go - 从 Tcl 脚本调用 golang 函数

Question

我们使用第三方 Tcl 解析库来验证 Tcl 脚本的语法和语义检查。驱动程序是用 C 语言编写的，并定义了一组实用函数。然后它调用 Tcl_CreateObjCommand 因此脚本可以调用这些 C 函数。现在我们正在将主程序移植到 go 中，但我找不到执行此操作的方法。有人知道从 Tcl 脚本调用 golang 函数的方法吗？

static int
create_utility_tcl_cmds(Tcl_Interp* interp)
{
    if (Tcl_CreateObjCommand(interp, "ip_v4_address",
                        ip_address, (ClientData)AF_INET, NULL) == NULL) {
        TCL_CHECKER_TCL_CMD_EVENT(0, "ip_v4_address");
        return -1;
    }

    .....
    return 0;
}

Answer 1

假设您已将相关函数设置为已导出并构建项目的 Go 部分

Using Go code in an existing C project

[…]

The important things to note are:

• The package needs to be called main
• You need to have a main function, although it can be empty.
• You need to import the package C
• You need special //export comments to mark the functions you want callable from C.

I can compile it as a C callable static library with the following command:

go build -buildmode=c-archive foo.go

那么剩下要做的核心工作就是将 Tcl 的 API 中的 C 粘合函数写入您的 Go 代码。这将涉及类似以下的功能:

static int ip_address_glue(
        ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const *objv) {
    // Need an explicit cast; ClientData is really void*
    GoInt address_family = (GoInt) clientData;

    // Check for the right number of arguments
    if (objc != 2) {
        Tcl_WrongNumArgs(interp, 1, objv, "address");
        return TCL_ERROR;
    }

    // Convert the argument to a Go string
    GoString address;
    int len;
    address.p = Tcl_GetStringFromObj(objv[1], &len);
    address.n = len; // This bit is hiding a type mismatch

    // Do the call; I assume your Go function is called ip_address
    ip_address(address_family, address);

    // Assume the Go code doesn't fail, so no need to map the failure back to Tcl

    return TCL_OK;
}

^{(感谢 https://medium.com/learning-the-go-programming-language/calling-go-functions-from-other-languages-4c7d8bcc69bf 为我提供了足够的信息来计算一些类型绑定(bind)。)}

这就是您向 Tcl 注册为回调的函数。

Tcl_CreateObjCommand(interp, "ip_v4_address", ip_address_glue, (ClientData)AF_INET, NULL);

理论上，命令注册可能会失败。实际上，只有在删除 Tcl 解释器(或其中的一些关键 namespace )时才会发生这种情况。

---

如果在 Go 级别将故障编码为枚举，则将故障映射到 Tcl 将是最简单的。可能最容易将成功表示为零。有了它，您就可以:

GoInt failure_code = ip_address(address_family, address);

switch (failure_code) {
case 0: // Success
    return TCL_OK;
case 1: // First type of failure
    Tcl_SetResult(interp, "failure of type #1", TCL_STATIC);
    return TCL_ERROR;
// ... etc for each expected case ...
default: // Should be unreachable, yes?
    Tcl_SetObjResult(interp, Tcl_ObjPrintf("unexpected failure: %d", failure_code));
    return TCL_ERROR;
}

用值元组传回更复杂的返回类型(尤其是成功指示器和“真实”结果值的组合)也应该是可能的，但我没有 Go 开发环境来探究它们是如何实现的'映射到 C 级。