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s2a.go
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s2a.go
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// Copyright 2023 Google LLC.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package internal
import (
"encoding/json"
"log"
"sync"
"time"
"cloud.google.com/go/compute/metadata"
)
const configEndpointSuffix = "instance/platform-security/auto-mtls-configuration"
// The period an MTLS config can be reused before needing refresh.
var configExpiry = time.Hour
// GetS2AAddress returns the S2A address to be reached via plaintext connection.
func GetS2AAddress() string {
c, err := getMetadataMTLSAutoConfig().Config()
if err != nil {
return ""
}
if !c.Valid() {
return ""
}
return c.S2A.PlaintextAddress
}
type mtlsConfigSource interface {
Config() (*mtlsConfig, error)
}
// mdsMTLSAutoConfigSource is an instance of reuseMTLSConfigSource, with metadataMTLSAutoConfig as its config source.
var (
mdsMTLSAutoConfigSource mtlsConfigSource
once sync.Once
)
// getMetadataMTLSAutoConfig returns mdsMTLSAutoConfigSource, which is backed by config from MDS with auto-refresh.
func getMetadataMTLSAutoConfig() mtlsConfigSource {
once.Do(func() {
mdsMTLSAutoConfigSource = &reuseMTLSConfigSource{
src: &metadataMTLSAutoConfig{},
}
})
return mdsMTLSAutoConfigSource
}
// reuseMTLSConfigSource caches a valid version of mtlsConfig, and uses `src` to refresh upon config expiry.
// It implements the mtlsConfigSource interface, so calling Config() on it returns an mtlsConfig.
type reuseMTLSConfigSource struct {
src mtlsConfigSource // src.Config() is called when config is expired
mu sync.Mutex // mutex guards config
config *mtlsConfig // cached config
}
func (cs *reuseMTLSConfigSource) Config() (*mtlsConfig, error) {
cs.mu.Lock()
defer cs.mu.Unlock()
if cs.config.Valid() {
return cs.config, nil
}
c, err := cs.src.Config()
if err != nil {
return nil, err
}
cs.config = c
return c, nil
}
// metadataMTLSAutoConfig is an implementation of the interface mtlsConfigSource
// It has the logic to query MDS and return an mtlsConfig
type metadataMTLSAutoConfig struct{}
var httpGetMetadataMTLSConfig = func() (string, error) {
return metadata.Get(configEndpointSuffix)
}
func (cs *metadataMTLSAutoConfig) Config() (*mtlsConfig, error) {
resp, err := httpGetMetadataMTLSConfig()
if err != nil {
log.Printf("querying MTLS config from MDS endpoint failed: %v", err)
return defaultMTLSConfig(), nil
}
var config mtlsConfig
err = json.Unmarshal([]byte(resp), &config)
if err != nil {
log.Printf("unmarshalling MTLS config from MDS endpoint failed: %v", err)
return defaultMTLSConfig(), nil
}
if config.S2A == nil {
log.Printf("returned MTLS config from MDS endpoint is invalid: %v", config)
return defaultMTLSConfig(), nil
}
// set new expiry
config.Expiry = time.Now().Add(configExpiry)
return &config, nil
}
func defaultMTLSConfig() *mtlsConfig {
return &mtlsConfig{
S2A: &s2aAddresses{
PlaintextAddress: "",
MTLSAddress: "",
},
Expiry: time.Now().Add(configExpiry),
}
}
// s2aAddresses contains the plaintext and/or MTLS S2A addresses.
type s2aAddresses struct {
// PlaintextAddress is the plaintext address to reach S2A
PlaintextAddress string `json:"plaintext_address"`
// MTLSAddress is the MTLS address to reach S2A
MTLSAddress string `json:"mtls_address"`
}
// mtlsConfig contains the configuration for establishing MTLS connections with Google APIs.
type mtlsConfig struct {
S2A *s2aAddresses `json:"s2a"`
Expiry time.Time
}
func (c *mtlsConfig) Valid() bool {
return c != nil && c.S2A != nil && !c.expired()
}
func (c *mtlsConfig) expired() bool {
return c.Expiry.Before(time.Now())
}