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[Part 0/6] fix(logging): stop os_log crashing on more than five arguments #8

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[Part 0/6] fix(logging): stop os_log crashing on more than five arguments #8

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8 changes: 4 additions & 4 deletions Sources/G6SensorCore/Session/TransmitterSession.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -466,10 +466,10 @@ public final class TransmitterSession: TransmitterConnectionDelegate {

let ack = try peripheral.requestBackfill(startTime: startTime, endTime: endTime)

log.default("Backfill acknowledged: status %{public}@, backfillStatus %{public}@, id %{public}@, range %{public}@-%{public}@, length %{public}@, crc %{public}@",
String(ack.status), String(ack.backfillStatus), String(ack.identifier),
String(ack.startTime), String(ack.endTime),
String(ack.bufferLength), String(format: "%04x", ack.bufferCRC))
log.default("Backfill acknowledged: %{public}@",
"status \(ack.status), backfillStatus \(ack.backfillStatus), id \(ack.identifier), " +
"range \(ack.startTime)-\(ack.endTime), length \(ack.bufferLength), " +
"crc \(String(format: "%04x", ack.bufferCRC))")

// Nothing stored for the window: an empty result, not a failure.
guard ack.bufferLength > 0 else {
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20 changes: 13 additions & 7 deletions Sources/G6SensorCore/Transport/OSLog.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,8 @@ extension OSLog {
}

private func log(_ message: StaticString, type: OSLogType, _ args: [CVarArg]) {
mirrorToFile(message, type: type, args)
let rendered = render(message, args)
mirrorToFile(rendered, type: type)

switch args.count {
case 0:
Expand All @@ -50,7 +51,10 @@ extension OSLog {
case 5:
os_log(message, log: self, type: type, args[0], args[1], args[2], args[3], args[4])
default:
os_log(message, log: self, type: type, args)
// os_log can't take the array as varargs: handing it over reads
// garbage pointers for each %@ and crashes. Log the rendered line.
assertionFailure("OSLog supports at most 5 arguments, got \(args.count): \(message)")
os_log("%{public}@", log: self, type: type, rendered)
}
}

Expand All @@ -65,15 +69,17 @@ extension OSLog {
return Self.categories[ObjectIdentifier(self)] ?? "G6SensorKit"
}

/// Mirrors every OSLog line into the exportable file log. Format
/// specifiers are OSLog-flavoured (%{public}@), so the privacy qualifier
/// is stripped before String(format:) sees them.
private func mirrorToFile(_ message: StaticString, type: OSLogType, _ args: [CVarArg]) {
/// Format specifiers are OSLog-flavoured (%{public}@), so the privacy
/// qualifier is stripped before String(format:) sees them.
private func render(_ message: StaticString, _ args: [CVarArg]) -> String {
let template = "\(message)"
.replacingOccurrences(of: "%{public}", with: "%")
.replacingOccurrences(of: "%{private}", with: "%")
let rendered = args.isEmpty ? template : String(format: template, arguments: args)
return args.isEmpty ? template : String(format: template, arguments: args)
}

/// Mirrors every OSLog line into the exportable file log.
private func mirrorToFile(_ rendered: String, type: OSLogType) {
let level: String
switch type {
case .debug: level = "DEBUG"
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