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Building a plugin

Learn to build a plugin with go build -buildmode=plugin.

Building a plugin

A plugin is a package with package main that doesn't need a main function. Every exported (upper-case) function and variable becomes a symbol of the plugin.

// selam/selam.go
package main

func Selam(ad string) string { return "Merhaba " + ad }

Build: go build -buildmode=plugin -o selam.so ./selam

Version matching

The safest way to build the main program and the plugin with the same module versions is to keep them in the same repository or share the same go.mod. Loading a plugin built differently gives the error "plugin was built with a different version of package".

Practice Write a plugin function

Add the function func Ikiye(n int) int to the code that will be built as a plugin (it returns twice n). In main, print fmt.Println(Ikiye(21)) as a test.

Starter code

main.go
package main

import "fmt"

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import "fmt"

func Ikiye(n int) int { return n * 2 }

func main() {
    fmt.Println(Ikiye(21))
}

Expected output

42

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which flag is needed to build a plugin?

  • -o plugin
  • -buildmode=plugin Correct answer
  • -plugin
  • -shared=true

Explanation: go build -buildmode=plugin produces a shared object (.so); -o sets the file name.

2 Build command

Question 
go build ____ -o selam.so ./selam
Answer 
go build -buildmode=plugin -o selam.so ./selam

Explanation: -buildmode=plugin makes the output a loadable .so file.

3 Plugin source

Term Meaning
package main Plugin package name
func Selam Exported symbol
func yardimci Hidden (lower case)
-o selam.so Output file

All lessons in Advanced

1 Reflection

  1. The reflect package
  2. reflect.Type
  3. reflect.Value
  4. Reflecting struct fields
  5. Dynamic call
  6. Summary - Reflection

2 unsafe

  1. The unsafe package
  2. unsafe.Pointer
  3. Sizeof and Alignof
  4. Offsetof
  5. unsafe and slice
  6. Summary - unsafe

3 cgo

  1. What is cgo?
  2. Calling C code
  3. C data types
  4. Go-C conversion
  5. cgo and memory
  6. Summary - cgo

4 plugin

  1. The plugin package
  2. Building a plugin
  3. Loading a plugin
  4. Plugin symbol
  5. Plugin and error
  6. Summary - plugin

5 database/sql

  1. The database/sql package
  2. sql.Open
  3. Query and Exec
  4. Prepared statement
  5. Transaction
  6. Summary - database/sql

6 Middleware

  1. The middleware concept
  2. HTTP middleware
  3. Middleware chain
  4. Logging middleware
  5. Auth middleware
  6. Summary - Middleware

7 gRPC

  1. What is gRPC?
  2. Protobuf definition
  3. Compiling with protoc
  4. gRPC server
  5. gRPC client
  6. Summary - gRPC

8 Project: Microservice

  1. Service skeleton
  2. Database layer
  3. HTTP API
  4. Docker and deployment

9 Docker

  1. Dockerfile
  2. Multi-stage build
  3. scratch image
  4. docker-compose
  5. Build args and labels
  6. Summary - Docker

10 pprof

  1. What is pprof?
  2. CPU profiling
  3. Memory profiling
  4. go test -cpuprofile
  5. The trace tool
  6. Summary - pprof

11 Observability

  1. log/slog
  2. Metrics
  3. Tracing
  4. OpenTelemetry
  5. Health check
  6. Summary - Observability

12 Advanced final

  1. Challenge 1 - Reflection
  2. Challenge 2 - Microservice
  3. Challenge 3 - Performance
  4. Challenge 4 - Database