38 lines
1.4 KiB
Swift
38 lines
1.4 KiB
Swift
//
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// Copyright 2022 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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//
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import Foundation
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// This code is ported from Android.
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// See <https://github.com/signalapp/Signal-Android/blob/cdcb1de3d4c0a6c7ff7f80eed37b490743c311e5/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/PushTransportDetails.java#L12-L57>.
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extension Data {
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public var paddedMessageBody: Data {
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let paddingLength: Int = {
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// We have our own padding scheme, but so does the cipher.
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// The +2 here is to ensure the cipher has room for a padding byte, plus the separator byte.
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// The -2 at the end of this undoes that.
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let messageLengthWithTerminator = self.count + 2
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var messagePartCount = messageLengthWithTerminator / 80
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if !messageLengthWithTerminator.isMultiple(of: 80) {
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messagePartCount += 1
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}
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let resultLength = messagePartCount * 80
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return resultLength - 2 - self.count
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}()
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return self + [0x80] + Data(count: paddingLength)
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}
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public func withoutPadding() -> Data {
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guard
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let lastNonZeroByteIndex = self.lastIndex(where: { $0 != 0 }),
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self[lastNonZeroByteIndex] == 0x80
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else {
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Logger.warn("Failed to find padding byte, returning unstripped data")
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return self
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}
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return self[..<lastNonZeroByteIndex]
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}
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}
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