Source file src/plugin/plugin.go

     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.
    66  package plugin
    67  
    68  // Plugin is a loaded Go plugin.
    69  type 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.
    79  func 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.
    87  func (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"
   120  type Symbol any
   121  

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