Add FileIO.writeFile (#2418)

* Add FileIO.write

* Refactor

* Change signature

* Refine test

* Add code example

Co-authored-by: Tanner <tannernelson@gmail.com>

Sources/Vapor/Utilities/FileIO.swift

@@ -186,4 +186,26 @@ public struct FileIO {
             return self.request.eventLoop.makeFailedFuture(error)
         }
     }
+
+    /// Write the contents of buffer to a file at the supplied path.
+    ///
+    ///     let data = ByteBuffer(string: "ByteBuffer")
+    ///     try req.fileio.writeFile(data, at: "/path/to/file.txt").wait()
+    ///
+    /// - parameters:
+    ///     - path: Path to file on the disk.
+    ///     - buffer: The `ByteBuffer` to write.
+    /// - returns: `Future` that will complete when the file write is finished.
+    public func writeFile(_ buffer: ByteBuffer, at path: String) -> EventLoopFuture<Void> {
+        do {
+            let fd = try NIOFileHandle(path: path, mode: .write, flags: .allowFileCreation())
+            let done = io.write(fileHandle: fd, buffer: buffer, eventLoop: self.request.eventLoop)
+            done.whenComplete { _ in
+                try? fd.close()
+            }
+            return done
+        } catch {
+            return self.request.eventLoop.makeFailedFuture(error)
+        }
+    }
 }

Tests/VaporTests/FileTests.swift

@@ -32,6 +32,22 @@ final class FileTests: XCTestCase {
             XCTAssertContains(res.body.string, test)
         }
     }
+
+    func testFileWrite() throws {
+        let app = Application(.testing)
+        defer { app.shutdown() }
+
+        let request = Request(application: app, on: app.eventLoopGroup.next())
+
+        let data = "Hello"
+        let path = "/tmp/fileio_write.txt"
+
+        try request.fileio.writeFile(ByteBuffer(string: data), at: path).wait()
+        defer { try? FileManager.default.removeItem(atPath: path) }
+
+        let result = try String(contentsOfFile: path)
+        XCTAssertEqual(result, data)
+    }
 
     func testPercentDecodedFilePath() throws {
         let app = Application(.testing)