EXC_BAD_ACCESS with concurrent access to inner's HTTPDataLoader running tasks

[malcommac]

Bug Report

The issue is triggered when multiple concurrent tasks try to access the dataLoaders's dictionary inside the HTTPDataLoader class. This dictionary stored in-progress tasks by using as a key the URLSessionTask instance created by the underlying URLSession and as a value the HTTPDataLoaderResponse object.

This error can trigger an EXC_BAD_ACCESS crash both on-device and on simulator.

You can reproduce this issue easily by executing a great amount of concurrent tasks:

func test_concurrentNetworkCallsCrash() async throws {
        var requests = [HTTPRequest]()
        let newClient = HTTPClient(baseURL: nil)

        for _ in 0..<100 {
            let req = try! HTTPRequest(method: .get, "https://www.apple.com")
            requests.append(req)
        }
        
        await withThrowingTaskGroup(of: HTTPResponse.self, body: { group in
            for req in requests {
                group.addTask(priority: .high) {
                    let result = try await req.fetch(newClient)
                    print(result.data?.count ?? 0)
                    return result
                }
            }
            
        })
    }

We could fix it by using a lock on write.