1// Copyright 2016 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Package plugin implements loading and symbol resolution of Go plugins.
6//
7// A plugin is a Go main package with exported functions and variables that
8// has been built with:
9//
10//	go build -buildmode=plugin
11//
12// When a plugin is first opened, the init functions of all packages not
13// already part of the program are called. The main function is not run.
14// A plugin is only initialized once, and cannot be closed.
15//
16// # Warnings
17//
18// The ability to dynamically load parts of an application during
19// execution, perhaps based on user-defined configuration, may be a
20// useful building block in some designs. In particular, because
21// applications and dynamically loaded functions can share data
22// structures directly, plugins may enable very high-performance
23// integration of separate parts.
24//
25// However, the plugin mechanism has many significant drawbacks that
26// should be considered carefully during the design. For example:
27//
28//   - Plugins are currently supported only on Linux, FreeBSD, and
29//     macOS, making them unsuitable for applications intended to be
30//     portable.
31//
32//   - Applications that use plugins may require careful configuration
33//     to ensure that the various parts of the program be made available
34//     in the correct location in the file system (or container image).
35//     By contrast, deploying an application consisting of a single static
36//     executable is straightforward.
37//
38//   - Reasoning about program initialization is more difficult when
39//     some packages may not be initialized until long after the
40//     application has started running.
41//
42//   - Bugs in applications that load plugins could be exploited by
43//     an attacker to load dangerous or untrusted libraries.
44//
45//   - Runtime crashes are likely to occur unless all parts of the
46//     program (the application and all its plugins) are compiled
47//     using exactly the same version of the toolchain, the same build
48//     tags, and the same values of certain flags and environment
49//     variables.
50//
51//   - Similar crashing problems are likely to arise unless all common
52//     dependencies of the application and its plugins are built from
53//     exactly the same source code.
54//
55//   - Together, these restrictions mean that, in practice, the
56//     application and its plugins must all be built together by a
57//     single person or component of a system. In that case, it may
58//     be simpler for that person or component to generate Go source
59//     files that blank-import the desired set of plugins and then
60//     compile a static executable in the usual way.
61//
62// For these reasons, many users decide that traditional interprocess
63// communication (IPC) mechanisms such as sockets, pipes, remote
64// procedure call (RPC), shared memory mappings, or file system
65// operations may be more suitable despite the performance overheads.
66package plugin
67
68// Plugin is a loaded Go plugin.
69type Plugin struct {
70	pluginpath string
71	err        string        // set if plugin failed to load
72	loaded     chan struct{} // closed when loaded
73	syms       map[string]any
74}
75
76// Open opens a Go plugin.
77// If a path has already been opened, then the existing *[Plugin] is returned.
78// It is safe for concurrent use by multiple goroutines.
79func Open(path string) (*Plugin, error) {
80	return open(path)
81}
82
83// Lookup searches for a symbol named symName in plugin p.
84// A symbol is any exported variable or function.
85// It reports an error if the symbol is not found.
86// It is safe for concurrent use by multiple goroutines.
87func (p *Plugin) Lookup(symName string) (Symbol, error) {
88	return lookup(p, symName)
89}
90
91// A Symbol is a pointer to a variable or function.
92//
93// For example, a plugin defined as
94//
95//	package main
96//
97//	import "fmt"
98//
99//	var V int
100//
101//	func F() { fmt.Printf("Hello, number %d\n", V) }
102//
103// may be loaded with the [Open] function and then the exported package
104// symbols V and F can be accessed
105//
106//	p, err := plugin.Open("plugin_name.so")
107//	if err != nil {
108//		panic(err)
109//	}
110//	v, err := p.Lookup("V")
111//	if err != nil {
112//		panic(err)
113//	}
114//	f, err := p.Lookup("F")
115//	if err != nil {
116//		panic(err)
117//	}
118//	*v.(*int) = 7
119//	f.(func())() // prints "Hello, number 7"
120type Symbol any
121