Initial implementation of APKINDEX, fetching, reading, parsing, & merging

Sources/apk/Index/ApkIndexUpdate.swift

@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: Apache-2.0
+
+import Foundation
+import SWCompression
+import CryptoKit
+
+public struct ApkIndexUpdater {
+  var repositories: [String]
+  var architectures: [String]
+
+  public init() {
+    self.repositories = [
+      "https://dl-cdn.alpinelinux.org/alpine/v3.21/main",
+      "https://dl-cdn.alpinelinux.org/alpine/edge/community"
+    ]
+    // other archs: "armhf", "armv7", "loongarch64", "ppc64le", "riscv64", "s390x", "x86"
+    self.architectures = [ "aarch64", "x86_64" ]
+  }
+
+  public func update() {
+    let repositories = self.repositories.flatMap { repo in
+      self.architectures.map { arch in
+        Repository(name: repo, arch: arch)
+      }
+    }
+
+    let downloader = ApkIndexDownloader()
+    for repo in repositories {
+      let localIndex = URL(filePath: repo.localName)
+#if false
+      let shouldDownload = true
+#else
+      let shouldDownload = !FileManager.default.fileExists(atPath: localIndex.path())
+#endif
+      if shouldDownload {
+        print("Fetching index for \"\(repo.name)\"")
+        downloader.downloadFile(remote: repo.url, destination: localIndex)
+      }
+    }
+
+    let index: ApkIndex
+    do {
+      let tables = try repositories.map { try readIndex(URL(filePath: $0.localName)) }
+      index = ApkIndex.merge(tables)
+    } catch {
+      fatalError(error.localizedDescription)
+    }
+
+    for package in index.packages {
+      print(package)
+    }
+  }
+
+  private func readIndex(_ indexURL: URL) throws -> ApkIndex {
+    let tarSignature: [TarReader.Entry]
+    let tarRecords: [TarReader.Entry]
+
+    let tars = try GzipArchive.multiUnarchive(  // Slow...
+      archive: Data(contentsOf: indexURL))
+    assert(tars.count >= 2)
+
+    var signatureStream = MemoryInputStream(buffer: tars[0].data)
+    tarSignature = try TarReader.read(&signatureStream)
+    var recordsStream = MemoryInputStream(buffer: tars[1].data)
+    tarRecords = try TarReader.read(&recordsStream)
+
+    guard case .file(let signatureName, _) = tarSignature.first
+    else { fatalError("Missing signature") }
+    print(signatureName)
+    guard let apkIndexFile = tarRecords.firstFile(name: "APKINDEX")
+    else { fatalError("APKINDEX missing") }
+    guard let description = tarRecords.firstFile(name: "DESCRIPTION")
+    else { fatalError("DESCRIPTION missing") }
+
+    let reader = TextInputStream(binaryStream: MemoryInputStream(buffer: apkIndexFile))
+    return try ApkIndex(raw:
+      try ApkRawIndex(lines: reader.lines))
+  }
+}
+
+extension ApkIndexUpdater {
+  struct Repository {
+    let name: String
+    let arch: String
+    let discriminator: String
+
+    private static func resolveApkIndex(_ repo: String, _ arch: String)
+      -> String { "\(repo)/\(arch)/APKINDEX.tar.gz" }
+    var url: URL { URL(string: Self.resolveApkIndex(self.name, self.arch))! }
+    var localName: String { "APKINDEX.\(discriminator).tar.gz" }
+
+    init(name repo: String, arch: String) {
+      self.name = repo
+      self.arch = arch
+
+      let urlSHA1Digest = Data(Insecure.SHA1.hash(data: Data(Self.resolveApkIndex(repo, arch).utf8)))
+      self.discriminator = urlSHA1Digest.subdata(in: 0..<3).map { String(format: "%02x", $0) }.joined()
+    }
+  }
+}