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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package secret
import (
"context"
"encoding/json"
"flag"
"fmt"
"strings"
"cloud.google.com/go/compute/metadata"
secretmanager "cloud.google.com/go/secretmanager/apiv1"
"cloud.google.com/go/secretmanager/apiv1/secretmanagerpb"
)
// FlagResolver contains the dependencies necessary to resolve a Secret flag.
type FlagResolver struct {
Context context.Context
Client secretClient
DefaultProjectID string
}
const secretSuffix = "[ specify `secret:[project name/]<secret name>` to read from Secret Manager ]"
// Flag defines a string flag on set that will be resolved using r.
// The return value is the address of a string variable that stores the value of the flag.
func (r *FlagResolver) Flag(set *flag.FlagSet, name, usage string) *string {
p := new(string)
r.FlagVar(set, p, name, usage)
return p
}
// FlagVar defines a string flag on set that will be resolved using r.
// The argument p points to a string variable in which to store the value of the flag.
func (r *FlagResolver) FlagVar(set *flag.FlagSet, p *string, name, usage string) {
suffixedUsage := usage + "\n" + secretSuffix
set.Func(name, suffixedUsage, func(flagValue string) error {
value, err := r.ResolveSecret(flagValue)
if err != nil {
return err
}
*p = value
return nil
})
}
// ResolveSecret resolves a string value, which need not be a flag.
func (r *FlagResolver) ResolveSecret(flagValue string) (string, error) {
if r.Client == nil || r.Context == nil {
return "", fmt.Errorf("secret resolver was not initialized")
}
if !strings.HasPrefix(flagValue, "secret:") {
return flagValue, nil
}
secretName := strings.TrimPrefix(flagValue, "secret:")
projectID := r.DefaultProjectID
if parts := strings.SplitN(secretName, "/", 2); len(parts) == 2 {
projectID, secretName = parts[0], parts[1]
}
if projectID == "" {
return "", fmt.Errorf("missing project ID: none specified in %q, and no default set (not on GCP?)", secretName)
}
result, err := r.Client.AccessSecretVersion(r.Context, &secretmanagerpb.AccessSecretVersionRequest{
Name: buildNamePath(projectID, secretName, "latest"),
})
if err != nil {
return "", fmt.Errorf("reading secret %q from project %v failed: %v", secretName, projectID, err)
}
return string(result.Payload.GetData()), nil
}
// JSONVarFlag defines a flag on set that behaves like Flag and then
// json.Unmarshals the resulting string into value.
func (r *FlagResolver) JSONVarFlag(set *flag.FlagSet, value interface{}, name, usage string) {
suffixedUsage := usage + "\n" + fmt.Sprintf("A JSON representation of a %T.", value) + "\n" + secretSuffix
set.Func(name, suffixedUsage, func(flagValue string) error {
stringValue, err := r.ResolveSecret(flagValue)
if err != nil {
return err
}
return json.Unmarshal([]byte(stringValue), value)
})
}
// DefaultResolver is the FlagResolver used by the convenience functions.
var DefaultResolver FlagResolver
// Flag defines a string flag on flag.CommandLine that supports Secret Manager
// resolution for values like "secret:<secret name>". InitFlagSupport must be
// called before flag.Parse.
func Flag(name, usage string) *string {
return DefaultResolver.Flag(flag.CommandLine, name, usage)
}
// FlagVar defines a string flag on flag.CommandLine that supports Secret Manager
// resolution for values like "secret:<secret name>". InitFlagSupport must be
// called before flag.Parse.
func FlagVar(p *string, name, usage string) {
DefaultResolver.FlagVar(flag.CommandLine, p, name, usage)
}
// JSONVarFlag defines a flag on flag.CommandLine that behaves like Flag
// and then json.Unmarshals the resulting string into value.
func JSONVarFlag(value interface{}, name, usage string) {
DefaultResolver.JSONVarFlag(flag.CommandLine, value, name, usage)
}
// InitFlagSupport initializes the dependencies for flags declared with Flag.
func InitFlagSupport(ctx context.Context) error {
client, err := secretmanager.NewClient(ctx)
if err != nil {
return err
}
DefaultResolver = FlagResolver{
Context: ctx,
Client: client,
}
if metadata.OnGCE() {
projectID, err := metadata.ProjectID()
if err != nil {
return err
}
DefaultResolver.DefaultProjectID = projectID
}
return nil
}