Add packed sequence encoding (#22)

* Add packed sequence encoding

* Revert some public initializers, fix test

Author: christophhagen

BinaryFormat.md

@@ -87,7 +87,7 @@ This is useful if the integer values are often large, e.g. for random numbers.
 ### Strings
 
 Swift `String` values are encoded using their `UTF-8` representations. 
-If a string can't be encoded this way, then encoding fails.
+If a string can't be encoded this way, then encoding fails.s
 
 ## Containers
 
@@ -148,6 +148,33 @@ which translates to:
 0x00 // Fourth element is not nil, length 0
 ```
 
+### Packed sequences
+
+Some of these basic types can be decoded from a continuous stream, either because they have a fixed length (like `Double`), or because their encoding can detect when the type ends (like variable-length encoded types).
+Since these types don't require a length, basic sequences (`Array` and `Set`) of these types are encoded in a "packed" format, where no additional length indicator is added for each element.
+
+For example, encoding a series of `Bool` values in an unkeyed container would result in the following encoded data:
+
+```
+// True, false, false
+02 01   02 00   02 00
+```
+
+The `02` bytes indicate the length of each `Bool`, which is unnecessary, since a `Bool` is always exactly one byte.
+
+When encoding a type of `[Bool]`, the encoded data is shortened to: 
+
+```
+// True, false, false
+01 00 00
+```
+
+This encoding is only used for the following types:
+
+- Fixed-width types: `Double`, `Float`, `Bool`, `Int8`, `UInt8`, `Int16`, `UInt16`, `FixedLengthEncoded<T>`
+- Zig-zag types: `Int32`, `Int64`, `Int`
+- Variable-length types: `UInt32`, `UInt64`, `UInt`, `VariableLengthEncoded<T>`
+
 ### Keyed containers
 
 Keyed containers work similar to unkeyed containers, except that each element also has a key inserted before the element data.
@@ -207,16 +234,15 @@ will give the following binary data:
 | 4 | 0x06 | Length 3
 | 5-7 | 0x42 0x6f 0x62 | String "Bob"
 | 8 | 0x06 | CodingKey(stringValue: 'references', intValue: 3)
-| 9 | 0x0A | Length 5
-| 10 | 0x02 | Length 1
-| 11 | 0x06 | Int `3`
-| 12 | 0x04 | Length 2
-| 13-14 | 0xAF 0x04 | Int `-280`
+| 9 | 0x0A | Length 3
+| 10 | 0x06 | Int `3`
+| 11-12 | 0xAF 0x04 | Int `-280`
 
 There are a few things to note:
 - The properties are all marked by their integer keys
 - The elements in the `references` array are also preceded by a length indicator
 - The top level keyed container has no length information, since it can be inferred from the length of the provided data
+- `[Int]` is a packed field, so no length data is inserted before each element
 
 ### Dictionaries
 

Sources/BinaryCodable/Decoding/DecodingDataProvider.swift

@@ -20,7 +20,7 @@ extension DecodingDataProvider {
      Decode an unsigned integer using variable-length encoding starting at a position.
      - Returns: `Nil`, if insufficient data is available
      */
-    private func decodeUInt64(at index: inout Index) -> UInt64? {
+    func decodeUInt64(at index: inout Index) -> UInt64? {
         guard let start = nextByte(at: &index) else { return nil }
         return decodeUInt64(startByte: start, at: &index)
     }

Sources/BinaryCodable/Primitives/Array+Coding.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+extension Array: EncodablePrimitive where Element: PackedEncodable {
+
+    var encodedData: Data {
+        mapAndJoin { $0.encodedData }
+    }
+}
+
+extension Array: DecodablePrimitive where Element: PackedDecodable {
+
+    init(data: Data) throws {
+        var index = data.startIndex
+        var elements = [Element]()
+        while !data.isAtEnd(at: index) {
+            let element = try Element.init(data: data, index: &index)
+            elements.append(element)
+        }
+        self.init(elements)
+    }
+}

Sources/BinaryCodable/Primitives/Bool+Coding.swift

@@ -10,6 +10,17 @@ extension Bool: EncodablePrimitive {
 
 extension Bool: DecodablePrimitive {
 
+    private init(byte: UInt8) throws {
+        switch byte {
+        case 0:
+            self = false
+        case 1:
+            self = true
+        default:
+            throw CorruptedDataError(invalidBoolByte: byte)
+        }
+    }
+
     /**
      Decode a boolean from encoded data.
      - Parameter data: The data to decode
@@ -19,14 +30,51 @@ extension Bool: DecodablePrimitive {
         guard data.count == 1 else {
             throw CorruptedDataError(invalidSize: data.count, for: "Bool")
         }
-        let byte = data[data.startIndex]
-        switch byte {
-        case 0:
-            self = false
-        case 1:
-            self = true
-        default:
-            throw CorruptedDataError(invalidBoolByte: byte)
+        try self.init(byte: data[data.startIndex])
+    }
+}
+
+// - MARK: Fixed size
+
+extension Bool: FixedSizeEncodable {
+
+    public var fixedSizeEncoded: Data {
+        encodedData
+    }
+}
+
+extension Bool: FixedSizeDecodable {
+
+    public init(fromFixedSize data: Data) throws {
+        try self.init(data: data)
+    }
+}
+
+extension FixedSizeEncoded where WrappedValue == Bool {
+
+    /**
+     Wrap a Bool to enforce fixed-size encoding.
+     - Parameter wrappedValue: The value to wrap
+     - Note: `Bool` is already encoded using fixed-size encoding, so wrapping it in `FixedSizeEncoded` does nothing.
+     */
+    @available(*, deprecated, message: "Property wrapper @FixedSizeEncoded has no effect on type Bool")
+    public init(wrappedValue: Bool) {
+        self.wrappedValue = wrappedValue
+    }
+}
+
+// - MARK: Packed
+
+extension Bool: PackedEncodable {
+
+}
+
+extension Bool: PackedDecodable {
+    
+    init(data: Data, index: inout Int) throws {
+        guard let bytes = data.nextBytes(Self.fixedEncodedByteCount, at: &index) else {
+            throw CorruptedDataError.init(prematureEndofDataDecoding: "Bool")
         }
+        try self.init(fromFixedSize: bytes)
     }
 }

Sources/BinaryCodable/Primitives/Double+Coding.swift

@@ -17,3 +17,48 @@ extension Double: DecodablePrimitive {
         self.init(bitPattern: value)
     }
 }
+
+// - MARK: Fixed size
+
+extension Double: FixedSizeEncodable {
+
+    public var fixedSizeEncoded: Data {
+        encodedData
+    }
+}
+
+extension Double: FixedSizeDecodable {
+
+    public init(fromFixedSize data: Data) throws {
+        try self.init(data: data)
+    }
+}
+
+extension FixedSizeEncoded where WrappedValue == Double {
+
+    /**
+     Wrap a double to enforce fixed-size encoding.
+     - Parameter wrappedValue: The value to wrap
+     - Note: `Double` is already encoded using fixed-size encoding, so wrapping it in `FixedSizeEncoded` does nothing.
+     */
+    @available(*, deprecated, message: "Property wrapper @FixedSizeEncoded has no effect on type Double")
+    public init(wrappedValue: Double) {
+        self.wrappedValue = wrappedValue
+    }
+}
+
+// - MARK: Packed
+
+extension Double: PackedEncodable {
+
+}
+
+extension Double: PackedDecodable {
+
+    init(data: Data, index: inout Int) throws {
+        guard let bytes = data.nextBytes(Self.fixedEncodedByteCount, at: &index) else {
+            throw CorruptedDataError.init(prematureEndofDataDecoding: "Double")
+        }
+        try self.init(data: bytes)
+    }
+}

Sources/BinaryCodable/Primitives/Float+Coding.swift

@@ -18,3 +18,47 @@ extension Float: DecodablePrimitive {
     }
 }
 
+// - MARK: Fixed size
+
+extension Float: FixedSizeEncodable {
+
+    public var fixedSizeEncoded: Data {
+        encodedData
+    }
+}
+
+extension Float: FixedSizeDecodable {
+
+    public init(fromFixedSize data: Data) throws {
+        try self.init(data: data)
+    }
+}
+
+extension FixedSizeEncoded where WrappedValue == Float {
+
+    /**
+     Wrap a float to enforce fixed-size encoding.
+     - Parameter wrappedValue: The value to wrap
+     - Note: `Float` is already encoded using fixed-size encoding, so wrapping it in `FixedSizeEncoded` does nothing.
+     */
+    @available(*, deprecated, message: "Property wrapper @FixedSizeEncoded has no effect on type Float")
+    public init(wrappedValue: Float) {
+        self.wrappedValue = wrappedValue
+    }
+}
+
+// - MARK: Packed
+
+extension Float: PackedEncodable {
+
+}
+
+extension Float: PackedDecodable {
+
+    init(data: Data, index: inout Int) throws {
+        guard let bytes = data.nextBytes(Self.fixedEncodedByteCount, at: &index) else {
+            throw CorruptedDataError.init(prematureEndofDataDecoding: "Float")
+        }
+        try self.init(data: bytes)
+    }
+}

Sources/BinaryCodable/Primitives/Int+Coding.swift

@@ -14,7 +14,8 @@ extension Int: DecodablePrimitive {
      - Throws: ``CorruptedDataError``
      */
     init(data: Data) throws {
-        try self.init(fromZigZag: data)
+        let raw = try UInt64(fromVarintData: data)
+        try self.init(fromZigZag: raw)
     }
 }
 
@@ -35,8 +36,8 @@ extension Int: ZigZagDecodable {
      - Parameter data: The data of the zig-zag encoded value.
      - Throws: ``CorruptedDataError``
      */
-    public init(fromZigZag data: Data) throws {
-        let raw = try Int64(data: data)
+    public init(fromZigZag raw: UInt64) throws {
+        let raw = Int64(fromZigZag: raw)
         guard let value = Int(exactly: raw) else {
             throw CorruptedDataError(outOfRange: raw, forType: "Int")
         }
@@ -74,8 +75,8 @@ extension Int: VariableLengthDecodable {
      - Parameter data: The data to decode.
      - Throws: ``CorruptedDataError``
      */
-    public init(fromVarint data: Data) throws {
-        let intValue = try Int64(fromVarint: data)
+    public init(fromVarint raw: UInt64) throws {
+        let intValue = Int64(fromVarint: raw)
         guard let value = Int(exactly: intValue) else {
             throw CorruptedDataError(outOfRange: intValue, forType: "Int")
         }
@@ -109,3 +110,18 @@ extension Int: FixedSizeDecodable {
     }
 }
 
+// - MARK: Packed
+
+extension Int: PackedEncodable {
+
+}
+
+extension Int: PackedDecodable {
+
+    init(data: Data, index: inout Int) throws {
+        guard let raw = data.decodeUInt64(at: &index) else {
+            throw CorruptedDataError(prematureEndofDataDecoding: "Int")
+        }
+        try self.init(fromZigZag: raw)
+    }
+}

Sources/BinaryCodable/Primitives/Int16+Coding.swift

@@ -72,8 +72,8 @@ extension Int16: VariableLengthDecodable {
      - Parameter data: The data to decode.
      - Throws: ``CorruptedDataError``
      */
-    public init(fromVarint data: Data) throws {
-        let value = try UInt16(fromVarint: data)
+    public init(fromVarint raw: UInt64) throws {
+        let value = try UInt16(fromVarint: raw)
         self = Int16(bitPattern: value)
     }
 }
@@ -95,11 +95,27 @@ extension Int16: ZigZagDecodable {
      - Parameter data: The data of the zig-zag encoded value.
      - Throws: ``CorruptedDataError``
      */
-    public init(fromZigZag data: Data) throws {
-        let raw = try Int64(fromZigZag: data)
+    public init(fromZigZag raw: UInt64) throws {
+        let raw = Int64(fromZigZag: raw)
         guard let value = Int16(exactly: raw) else {
             throw CorruptedDataError(outOfRange: raw, forType: "Int16")
         }
         self = value
     }
 }
+
+// - MARK: Packed
+
+extension Int16: PackedEncodable {
+
+}
+
+extension Int16: PackedDecodable {
+
+    init(data: Data, index: inout Int) throws {
+        guard let bytes = data.nextBytes(Self.fixedEncodedByteCount, at: &index) else {
+            throw CorruptedDataError.init(prematureEndofDataDecoding: "Int16")
+        }
+        try self.init(data: bytes)
+    }
+}