Referencing AWS S3 bucket name programmatically instead of hardcoded

Question

I'm working with AWS Amplify to develop an iOS application. I've added storage through S3 to host some assets and am trying to configure the application to download them. The only issue is that every example I see has the bucket name and path hardcoded, but because I have multiple environments and make new environments sometimes and each bucket has the environment name appended to it, I don't want to have to rewrite the bucket name each time.

For example if I'm in my test environment the bucket name might be assetsxxxxxx-test but if I switch to a new environment, I might be referencing assetsyyyyy-dev let's say.

The thing is the bucket name is referenced in the aswconfiguration.json file:

"S3TransferUtility": {
    "Default": {
        "Bucket": "assetsxxxxx-test",
        "Region": "us-east-2"
    }
}

So my question is how can I reference that bucket name programmatically so that when that field is rewritten when I switch environments, I won't have to change my code.

Thanks

score 1 · Answer 1 · answered Apr 17 '20 at 23:14

I am unclear what your using to build your Amplify resources (cloudformation, terrraform, ?console? etc) and in turn create your 'aswconfiguration.json file'. But it sound like you need to pass in a dynamic variable which is very achievable.

If your using a codepipeline, codebuild arrangement to deploy your resources and config file you could either use bash commands (sed or perl) during the codebuild stage to change the variable. Or a custom lambda to update the file contents and copy to S3, which you would then pass the dynamic variable into the environment variable paramter.

Normally if this was a cloudformation template you could use a Pseudo Parameter Reference !Sub command, and then the parameter would be declared early on and reference whatever environment it is, e.g.

"Bucket": "asssetsxxxxxx-${Environment}"

Thanks! The amplify resources are configured using the Amplify CLI, which for each resource generates its own cloudformation templates. I have no issue with actually switching environments as amplify makes it as simple as calling "amplify env checkout {env name}" and then "amplify pull" the awsconfiguration.json bucket name will automatically change to the right bucket. My question is how to reference that bucket name in the swift code instead of hardcoding a string when the transfer utility asks for bucket name? — Julien S., Apr 18 '20 at 00:49

score 1 · Answer 2 · answered May 07 '20 at 17:21

I just had this same question. My solution was similar but not quite the same. First I created the Codable struct like this

import Foundation

struct AwsConfiguration: Codable {
    struct S3TransferUtility : Codable {
        private enum CodingKeys: String, CodingKey {
            case defaultConfig = "Default"
        }

        struct DefaultConfig : Codable {
            private enum CodingKeys: String, CodingKey {
                case bucket = "Bucket"
                case region = "Region"
            }
            var bucket: String
            var region: String
        }

        var defaultConfig: DefaultConfig
    }

    private enum CodingKeys: String, CodingKey {
        case s3TransferUtility = "S3TransferUtility"
    }

    var s3TransferUtility: S3TransferUtility
}

Then I have a DataHelper class defined

final class DataHelper {
    static func load<T: Decodable>(_ filename: String, as type: T.Type = T.self) -> T {
        let data: Data

        guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
            else {
                fatalError("Couldn't find \(filename) in main bundle.")
        }

        do {
            data = try Data(contentsOf: file)
        } catch {
            fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
        }

        do {
            let decoder = JSONDecoder()
            return try decoder.decode(T.self, from: data)
        } catch {
            fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
        }
    }
}

Then put awsconfiguration.json in your test target. Then you can write a unit test like so

    func testReadAWSConfiguration() throws {
        let config: AwsConfiguration = DataHelper.load("awsconfiguration.json")

        print ("************config bucket: \(config.s3TransferUtility.defaultConfig.bucket) " +
            "\n************config region: \(config.s3TransferUtility.defaultConfig.region)")
        XCTAssertNotEqual("", config.s3TransferUtility.defaultConfig.bucket)
        XCTAssertNotEqual("", config.s3TransferUtility.defaultConfig.region)
    }

score 0 · Accepted Answer · answered Apr 24 '20 at 05:01

I solved it. For anybody else wondering, I'm still not sure if there's a field built in to the AWS SDK, but I decided to parse the awsconfiguration.json file directly int a custom struct:

struct AWSConfigurationJSON: Codable{
    let S3TransferUtility: S3TransferUtility
}

struct S3TransferUtility: Codable{
    let Default: S3TransferUtilityDefault
}

struct S3TransferUtilityDefault: Codable{
    let Bucket: String
    let Region: String
}

and then I read the file and parsed the JSON.

if let path = Bundle.main.path(forResource: "awsconfiguration", ofType: "json") {
            do{
                let data = try Data(contentsOf: URL(fileURLWithPath: path), options: .mappedIfSafe)
                let jsonResult = try JSONDecoder().decode(AWSConfigurationJSON.self, from: data)
                print(jsonResult.S3TransferUtility.Default.Bucket)
                bucketPath = jsonResult.S3TransferUtility.Default.Bucket
            }catch let e{
                print("error \(e)")
                bucketPath = ""

            }
        }else{
            bucketPath = ""

        }

score 0 · Answer 4 · answered Nov 10 '21 at 02:41

You can access the bucket name using the following:

if let s3TransferInfo = AWSInfo.default().defaultServiceInfo("S3TransferUtility") {
    self.bucket = s3TransferInfo.infoDictionary["Bucket"] as? String
}

so you don't need to roll your own JSON parsing of the config

Referencing AWS S3 bucket name programmatically instead of hardcoded

4 Answers4

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