mirror of https://go.googlesource.com/go
121 lines
4.3 KiB
Go
121 lines
4.3 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package plugin implements loading and symbol resolution of Go plugins.
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//
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// A plugin is a Go main package with exported functions and variables that
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// has been built with:
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//
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// go build -buildmode=plugin
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//
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// When a plugin is first opened, the init functions of all packages not
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// already part of the program are called. The main function is not run.
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// A plugin is only initialized once, and cannot be closed.
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//
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// # Warnings
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//
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// The ability to dynamically load parts of an application during
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// execution, perhaps based on user-defined configuration, may be a
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// useful building block in some designs. In particular, because
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// applications and dynamically loaded functions can share data
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// structures directly, plugins may enable very high-performance
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// integration of separate parts.
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//
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// However, the plugin mechanism has many significant drawbacks that
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// should be considered carefully during the design. For example:
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//
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// - Plugins are currently supported only on Linux, FreeBSD, and
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// macOS, making them unsuitable for applications intended to be
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// portable.
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//
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// - Applications that use plugins may require careful configuration
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// to ensure that the various parts of the program be made available
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// in the correct location in the file system (or container image).
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// By contrast, deploying an application consisting of a single static
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// executable is straightforward.
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//
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// - Reasoning about program initialization is more difficult when
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// some packages may not be initialized until long after the
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// application has started running.
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//
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// - Bugs in applications that load plugins could be exploited by
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// an attacker to load dangerous or untrusted libraries.
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//
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// - Runtime crashes are likely to occur unless all parts of the
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// program (the application and all its plugins) are compiled
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// using exactly the same version of the toolchain, the same build
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// tags, and the same values of certain flags and environment
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// variables.
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//
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// - Similar crashing problems are likely to arise unless all common
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// dependencies of the application and its plugins are built from
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// exactly the same source code.
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//
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// - Together, these restrictions mean that, in practice, the
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// application and its plugins must all be built together by a
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// single person or component of a system. In that case, it may
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// be simpler for that person or component to generate Go source
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// files that blank-import the desired set of plugins and then
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// compile a static executable in the usual way.
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//
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// For these reasons, many users decide that traditional interprocess
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// communication (IPC) mechanisms such as sockets, pipes, remote
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// procedure call (RPC), shared memory mappings, or file system
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// operations may be more suitable despite the performance overheads.
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package plugin
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// Plugin is a loaded Go plugin.
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type Plugin struct {
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pluginpath string
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err string // set if plugin failed to load
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loaded chan struct{} // closed when loaded
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syms map[string]any
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}
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// Open opens a Go plugin.
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// If a path has already been opened, then the existing *[Plugin] is returned.
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// It is safe for concurrent use by multiple goroutines.
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func Open(path string) (*Plugin, error) {
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return open(path)
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}
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// Lookup searches for a symbol named symName in plugin p.
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// A symbol is any exported variable or function.
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// It reports an error if the symbol is not found.
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// It is safe for concurrent use by multiple goroutines.
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func (p *Plugin) Lookup(symName string) (Symbol, error) {
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return lookup(p, symName)
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}
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// A Symbol is a pointer to a variable or function.
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//
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// For example, a plugin defined as
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//
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// package main
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//
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// import "fmt"
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//
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// var V int
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//
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// func F() { fmt.Printf("Hello, number %d\n", V) }
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//
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// may be loaded with the [Open] function and then the exported package
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// symbols V and F can be accessed
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//
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// p, err := plugin.Open("plugin_name.so")
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// if err != nil {
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// panic(err)
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// }
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// v, err := p.Lookup("V")
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// if err != nil {
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// panic(err)
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// }
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// f, err := p.Lookup("F")
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// if err != nil {
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// panic(err)
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// }
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// *v.(*int) = 7
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// f.(func())() // prints "Hello, number 7"
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type Symbol any
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