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// Copyright 2020 Matthew Holt
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package acme full implements the ACME protocol specification as
// described in RFC 8555: https://tools.ietf.org/html/rfc8555.
//
// It is designed to work smoothly in large-scale deployments with
// high resilience to errors and intermittent network or server issues,
// with retries built-in at every layer of the HTTP request stack.
//
// NOTE: This is a low-level API. Most users will want the mholt/acmez
// package which is more concerned with configuring challenges and
// implementing the order flow. However, using this package directly
// is recommended for advanced use cases having niche requirements.
// See the examples in the examples/plumbing folder for a tutorial.
package acme
import (
"context"
"fmt"
"net/http"
"sync"
"time"
"go.uber.org/zap"
)
// Client facilitates ACME client operations as defined by the spec.
//
// Because the client is synchronized for concurrent use, it should
// not be copied.
//
// Many errors that are returned by a Client are likely to be of type
// Problem as long as the ACME server returns a structured error
// response. This package wraps errors that may be of type Problem,
// so you can access the details using the conventional Go pattern:
//
// var problem Problem
// if errors.As(err, &problem) {
// log.Printf("Houston, we have a problem: %+v", problem)
// }
//
// All Problem errors originate from the ACME server.
type Client struct {
// The ACME server's directory endpoint.
Directory string
// Custom HTTP client.
HTTPClient *http.Client
// Augmentation of the User-Agent header. Please set
// this so that CAs can troubleshoot bugs more easily.
UserAgent string
// Delay between poll attempts. Only used if server
// does not supply a Retry-Afer header. Default: 250ms
PollInterval time.Duration
// Maximum duration for polling. Default: 5m
PollTimeout time.Duration
// An optional logger. Default: no logs
Logger *zap.Logger
mu sync.Mutex // protects all unexported fields
dir Directory
nonces *stack
}
// GetDirectory retrieves the directory configured at c.Directory. It is
// NOT necessary to call this to provision the client. It is only useful
// if you want to access a copy of the directory yourself.
func (c *Client) GetDirectory(ctx context.Context) (Directory, error) {
if err := c.provision(ctx); err != nil {
return Directory{}, err
}
return c.dir, nil
}
func (c *Client) provision(ctx context.Context) error {
c.mu.Lock()
defer c.mu.Unlock()
if c.nonces == nil {
c.nonces = new(stack)
}
err := c.provisionDirectory(ctx)
if err != nil {
return fmt.Errorf("provisioning client: %w", err)
}
return nil
}
func (c *Client) provisionDirectory(ctx context.Context) error {
// don't get directory again if we already have it;
// checking any one of the required fields will do
if c.dir.NewNonce != "" {
return nil
}
if c.Directory == "" {
return fmt.Errorf("missing directory URL")
}
// prefer cached version if it's recent enough
directoriesMu.Lock()
defer directoriesMu.Unlock()
if dir, ok := directories[c.Directory]; ok {
if time.Since(dir.retrieved) < 12*time.Hour {
c.dir = dir.Directory
return nil
}
}
_, err := c.httpReq(ctx, http.MethodGet, c.Directory, nil, &c.dir)
if err != nil {
return err
}
directories[c.Directory] = cachedDirectory{c.dir, time.Now()}
return nil
}
func (c *Client) nonce(ctx context.Context) (string, error) {
nonce := c.nonces.pop()
if nonce != "" {
return nonce, nil
}
if c.dir.NewNonce == "" {
return "", fmt.Errorf("directory missing newNonce endpoint")
}
resp, err := c.httpReq(ctx, http.MethodHead, c.dir.NewNonce, nil, nil)
if err != nil {
return "", fmt.Errorf("fetching new nonce from server: %w", err)
}
return resp.Header.Get(replayNonce), nil
}
func (c *Client) pollInterval() time.Duration {
if c.PollInterval == 0 {
return defaultPollInterval
}
return c.PollInterval
}
func (c *Client) pollTimeout() time.Duration {
if c.PollTimeout == 0 {
return defaultPollTimeout
}
return c.PollTimeout
}
// Directory acts as an index for the ACME server as
// specified in the spec: "In order to help clients
// configure themselves with the right URLs for each
// ACME operation, ACME servers provide a directory
// object." §7.1.1
type Directory struct {
NewNonce string `json:"newNonce"`
NewAccount string `json:"newAccount"`
NewOrder string `json:"newOrder"`
NewAuthz string `json:"newAuthz,omitempty"`
RevokeCert string `json:"revokeCert"`
KeyChange string `json:"keyChange"`
Meta *DirectoryMeta `json:"meta,omitempty"`
}
// DirectoryMeta is optional extra data that may be
// included in an ACME server directory. §7.1.1
type DirectoryMeta struct {
TermsOfService string `json:"termsOfService,omitempty"`
Website string `json:"website,omitempty"`
CAAIdentities []string `json:"caaIdentities,omitempty"`
ExternalAccountRequired bool `json:"externalAccountRequired,omitempty"`
}
// stack is a simple thread-safe stack.
type stack struct {
stack []string
stackMu sync.Mutex
}
func (s *stack) push(v string) {
if v == "" {
return
}
s.stackMu.Lock()
defer s.stackMu.Unlock()
if len(s.stack) >= 64 {
return
}
s.stack = append(s.stack, v)
}
func (s *stack) pop() string {
s.stackMu.Lock()
defer s.stackMu.Unlock()
n := len(s.stack)
if n == 0 {
return ""
}
v := s.stack[n-1]
s.stack = s.stack[:n-1]
return v
}
// Directories seldom (if ever) change in practice, and
// client structs are often ephemeral, so we can cache
// directories to speed things up a bit for the user.
// Keyed by directory URL.
var (
directories = make(map[string]cachedDirectory)
directoriesMu sync.Mutex
)
type cachedDirectory struct {
Directory
retrieved time.Time
}
// replayNonce is the header field that contains a new
// anti-replay nonce from the server.
const replayNonce = "Replay-Nonce"
const (
defaultPollInterval = 250 * time.Millisecond
defaultPollTimeout = 5 * time.Minute
)
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