feat(NIOFileSystem): Add idempotent directory creation behavior (#3404)

Sources/NIOFS/FileSystem.swift

@@ -825,6 +825,20 @@ extension FileSystem {
                 break loop
 
             case let .failure(errno):
+                if errno == .fileExists {
+                    switch self._info(forFileAt: path, infoAboutSymbolicLink: false) {
+                    case let .success(maybeInfo):
+                        if let info = maybeInfo, info.type == .directory {
+                            break loop
+                        } else {
+                            // A file exists at this path.
+                            return .failure(.mkdir(errno: errno, path: path, location: .here()))
+                        }
+                    case .failure:
+                        // Unable to determine what exists at this path.
+                        return .failure(.mkdir(errno: errno, path: path, location: .here()))
+                    }
+                }
                 guard createIntermediateDirectories, errno == .noSuchFileOrDirectory else {
                     return .failure(.mkdir(errno: errno, path: path, location: .here()))
                 }

Sources/_NIOFileSystem/FileSystem.swift

@@ -839,6 +839,20 @@ extension FileSystem {
                 break loop
 
             case let .failure(errno):
+                if errno == .fileExists {
+                    switch self._info(forFileAt: path, infoAboutSymbolicLink: false) {
+                    case let .success(maybeInfo):
+                        if let info = maybeInfo, info.type == .directory {
+                            break loop
+                        } else {
+                            // A file exists at this path.
+                            return .failure(.mkdir(errno: errno, path: path, location: .here()))
+                        }
+                    case .failure:
+                        // Unable to determine what exists at this path.
+                        return .failure(.mkdir(errno: errno, path: path, location: .here()))
+                    }
+                }
                 guard createIntermediateDirectories, errno == .noSuchFileOrDirectory else {
                     return .failure(.mkdir(errno: errno, path: path, location: .here()))
                 }

Tests/NIOFSIntegrationTests/FileSystemTests.swift

@@ -505,6 +505,37 @@ final class FileSystemTests: XCTestCase {
         }
     }
 
+    func testCreateDirectoryIsIdempotentWhenAlreadyExists() async throws {
+        let path = try await self.fs.temporaryFilePath()
+
+        try await self.fs.createDirectory(at: path, withIntermediateDirectories: false)
+
+        try await self.fs.createDirectory(at: path, withIntermediateDirectories: false)
+        try await self.fs.createDirectory(at: path, withIntermediateDirectories: true)
+
+        try await self.fs.withDirectoryHandle(atPath: path) { dir in
+            let info = try await dir.info()
+            XCTAssertEqual(info.type, .directory)
+            XCTAssertGreaterThan(info.size, 0)
+        }
+    }
+
+    func testCreateDirectoryThroughSymlinkToExistingDirectoryIsIdempotent() async throws {
+        let realDir = try await self.fs.temporaryFilePath()
+        try await self.fs.createDirectory(at: realDir, withIntermediateDirectories: false)
+
+        let linkPath = try await self.fs.temporaryFilePath()
+        try await self.fs.createSymbolicLink(at: linkPath, withDestination: realDir)
+
+        try await self.fs.createDirectory(at: linkPath, withIntermediateDirectories: false)
+
+        try await self.fs.withDirectoryHandle(atPath: linkPath) { dir in
+            let info = try await dir.info()
+            XCTAssertEqual(info.type, .directory)
+            XCTAssertGreaterThan(info.size, 0)
+        }
+    }
+
     func testCurrentWorkingDirectory() async throws {
         let directory = try await self.fs.currentWorkingDirectory
         XCTAssert(!directory.underlying.isEmpty)