working-config-otel

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

vendor/google.golang.org/api/internal/s2a.go

@@ -0,0 +1,136 @@
+// 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 = "googleAutoMtlsConfiguration"
+
+// 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())
+}