micro/go-micro · error

unsupported format

Error message

unsupported format

What it means

The JSON config reader only accepts changesets whose Format field is exactly "json". Values checks ch.Format != "json" and returns "unsupported format" otherwise. Each go-micro reader (json, yaml, etc.) handles only its own format, so a changeset produced by a different source format must be routed to the matching reader.

Source

Thrown at config/reader/json/json.go:67

	}

	cs := &source.ChangeSet{
		Timestamp: time.Now(),
		Data:      b,
		Source:    "json",
		Format:    j.json.String(),
	}
	cs.Checksum = cs.Sum()

	return cs, nil
}

func (j *jsonReader) Values(ch *source.ChangeSet) (reader.Values, error) {
	if ch == nil {
		return nil, errors.New("changeset is nil")
	}
	if ch.Format != "json" {
		return nil, errors.New("unsupported format")
	}
	return newValues(ch)
}

func (j *jsonReader) String() string {
	return "json"
}

// NewReader creates a json reader.
func NewReader(opts ...reader.Option) reader.Reader {
	options := reader.NewOptions(opts...)
	return &jsonReader{
		json: json.NewEncoder(),
		opts: options,
	}
}

View on GitHub (pinned to 24529f1404)

Solutions

1. Ensure ChangeSet.Format is set to "json" for changesets passed to the json reader (fix the source if it leaves Format empty).
2. Use the reader matching the file format: yaml reader for YAML files, toml reader for TOML, etc.
3. Verify config source options (e.g. file.Extension / format option) match the actual file's format.
4. If you must accept multiple formats, dispatch on ch.Format to the appropriate reader instead of hardcoding json.

Example fix

// before
// yaml file loaded with json reader
conf := json.New()
v, _ := conf.Values(yamlChangeSet) // unsupported format
// after
conf := yaml.New()
v, err := conf.Values(yamlChangeSet)

if cs == nil || cs.Format != "json" {
    return fmt.Errorf("json reader requires Format=json, got %q", cs.GetFormat())
}
vals, err := rdr.Values(cs)

func isJSONChangeSet(ch *source.ChangeSet) bool { return ch != nil && ch.Format == "json" }

When it happens

Trigger: Passing a *source.ChangeSet with Format "yaml", "toml", "hcl", or "" (unset) to jsonReader.Values — e.g. a YAML source's output fed into the JSON reader, or a custom source that forgot to set ChangeSet.Format.

Common situations: Loading a .yaml file but using the json reader in the config options; a custom source that returns a changeset without setting Format; changing a config file's format on disk without updating the reader codec selection.

Related errors

• changeset is nil
• no values
• <joined load errors>
• watcher is disabled
• watcher stopped

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/fce44c8b76671a0b. Report an issue: GitHub.