feat: Add String(contentsOf: FilePath ...)

Sources/NIOFileSystem/String+FileSystem.swift

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2025 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
+//
+//===----------------------------------------------------------------------===//
+
+import NIOCore
+
+@available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
+extension String {
+    /// Reads the contents of the file at the path into a String.
+    ///
+    /// - Parameters:
+    ///   - path: The path of the file to read.
+    ///   - maximumSizeAllowed: The maximum size of file which can be read, in bytes, as a ``ByteCount``. If the file is larger than this, an error is thrown.
+    ///   - fileSystem: The ``FileSystemProtocol`` instance to use to read the file.
+    ///
+    /// - Throws: If the file is larger than `maximumSizeAllowed`, an ``FileSystemError/Code-swift.struct/resourceExhausted`` error will be thrown.
+    public init(
+        contentsOf path: FilePath,
+        maximumSizeAllowed: ByteCount,
+        fileSystem: some FileSystemProtocol
+    ) async throws {
+        let byteBuffer = try await fileSystem.withFileHandle(forReadingAt: path) { handle in
+            try await handle.readToEnd(maximumSizeAllowed: maximumSizeAllowed)
+        }
+
+        self = Self(buffer: byteBuffer)
+    }
+
+    /// Reads the contents of the file at the path using ``FileSystem``.
+    ///
+    /// - Parameters:
+    ///   - path: The path of the file to read.
+    ///   - maximumSizeAllowed: The maximum size of file which can be read, in bytes, as a ``ByteCount``. If the file is larger than this, an error is thrown.
+    ///
+    /// - Throws: If the file is larger than `maximumSizeAllowed`, an ``FileSystemError/Code-swift.struct/resourceExhausted`` error will be thrown.
+    public init(
+        contentsOf path: FilePath,
+        maximumSizeAllowed: ByteCount
+    ) async throws {
+        self = try await Self(
+            contentsOf: path,
+            maximumSizeAllowed: maximumSizeAllowed,
+            fileSystem: .shared
+        )
+    }
+}

Tests/NIOFileSystemIntegrationTests/ConvenienceTests.swift

@@ -70,4 +70,31 @@ final class ConvenienceTests: XCTestCase {
         let bytes = try await ByteBuffer(contentsOf: path, maximumSizeAllowed: .bytes(1024))
         XCTAssertEqual(bytes, ByteBuffer(bytes: Array(0..<64)))
     }
+
+    // MARK: - String + FileSystem
+
+    func testStringFromFullFile() async throws {
+        let path = try await Self.fs.temporaryFilePath()
+        try await "some text".write(toFileAt: path)
+
+        let string = try await String(contentsOf: path, maximumSizeAllowed: .bytes(1024))
+        XCTAssertEqual(string, "some text")
+    }
+
+    func testStringFromPartOfAFile() async throws {
+        let path = try await Self.fs.temporaryFilePath()
+        try await "some text".write(toFileAt: path)
+
+        await XCTAssertThrowsFileSystemErrorAsync {
+            try await String(contentsOf: path, maximumSizeAllowed: .bytes(4))
+        }
+    }
+
+    // MARK: - Array + FileSystem
+    func testArrayFromFullFile() async throws {
+        let path = try await Self.fs.temporaryFilePath()
+        try await Array("some text".utf8).write(toFileAt: path)
+        let array = try await Array(contentsOf: path, maximumSizeAllowed: .bytes(1024))
+        XCTAssertEqual(array, Array("some text".utf8))
+    }
 }