Repository: apple/swift-nio
File: Sources/NIOCore/ByteBuffer-hexdump.swift (Swift)

Code before:
        // If the buffer length fits in the max bytes limit in the hex dump, just dump the whole thing.
        if self.readableBytes <= maxBytes {
            return self.hexDump(format: .plain)
        }

        var buffer = self

        // Safe to force-unwrap because we just checked readableBytes is > maxBytes above.
        let front = buffer.readSlice(length: maxBytes / 2)!
        buffer.moveReaderIndex(to: buffer.writerIndex - maxBytes / 2)
        let back = buffer.readSlice(length: buffer.readableBytes)!

        let startHex = front.hexDumpCompact()
        let endHex = back.hexDumpCompact()
        return startHex + " ... " + endHex
    }

    /// Returns a `String` containing a detailed hex dump of this buffer.
    /// Intended to be used internally in ``hexDump(format:)``
    /// - parameters:
    ///     - lineOffset: an offset from the beginning of the outer buffer that is being dumped. It's used to print the line offset in hexdump -C format.
    ///     - paddingBefore: the amount of space to pad before the first byte dumped on this line, used in center and right columns.
    ///     - paddingAfter: the amount of sapce to pad after the last byte on this line, used in center and right columns.
    private func _hexDumpLine(lineOffset: Int, paddingBefore: Int = 0, paddingAfter: Int = 0) -> String {
        // Each line takes 78 visible characters + \n
        var result = ""
        result.reserveCapacity(79)

        // Left column of the hex dump signifies the offset from the beginning of the dumped buffer
        // and is separated from the next column with two spaces.
        result += String(lineOffset, radix: 16, padding: 8)
        result += "  "

        // Center column consists of:
        // - xxd-compatible dump of the first 8 bytes
        // - space
        // - xxd-compatible dump of the rest 8 bytes
        // If there are not enough bytes to dump, the column is padded with space.

        // If there's any padding on the left, apply that first.
        result += String(repeating: " ", count: paddingBefore * 3)

        // Add the left side of the central column
        let bytesInLeftColumn = max(8 - paddingBefore, 0)
        for byte in self.readableBytesView.prefix(bytesInLeftColumn) {
            result += String(byte, radix: 16, padding: 2)
            result += " "
        }

        // Add an extra space for the centre column.
        result += " "

Review comment (refactor):
Both these methods are almost identical to the `plain` ones. Can we refactor them to reuse the code instead?

Code after:
    /// so you should set those indices to desired location to get the offset and length that you need to dump.
    private func hexDumpPlain() -> String {
        self._hexDump(separateWithWhitespace: true)
    }

    /// Return a `String` of space delimited hexadecimal digits of the readable bytes in the buffer,
    /// in a format that's compatible with `xxd -r -p`, but clips the output to the max length of `maxBytes` bytes.
    /// If the dump contains more than the `maxBytes` bytes, this function will return the first `maxBytes/2`
    /// and the last `maxBytes/2` of that, replacing the rest with `...`, i.e. `01 02 03 ... 09 11 12`.
    ///
    /// - parameters:
    ///     - maxBytes: The maximum amount of bytes presented in the dump.
    private func hexDumpPlain(maxBytes: Int) -> String {
        self._hexDump(maxBytes: maxBytes, separateWithWhitespace: true)
    }

    /// Return a `String` of  hexadecimal digits of the readable bytes in the buffer,
    /// analog to `.plain` format but without whitespaces. This format guarantees not to emit whitespaces.
    /// `hexDumpCompact()` always dumps all readable bytes, i.e. from `readerIndex` to `writerIndex`,
    /// so you should set those indices to desired location to get the offset and length that you need to dump.
    private func hexDumpCompact() -> String {
        self._hexDump(separateWithWhitespace: false)
    }

    /// Return a `String` of  hexadecimal digits of the readable bytes in the buffer,
    /// analog to `.plain` format but without whitespaces and clips the output to the max length of `maxBytes` bytes.
    /// This format guarantees not to emmit whitespaces.
    /// If the dump contains more than the `maxBytes` bytes, this function will return the first `maxBytes/2`
    /// and the last `maxBytes/2` of that, replacing the rest with `...`, i.e. `010203...091112`.
    ///
    /// - parameters:
    ///     - maxBytes: The maximum amount of bytes presented in the dump.
    private func hexDumpCompact(maxBytes: Int) -> String {
        self._hexDump(maxBytes: maxBytes, separateWithWhitespace: false)
    }

    /// Returns a `String` containing a detailed hex dump of this buffer.
    /// Intended to be used internally in ``hexDump(format:)``
    /// - parameters:
    ///     - lineOffset: an offset from the beginning of the outer buffer that is being dumped. It's used to print the line offset in hexdump -C format.
    ///     - paddingBefore: the amount of space to pad before the first byte dumped on this line, used in center and right columns.
    ///     - paddingAfter: the amount of sapce to pad after the last byte on this line, used in center and right columns.
    private func _hexDumpLine(lineOffset: Int, paddingBefore: Int = 0, paddingAfter: Int = 0) -> String {
        // Each line takes 78 visible characters + \n
        var result = ""
        result.reserveCapacity(79)

        // Left column of the hex dump signifies the offset from the beginning of the dumped buffer
        // and is separated from the next column with two spaces.
        result += String(lineOffset, radix: 16, padding: 8)
        result += "  "