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package ec2rolecreds
import (
"bufio"
"encoding/json"
"fmt"
"path"
"strings"
"time"
"github.com/aws/aws-sdk-go/aws/awserr"
"github.com/aws/aws-sdk-go/aws/client"
"github.com/aws/aws-sdk-go/aws/credentials"
"github.com/aws/aws-sdk-go/aws/ec2metadata"
)
// ProviderName provides a name of EC2Role provider
const ProviderName = "EC2RoleProvider"
// A EC2RoleProvider retrieves credentials from the EC2 service, and keeps track if
// those credentials are expired.
//
// Example how to configure the EC2RoleProvider with custom http Client, Endpoint
// or ExpiryWindow
//
// p := &ec2rolecreds.EC2RoleProvider{
// // Pass in a custom timeout to be used when requesting
// // IAM EC2 Role credentials.
// Client: ec2metadata.New(sess, aws.Config{
// HTTPClient: &http.Client{Timeout: 10 * time.Second},
// }),
//
// // Do not use early expiry of credentials. If a non zero value is
// // specified the credentials will be expired early
// ExpiryWindow: 0,
// }
type EC2RoleProvider struct {
credentials.Expiry
// Required EC2Metadata client to use when connecting to EC2 metadata service.
Client *ec2metadata.EC2Metadata
// ExpiryWindow will allow the credentials to trigger refreshing prior to
// the credentials actually expiring. This is beneficial so race conditions
// with expiring credentials do not cause request to fail unexpectedly
// due to ExpiredTokenException exceptions.
//
// So a ExpiryWindow of 10s would cause calls to IsExpired() to return true
// 10 seconds before the credentials are actually expired.
//
// If ExpiryWindow is 0 or less it will be ignored.
ExpiryWindow time.Duration
}
// NewCredentials returns a pointer to a new Credentials object wrapping
// the EC2RoleProvider. Takes a ConfigProvider to create a EC2Metadata client.
// The ConfigProvider is satisfied by the session.Session type.
func NewCredentials(c client.ConfigProvider, options ...func(*EC2RoleProvider)) *credentials.Credentials {
p := &EC2RoleProvider{
Client: ec2metadata.New(c),
}
for _, option := range options {
option(p)
}
return credentials.NewCredentials(p)
}
// NewCredentialsWithClient returns a pointer to a new Credentials object wrapping
// the EC2RoleProvider. Takes a EC2Metadata client to use when connecting to EC2
// metadata service.
func NewCredentialsWithClient(client *ec2metadata.EC2Metadata, options ...func(*EC2RoleProvider)) *credentials.Credentials {
p := &EC2RoleProvider{
Client: client,
}
for _, option := range options {
option(p)
}
return credentials.NewCredentials(p)
}
// Retrieve retrieves credentials from the EC2 service.
// Error will be returned if the request fails, or unable to extract
// the desired credentials.
func (m *EC2RoleProvider) Retrieve() (credentials.Value, error) {
credsList, err := requestCredList(m.Client)
if err != nil {
return credentials.Value{ProviderName: ProviderName}, err
}
if len(credsList) == 0 {
return credentials.Value{ProviderName: ProviderName}, awserr.New("EmptyEC2RoleList", "empty EC2 Role list", nil)
}
credsName := credsList[0]
roleCreds, err := requestCred(m.Client, credsName)
if err != nil {
return credentials.Value{ProviderName: ProviderName}, err
}
m.SetExpiration(roleCreds.Expiration, m.ExpiryWindow)
return credentials.Value{
AccessKeyID: roleCreds.AccessKeyID,
SecretAccessKey: roleCreds.SecretAccessKey,
SessionToken: roleCreds.Token,
ProviderName: ProviderName,
}, nil
}
// A ec2RoleCredRespBody provides the shape for unmarshalling credential
// request responses.
type ec2RoleCredRespBody struct {
// Success State
Expiration time.Time
AccessKeyID string
SecretAccessKey string
Token string
// Error state
Code string
Message string
}
const iamSecurityCredsPath = "/iam/security-credentials"
// requestCredList requests a list of credentials from the EC2 service.
// If there are no credentials, or there is an error making or receiving the request
func requestCredList(client *ec2metadata.EC2Metadata) ([]string, error) {
resp, err := client.GetMetadata(iamSecurityCredsPath)
if err != nil {
return nil, awserr.New("EC2RoleRequestError", "no EC2 instance role found", err)
}
credsList := []string{}
s := bufio.NewScanner(strings.NewReader(resp))
for s.Scan() {
credsList = append(credsList, s.Text())
}
if err := s.Err(); err != nil {
return nil, awserr.New("SerializationError", "failed to read EC2 instance role from metadata service", err)
}
return credsList, nil
}
// requestCred requests the credentials for a specific credentials from the EC2 service.
//
// If the credentials cannot be found, or there is an error reading the response
// and error will be returned.
func requestCred(client *ec2metadata.EC2Metadata, credsName string) (ec2RoleCredRespBody, error) {
resp, err := client.GetMetadata(path.Join(iamSecurityCredsPath, credsName))
if err != nil {
return ec2RoleCredRespBody{},
awserr.New("EC2RoleRequestError",
fmt.Sprintf("failed to get %s EC2 instance role credentials", credsName),
err)
}
respCreds := ec2RoleCredRespBody{}
if err := json.NewDecoder(strings.NewReader(resp)).Decode(&respCreds); err != nil {
return ec2RoleCredRespBody{},
awserr.New("SerializationError",
fmt.Sprintf("failed to decode %s EC2 instance role credentials", credsName),
err)
}
if respCreds.Code != "Success" {
// If an error code was returned something failed requesting the role.
return ec2RoleCredRespBody{}, awserr.New(respCreds.Code, respCreds.Message, nil)
}
return respCreds, nil
}
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