refactor: random bytes generation; data and string extensions update (#791)

* Update HexDecodable+Extensions.swift

* Update Data+Extension.swift

* Update String+Extension.swift

* chore: refactoring + documentation for Data.fromHex function

* updates as per conversations

* chore: updated docs for randomBytes + minor refactoring

* chore: fixed typo in Data+Extension.swift

* chore: lint issue fixed

* add string spit test

* Revert "add string spit test" github issue

This reverts commit e8a5e2b.

---------

Co-authored-by: Jenea Vranceanu <jeneavranceanu@gmail.com>
Co-authored-by: Jenea Vranceanu <36865532+JeneaVranceanu@users.noreply.github.com>

Author: pharms-eth

Sources/Web3Core/EthereumNetwork/Utility/HexDecodable+Extensions.swift

@@ -17,16 +17,17 @@ extension BigInt: LiteralInitiableFromString { }
 extension BigUInt: LiteralInitiableFromString { }
 
 extension Data: LiteralInitiableFromString {
+    /// Converts hexadecimal string representation of some bytes into actual bytes.
+    /// Notes:
+    ///  - empty string will return `nil`;
+    ///  - empty hex string, meaning it's equal to `"0x"`, will return empty `Data` object.
+    /// - Parameter hex: bytes represented as string.
+    /// - Returns: optional raw bytes.
     public static func fromHex(_ hex: String) -> Data? {
-        let string = hex.lowercased().stripHexPrefix()
-        let array = [UInt8](hex: string)
-        if array.count == 0 {
-            if hex == "0x" || hex == "" {
-                return Data()
-            } else {
-                return nil
-            }
-        }
-        return Data(array)
+        let hex = hex.lowercased().trim()
+        guard !hex.isEmpty else { return nil }
+        guard hex != "0x" else { return Data() }
+        let bytes = [UInt8](hex: hex.stripHexPrefix())
+        return bytes.isEmpty ? nil : Data(bytes)
     }
 }

Sources/Web3Core/Utility/Data+Extension.swift

@@ -5,7 +5,8 @@
 
 import Foundation
 
-extension Data {
+public extension Data {
+
     init<T>(fromArray values: [T]) {
         let values = values
         let ptrUB = values.withUnsafeBufferPointer { (ptr: UnsafeBufferPointer) in return ptr }
@@ -33,32 +34,34 @@ extension Data {
         return difference == UInt8(0x00)
     }
 
-    public static func zero(_ data: inout Data) {
+    static func zero(_ data: inout Data) {
         let count = data.count
         data.withUnsafeMutableBytes { (body: UnsafeMutableRawBufferPointer) in
             body.baseAddress?.assumingMemoryBound(to: UInt8.self).initialize(repeating: 0, count: count)
         }
     }
 
-    public static func randomBytes(length: Int) -> Data? {
-        for _ in 0...1024 {
-            var data = Data(repeating: 0, count: length)
-            let result = data.withUnsafeMutableBytes { (body: UnsafeMutableRawBufferPointer) -> Int32? in
-                if let bodyAddress = body.baseAddress, body.count > 0 {
-                    let pointer = bodyAddress.assumingMemoryBound(to: UInt8.self)
-                    return SecRandomCopyBytes(kSecRandomDefault, length, pointer)
-                } else {
-                    return nil
-                }
-            }
-            if let notNilResult = result, notNilResult == errSecSuccess {
-                return data
-            }
+    /**
+     Generates an array of random bytes of the specified length.
+     This function uses `SecRandomCopyBytes` to generate random bytes returning it as a `Data` object.
+     If an error occurs during random bytes generation, the function returns `nil`.
+     Error occurs only if `SecRandomCopyBytes` returns status that is not `errSecSuccess`.
+     See [all status codes](https://developer.apple.com/documentation/security/1542001-security_framework_result_codes) for possible error reasons.
+     Note: in v4 of web3swift this function will be deprecated and a new implementation will be provided that will throw occurred error.
+     - Parameter length: The number of random bytes to generate.
+
+     - Returns: optional `Data` object containing the generated random bytes, or `nil` if an error occurred during generation.
+     */
+    static func randomBytes(length: Int) -> Data? {
+        var entropyBytes = [UInt8](repeating: 0, count: length)
+        let status = SecRandomCopyBytes(kSecRandomDefault, entropyBytes.count, &entropyBytes)
+        guard status == errSecSuccess else {
+            return nil
         }
-        return nil
+        return Data(entropyBytes)
     }
 
-    public func bitsInRange(_ startingBit: Int, _ length: Int) -> UInt64? { // return max of 8 bytes for simplicity, non-public
+    func bitsInRange(_ startingBit: Int, _ length: Int) -> UInt64? { // return max of 8 bytes for simplicity, non-public
         if startingBit + length / 8 > self.count, length > 64, startingBit > 0, length >= 1 { return nil }
         let bytes = self[(startingBit/8) ..< (startingBit+length+7)/8]
         let padding = Data(repeating: 0, count: 8 - bytes.count)

Sources/Web3Core/Utility/String+Extension.swift

@@ -135,6 +135,26 @@ extension String {
     func trim() -> String {
         trimmingCharacters(in: .whitespacesAndNewlines)
     }
+
+   /// Splits a string into groups of `every` n characters, grouping from left-to-right by default. If `backwards` is true, right-to-left.
+   public func split(every: Int, backwards: Bool = false) -> [String] {
+       var result = [String]()
+
+       for i in stride(from: 0, to: self.count, by: every) {
+           switch backwards {
+           case true:
+               let endIndex = self.index(self.endIndex, offsetBy: -i)
+               let startIndex = self.index(endIndex, offsetBy: -every, limitedBy: self.startIndex) ?? self.startIndex
+               result.insert(String(self[startIndex..<endIndex]), at: 0)
+           case false:
+               let startIndex = self.index(self.startIndex, offsetBy: i)
+               let endIndex = self.index(startIndex, offsetBy: every, limitedBy: self.endIndex) ?? self.endIndex
+               result.append(String(self[startIndex..<endIndex]))
+           }
+       }
+
+       return result
+   }
 }
 
 extension Character {

Tests/web3swiftTests/localTests/UncategorizedTests.swift

@@ -51,6 +51,17 @@ class UncategorizedTests: XCTestCase {
         XCTAssert(biguint == BigUInt("126978086000000000"))
     }
 
+    func testStringSplit() {
+        XCTAssertEqual("abcdefgh".split(every: 3), ["abc", "def", "gh"])
+        XCTAssertEqual("abcdefgh".split(every: 3, backwards: true), ["ab", "cde", "fgh"])
+
+        XCTAssertEqual("abcdefgh".split(every: 10), ["abcdefgh"])
+        XCTAssertEqual("".split(every: 3), [])
+
+        XCTAssertEqual("abcdefgh".split(every: 1), ["a", "b", "c", "d", "e", "f", "g", "h"])
+        XCTAssertEqual("abcdefgh".split(every: 1, backwards: true), ["a", "b", "c", "d", "e", "f", "g", "h"])  // should be the same as from the front
+    }
+
     func testBloom() throws {
         let positive = [
                 "testtest",