s3_get_bucket_policy.go

// snippet-comment:[These are tags for the AWS doc team's sample catalog. Do not remove.]
// snippet-sourceauthor:[Doug-AWS]
// snippet-sourcedescription:[Gets the policy of an S3 bucket.]
// snippet-keyword:[Amazon Simple Storage Service]
// snippet-keyword:[Amazon S3]
// snippet-keyword:[GetBucketPolicy function]
// snippet-keyword:[Go]
// snippet-sourcesyntax:[go]
// snippet-service:[s3]
// snippet-keyword:[Code Sample]
// snippet-sourcetype:[full-example]
// snippet-sourcedate:[2018-03-16]
/*
   Copyright 2010-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.

   This file is licensed under the Apache License, Version 2.0 (the "License").
   You may not use this file except in compliance with the License. A copy of
   the License is located at

    http://aws.amazon.com/apache2.0/

   This file 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 main

import (
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/awserr"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/s3"
    "bytes"
    "encoding/json"
    "fmt"
    "os"
    "path/filepath"
)

// Prints the policy for a bucket. If the bucket doesn't exist, or there was
// and error an error message will be printed instead.
//
// Usage:
//    go run s3_get_bucket_policy.go BUCKET_NAME
func main() {
    if len(os.Args) != 2 {
        exitErrorf("bucket name required\nUsage: %s bucket_name",
            filepath.Base(os.Args[0]))
    }
    
    bucket := os.Args[1]

    // Initialize a session in us-west-2 that the SDK will use to load
    // credentials from the shared credentials file ~/.aws/credentials.
    sess, err := session.NewSession(&aws.Config{
        Region: aws.String("us-west-2")},
    )

    // Create S3 service client
    svc := s3.New(sess)

    // Call S3 to retrieve the policy for the selected bucket.
    result, err := svc.GetBucketPolicy(&s3.GetBucketPolicyInput{
        Bucket: aws.String(bucket),
    })
    if err != nil {
        // Special error handling for the when the bucket doesn't
        // exists so we can give a more direct error message from the CLI.
        if aerr, ok := err.(awserr.Error); ok {
            switch aerr.Code() {
            case s3.ErrCodeNoSuchBucket:
                exitErrorf("Bucket %q does not exist.", bucket)
            case "NoSuchBucketPolicy":
                exitErrorf("Bucket %q does not have a policy.", bucket)
            }
        }
        exitErrorf("Unable to get bucket %q policy, %v.", bucket, err)
    }

    out := bytes.Buffer{}
    policyStr := aws.StringValue(result.Policy)
    if err := json.Indent(&out, []byte(policyStr), "", "  "); err != nil {
        exitErrorf("Failed to pretty print bucket policy, %v.", err)
    }

    fmt.Printf("%q's Bucket Policy:\n", bucket)
    fmt.Println(out.String())
}

func exitErrorf(msg string, args ...interface{}) {
    fmt.Fprintf(os.Stderr, msg+"\n", args...)
    os.Exit(1)
}