WIP: refactor: add remote_roundtrip_test

build.zig

@@ -110,6 +110,19 @@ pub fn build(b: *std.Build) void {
         }),
     });
 
+    const remote_child_roundtrip = b.addExecutable(.{
+        .name = "remote_child_roundtrip",
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("test/remote_child_roundtrip.zig"),
+            .target = target,
+            .optimize = optimize,
+            .imports = &.{
+                .{ .name = "cbor", .module = cbor_mod },
+                .{ .name = "framing", .module = framing_mod },
+            },
+        }),
+    });
+
     const thespian_mod = b.addModule("thespian", .{
         .root_source_file = b.path("src/thespian.zig"),
         .imports = &.{
@@ -128,6 +141,7 @@ pub fn build(b: *std.Build) void {
     });
 
     options.addOptionPath("remote_child_path", remote_child.getEmittedBin());
+    options.addOptionPath("remote_child_roundtrip_path", remote_child_roundtrip.getEmittedBin());
 
     tests.root_module.addImport("build_options", options_mod);
     tests.root_module.addImport("cbor", cbor_mod);

test/remote_child_roundtrip.zig

@@ -0,0 +1,24 @@
+/// Child process for the remoting round-trip test.
+/// Reads one framed CBOR message from stdin, expects ["ping"],
+/// and replies with ["pong"] on stdout.
+const std = @import("std");
+const cbor = @import("cbor");
+const framing = @import("framing");
+
+pub fn main() !void {
+    var acc: framing.Accumulator = .{};
+    var read_buf: [4096]u8 = undefined;
+
+    const frame = while (true) {
+        const n = try std.fs.File.stdin().read(&read_buf);
+        if (n == 0) return error.UnexpectedEof;
+        if (acc.feed(read_buf[0..n])) |f| break f;
+    };
+
+    if (!try cbor.match(frame, .{"ping"})) return error.UnexpectedMessage;
+
+    var msg_buf: [64]u8 = undefined;
+    var stream: std.Io.Writer = .fixed(&msg_buf);
+    try cbor.writeValue(&stream, .{"pong"});
+    try framing.write_frame(std.fs.File.stdout(), stream.buffered());
+}

test/remote_roundtrip_test.zig

@@ -0,0 +1,113 @@
+const std = @import("std");
+const thespian = @import("thespian");
+const cbor = @import("cbor");
+const framing = @import("framing");
+const build_options = @import("build_options");
+
+const Allocator = std.mem.Allocator;
+const result = thespian.result;
+const unexpected = thespian.unexpected;
+const pid_ref = thespian.pid_ref;
+const Receiver = thespian.Receiver;
+const message = thespian.message;
+const extract = thespian.extract;
+const subprocess = thespian.subprocess;
+
+const tag = "subprocess";
+
+const Parent = struct {
+    allocator: Allocator,
+    proc: subprocess,
+    accumulator: framing.Accumulator,
+    receiver: Receiver(*@This()),
+    pong_received: bool = false,
+
+    const Args = struct { allocator: Allocator };
+
+    fn start(args: Args) result {
+        return init(args) catch |e| return thespian.exit_error(e, @errorReturnTrace());
+    }
+
+    fn init(args: Args) !void {
+        var proc = try subprocess.init(
+            args.allocator,
+            message.fmt(.{build_options.remote_child_roundtrip_path}),
+            tag,
+            .Pipe,
+        );
+
+        // Encode ["ping"] and send it as a framed message to the child's stdin.
+        var msg_buf: [64]u8 = undefined;
+        var msg_stream: std.Io.Writer = .fixed(&msg_buf);
+        try cbor.writeValue(&msg_stream, .{"ping"});
+
+        var frame_buf: [68]u8 = undefined;
+        var frame_stream: std.Io.Writer = .fixed(&frame_buf);
+        try framing.write_frame(&frame_stream, msg_stream.buffered());
+        try proc.send(frame_stream.buffered());
+
+        const self = try args.allocator.create(@This());
+        self.* = .{
+            .allocator = args.allocator,
+            .proc = proc,
+            .accumulator = .{},
+            .receiver = .init(receive_fn, deinit, self),
+        };
+        errdefer self.deinit();
+        thespian.receive(&self.receiver);
+    }
+
+    fn deinit(self: *@This()) void {
+        self.proc.deinit();
+        self.allocator.destroy(self);
+    }
+
+    fn receive_fn(self: *@This(), from: pid_ref, m: message) result {
+        return self.receive(from, m) catch |e| return thespian.exit_error(e, @errorReturnTrace());
+    }
+
+    fn receive(self: *@This(), _: pid_ref, m: message) !void {
+        var bytes: []const u8 = "";
+        var exit_code: i64 = 0;
+
+        if (try m.match(.{ tag, "stdout", extract(&bytes) })) {
+            if (self.accumulator.feed(bytes)) |frame| {
+                try std.testing.expect(try cbor.match(frame, .{"pong"}));
+                self.pong_received = true;
+            }
+        } else if (try m.match(.{ tag, "term", "exited", extract(&exit_code) })) {
+            try std.testing.expect(self.pong_received);
+            try std.testing.expectEqual(@as(i64, 0), exit_code);
+            return thespian.exit("success");
+        } else if (try m.match(.{ tag, "stderr", extract(&bytes) })) {
+            // ignore stderr from child
+        } else {
+            return unexpected(m);
+        }
+    }
+};
+
+test "remote: round-trip ping/pong between parent and child" {
+    const allocator = std.testing.allocator;
+    var ctx = try thespian.context.init(allocator);
+    defer ctx.deinit();
+
+    var success = false;
+    var exit_handler = thespian.make_exit_handler(&success, struct {
+        fn handle(ok: *bool, status: []const u8) void {
+            ok.* = std.mem.eql(u8, status, "success");
+        }
+    }.handle);
+
+    _ = try ctx.spawn_link(
+        Parent.Args{ .allocator = allocator },
+        Parent.start,
+        "remote_roundtrip",
+        &exit_handler,
+        null,
+    );
+
+    ctx.run();
+
+    if (!success) return error.TestFailed;
+}

test/tests.zig

@@ -3,6 +3,7 @@ pub const cpp = @import("tests_cpp.zig");
 pub const thespian = @import("tests_thespian.zig");
 pub const ip_tcp_client_server = @import("ip_tcp_client_server.zig");
 pub const remote_poc = @import("remote_poc_test.zig");
+pub const remote_roundtrip = @import("remote_roundtrip_test.zig");
 
 test {
     std.testing.refAllDecls(@This());