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Store: save one Fuel Savings field per edit, and update keychain items in place

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The Settings sliders called persistFuelSavingsSettings() on every value change,
which rewrote all four keys — four UserDefaults writes and four keychain round
trips per step, on the main thread, up to 90 times per drag. That is what made
them stutter.

saveFuelSavingsField(_:from:) writes just the field that moved, so a slider
gesture touches one key.

writeKeychain now uses SecItemUpdate and only falls back to SecItemAdd on
errSecItemNotFound. Delete-then-add cost two round trips to securityd and
briefly left the key holding no value at all — a window where the keychain, the
authoritative mirror on read, could disagree with the app-group defaults.

Tests pin the store half: a single-field save leaves the other three keys alone,
and the whole-settings save still writes all four.
This commit is contained in:
FuelBoard Contributor
2026-10-16 20:33:10 +01:00
parent 6ed4fe1210
commit 965a506a43
2 changed files with 91 additions and 2 deletions
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Shared/FuelStore.swift
+29 -2
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@@ -850,6 +850,26 @@ struct FuelStore {
saveString(settings.preferredAmount.unit.rawValue, service: fuelSavingsUnitKey)
}
/// One field of the Fuel Savings settings. A control that edits a single
/// value saves just that field, so moving the MPG slider rewrites the MPG key
/// instead of all four — four UserDefaults writes and four keychain round
/// trips per gesture is what made those sliders stutter.
enum FuelSavingsField {
case enabled
case mpg
case amount
case unit
}
static func saveFuelSavingsField(_ field: FuelSavingsField, from settings: FuelSavingsSettings) {
switch field {
case .enabled: saveString(settings.enabled ? "1" : "0", service: fuelSavingsEnabledKey)
case .mpg: saveString(String(settings.mpg), service: fuelSavingsMPGKey)
case .amount: saveString(String(settings.preferredAmount.value), service: fuelSavingsAmountKey)
case .unit: saveString(settings.preferredAmount.unit.rawValue, service: fuelSavingsUnitKey)
}
}
/// Superscript digit glyphs for the pounds & pence format's small raised
/// third digit (the forecourt style: "£1.29⁹").
private static let superscriptDigits: [Character] = ["⁰", "¹", "²", "³", "⁴", "⁵", "⁶", "⁷", "⁸", "⁹"]
@@ -1719,11 +1739,18 @@ struct FuelStore {
}
private static func writeKeychain(data: Data, service: String) {
let deleteQuery: [String: Any] = [
// Update in place when the item already exists. Delete-then-add cost two
// round trips to securityd and briefly left the key holding no value at
// all, which is half of why a setting could disagree between launches.
let query: [String: Any] = [
kSecClass as String: kSecClassGenericPassword,
kSecAttrService as String: service,
]
SecItemDelete(deleteQuery as CFDictionary)
let status = SecItemUpdate(query as CFDictionary,
[kSecValueData as String: data] as CFDictionary)
guard status == errSecItemNotFound else { return }
// Nothing stored under this service yet — the first write after the app
// was deleted, or a key added since. Add it.
let addQuery: [String: Any] = [
kSecClass as String: kSecClassGenericPassword,
kSecAttrService as String: service,