test: Add tests for the tar writer (#50)

Motivation
----------

The `tar` writer is tested by the end to end tests, but unit tests are
more helpful for refactoring and extending it.

Modifications
-------------
 
* Extract `tar` into its own module
* Extract tar header construction into a separate function
* Add initial unit tests for the helper methods used to build `tar`
headers
* Stop using `Swift(format:)` to convert integers into octal strings
because of
swiftlang/swift-corelibs-foundation#5152

Result
------

The basic helper functions underpinning the tar writer will have unit
tests, making it easier to test, refactor and extend the tar writer in
future.

Test Plan
---------

This pull request adds new tests. All existing tests continue to pass.

Author: euanh

.swift-format

@@ -14,7 +14,7 @@
   "lineLength" : 120,
   "maximumBlankLines" : 1,
   "prioritizeKeepingFunctionOutputTogether" : false,
-  "respectsExistingLineBreaks" : false,
+  "respectsExistingLineBreaks" : true,
   "rules" : {
     "AllPublicDeclarationsHaveDocumentation" : true,
     "AlwaysUseLowerCamelCase" : false,

Package.swift

@@ -40,7 +40,7 @@ let package = Package(
         .executableTarget(
             name: "containertool",
             dependencies: [
-                .target(name: "ContainerRegistry"), .target(name: "VendorCNIOExtrasZlib"),
+                .target(name: "ContainerRegistry"), .target(name: "VendorCNIOExtrasZlib"), .target(name: "Tar"),
                 .product(name: "ArgumentParser", package: "swift-argument-parser"),
             ],
             swiftSettings: [.swiftLanguageMode(.v5)]
@@ -51,7 +51,7 @@ let package = Package(
             dependencies: [],
             path: "Vendor/github.com/apple/swift-nio-extras/Sources/CNIOExtrasZlib",
             linkerSettings: [.linkedLibrary("z")]
-        ),
+        ), .target(name: "Tar"),
         .target(
             // Vendored from https://github.com/apple/swift-package-manager with modifications
             name: "Basics",
@@ -87,6 +87,7 @@ let package = Package(
             dependencies: [.target(name: "ContainerRegistry")],
             resources: [.process("Resources")]
         ), .testTarget(name: "containertoolTests", dependencies: [.target(name: "containertool")]),
+        .testTarget(name: "TarTests", dependencies: [.target(name: "Tar")]),
     ],
     swiftLanguageModes: [.v6]
 )

Sources/containertool/tar.swift renamed to Sources/Tar/tar.swift

@@ -72,16 +72,24 @@ extension [UInt8] {
 func octal6(_ value: Int) -> String {
     precondition(value >= 0)
     precondition(value < 0o777777)
-    return String(format: "%06o", value)
+    // String(format: "%06o", value) cannot be used because of a race in Foundation
+    // which causes it to return an empty string from time to time when running the tests
+    // in parallel using swift-testing: https://github.com/swiftlang/swift-corelibs-foundation/issues/5152
+    let str = String(value, radix: 8)
+    return String(repeating: "0", count: 6 - str.count).appending(str)
 }
 
-/// Serializes an integer to a 11 character octal representation.
+/// Serializes an integer to an 11 character octal representation.
 /// - Parameter value: The integer to serialize.
 /// - Returns: The serialized form of `value`.
 func octal11(_ value: Int) -> String {
     precondition(value >= 0)
     precondition(value < 0o777_7777_7777)
-    return String(format: "%011o", value)
+    // String(format: "%011o", value) cannot be used because of a race in Foundation
+    // which causes it to return an empty string from time to time when running the tests
+    // in parallel using swift-testing: https://github.com/swiftlang/swift-corelibs-foundation/issues/5152
+    let str = String(value, radix: 8)
+    return String(repeating: "0", count: 11 - str.count).appending(str)
 }
 
 // These ranges define the offsets of the standard fields in a Tar header.
@@ -143,7 +151,12 @@ let CONTTYPE = "7"  // reserved
 let XHDTYPE = "x"  // Extended header referring to the next file in the archive
 let XGLTYPE = "g"  // Global extended header
 
-func tar(_ bytes: [UInt8], filename: String = "app") -> [UInt8] {
+/// Creates a tar header for a single file
+/// - Parameters:
+///   - filesize: The size of the file
+///   - filename: The file's name in the archive
+/// - Returns: A tar header representing the file
+public func tarHeader(filesize: Int, filename: String = "app") -> [UInt8] {
     // A file entry consists of a file header followed by the
     // contents of the file. The header includes information such as
     // the file name, size and permissions.   Different versions of
@@ -158,7 +171,7 @@ func tar(_ bytes: [UInt8], filename: String = "app") -> [UInt8] {
     hdr.writeString(octal6(0o555), inField: mode, withTermination: .spaceAndNull)
     hdr.writeString(octal6(0o000000), inField: uid, withTermination: .spaceAndNull)
     hdr.writeString(octal6(0o000000), inField: gid, withTermination: .spaceAndNull)
-    hdr.writeString(octal11(bytes.count), inField: size, withTermination: .space)
+    hdr.writeString(octal11(filesize), inField: size, withTermination: .space)
     hdr.writeString(octal11(0), inField: mtime, withTermination: .space)
     hdr.writeString(INIT_CHECKSUM, inField: chksum, withTermination: .none)
     hdr.writeString(REGTYPE, inField: typeflag, withTermination: .none)
@@ -174,6 +187,17 @@ func tar(_ bytes: [UInt8], filename: String = "app") -> [UInt8] {
     // Fill in the checksum.
     hdr.writeString(octal6(checksum(header: hdr)), inField: chksum, withTermination: .nullAndSpace)
 
+    return hdr
+}
+
+/// Creates a tar archive containing a single file
+/// - Parameters:
+///   - bytes: The file's body data
+///   - filename: The file's name in the archive
+/// - Returns: A tar archive containing the file
+public func tar(_ bytes: [UInt8], filename: String = "app") -> [UInt8] {
+    var hdr = tarHeader(filesize: bytes.count, filename: filename)
+
     // Append the file data to the header
     hdr.append(contentsOf: bytes)
 
@@ -187,4 +211,9 @@ func tar(_ bytes: [UInt8], filename: String = "app") -> [UInt8] {
     return hdr
 }
 
-func tar(_ data: Data, filename: String) -> [UInt8] { tar([UInt8](data), filename: filename) }
+/// Creates a tar archive containing a single file
+/// - Parameters:
+///   - data: The file's body data
+///   - filename: The file's name in the archive
+/// - Returns: A tar archive containing the file
+public func tar(_ data: Data, filename: String) -> [UInt8] { tar([UInt8](data), filename: filename) }

Sources/containertool/containertool.swift

@@ -15,6 +15,7 @@
 import ArgumentParser
 import Foundation
 import ContainerRegistry
+import Tar
 import Basics
 
 extension Swift.String: Swift.Error {}

Tests/TarTests/TarUnitTests.swift

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftContainerPlugin open source project
+//
+// Copyright (c) 2024 Apple Inc. and the SwiftContainerPlugin project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftContainerPlugin project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Testing
+
+@testable import Tar
+
+let blocksize = 512
+let headerLen = blocksize
+let trailerLen = 2 * blocksize
+
+@Suite struct TarUnitTests {
+    @Test(arguments: [
+        (input: 0o000, expected: "000000"),
+        (input: 0o555, expected: "000555"),
+        (input: 0o750, expected: "000750"),
+        (input: 0o777, expected: "000777"),
+        (input: 0o1777, expected: "001777"),
+    ])
+    func testOctal6(input: Int, expected: String) async throws {
+        #expect(octal6(input) == expected)
+    }
+
+    @Test(arguments: [
+        (input: 0, expected: "00000000000"),
+        (input: 1024, expected: "00000002000"),
+        (input: 0o2000, expected: "00000002000"),
+        (input: 1024 * 1024, expected: "00004000000"),
+    ])
+    func testOctal11(input: Int, expected: String) async throws {
+        #expect(octal11(input) == expected)
+    }
+
+    @Test func testUInt8writeString() async throws {
+        // Fill the buffer with 0xFF to show null termination
+        var hdr = [UInt8](repeating: 255, count: 21)
+
+        // The typechecker timed out when these test cases were passed as arguments, in the style of the octal tests
+        hdr.writeString("abc", inField: 0..<5, withTermination: .none)
+        #expect(
+            hdr == [
+                97, 98, 99, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+            ]
+        )
+
+        hdr.writeString("def", inField: 3..<7, withTermination: .null)
+        #expect(
+            hdr == [97, 98, 99, 100, 101, 102, 0, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255]
+        )
+
+        hdr.writeString("ghi", inField: 7..<11, withTermination: .space)
+        #expect(
+            hdr == [97, 98, 99, 100, 101, 102, 0, 103, 104, 105, 32, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255]
+        )
+
+        hdr.writeString("jkl", inField: 11..<16, withTermination: .nullAndSpace)
+        #expect(
+            hdr == [97, 98, 99, 100, 101, 102, 0, 103, 104, 105, 32, 106, 107, 108, 0, 32, 255, 255, 255, 255, 255]
+        )
+
+        hdr.writeString("mno", inField: 16..<21, withTermination: .spaceAndNull)
+        #expect(
+            hdr == [97, 98, 99, 100, 101, 102, 0, 103, 104, 105, 32, 106, 107, 108, 0, 32, 109, 110, 111, 32, 0]
+        )
+    }
+}