Cannot load Go plugin: "plugin: not implemented"

[mbrozzo]

What I did

• I cloned the repo
• I checked out tag v6.7.21
• I added these files in docker/plugin

plugin.go

package main
import (
    "github.com/rwynn/monstache/v6/monstachemap"
    "strings"
)
// a plugin to convert document values to uppercase
func Map(input *monstachemap.MapperPluginInput) (output *monstachemap.MapperPluginOutput, err error) {
    doc := input.Document
    for k, v := range doc {
        switch v.(type) {
        case string:
            doc[k] = strings.ToUpper(v.(string))
        }
    }
    output = &monstachemap.MapperPluginOutput{Document: doc}
    return
}

Taken from your docs.

go.mod

module monstacheplugin

go 1.13

require (
	github.com/json-iterator/go v1.1.12
	github.com/rwynn/monstache/v6 v6.7.21
)

Note that without go.mod and go.sum, it would not compile with the following error:

 => ERROR [8/8] RUN go build -buildmode=plugin -o plu  0.3s
------
 > [8/8] RUN go build -buildmode=plugin -o plugin.so plugin.go:
#0 0.283 plugin.go:3:5: no required module provides package github.com/rwynn/monstache/monstachemap; to add it:
#0 0.283        go get github.com/rwynn/monstache/monstachemap
------
Dockerfile:17
--------------------
  15 |     RUN go mod download
  16 |     
  17 | >>> RUN go build -buildmode=plugin -o $PLUGIN.so $PLUGIN.go
  18 |     
--------------------
ERROR: failed to solve: process "/bin/sh -c go build -buildmode=plugin -o $PLUGIN.so $PLUGIN.go" did not complete successfully: exit code: 1

• I generated go.sum with go mod tidy
• I compiled the plugin with build.sh
• I executed Monstache with the following compose:

services:
  monstache-statistics:
    image: rwynn/monstache:6.7.21
    command: -f /app/configs/statistics.toml
    volumes:
      - ./config.toml:/app/configs/statistics.toml
      - ./docker-build:/app/plugins
    network_mode: host
    healthcheck:
      test: "wget -q -O - http://localhost:18083/healthz"
      interval: 10s
      timeout: 30s
      retries: 60
    restart: unless-stopped
    working_dir: /app

The error I get

plugin-monstache-statistics-1 | ERROR 2025/06/09 15:16:38 Unable to load mapper plugin plugins/plugin.so: plugin: not implemented

Note that I have checked inside the container and it is using the correct plugin.so file.

Have you got any idea why it is not working? Thank you in advance!

[weahforsage]

Did you solve?

[mbrozzo]

Hello @weahforsage, I did not. I ended up managing the transformation logic using an Elasticsearch ingest pipeline instead since I did not need to perform excessively complex operations.