Container Network Attachment Failure

[DefSecSentinel]

I am trying to do a simple load container, configure it, and run it using the Swift APIs but keep running into an error when the container gets created. I'm not sure if I'm doing something wrong or if its a deserialization bug in the json encoder/decoder. When I don't include any network configuration the container can't access the internet. Below is a section of my code and the error I'm receiving. Help here would be appreciated. I'm somewhat new to Swift so I could be overlooking something simple here. Default kernel works fine, container image loads fine and the dns configuration is written along with the network configuration options I add but when the container goes to run is when the error pops up.

Code:

var configuration = ContainerConfiguration(
    id: "sample-container-\(UUID().uuidString.prefix(8))",
    image: imageDescription,
    process: processConfig
    )

configuration.dns = ContainerConfiguration.DNSConfiguration(
    nameservers: ["8.8.8.8", "1.1.1.1"]
    )
    
let options = AttachmentOptions(hostname : configuration.id)
let attachment = AttachmentConfiguration(network: "default", options: options)

configuration.networks = [attachment]

let container = try await ClientContainer.create(
    configuration: configuration,
    kernel: kernel
    )
    
let stdio: [FIleHandle?] = [
    FileHandle.standardInput,
    FileHandle.standardOutput,
    FileHandle.standardError
    ]
    
let process = try await container.bootstrap(stdio: stdio)
    _ = try await process.start()

Error:

Error: internalError: "failed to create container" (cause: "unknown: "typeMismatch(Swift.String, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "networks", intValue: nil) _CodingKey(stringValue: "Index 0", intValue: 0)], debugDescription: "Expected to decode String but found a dictionary instead.", underlyingError: nil))"")

[DefSecSentinel]

Summary

The Swift API for Apple's container framework fails to create
containers when using AttachmentConfiguration objects in
ContainerConfiguration.networks, despite this being the documented
API. The CLI works correctly, but the Swift API throws a
typeMismatch decoding error.

Expected Behavior

According to the /container/documentation/c
ontainerclient/containerconfiguration/networks,
ContainerConfiguration.networks should accept
[AttachmentConfiguration] and containers should be created with
proper network connectivity.

Actual Behavior

When using AttachmentConfiguration objects as documented,
ClientContainer.create() fails with:
typeMismatch(Swift.String, Swift.DecodingError.Context(
codingPath: [CodingKeys(stringValue: "networks", intValue: nil),
_CodingKey(stringValue: "Index 0", intValue: 0)],
debugDescription: "Expected to decode String but found a
dictionary instead."
))

Investigation Results

Configuration Serialization Test

The configuration itself is valid - it encodes and decodes
correctly:
let encoder = JSONEncoder()
let data = try encoder.encode(configuration)
let decoder = JSONDecoder()
let decoded = try decoder.decode(ContainerConfiguration.self,
from: data)

CLI vs Swift API Comparison

CLI approach: container run --dns 8.8.8.8 --dns 1.1.1.1 colsonwilhoit/test:latest → Works perfectly

Swift API with networks: Configuration with AttachmentConfiguration → typeMismatch error

Swift API without networks: Configuration with empty networks → Container has no network interface

Error Location

The error occurs inside ClientContainer.create(), not in user
code. The serialization test proves the configuration is valid
before being passed to the container creation service.

Root Cause Analysis

The error path suggests that somewhere in the container creation
pipeline, the system expects networks[0] to be a String but finds
an AttachmentConfiguration dictionary. This indicates:

1. The Swift API documentation shows [AttachmentConfiguration] as
   the correct type
2. The internal implementation expects [String] (legacy format)
3. There's a mismatch between the public API and internal
   serialization

Looking at the source code, ContainerConfiguration has fallback
logic to handle both formats. However, somewhere in the ClientContainer.create() pipeline, this
conversion isn't working correctly.

Environment

MacOS Version: MacBook Pro Apple M1 - MacOS Tahoe Version 26 Beta (25A5346a)
Container Framework Version: container CLI version 0.3.0 (build: release, commit: 3fcf647)
Swift Version: swift-driver version: 1.127.14.1 Apple Swift version 6.2 (swiftlang-6.2.0.19.9 clang-1700.3.19.1)