{"record":{"id":"d2de7367f3b56f73","repo":"hashicorp/nomad","slug":"failed-to-msgpack-encode-config-v","errorCode":null,"errorMessage":"failed to msgpack encode config: %v","messagePattern":"failed to msgpack encode config: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"helper/pluginutils/loader/init.go","lineNumber":501,"sourceCode":"\n\t// If there is no config, initialize it to an empty map so we can still\n\t// handle defaults\n\tif info.config == nil {\n\t\tinfo.config = map[string]interface{}{}\n\t}\n\n\t// Parse the config using the spec\n\tval, diag, diagErrs := hclutils.ParseHclInterface(info.config, spec, nil)\n\tif diag.HasErrors() {\n\t\t_ = multierror.Append(&mErr, diagErrs...)\n\t\treturn nil, multierror.Prefix(&mErr, \"failed to parse config: \")\n\n\t}\n\n\t// Marshal the value\n\tcdata, err := msgpack.Marshal(val, val.Type())\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to msgpack encode config: %v\", err)\n\t}\n\n\t// Store the marshalled config\n\tinfo.msgpackConfig = cdata\n\n\t// Dispense the plugin and set its config and ensure it is error free\n\tinstance, err := l.Dispense(id.Name, id.PluginType, nil, l.logger)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to dispense plugin: %v\", err)\n\t}\n\tdefer instance.Kill()\n\n\tb, ok := instance.Plugin().(base.BasePlugin)\n\tif !ok {\n\t\treturn nil, fmt.Errorf(\"dispensed plugin %s doesn't meet base plugin interface\", id)\n\t}\n\n\tc := &base.Config{","sourceCodeStart":483,"sourceCodeEnd":519,"githubUrl":"https://github.com/hashicorp/nomad/blob/482b49bf1aec006f089bcfc7e632d8f6ac303e5e/helper/pluginutils/loader/init.go#L483-L519","documentation":"After decoding the user's config via the plugin's schema, validatePluginConfig msgpack-encodes the resulting value (msgpack.Marshal(val, val.Type())) so it can be shipped to the plugin over the go-plugin msgpack connection. If encoding fails — typically because the decoded value contains types msgpack cannot serialize — the loader wraps the marshal error with this message.","triggerScenarios":"validatePluginConfig obtains a decoded cty value from schema-implied decoding (hcldec) and msgpack.Marshal of that value errors — e.g. schema produces a type the codec can't encode, or an internal mismatch between the schema-decoded value type and the encoder's expected type.","commonSituations":"Plugin schema (hclspec) is malformed or declares types inconsistent with what decoding produced; custom/unknown cty types from user config; host and plugin built with different versions of the base/msgpack encoding libraries.","solutions":["Fix the plugin's ConfigSchema so it declares valid, encodable types (string/number/bool/list/map/object) — redecode your config against it.","Simplify the offending config value (avoid exotic nested structures or nulls) until encoding succeeds, to isolate the failing attribute.","Rebuild host and plugin against the same versions of the sdk/base and msgpack libraries.","Report/inspect via the wrapped %v cause — it names the exact type or field that failed to encode."],"exampleFix":"// before (plugin schema uses a type decoding can't round-trip)\nspec = hclspec.NewAttr(\"opts\", \"any\", false)\n// after (use a concrete encodable type)\nspec = hclspec.NewAttr(\"opts\", \"map(string)\", false)","handlingStrategy":"validation","validationCode":"// Validate config values against the schema and keep to plain encodable types\nval, err := schema.Decode(userConfig)\nif err != nil {\n    return fmt.Errorf(\"config does not match plugin schema: %w\", err)\n}\nif err := val.Canonicalize(); err != nil {\n    return fmt.Errorf(\"config value not encodable: %w\", err)\n}","typeGuard":null,"tryCatchPattern":"if err := loader.Load(cfg); err != nil {\n    if strings.Contains(err.Error(), \"failed to msgpack encode config\") {\n        return fmt.Errorf(\"config for %s contains a value the plugin cannot accept; check schema types: %w\", name, err)\n    }\n    return err\n}","preventionTips":["Use simple, documented config types (strings, numbers, bools, lists, maps).","Keep host and plugin msgpack/base library versions in lockstep.","Test plugin config round-trips (agent -> plugin SetConfig) in plugin CI."],"tags":["plugin-loader","msgpack","serialization","config-validation"],"backgroundTag":"msgpack-encode-failed","analyzedSha":"482b49bf1aec006f089bcfc7e632d8f6ac303e5e","analyzedAt":"2026-09-04T07:54:14.808Z","contentChangedAt":"2026-09-04T07:54:14.808Z","schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}