go-plugins-demo/PITCHME.md

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Go plugins

Gildas Chabot, leboncoin

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Demo!

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• Released in 1.8
• Add Go code at runtime
• Works only on linux for now
• Based on C's dlfcn.h (dynamic linking) with cgo
  • See src/plugin/plugin_dlopen.go

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Need?

• Extend a service with third party functions
  • Web server
  • Media player
• Update behaviour at runtime

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Before

• Add plugins at compile time (Caddy)
• HTTP/RPC calls

https://github.com/hashicorp/go-plugin https://github.com/natefinch/pie

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Now: Plugin side

• Nothing special on the code of the plugin
  • -buildmode=plugin build option
• Creates a .so

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Now: Caller side

• Only two functions:
  • Open(path string) (*Plugin, error)
  • (p *Plugin) Lookup(symName string) (Symbol, error)
• Two types:
  • Plugin
  • Symbol
• When the plugin if first Open, all new packages have their init function called

See https://tip.golang.org/pkg/plugin/

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Example

p, err := plugin.Open("plugin.so")

fs, err := p.Lookup("Transform")
f, ok := fs.(func(image.Image) image.Image)

vs, err := p.Lookup("Priority")
v, ok = *vs.(*int)

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Safety?

• Plugin == safe?
• Same rights as caller
• Check the sources of the plugins!

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Stable?

• Invalid .so file
  • fatal error: runtime: no plugin module data
• Can panic during execution

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Go + C?

• Go plugin used in C
  • Already done with -buildmode=shared
• C .so loaded in Go
  • For now, error "no plugin module data"

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Thank you

Questions?

Find the code and slides on Github: https://github.com/GildasCh/go-plugins-demo