How Can I Share Custom Data Types Between a Go Plugin and Its Application?

Sharing Custom Data Types Between a Go Plugin and an Application

In Go plugins, it's possible to share custom data types between the plugin and the application, but not through direct type assertion.

Shared Data Types in Separate Packages

To define shared types, create them in a separate package and import it into both the plugin and the main application. For example:

Shared Type Package:

<code class="go">package shared

type Person struct {
    Name string
}</code>

Plugin Code:

<code class="go">package main

import (
    "shared"
)

var P = shared.Person{Name: "Emma"}</code>

Main Application Code:

<code class="go">package main

import (
    "fmt"
    "plugin"
    "shared"
    "os"
)

func main() {
    plug, err := plugin.Open("./plugin.so")
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }

    // Lookup shared type symbol
    sym, err := plug.Lookup("P")
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }

    // Type-assert symbol into shared type
    var p shared.Person
    p, ok := sym.(shared.Person)
    if !ok {
        fmt.Println("Wrong symbol type")
        os.Exit(1)
    }

    // Use shared type as expected
    fmt.Println(p.Name)
}</code>

Non-Pointer Types and Pointer Symbols

When looking up variable symbols from a plugin, the result is a pointer to the variable, even if it's a non-pointer type. This allows modification of the variable's value from the plugin.

Conclusion

By using shared types defined in a separate package, it's possible to pass custom data types between a Go plugin and an application, enabling efficient data exchange and extending the plugin's capabilities.

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