commit signing hell

mac/Sources/Byre/Remote.swift

@@ -14,6 +14,17 @@ private let maxMessage = 256 << 20
 private let maxRead = 64 << 20
 private let copyTimeoutMs = 10 * 60 * 1000
 
+// The signature goes to a file, since a login shell's startup files can print to stdout.
+private let signScript = """
+    format=$(git config gpg.format || echo openpgp)
+    case $format in
+    openpgp) program=$(git config gpg.openpgp.program || git config gpg.program || echo gpg) ;;
+    x509) program=$(git config gpg.x509.program || echo gpgsm) ;;
+    *) echo "byre can't sign with gpg.format $format" >&2; exit 1 ;;
+    esac
+    exec "$program" --status-fd=2 -bsau "$(git config user.signingkey || echo "$1")" >"$2"
+    """
+
 @MainActor
 final class Remote {
     let api: API
@@ -158,9 +169,31 @@ final class Remote {
         case .hands:
             let result = try await hands.call(req.tool ?? "", req.arguments?.additionalProperties ?? OpenAPIObjectContainer())
             return ClientReply(id: req.id, result: .init(additionalProperties: result))
+        case .sign:
+            let (code, status, signature) = try await sign(Data(req.data?.data ?? []), as: req.ident ?? "", timeoutMs: req.timeoutMs ?? 120_000)
+            return ClientReply(id: req.id, exitCode: code, output: status, data: Base64EncodedData(signature))
         }
     }
 
+    private func sign(_ payload: Data, as ident: String, timeoutMs: Int) async throws -> (Int, String, Data) {
+        let fm = FileManager.default
+        let dir = fm.temporaryDirectory.appending(path: "byre-sign-\(UUID().uuidString)", directoryHint: .isDirectory)
+        try fm.createDirectory(at: dir, withIntermediateDirectories: false, attributes: [.posixPermissions: 0o700])
+        defer {
+            try? fm.removeItem(at: dir)
+        }
+        let input = dir.appending(path: "commit")
+        let output = dir.appending(path: "signature")
+        try payload.write(to: input)
+        let stdin = try FileHandle(forReadingFrom: input)
+        defer {
+            try? stdin.close()
+        }
+        let home = fm.homeDirectoryForCurrentUser.path
+        let (code, status) = try await spawn(["/bin/zsh", "-l", "-c", signScript, "byre-sign", ident, output.path], in: home, timeoutMs: timeoutMs, input: stdin)
+        return (code, status, (try? Data(contentsOf: output)) ?? Data())
+    }
+
     private func download(_ path: String, transfer: String) async throws {
         let source = expand(path)
         let archive = FileManager.default.temporaryDirectory.appending(path: "byre-download-\(UUID().uuidString).tgz")
@@ -258,7 +291,7 @@ private func start(_ p: Process) throws -> AsyncStream<Void> {
     return exit
 }
 
-private func spawn(_ argv: [String], in dir: String, timeoutMs: Int) async throws -> (Int, String) {
+private func spawn(_ argv: [String], in dir: String, timeoutMs: Int, input: FileHandle = .nullDevice) async throws -> (Int, String) {
     let fm = FileManager.default
     let out = fm.temporaryDirectory.appending(path: "byre-\(UUID().uuidString).log")
     defer {
@@ -274,7 +307,7 @@ private func spawn(_ argv: [String], in dir: String, timeoutMs: Int) async throw
     p.executableURL = URL(filePath: argv[0])
     p.arguments = Array(argv.dropFirst())
     p.currentDirectoryURL = URL(filePath: dir)
-    p.standardInput = FileHandle.nullDevice
+    p.standardInput = input
     p.standardOutput = sink
     p.standardError = sink
     let exit: AsyncStream<Void>