In this second step, we are going to analyse how to use the API of go-whatsapp described in the previous blog post, and what considerations we should take into account in order to create a bot.

---

Sending a text message

The WhatsApp Connection instance that is returned when creating a Session has several messages to send text messages, images, create groups, receive messages and even query for the contact list.

For sending a text message you have to create an instance of TextMessage indicating at least the text message an a receipt.

text := whatsapp.TextMessage{
    Info: whatsapp.MessageInfo{
	RemoteJid: "<receiver's phone number>@s.whatsapp.net",
    },
    Text: "Text message sent from Golang bot",
}
sendResult, err := waconn.Send(text)

where whatsApp refers to the module go-whatsapp imported as

import (
    "github.com/Rhymen/go-whatsapp"
)

whatsApp.TextMessage is an struct which fields are

type TextMessage struct {
	Info        MessageInfo
	Text        string
	ContextInfo ContextInfo
}

and whatsApp.MessageInfo contains

type MessageInfo struct {
	Id        string
	RemoteJid string
	SenderJid string
	FromMe    bool
	Timestamp uint64
	PushName  string
	Status    MessageStatus
	Source *proto.WebMessageInfo
}

The first important thing to notice is that MesssageInfo only contains on RemoteJid, so it’s not possible to a single message to multiple receivers (broadcasting).

Note: Trying to concatenate several RemoteJid (separated with comma, for example) leads to a crash in the mobile app where WhatsApp runs! unbelievable.

The response to the Send command is a string and an error. Where error is nil if the operation succeeded, and string contains either the MessageId if everything is okey, or the literal string ERROR in case of failure.

---

Other types of messages can be sent using this module. The existent implementation of go-whatsapp, by the time this post was created, allows a user to send text, photos, videos, documents (files), audio, locations, live locations contact information (vCards), and even Stickers!.

Image, Audio and Video messages receive its content in a io.Reader property. Several fields of these structs remain unexpected as they are needed for media upload/download and validations.

The definition of each of these structures are

Image Message

type ImageMessage struct {
	Info          MessageInfo
	Caption       string
	Thumbnail     []byte
	Type          string
	Content       io.Reader
	url           string
	mediaKey      []byte
	fileEncSha256 []byte
	fileSha256    []byte
	fileLength    uint64
	ContextInfo   ContextInfo
}

Video Message

type VideoMessage struct {
	Info          MessageInfo
	Caption       string
	Thumbnail     []byte
	Length        uint32
	Type          string
	Content       io.Reader
	GifPlayback   bool
	url           string
	mediaKey      []byte
	fileEncSha256 []byte
	fileSha256    []byte
	fileLength    uint64
	ContextInfo   ContextInfo
}

Audio Message

type AudioMessage struct {
	Info          MessageInfo
	Length        uint32
	Type          string
	Content       io.Reader
	Ptt           bool
	url           string
	mediaKey      []byte
	fileEncSha256 []byte
	fileSha256    []byte
	fileLength    uint64
	ContextInfo   ContextInfo
}

Document Message

type DocumentMessage struct {
	Info          MessageInfo
	Title         string
	PageCount     uint32
	Type          string
	FileName      string
	Thumbnail     []byte
	Content       io.Reader
	url           string
	mediaKey      []byte
	fileEncSha256 []byte
	fileSha256    []byte
	fileLength    uint64
	ContextInfo   ContextInfo
}

Location Message

type LocationMessage struct {
	Info             MessageInfo
	DegreesLatitude  float64
	DegreesLongitude float64
	Name             string
	Address          string
	Url              string
	JpegThumbnail    []byte
	ContextInfo      ContextInfo
}

Live Location Message

type LiveLocationMessage struct {
	Info                              MessageInfo
	DegreesLatitude                   float64
	DegreesLongitude                  float64
	AccuracyInMeters                  uint32
	SpeedInMps                        float32
	DegreesClockwiseFromMagneticNorth uint32
	Caption                           string
	SequenceNumber                    int64
	JpegThumbnail                     []byte
	ContextInfo                       ContextInfo
}

Stickers

type StickerMessage struct {
	Info MessageInfo
	Type          string
	Content       io.Reader
	url           string
	mediaKey      []byte
	fileEncSha256 []byte
	fileSha256    []byte
	fileLength    uint64
	ContextInfo ContextInfo
}

Contact Message (vCard)

type ContactMessage struct {
	Info MessageInfo
	DisplayName string
	Vcard       string
	ContextInfo ContextInfo
}