch or changing the node value. A
	// value must not provided when refreshing a key.
	Refresh bool

	// Dir specifies whether or not this Node should be created as a directory.
	Dir bool
}

type User 

type User struct {
	User     string   `json:"user"`
	Password string   `json:"password,omitempty"`
	Roles    []string `json:"roles"`
	Grant    []string `json:"grant,omitempty"`
	Revoke   []string `json:"revoke,omitempty"`
}

type Watcher 

type Watcher interface {
	// Next blocks until an etcd event occurs, then returns a Response
	// representing that event. The behavior of Next depends on the
	// WatcherOptions used to construct the Watcher. Next is designed to
	// be called repeatedly, each time blocking until a subsequent event
	// is available.
	//
	// If the provided context is cancelled, Next will return a non-nil
	// error. Any other failures encountered while waiting for the next
	// event (connection issues, deserialization failures, etc) will
	// also result in a non-nil error.
	Next(context.Context) (*Response, error)
}

type WatcherOptions 

type WatcherOptions struct {
	// AfterIndex defines the index after-which the Watcher should
	// start emitting events. For example, if a value of 5 is
	// provided, the first event will have an index >= 6.
	//
	// Setting AfterIndex to 0 (default) means that the Watcher
	// should start watching for events starting at the current
	// index, whatever that may be.
	AfterIndex uint64

	// Recursive specifies whether or not the Watcher should emit
	// events that occur in children of the given keyspace. If set
	// to false (default), events will be limited to those that
	// occur for the exact key.
	Recursive bool
}

Source Files

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