AWS SDK for Swift

The SDK is composed of several core runtime modules located under Sources/Core/ that provide essential functionalities. Understanding these helps in navigating the SDK's underlying architecture:

• AWSClientRuntime: Provides most AWS-specific runtime functionalities, including concrete types, protocols, and enums. It serves as a central module with several other runtime dependencies.
• AWSSDKChecksums: Handles checksum implementations for AWS requests.
• AWSSDKCommon: Contains concrete types used across other runtime modules.
• AWSSDKEventStreamsAuth: Provides concrete types for signing AWS event stream messages.
• AWSSDKHTTPAuth: Contains the AWS SigV4 signer and types related to the authentication flow.
• AWSSDKIdentity: Manages AWS credentials and identity resolvers.

For deeper technical details, refer to the AWS Runtime Module Documentation in the API reference.

The AWS SDK for Swift has moved away from MD5 for payload checksums in favor of more secure algorithms. This change can cause issues with certain third-party "S3-like" storage services that expect MD5 for the S3 DeleteObjects operation.

To resolve this, you can implement and register a custom HttpInterceptorProvider that forces the SDK to use the Content-MD5 header for DeleteObjects requests.

Warning: This approach requires reading the entire request body into memory to compute the MD5 hash, which may cause performance issues or high memory usage for extremely large request bodies. Do not use this interceptor with AWS services or third-party services that already support the SDK's modern checksum options.

class DeleteObjectsMD5InterceptorProvider: HttpInterceptorProvider {

    class DeleteObjectsMD5Interceptor<InputType, OutputType>: Interceptor {
        typealias RequestType = HTTPRequest
        typealias ResponseType = HTTPResponse

        let MD5_HEADER = "Content-MD5"
        let OTHER_CHECKSUMS_PREFIX = "x-amz-checksum-"
        let OTHER_CHECKSUMS_SDK_PREFIX = "x-amz-sdk-checksum-"

        func readAfterSerialization(context: some AfterSerialization<InputType, HTTPRequest>) async throws {
            let request = context.getRequest()

            let bodyData: Data?
            switch request.body {
            case .stream(let stream):
                bodyData = try await stream.readToEndAsync()
            case .data:
                return
            case .noStream:
                bodyData = nil
            }

            request.body = .data(bodyData)
        }

        func modifyBeforeSigning(context: some MutableRequest<InputType, HTTPRequest>) async throws {
            let attributes = context.getAttributes()
            let request = context.getRequest()
            let body = request.body

            guard attributes.getServiceName() == "S3", attributes.getOperation() == "deleteObjects" else { return }

            let checksumHeaders = request.headers.headers.map { $0.name }.filter { $0.hasPrefix(OTHER_CHECKSUMS_PREFIX) }
            checksumHeaders.forEach { request.headers.remove(name: $0) }
            let checksumSDKHeaders = request.headers.headers.map { $0.name }.filter { $0.hasPrefix(OTHER_CHECKSUMS_SDK_PREFIX) }
            checksumSDKHeaders.forEach { request.headers.remove(name: $0) }
            let checksumTrailingHeaders = request.trailingHeaders.headers.map { $0.name }.filter { $0.hasPrefix(OTHER_CHECKSUMS_PREFIX) }
            checksumTrailingHeaders.forEach { request.trailingHeaders.remove(name: $0) }

            if case .data(let data) = body, let data {
                let md5data = try data.computeMD5()
                request.headers.add(name: MD5_HEADER, value: md5data.base64EncodedString())
            }
        }
    }

    func create<InputType, OutputType>() -> any Interceptor<InputType, OutputType, HTTPRequest, HTTPResponse> {
        return DeleteObjectsMD5Interceptor()
    }
}

// Configuration
let config = try await S3Client.Config(
    region: "us-east-1",
    httpInterceptorProviders: [DeleteObjectsMD5InterceptorProvider()]
)
let client = S3Client(config: config)

Developers of the SDK can modify build behavior by defining a local.properties file at the root of the project. This file allows for customizing service generation and including external builds (like smithy-swift) for local development.

Important Note: These instructions are intended for contributors to the SDK itself. End-users looking to use the SDK to access AWS services should refer to the main README.

# comma separated list of paths to `includeBuild()`
# This is useful for local development of smithy-swift in particular 
compositeProjects=../smithy-swift

# comma separated list of services to exclude from generation from sdk-codegen.
# specify service.VERSION matching the filenames in the models directory `aws-models -> service.VERSION.json`
excludeModels=rds-data.2018-08-01, groundstation.2019-05-23 

# comma separated list of services to generate from sdk-codegen.
# specify service.VERSION matching the filenames in the models directory `aws-models -> service.VERSION.json`.
onlyIncludeModels=lambda.2015-03-31

# when generating aws services build as a standalong project or not (rootProject = true)
buildStandaloneSdk=true