WIP: make libipc compatible with zig 0.15.2.

build.zig

@@ -1,70 +1,169 @@
 const std = @import("std");
 
-const VERSION = "0.2.0";
+// Although this function looks imperative, it does not perform the build
-
+// directly and instead it mutates the build graph (`b`) that will be then
-// Although this function looks imperative, note that its job is to
+// executed by an external runner. The functions in `std.Build` implement a DSL
-// declaratively construct a build graph that will be executed by an external
+// for defining build steps and express dependencies between them, allowing the
-// runner.
+// build runner to parallelize the build automatically (and the cache system to
+// know when a step doesn't need to be re-run).
 pub fn build(b: *std.Build) void {
-    // Standard target options allows the person running `zig build` to choose
+    // Standard target options allow the person running `zig build` to choose
     // what target to build for. Here we do not override the defaults, which
     // means any target is allowed, and the default is native. Other options
     // for restricting supported target set are available.
     const target = b.standardTargetOptions(.{});
-
     // Standard optimization options allow the person running `zig build` to select
     // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
     // set a preferred release mode, allowing the user to decide how to optimize.
     const optimize = b.standardOptimizeOption(.{});
+    // It's also possible to define more custom flags to toggle optional features
+    // of this build script using `b.option()`. All defined flags (including
+    // target and optimize options) will be listed when running `zig build --help`
+    // in this directory.
 
-    const static_lib = b.addStaticLibrary(.{
+    // This creates a module, which represents a collection of source files alongside
-        .name = "ipc",
+    // some compilation options, such as optimization mode and linked system libraries.
-        // In this case the main source file is merely a path, however, in more
+    // Zig modules are the preferred way of making Zig code available to consumers.
-        // complicated build scripts, this could be a generated file.
+    // addModule defines a module that we intend to make available for importing
-        .root_source_file = .{ .cwd_relative = "src/bindings.zig" },
+    // to our consumers. We must give it a name because a Zig package can expose
+    // multiple modules and consumers will need to be able to specify which
+    // module they want to access.
+    const mod = b.addModule("libipc", .{
+        // The root source file is the "entry point" of this module. Users of
+        // this module will only be able to access public declarations contained
+        // in this file, which means that if you have declarations that you
+        // intend to expose to consumers that were defined in other files part
+        // of this module, you will have to make sure to re-export them from
+        // the root file.
+        .root_source_file = b.path("src/root.zig"),
+        // Later on we'll use this module as the root module of a test executable
+        // which requires us to specify a target.
         .target = target,
-        .optimize = optimize,
     });
 
-    // Link with the libc of the target system since the C allocator
+    // Here we define an executable. An executable needs to have a root module
-    // is required in the bindings.
+    // which needs to expose a `main` function. While we could add a main function
-    static_lib.linkLibC();
+    // to the module defined above, it's sometimes preferable to split business
-
+    // business logic and the CLI into two separate modules.
-    // This declares intent for the library to be installed into the standard
+    //
-    // location when the user invokes the "install" step (the default step when
+    // If your goal is to create a Zig library for others to use, consider if
-    // running `zig build`).
+    // it might benefit from also exposing a CLI tool. A parser library for a
-    b.installArtifact(static_lib);
+    // data serialization format could also bundle a CLI syntax checker, for example.
-
+    //
-    const shared_lib = b.addSharedLibrary(.{
+    // If instead your goal is to create an executable, consider if users might
-        .name = "ipc",
+    // be interested in also being able to embed the core functionality of your
-        .root_source_file = .{ .cwd_relative = "src/bindings.zig" },
+    // program in their own executable in order to avoid the overhead involved in
-        .version = comptime (try std.SemanticVersion.parse(VERSION)),
+    // subprocessing your CLI tool.
+    //
+    // If neither case applies to you, feel free to delete the declaration you
+    // don't need and to put everything under a single module.
+    const exe = b.addExecutable(.{
+        .name = "ping", // name of the executable
+        .root_module = b.createModule(.{
+            // b.createModule defines a new module just like b.addModule but,
+            // unlike b.addModule, it does not expose the module to consumers of
+            // this package, which is why in this case we don't have to give it a name.
+            .root_source_file = b.path("src/main.zig"),
+            // Target and optimization levels must be explicitly wired in when
+            // defining an executable or library (in the root module), and you
+            // can also hardcode a specific target for an executable or library
+            // definition if desireable (e.g. firmware for embedded devices).
             .target = target,
             .optimize = optimize,
+            // List of modules available for import in source files part of the
+            // root module.
+            .imports = &.{
+                // Here "libipc" is the name you will use in your source code to
+                // import this module (e.g. `@import("libipc")`). The name is
+                // repeated because you are allowed to rename your imports, which
+                // can be extremely useful in case of collisions (which can happen
+                // importing modules from different packages).
+                .{ .name = "libipc", .module = mod },
+            },
+        }),
     });
-    shared_lib.linkLibC();
-    b.installArtifact(shared_lib);
 
-    // Creates a step for unit testing.
+    // This declares intent for the executable to be installed into the
-    const main_tests = b.addTest(.{
+    // install prefix when running `zig build` (i.e. when executing the default
-        .root_source_file = .{ .cwd_relative = "src/main.zig" },
+    // step). By default the install prefix is `zig-out/` but can be overridden
+    // by passing `--prefix` or `-p`.
+    b.installArtifact(exe);
+
+    // Here we define a library.
+    const lib = b.addLibrary(.{
+        .name = "libipc", // name of the library
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/root.zig"),
             .target = target,
             .optimize = optimize,
+        }),
     });
-    main_tests.linkLibC();
+    // Tell the compiler we need libc.
+    lib.root_module.link_libc = true;
+    b.installArtifact(lib);
 
-    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // This creates a top level step. Top level steps have a name and can be
-    // and can be selected like this: `zig build test`
+    // invoked by name when running `zig build` (e.g. `zig build run`).
-    // This will evaluate the `test` step rather than the default, which is "install".
+    // This will evaluate the `run` step rather than the default step.
-    const test_step = b.step("test", "Run library tests");
+    // For a top level step to actually do something, it must depend on other
-    test_step.dependOn(&main_tests.step);
+    // steps (e.g. a Run step, as we will see in a moment).
+    const run_step = b.step("run", "Run the app");
 
-    const install_static_lib = b.addInstallArtifact(static_lib, .{});
+    // This creates a RunArtifact step in the build graph. A RunArtifact step
-    const static_lib_step = b.step("static", "Compile LibIPC as a static library.");
+    // invokes an executable compiled by Zig. Steps will only be executed by the
-    static_lib_step.dependOn(&install_static_lib.step);
+    // runner if invoked directly by the user (in the case of top level steps)
+    // or if another step depends on it, so it's up to you to define when and
+    // how this Run step will be executed. In our case we want to run it when
+    // the user runs `zig build run`, so we create a dependency link.
+    const run_cmd = b.addRunArtifact(exe);
+    run_step.dependOn(&run_cmd.step);
 
-    const install_shared_lib = b.addInstallArtifact(shared_lib, .{});
+    // By making the run step depend on the default step, it will be run from the
-    // b.getInstallStep().dependOn(&install_shared_lib.step);
+    // installation directory rather than directly from within the cache directory.
-    const shared_lib_step = b.step("shared", "Compile LibIPC as a shared library.");
+    run_cmd.step.dependOn(b.getInstallStep());
-    shared_lib_step.dependOn(&install_shared_lib.step);
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // Creates an executable that will run `test` blocks from the provided module.
+    // Here `mod` needs to define a target, which is why earlier we made sure to
+    // set the releative field.
+    const mod_tests = b.addTest(.{
+        .root_module = mod,
+    });
+
+    // A run step that will run the test executable.
+    const run_mod_tests = b.addRunArtifact(mod_tests);
+
+    // Creates an executable that will run `test` blocks from the executable's
+    // root module. Note that test executables only test one module at a time,
+    // hence why we have to create two separate ones.
+    const exe_tests = b.addTest(.{
+        .root_module = exe.root_module,
+    });
+
+    // A run step that will run the second test executable.
+    const run_exe_tests = b.addRunArtifact(exe_tests);
+
+    // A top level step for running all tests. dependOn can be called multiple
+    // times and since the two run steps do not depend on one another, this will
+    // make the two of them run in parallel.
+    const test_step = b.step("test", "Run tests");
+    test_step.dependOn(&run_mod_tests.step);
+    test_step.dependOn(&run_exe_tests.step);
+
+    // Just like flags, top level steps are also listed in the `--help` menu.
+    //
+    // The Zig build system is entirely implemented in userland, which means
+    // that it cannot hook into private compiler APIs. All compilation work
+    // orchestrated by the build system will result in other Zig compiler
+    // subcommands being invoked with the right flags defined. You can observe
+    // these invocations when one fails (or you pass a flag to increase
+    // verbosity) to validate assumptions and diagnose problems.
+    //
+    // Lastly, the Zig build system is relatively simple and self-contained,
+    // and reading its source code will allow you to master it.
 }

build.zig.zon

@@ -0,0 +1,81 @@
+.{
+    // This is the default name used by packages depending on this one. For
+    // example, when a user runs `zig fetch --save <url>`, this field is used
+    // as the key in the `dependencies` table. Although the user can choose a
+    // different name, most users will stick with this provided value.
+    //
+    // It is redundant to include "zig" in this name because it is already
+    // within the Zig package namespace.
+    .name = .libipc,
+    // This is a [Semantic Version](https://semver.org/).
+    // In a future version of Zig it will be used for package deduplication.
+    .version = "0.0.0",
+    // Together with name, this represents a globally unique package
+    // identifier. This field is generated by the Zig toolchain when the
+    // package is first created, and then *never changes*. This allows
+    // unambiguous detection of one package being an updated version of
+    // another.
+    //
+    // When forking a Zig project, this id should be regenerated (delete the
+    // field and run `zig build`) if the upstream project is still maintained.
+    // Otherwise, the fork is *hostile*, attempting to take control over the
+    // original project's identity. Thus it is recommended to leave the comment
+    // on the following line intact, so that it shows up in code reviews that
+    // modify the field.
+    .fingerprint = 0x777bfd8d5e058778, // Changing this has security and trust implications.
+    // Tracks the earliest Zig version that the package considers to be a
+    // supported use case.
+    .minimum_zig_version = "0.15.1",
+    // This field is optional.
+    // Each dependency must either provide a `url` and `hash`, or a `path`.
+    // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
+    // Once all dependencies are fetched, `zig build` no longer requires
+    // internet connectivity.
+    .dependencies = .{
+        // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
+        //.example = .{
+        //    // When updating this field to a new URL, be sure to delete the corresponding
+        //    // `hash`, otherwise you are communicating that you expect to find the old hash at
+        //    // the new URL. If the contents of a URL change this will result in a hash mismatch
+        //    // which will prevent zig from using it.
+        //    .url = "https://example.com/foo.tar.gz",
+        //
+        //    // This is computed from the file contents of the directory of files that is
+        //    // obtained after fetching `url` and applying the inclusion rules given by
+        //    // `paths`.
+        //    //
+        //    // This field is the source of truth; packages do not come from a `url`; they
+        //    // come from a `hash`. `url` is just one of many possible mirrors for how to
+        //    // obtain a package matching this `hash`.
+        //    //
+        //    // Uses the [multihash](https://multiformats.io/multihash/) format.
+        //    .hash = "...",
+        //
+        //    // When this is provided, the package is found in a directory relative to the
+        //    // build root. In this case the package's hash is irrelevant and therefore not
+        //    // computed. This field and `url` are mutually exclusive.
+        //    .path = "foo",
+        //
+        //    // When this is set to `true`, a package is declared to be lazily
+        //    // fetched. This makes the dependency only get fetched if it is
+        //    // actually used.
+        //    .lazy = false,
+        //},
+    },
+    // Specifies the set of files and directories that are included in this package.
+    // Only files and directories listed here are included in the `hash` that
+    // is computed for this package. Only files listed here will remain on disk
+    // when using the zig package manager. As a rule of thumb, one should list
+    // files required for compilation plus any license(s).
+    // Paths are relative to the build root. Use the empty string (`""`) to refer to
+    // the build root itself.
+    // A directory listed here means that all files within, recursively, are included.
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+        // For example...
+        //"LICENSE",
+        //"README.md",
+    },
+}

src/context.zig

@@ -22,7 +22,7 @@ const print_eq = @import("./util.zig").print_eq;
 const Messages = @import("./message.zig").Messages;
 const SwitchDB = @import("./switch.zig").SwitchDB;
 const Connections = @import("./connection.zig").Connections;
-const CBEventType = @import("./main.zig").CBEvent.Type;
+const CBEventType = CBEvent.Type;
 
 pub const PollFD = std.ArrayList(posix.pollfd);
 

src/main.zig

@@ -13,6 +13,14 @@ pub const util = @import("./util.zig");
 pub const hexdump = @import("./hexdump.zig");
 pub const exchangefd = @import("./exchange-fd.zig");
 
+// PING source code
+const std = @import("std");
+// const libipc = @import("libipc");
+pub fn main() !void {
+    // Prints to stderr, ignoring potential errors.
+    std.debug.print("All your {s} are belong to us.\n", .{"codebase"});
+}
+
 test {
     _ = @import("./callback.zig");
     _ = @import("./connection.zig");

src/root.zig

@@ -1,11 +1,10 @@
 const std = @import("std");
 const log = std.log.scoped(.libipc_bindings);
-const ipc = @import("./main.zig");
+const Context = @import("./context.zig").Context;
-const Context = ipc.Context;
+const Message = @import("./message.zig").Message;
-const Message = ipc.Message;
+const CBEventType = @import("./callback.zig").CBEvent.Type;
-const CBEventType = ipc.CBEvent.Type;
 
-export fn ipc_context_init(ptr: **Context) callconv(.C) i32 {
+export fn ipc_context_init(ptr: **Context) callconv(.c) i32 {
     ptr.* = std.heap.c_allocator.create(Context) catch return -1;
 
     ptr.*.* = Context.init(std.heap.c_allocator) catch |err| {
@@ -16,27 +15,27 @@ export fn ipc_context_init(ptr: **Context) callconv(.C) i32 {
 }
 
 /// Start a libipc service.
-export fn ipc_service_init(ctx: *Context, servicefd: *i32, service_name: [*]const u8, service_name_len: u16) callconv(.C) i32 {
+export fn ipc_service_init(ctx: *Context, servicefd: *i32, service_name: [*]const u8, service_name_len: u16) callconv(.c) i32 {
     const streamserver = ctx.server_init(service_name[0..service_name_len]) catch return -1;
     servicefd.* = streamserver.stream.handle;
     return 0;
 }
 
 /// Connect to a libipc service, possibly through IPCd.
-export fn ipc_connect_service(ctx: *Context, servicefd: *i32, service_name: [*]const u8, service_name_len: u16) callconv(.C) i32 {
+export fn ipc_connect_service(ctx: *Context, servicefd: *i32, service_name: [*]const u8, service_name_len: u16) callconv(.c) i32 {
     const fd = ctx.connect_ipc(service_name[0..service_name_len]) catch return -1;
     servicefd.* = fd;
     return 0;
 }
 
-export fn ipc_context_deinit(ctx: **Context) callconv(.C) void {
+export fn ipc_context_deinit(ctx: **Context) callconv(.c) void {
     var ptr: *Context = ctx.*;
     ptr.deinit();
     std.heap.c_allocator.destroy(ptr);
 }
 
 /// Write a message (no waiting).
-export fn ipc_write(ctx: *Context, servicefd: i32, mcontent: [*]const u8, mlen: usize) callconv(.C) i32 {
+export fn ipc_write(ctx: *Context, servicefd: i32, mcontent: [*]const u8, mlen: usize) callconv(.c) i32 {
     // TODO: better default length.
     var buffer = [_]u8{0} ** 100000;
     var fba = std.heap.FixedBufferAllocator.init(&buffer);
@@ -48,7 +47,7 @@ export fn ipc_write(ctx: *Context, servicefd: i32, mcontent: [*]const u8, mlen:
 
 /// Schedule a message.
 /// Use the same allocator as the context.
-export fn ipc_schedule(ctx: *Context, servicefd: i32, mcontent: [*]const u8, mlen: usize) callconv(.C) i32 {
+export fn ipc_schedule(ctx: *Context, servicefd: i32, mcontent: [*]const u8, mlen: usize) callconv(.c) i32 {
     const message = Message.init(servicefd, ctx.allocator, mcontent[0..mlen]) catch return -1;
     ctx.schedule(message) catch return -2;
     return 0;
@@ -56,7 +55,7 @@ export fn ipc_schedule(ctx: *Context, servicefd: i32, mcontent: [*]const u8, mle
 
 /// Read a message from a file descriptor.
 /// Buffer length will be changed to the size of the received message.
-export fn ipc_read_fd(ctx: *Context, fd: i32, buffer: [*]u8, buflen: *usize) callconv(.C) i32 {
+export fn ipc_read_fd(ctx: *Context, fd: i32, buffer: [*]u8, buflen: *usize) callconv(.c) i32 {
     var m = ctx.read_fd(fd) catch {
         return -1;
     } orelse return -2;
@@ -73,7 +72,7 @@ export fn ipc_read_fd(ctx: *Context, fd: i32, buffer: [*]u8, buflen: *usize) cal
 
 /// Read a message.
 /// Buffer length will be changed to the size of the received message.
-export fn ipc_read(ctx: *Context, index: usize, buffer: [*]u8, buflen: *usize) callconv(.C) i32 {
+export fn ipc_read(ctx: *Context, index: usize, buffer: [*]u8, buflen: *usize) callconv(.c) i32 {
     var m = ctx.read(index) catch {
         return -1;
     } orelse return -2;
@@ -90,7 +89,7 @@ export fn ipc_read(ctx: *Context, index: usize, buffer: [*]u8, buflen: *usize) c
 
 /// Wait for an event.
 /// Buffer length will be changed to the size of the received message.
-export fn ipc_wait_event(ctx: *Context, t: *u8, index: *usize, originfd: *i32, newfd: *i32, buffer: [*]u8, buflen: *usize) callconv(.C) i32 {
+export fn ipc_wait_event(ctx: *Context, t: *u8, index: *usize, originfd: *i32, newfd: *i32, buffer: [*]u8, buflen: *usize) callconv(.c) i32 {
     const event = ctx.wait_event() catch |err| switch (err) {
         else => {
             log.warn("error while waiting for an event: {}\n", .{err});
@@ -119,21 +118,21 @@ export fn ipc_wait_event(ctx: *Context, t: *u8, index: *usize, originfd: *i32, n
 }
 
 /// Change the timer (ms).
-export fn ipc_context_timer(ctx: *Context, timer: i32) callconv(.C) void {
+export fn ipc_context_timer(ctx: *Context, timer: i32) callconv(.c) void {
     ctx.timer = timer;
 }
 
-export fn ipc_close_fd(ctx: *Context, fd: i32) callconv(.C) i32 {
+export fn ipc_close_fd(ctx: *Context, fd: i32) callconv(.c) i32 {
     ctx.close_fd(fd) catch return -1;
     return 0;
 }
 
-export fn ipc_close(ctx: *Context, index: usize) callconv(.C) i32 {
+export fn ipc_close(ctx: *Context, index: usize) callconv(.c) i32 {
     ctx.close(index) catch return -1;
     return 0;
 }
 
-export fn ipc_close_all(ctx: *Context) callconv(.C) i32 {
+export fn ipc_close_all(ctx: *Context) callconv(.c) i32 {
     ctx.close_all() catch return -1;
     return 0;
 }
@@ -141,19 +140,19 @@ export fn ipc_close_all(ctx: *Context) callconv(.C) i32 {
 /// Add a new file descriptor to listen to.
 /// The FD is marked as "external"; it isn't a simple libipc connection.
 /// You may want to handle any operation on it by yourself.
-export fn ipc_add_external(ctx: *Context, newfd: i32) callconv(.C) i32 {
+export fn ipc_add_external(ctx: *Context, newfd: i32) callconv(.c) i32 {
     ctx.add_external(newfd) catch return -1;
     return 0;
 }
 
-export fn ipc_add_switch(ctx: *Context, fd1: i32, fd2: i32) callconv(.C) i32 {
+export fn ipc_add_switch(ctx: *Context, fd1: i32, fd2: i32) callconv(.c) i32 {
     ctx.add_switch(fd1, fd2) catch return -1;
     return 0;
 }
 
 export fn ipc_set_switch_callbacks(ctx: *Context, fd: i32,
-        in:  ?*const fn (origin: i32, mcontent:       [*]u8, mlen: *usize) callconv(.C) u8,
+        in:  ?*const fn (origin: i32, mcontent:       [*]u8, mlen: *usize) callconv(.c) u8,
-        out: ?*const fn (origin: i32, mcontent: [*]const u8, mlen:  usize) callconv(.C) u8) callconv(.C) i32 {
+        out: ?*const fn (origin: i32, mcontent: [*]const u8, mlen:  usize) callconv(.c) u8) callconv(.c) i32 {
     ctx.set_switch_callbacks(fd, in, out) catch return -1;
     return 0;
 }

src/switch.zig

@@ -4,9 +4,8 @@ const fmt = std.fmt;
 
 const net = std.net;
 
-const ipc = @import("./main.zig");
+const Message = @import("./message.zig").Message;
-const Message = ipc.Message;
+const CBEventType = @import("./callback.zig").CBEvent.Type;
-const CBEventType = ipc.CBEvent.Type;
 
 const Allocator = std.mem.Allocator;
 
@@ -14,7 +13,7 @@ const util = @import("./util.zig");
 const print_eq = util.print_eq;
 const log = std.log.scoped(.libipc_switch);
 
-const Event = ipc.Event;
+const Event = @import("./event.zig").Event;
 
 /// SwitchDB: store relations between clients and services.
 ///
@@ -65,8 +64,8 @@ pub const SwitchDB = struct {
     }
 
     pub fn set_callbacks(self: *Self, fd: i32,
-            in:  ?*const fn (origin: i32, mcontent:       [*]u8, mlen: *usize) callconv(.C) u8,
+            in:  ?*const fn (origin: i32, mcontent:       [*]u8, mlen: *usize) callconv(.c) u8,
-            out: ?*const fn (origin: i32, mcontent: [*]const u8, mlen:  usize) callconv(.C) u8) !void {
+            out: ?*const fn (origin: i32, mcontent: [*]const u8, mlen:  usize) callconv(.c) u8) !void {
         var managedconnection = self.db.get(fd) orelse return error.unregisteredFD;
         if (in)  |f| { managedconnection.in  = f; }
         if (out) |f| { managedconnection.out = f; }
@@ -186,8 +185,8 @@ pub const SwitchDB = struct {
 
 const ManagedConnection = struct {
     dest: i32,
-    in:  *const fn (origin: i32, mcontent:       [*]u8, mlen: *usize) callconv(.C) u8 = default_in,
+    in:  *const fn (origin: i32, mcontent:       [*]u8, mlen: *usize) callconv(.c) u8 = default_in,
-    out: *const fn (origin: i32, mcontent: [*]const u8, mlen:  usize) callconv(.C) u8 = default_out,
+    out: *const fn (origin: i32, mcontent: [*]const u8, mlen:  usize) callconv(.c) u8 = default_out,
 };
 
 test "creation and display" {
@@ -311,7 +310,7 @@ test "nuke 'em" {
     try testing.expect(switchdb.db.count() == 0);
 }
 
-fn default_in(origin: i32, mcontent: [*]u8, mlen: *usize) callconv(.C) u8 {
+fn default_in(origin: i32, mcontent: [*]u8, mlen: *usize) callconv(.c) u8 {
     // This may be kinda hacky, idk.
     var stream: net.Stream = .{ .handle = origin };
     const packet_size: usize = stream.read(mcontent[0..mlen.*]) catch return @intFromEnum(CBEventType.ERROR);
@@ -327,7 +326,7 @@ fn default_in(origin: i32, mcontent: [*]u8, mlen: *usize) callconv(.C) u8 {
     return @intFromEnum(CBEventType.NO_ERROR);
 }
 
-fn default_out(fd: i32, mcontent: [*]const u8, mlen: usize) callconv(.C) u8 {
+fn default_out(fd: i32, mcontent: [*]const u8, mlen: usize) callconv(.c) u8 {
     // Message contains the fd, no need to search for the right structure to copy,
     // let's just recreate a Stream from the fd.