Implemented the "availableData" property for the Pipe+Properties extension in the library target and also, implemented its "append()" function that appends its data concurrently.

Library/Sources/Internal/Extensions/Pipe+Properties.swift

@@ -0,0 +1,72 @@
+import Foundation
+
+extension Pipe {
+    
+    // MARK: Computed
+    
+    var availableData: AsyncAvailableData { .init(self) }
+    
+}
+
+// MARK: - AsyncAvailableData
+
+extension Pipe {
+    struct AsyncAvailableData {
+        
+        // MARK: Properties
+        
+        private let pipe: Pipe
+        
+        // MARK: Initialisers
+        
+        init(_ pipe: Pipe) {
+            self.pipe = pipe
+        }
+        
+        // MARK: Functions
+        
+        func append() async -> Data {
+            var data = Data()
+            
+            for await availableData in self {
+                data.append(availableData)
+            }
+            
+            return data
+        }
+        
+    }
+}
+
+// MARK: - AsyncSequence
+
+extension Pipe.AsyncAvailableData: AsyncSequence {
+    
+    // MARK: Type aliases
+    
+    typealias AsyncIterator = AsyncStream<Data>.Iterator
+    typealias Element = Data
+    
+    // MARK: Functions
+    
+    func makeAsyncIterator() -> AsyncIterator {
+        AsyncStream { continuation in
+            pipe.fileHandleForReading.readabilityHandler = { @Sendable handler in
+                let data = handler.availableData
+                
+                guard !data.isEmpty else {
+                    continuation.finish()
+                    return
+                }
+                
+                continuation.yield(data)
+            }
+            
+            continuation.onTermination = { _ in
+                pipe.fileHandleForReading.readabilityHandler = nil
+            }
+        }
+        .makeAsyncIterator()
+    }
+    
+}