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

Code before:
//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftNIO open source project
//
// Copyright (c) 2017-2023 Apple Inc. and the SwiftNIO project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//

extension ByteBuffer {

    /// Return a `String` of hexadecimal digits of bytes in the Buffer,
    /// in a format that's compatible with `xxd -r -p`.
    /// `hexDumpShort()` 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.
    func hexDumpShort() -> String {
        var hexString = ""
        hexString.reserveCapacity(self.readableBytes*3)

        for byte in self.readableBytesView {
            hexString += "\(String(byte: byte, padding: 2)) "
        }

        return String(hexString.dropLast())
    }

    /// Return a `String` of hexadecimal digits of bytes in the Buffer.,
    /// in a format that's compatible with `xxd -r -p`, but clips the output to the max length of `limit` bytes.
    /// If the dump contains more than the `limit` bytes, this function will return the first `limit/2`
    /// and the last `limit/2` of that, replacing the rest with `...`, i.e. `01 02 03 ... 09 11 12`.
    ///
    /// - parameters:
    ///     - limit: The maximum amount of bytes presented in the dump.
    func hexDumpShort(limit: Int) -> String {
        // If the length of the resulting hex dump is smaller than the maximum allowed dump length,
        // return the full dump. Otherwise, dump the first and last pieces of the buffer, then concatenate them.
        if readableBytes <= limit {
            return self.hexDumpShort()
        } else {
            let startHex = self.getSlice(at: 0, length: limit/2)!.hexDumpShort()
            let endHex  = self.getSlice(at: self.readableBytes - limit/2, length: limit/2)!.hexDumpShort()
            return startHex + " ... " + endHex
        }

Review comment (suggestion):
```suggestion
        hexString.reserveCapacity(self.readableBytes * 3)
```

Code after:
//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftNIO open source project
//
// Copyright (c) 2023 Apple Inc. and the SwiftNIO project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//

extension ByteBuffer {

    /// Describes a ByteBuffer hexDump format.
    /// Can be either xxd output compatible, or hexdump compatible.
    public struct HexDumpFormat: Hashable, Sendable {

        enum Value: Hashable {
            case plain(maxBytes: Int? = nil)
            case detailed(maxBytes: Int? = nil)
        }

        let value: Value
        init(_ value: Value) { self.value = value }

        /// A plain hex dump format compatible with `xxd` CLI utility.
        public static let plain = Self(.plain(maxBytes: nil))

        /// A hex dump format compatible with `hexdump` command line utility.
        public static let detailed = Self(.detailed(maxBytes: nil))

        /// A detailed hex dump format compatible with `xxd`, clipped to `maxBytes` bytes dumped.
        /// This format will dump first `maxBytes / 2` bytes, and the last `maxBytes / 2` bytes, replacing the rest with " ... ".
        public static func plain(maxBytes: Int) -> Self {
            Self(.plain(maxBytes: maxBytes))
        }

        /// A hex dump format compatible with `hexdump` command line tool.
        /// This format will dump first `maxBytes / 2` bytes, and the last `maxBytes / 2` bytes, with a placeholder in between.
        public static func detailed(maxBytes: Int) -> Self {
            Self(.detailed(maxBytes: maxBytes))
        }
    }

    /// Return a `String` of space separated hexadecimal digits of the readable bytes in the buffer,