HTTP Client Lifetime (ARCH9083)

Key swift.performance.http-client-lifetime · Severity error · Category performance

Flags URLSession(configuration:) created inside a function body - each call rebuilds the connection pool.

Incorrect

func fetch(_ url: URL) async throws -> Data {
    let session = URLSession(configuration: .default)
    return try await session.data(from: url).0
}

Correct

private let session = URLSession(configuration: .default)
func fetch(_ url: URL) async throws -> Data { try await session.data(from: url).0 }

Fix

Create the session once and reuse it (or use URLSession.shared).