mmdbdata

Overview ¶

Package mmdbdata provides low-level types and interfaces for custom MaxMind DB decoding.

This package allows custom decoding logic for applications that need fine-grained control over how MaxMind DB data is processed. For most use cases, the high-level maxminddb.Reader API is recommended instead.

Manual Decoding Example ¶

Custom types can implement the Unmarshaler interface for custom decoding:

type City struct {
	Names     map[string]string `maxminddb:"names"`
	GeoNameID uint              `maxminddb:"geoname_id"`
}

func (c *City) UnmarshalMaxMindDB(d *mmdbdata.Decoder) error {
	mapIter, _, err := d.ReadMap()
	if err != nil { return err }
	for key, err := range mapIter {
		if err != nil { return err }
		switch string(key) {
		case "names":
			nameIter, size, err := d.ReadMap()
			if err != nil { return err }
			names := make(map[string]string, size) // Pre-allocate with size
			for nameKey, nameErr := range nameIter {
				if nameErr != nil { return nameErr }
				value, valueErr := d.ReadString()
				if valueErr != nil { return valueErr }
				names[string(nameKey)] = value
			}
			c.Names = names
		case "geoname_id":
			geoID, err := d.ReadUint32()
			if err != nil { return err }
			c.GeoNameID = uint(geoID)
		default:
			if err := d.SkipValue(); err != nil { return err }
		}
	}
	return nil
}

Types implementing Unmarshaler will automatically use custom decoding logic instead of reflection when used with maxminddb.Reader.Lookup, similar to how json.Unmarshaler works with encoding/json.

Direct Decoder Usage ¶

For even more control, you can use the Decoder directly:

decoder := mmdbdata.NewDecoder(buffer, offset)
value, err := decoder.ReadString()
if err != nil {
	return err
}