feat: Automatic clock skew adjustment #968

jbelkins · 2025-09-25T01:22:10Z

Description of changes

Automatically adjusts for differences between client and server wall clock time, to prevent signed requests from being rejected due to expired signature.

The basic smithy-swift implementation has a customization point for clock skew determination, but never detects a clock skew by default. The actual clock-skew determination to be used on AWS services is implemented in the companion aws-sdk-swift PR.

When clock skew is detected:
- Clock skew is calculated.
- The time difference is stored in a global store for future use when talking to that server.
- A retry of the request is initiated. The retry will use the calculated clock skew to adjust its signature expiration.
Subsequent requests to the same host will continue to use the previously calculated clock skew.
SignerMiddleware and SigV4Signer are modified to use clock skew when one is set.

Also:

Removed unneeded SmithyRetries dependency on CRT
Code cleanup of imports, unused code, etc.

Scope

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

jbelkins · 2025-09-26T22:39:17Z

...n/kotlin/software/amazon/smithy/swift/codegen/integration/middlewares/ClockSkewMiddleware.kt

+import software.amazon.smithy.swift.codegen.SwiftWriter
+import software.amazon.smithy.swift.codegen.integration.ProtocolGenerator
+import software.amazon.smithy.swift.codegen.middleware.MiddlewareRenderable
+


This type renders the clock skew provider into the orchestrator.

jbelkins · 2025-09-26T22:40:02Z

...main/kotlin/software/amazon/smithy/swift/codegen/integration/HTTPBindingProtocolGenerator.kt

            )
            operationMiddleware.appendMiddleware(operation, DeserializeMiddleware(ctx.model, ctx.symbolProvider))
            operationMiddleware.appendMiddleware(operation, LoggingMiddleware(ctx.model, ctx.symbolProvider))
+            operationMiddleware.appendMiddleware(operation, ClockSkewMiddleware(ctx.model, ctx.symbolProvider, clockSkewProviderSymbol))


Creates the type directly above to render the proper middleware.

jbelkins · 2025-09-26T22:41:17Z

...odegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/ProtocolGenerator.kt


+    val clockSkewProviderSymbol: Symbol
+        get() = DefaultClockSkewProviderSymbol
+


Here & above is the symbol for the clock skew provider.

In aws-sdk-swift, this property is overridden to provide an AWS-specific implementation.

jbelkins · 2025-09-26T22:41:57Z

Sources/ClientRuntime/ClockSkew/ClockSkewProvider.swift

+import struct Foundation.Date
+import struct Foundation.TimeInterval
+
+public typealias ClockSkewProvider<Request, Response> = @Sendable (Request, Response, Error, Date) -> TimeInterval?


Just a typealias for the closure type, since it's pretty long.

jbelkins · 2025-09-26T22:42:55Z

Sources/ClientRuntime/ClockSkew/ClockSkewStore.swift

+// SPDX-License-Identifier: Apache-2.0
+//
+
+import struct Foundation.TimeInterval


This type is just a concurrency-safe store for clock skew values, keyed by the hostname of the server where that clock skew was measured.

jbelkins · 2025-09-26T22:52:20Z

Sources/SmithyHTTPAuth/SigV4Signer.swift

            signedBodyValue: signedBodyValue,
            flags: flags,
-            date: Date(),
+            date: Date().addingTimeInterval(clockSkew),


Clock skew is applied to current date in the signing config to adjust signature expiration for the difference in client vs. server clock time.

jbelkins · 2025-09-26T22:52:52Z

Sources/SmithyRetries/ExponentialBackOffJitterType.swift

 //
 // SPDX-License-Identifier: Apache-2.0
 //
-import AwsCommonRuntimeKit


The extension below is unused so it & the CRT dependency are removed.

RetryErrorType+CRT below is entirely unneeded and is removed.

jbelkins · 2025-09-26T22:54:59Z

Tests/SmithyRetriesTests/RetryIntegrationTests.swift

+                } else {
+                    throw TestHTTPError(statusCode: response.statusCode)
+                }
+            })


The deserializer above and the switch statement below were corrected to ensure that a HTTP response is available during retries.

jbelkins · 2025-09-26T22:56:24Z

Tests/SmithyRetriesTests/RetryIntegrationTests.swift

        case .httpError(let statusCode):
-            throw TestHTTPError(statusCode: statusCode)
+            let httpStatusCode = HTTPStatusCode(rawValue: statusCode)!
+            return HTTPResponse(statusCode: httpStatusCode)


Rather than throw here, successfully return an HTTP response that indicates a non-success error code.
Instead, the service error will get thrown in the deserializer above (this is how "real" clients work.)

jbelkins · 2025-09-26T22:57:20Z

Package.swift

-                "SmithyRetriesAPI",
-                .product(name: "AwsCommonRuntimeKit", package: "aws-crt-swift"),
-            ]
+            dependencies: ["SmithyRetriesAPI"]


Removed the CRT dependency from SmithyRetries since the only CRT references in that target were unused and are now removed.

jbelkins · 2025-10-03T14:57:25Z

Sources/ClientRuntime/Orchestrator/OrchestratorBuilder.swift

    internal var deserialize: ((ResponseType, Context) async throws -> OutputType)?
    internal var retryStrategy: (any RetryStrategy)?
    internal var retryErrorInfoProvider: ((Error) -> RetryErrorInfo?)?
+    internal var clockSkewProvider: (ClockSkewProvider<RequestType, ResponseType>)?


The OrchestratorBuilder is modified to accept a clock skew provider. This is set in codegen when the orchestrator is constructed for an operation.

jbelkins · 2025-10-03T14:58:44Z

Sources/Smithy/RequestMessage.swift


 /// Message that is sent from client to service.
-public protocol RequestMessage {
+public protocol RequestMessage: Sendable {


Sendable is added to request & response types so they can be safely passed through async contexts.

(HTTPRequest and HTTPResponse are both already Sendable so no implementation change needed for this.)

jbelkins · 2025-10-03T14:59:59Z

Sources/SmithyHTTPAPI/HTTPRequest.swift

-        return Endpoint(uri: self.destination, headers: self.headers)
-    }
+    public var endpoint: Endpoint { .init(uri: destination, headers: headers) }
+    public internal(set) var signedAt: Date?


signedAt property is added to HTTPRequest. It is nil until the request is signed, then it is set with the Date that was used as "now" for signing.

jbelkins · 2025-10-03T15:00:42Z

Sources/SmithyHTTPAPI/HTTPRequest.swift

    public private(set) var port: UInt16?
    public private(set) var protocolType: URIScheme = .https
    public private(set) var trailingHeaders: Headers = Headers()
+    public private(set) var signedAt: Date?


Here, signedAt is added to the builder for HTTPRequest.

jbelkins · 2025-10-03T15:01:59Z

Sources/SmithyHTTPAuth/SigV4Signer.swift

        }

-        let signingConfig = try constructSigningConfig(identity: identity, signingProperties: signingProperties)
+        let signedAt = Date()


The signer gets current Date and keeps it in a var, so the same date can be used for signing and for updating the HTTPRequest.signedAt property.

jbelkins · 2025-10-03T15:03:26Z

Sources/SmithyHTTPAuth/SigV4Signer.swift

            signedBodyValue: signedBodyValue,
            flags: flags,
-            date: Date(),
+            date: signedAt.addingTimeInterval(clockSkew),


Correct the signedAt value with clock skew, then pass it into the signer.

jbelkins · 2025-10-03T15:05:09Z

Sources/SmithyHTTPClient/SdkHttpRequestBuilder+HTTPRequestBase.swift

+        from crtRequest: HTTPRequestBase,
+        originalRequest: HTTPRequest,
+        signedAt: Date
+    ) -> HTTPRequestBuilder {


Here, the update() function on HTTPRequestBuilder, which is used to apply a signature to an unsigned HTTPRequest, is modified to also set the updated request's signedAt property.

jbelkins · 2025-10-03T15:05:58Z

Tests/ClientRuntimeTests/NetworkingTests/Http/SdkRequestBuilderTests.swift

        crtRequest.path = pathToMatch

-        let updatedRequest = HTTPRequestBuilder().update(from: crtRequest, originalRequest: originalRequest).build()
+        let updatedRequest = HTTPRequestBuilder().update(from: crtRequest, originalRequest: originalRequest, signedAt: Date()).build()


A signedAt value had to be passed to allow compile. It is not used in this test.

jbelkins · 2025-10-03T15:08:14Z

Tests/ClientRuntimeTests/OrchestratorTests/OrchestratorTests.swift

        func computeNextBackoffDelay(attempt: Int) -> TimeInterval { 0.0 }
    }

+    func test_clockSkew_retriesWithClockSkewApplied() async throws {


This is an orchestrator test that verifies:

clock skew is obtained from the provider & stored

retry is performed when clock skew changes

retry is not performed when the error isn't retriable & clock skew didn't change

retry eventually succeeds if max attempts wasn't exceeded

jbelkins · 2025-10-03T15:08:52Z

Tests/SmithyHTTPClientTests/HttpRequestTests.swift

        XCTAssertNil(endpoint.url, "An invalid endpoint should result in a nil URL.")
    }
+
+    func test_requestBuilder_SignedAt() {


Simple test to verify builder sets signedAt field in built request

sichanyoo

Nit on a comment, everything lgtm

sichanyoo · 2025-10-07T16:25:16Z

Sources/ClientRuntime/ClockSkew/ClockSkewProvider.swift

+///   - response: The response that was returned from the server. (Typically this is a `HTTPResponse`)
+///   - error: The error that was returned by the server; typically this is a `ServiceError` with an error code that
+///   indicates clock skew is or might be the cause of the failed request.
+///   - previous: The previously clock skew value, or `nil` if non was recorded.


nit: The previously measured ...

jbelkins added 10 commits September 24, 2025 20:17

feat: Automatic clock skew adjustment

d0dd976

Add clock skew to orchestrator

049737e

Add clock skew to clients

0e113e8

Fix lint

cce2bb9

Fix codegen tests

ac093b5

Add @preconcurrency to clock closure

ca13a9f

Fix retry integration tests

e4beca8

Ensure response is received before calculating clock skew

8c9e5d2

Take offset out of WallClock

44ac3c9

Eliminate WallClock

614285d

jbelkins commented Sep 26, 2025

View reviewed changes

jbelkins added 6 commits October 1, 2025 15:17

Use signedAt date for client time

1576a53

Fix tests

ab142e1

Added test coverage

9de28f0

Fix tests

d1bc67a

Correct Swift 6 issues

70926f1

Fix codegen test

d95d2d3

jbelkins commented Oct 3, 2025

View reviewed changes

Pre-review cleanup

0931eda

jbelkins requested review from dayaffe and sichanyoo October 3, 2025 15:41

dayaffe approved these changes Oct 7, 2025

View reviewed changes

sichanyoo approved these changes Oct 7, 2025

View reviewed changes

jbelkins added 2 commits October 7, 2025 13:39

Merge branch 'main' into jbe/clock_skew

c8a9789

Correct error in doc comment

e5b6694

jbelkins mentioned this pull request Oct 7, 2025

feat: Automatic clock skew adjustment awslabs/aws-sdk-swift#2023

Merged

Merge branch 'main' into jbe/clock_skew

b187d32

jbelkins merged commit d31f1f0 into main Oct 7, 2025
33 checks passed

jbelkins deleted the jbe/clock_skew branch October 7, 2025 21:06


		val clockSkewProviderSymbol: Symbol
		get() = DefaultClockSkewProviderSymbol

feat: Automatic clock skew adjustment #968

feat: Automatic clock skew adjustment #968

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jbelkins commented Sep 25, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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jbelkins commented Sep 25, 2025 •

edited

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