How to extract and process MIME parts (e.g., XML, JSON) from MIME messages in Go?

To extract and process MIME parts from MIME messages in Go, you can use the net/mail and net/textproto packages. Here's a step-by-step guide:

Import the necessary packages:

import (
	"net/mail"
	"net/textproto"
)

Parse the MIME message:

func parseMIMEMessage(data []byte) (*mail.Message, error) {
	msg, err := mail.ReadMessage(bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	return msg, nil
}

Extract the MIME parts:

func extractMIMEParts(msg *mail.Message) ([]*mail.Part, error) {
	mediaType, params, err := mime.ParseMediaType(msg.Header.Get("Content-Type"))
	if err != nil {
		return nil, err
	}
	if strings.HasPrefix(mediaType, "multipart/") {
		mr := multipart.NewReader(msg.Body, params["boundary"])
		parts := make([]*mail.Part, 0)
		for {
			part, err := mr.NextPart()
			if err == io.EOF {
				break
			} else if err != nil {
				return nil, err
			}
			parts = append(parts, part)
		}
		return parts, nil
	}
	return nil, nil
}

Process the desired MIME parts (e.g., XML, JSON):

func processMIMEXMLPart(part *mail.Part) (string, error) {
	content, err := ioutil.ReadAll(part)
	if err != nil {
		return "", err
	}
	return string(content), nil
}

func processMIMEJSONPart(part *mail.Part) (map[string]interface{}, error) {
	content, err := ioutil.ReadAll(part)
	if err != nil {
		return nil, err
	}
	var data map[string]interface{}
	err = json.Unmarshal(content, &data)
	if err != nil {
		return nil, err
	}
	return data, nil
}

Note: Remember to handle any potential errors appropriately in your code.

With these functions in place, you can use them to extract and process the desired MIME parts:

message, err := parseMIMEMessage(data)
if err != nil {
	// handle error
}

parts, err := extractMIMEParts(message)
if err != nil {
	// handle error
}

for _, part := range parts {
	if part.FileName() != "" {
		// process attachment
	} else if part.Header.Get("Content-Type") == "application/xml" {
		xmlContent, err := processMIMEXMLPart(part)
		if err != nil {
			// handle error
		}
		// process XML content
	} else if part.Header.Get("Content-Type") == "application/json" {
		jsonData, err := processMIMEJSONPart(part)
		if err != nil {
			// handle error
		}
		// process JSON data
	}
}

This is a basic example of extracting and processing MIME parts like XML and JSON from a MIME message. You can customize and extend the processing logic based on your specific requirements.