1 files changed, 183 insertions, 0 deletions
diff --git a/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/RustBufferTemplate.swift b/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/RustBufferTemplate.swift
new file mode 100644
index 0000000000..2f737b6635
--- /dev/null
+++ b/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/RustBufferTemplate.swift
@@ -0,0 +1,183 @@
+fileprivate extension RustBuffer {
+    // Allocate a new buffer, copying the contents of a `UInt8` array.
+    init(bytes: [UInt8]) {
+        let rbuf = bytes.withUnsafeBufferPointer { ptr in
+            RustBuffer.from(ptr)
+        }
+        self.init(capacity: rbuf.capacity, len: rbuf.len, data: rbuf.data)
+    }
+
+    static func from(_ ptr: UnsafeBufferPointer<UInt8>) -> RustBuffer {
+        try! rustCall { {{ ci.ffi_rustbuffer_from_bytes().name() }}(ForeignBytes(bufferPointer: ptr), $0) }
+    }
+
+    // Frees the buffer in place.
+    // The buffer must not be used after this is called.
+    func deallocate() {
+        try! rustCall { {{ ci.ffi_rustbuffer_free().name() }}(self, $0) }
+    }
+}
+
+fileprivate extension ForeignBytes {
+    init(bufferPointer: UnsafeBufferPointer<UInt8>) {
+        self.init(len: Int32(bufferPointer.count), data: bufferPointer.baseAddress)
+    }
+}
+
+// For every type used in the interface, we provide helper methods for conveniently
+// lifting and lowering that type from C-compatible data, and for reading and writing
+// values of that type in a buffer.
+
+// Helper classes/extensions that don't change.
+// Someday, this will be in a library of its own.
+
+fileprivate extension Data {
+    init(rustBuffer: RustBuffer) {
+        // TODO: This copies the buffer. Can we read directly from a
+        // Rust buffer?
+        self.init(bytes: rustBuffer.data!, count: Int(rustBuffer.len))
+    }
+}
+
+// Define reader functionality.  Normally this would be defined in a class or
+// struct, but we use standalone functions instead in order to make external
+// types work.
+//
+// With external types, one swift source file needs to be able to call the read
+// method on another source file's FfiConverter, but then what visibility
+// should Reader have?
+// - If Reader is fileprivate, then this means the read() must also
+//   be fileprivate, which doesn't work with external types.
+// - If Reader is internal/public, we'll get compile errors since both source
+//   files will try define the same type.
+//
+// Instead, the read() method and these helper functions input a tuple of data
+
+fileprivate func createReader(data: Data) -> (data: Data, offset: Data.Index) {
+    (data: data, offset: 0)
+}
+
+// Reads an integer at the current offset, in big-endian order, and advances
+// the offset on success. Throws if reading the integer would move the
+// offset past the end of the buffer.
+fileprivate func readInt<T: FixedWidthInteger>(_ reader: inout (data: Data, offset: Data.Index)) throws -> T {
+    let range = reader.offset..<reader.offset + MemoryLayout<T>.size
+    guard reader.data.count >= range.upperBound else {
+        throw UniffiInternalError.bufferOverflow
+    }
+    if T.self == UInt8.self {
+        let value = reader.data[reader.offset]
+        reader.offset += 1
+        return value as! T
+    }
+    var value: T = 0
+    let _ = withUnsafeMutableBytes(of: &value, { reader.data.copyBytes(to: $0, from: range)})
+    reader.offset = range.upperBound
+    return value.bigEndian
+}
+
+// Reads an arbitrary number of bytes, to be used to read
+// raw bytes, this is useful when lifting strings
+fileprivate func readBytes(_ reader: inout (data: Data, offset: Data.Index), count: Int) throws -> Array<UInt8> {
+    let range = reader.offset..<(reader.offset+count)
+    guard reader.data.count >= range.upperBound else {
+        throw UniffiInternalError.bufferOverflow
+    }
+    var value = [UInt8](repeating: 0, count: count)
+    value.withUnsafeMutableBufferPointer({ buffer in
+        reader.data.copyBytes(to: buffer, from: range)
+    })
+    reader.offset = range.upperBound
+    return value
+}
+
+// Reads a float at the current offset.
+fileprivate func readFloat(_ reader: inout (data: Data, offset: Data.Index)) throws -> Float {
+    return Float(bitPattern: try readInt(&reader))
+}
+
+// Reads a float at the current offset.
+fileprivate func readDouble(_ reader: inout (data: Data, offset: Data.Index)) throws -> Double {
+    return Double(bitPattern: try readInt(&reader))
+}
+
+// Indicates if the offset has reached the end of the buffer.
+fileprivate func hasRemaining(_ reader: (data: Data, offset: Data.Index)) -> Bool {
+    return reader.offset < reader.data.count
+}
+
+// Define writer functionality.  Normally this would be defined in a class or
+// struct, but we use standalone functions instead in order to make external
+// types work.  See the above discussion on Readers for details.
+
+fileprivate func createWriter() -> [UInt8] {
+    return []
+}
+
+fileprivate func writeBytes<S>(_ writer: inout [UInt8], _ byteArr: S) where S: Sequence, S.Element == UInt8 {
+    writer.append(contentsOf: byteArr)
+}
+
+// Writes an integer in big-endian order.
+//
+// Warning: make sure what you are trying to write
+// is in the correct type!
+fileprivate func writeInt<T: FixedWidthInteger>(_ writer: inout [UInt8], _ value: T) {
+    var value = value.bigEndian
+    withUnsafeBytes(of: &value) { writer.append(contentsOf: $0) }
+}
+
+fileprivate func writeFloat(_ writer: inout [UInt8], _ value: Float) {
+    writeInt(&writer, value.bitPattern)
+}
+
+fileprivate func writeDouble(_ writer: inout [UInt8], _ value: Double) {
+    writeInt(&writer, value.bitPattern)
+}
+
+// Protocol for types that transfer other types across the FFI. This is
+// analogous go the Rust trait of the same name.
+fileprivate protocol FfiConverter {
+    associatedtype FfiType
+    associatedtype SwiftType
+
+    static func lift(_ value: FfiType) throws -> SwiftType
+    static func lower(_ value: SwiftType) -> FfiType
+    static func read(from buf: inout (data: Data, offset: Data.Index)) throws -> SwiftType
+    static func write(_ value: SwiftType, into buf: inout [UInt8])
+}
+
+// Types conforming to `Primitive` pass themselves directly over the FFI.
+fileprivate protocol FfiConverterPrimitive: FfiConverter where FfiType == SwiftType { }
+
+extension FfiConverterPrimitive {
+    public static func lift(_ value: FfiType) throws -> SwiftType {
+        return value
+    }
+
+    public static func lower(_ value: SwiftType) -> FfiType {
+        return value
+    }
+}
+
+// Types conforming to `FfiConverterRustBuffer` lift and lower into a `RustBuffer`.
+// Used for complex types where it's hard to write a custom lift/lower.
+fileprivate protocol FfiConverterRustBuffer: FfiConverter where FfiType == RustBuffer {}
+
+extension FfiConverterRustBuffer {
+    public static func lift(_ buf: RustBuffer) throws -> SwiftType {
+        var reader = createReader(data: Data(rustBuffer: buf))
+        let value = try read(from: &reader)
+        if hasRemaining(reader) {
+            throw UniffiInternalError.incompleteData
+        }
+        buf.deallocate()
+        return value
+    }
+
+    public static func lower(_ value: SwiftType) -> RustBuffer {
+          var writer = createWriter()
+          write(value, into: &writer)
+          return RustBuffer(bytes: writer)
+    }
+}