truncating for big contentLength (#119)

Daiki Matsudate · web-flow · commit 03399ef4651d · 2022-06-16T23:44:20.000-07:00
When contentLength is greater than 8 bits, i.e., greater than UInt8.max, the original implementation crashes.
To work around this, use UInt8.init(truncatingIfNeeded:) to truncate only the lower 8 bits.
diff --git a/Sources/Crypto/ASN1/ASN1.swift b/Sources/Crypto/ASN1/ASN1.swift
@@ -438,7 +438,7 @@ extension ASN1 {
             for shift in (0..<(lengthBytesNeeded - 1)).reversed() {
                 // Shift and mask the integer.
                 self.serializedBytes.formIndex(after: &writeIndex)
-                self.serializedBytes[writeIndex] = UInt8((contentLength >> (shift * 8)) | 0x80 )
+                self.serializedBytes[writeIndex] = UInt8(truncatingIfNeeded: (contentLength >> (shift * 8)) | 0x80 )
             }
 
             assert(writeIndex == self.serializedBytes.index(lengthIndex, offsetBy: lengthBytesNeeded - 1))

Original file line number	Diff line number	Diff line change
`@@ -438,7 +438,7 @@ extension ASN1 {`
`438`	`438`	`for shift in (0..<(lengthBytesNeeded - 1)).reversed() {`
`439`	`439`	`// Shift and mask the integer.`
`440`	`440`	`self.serializedBytes.formIndex(after: &writeIndex)`
`441`		`- self.serializedBytes[writeIndex] = UInt8((contentLength >> (shift * 8)) \| 0x80 )`
	`441`	`+ self.serializedBytes[writeIndex] = UInt8(truncatingIfNeeded: (contentLength >> (shift * 8)) \| 0x80 )`
`442`	`442`	`}`
`443`	`443`
`444`	`444`	`assert(writeIndex == self.serializedBytes.index(lengthIndex, offsetBy: lengthBytesNeeded - 1))`