Merge branch 'feature/gmail_api'

exerr/data.go

@@ -59,6 +59,9 @@ var (
 	TypeMarshalEntityID = NewType("MARSHAL_ENTITY_ID", langext.Ptr(400))
 	TypeInvalidCSID     = NewType("INVALID_CSID", langext.Ptr(400))
 
+	TypeGoogleStatuscode = NewType("GOOGLE_STATUSCODE", langext.Ptr(400))
+	TypeGoogleResponse   = NewType("GOOGLE_RESPONSE", langext.Ptr(400))
+
 	TypeUnauthorized = NewType("UNAUTHORIZED", langext.Ptr(401))
 	TypeAuthFailed   = NewType("AUTH_FAILED", langext.Ptr(401))
 

goextVersion.go

@@ -1,5 +1,5 @@
 package goext
 
-const GoextVersion = "0.0.329"
+const GoextVersion = "0.0.333"
 
-const GoextVersionTimestamp = "2023-12-02T13:38:17+0100"
+const GoextVersionTimestamp = "2023-12-02T13:56:00+0100"

googleapi/README.md

@@ -0,0 +1,54 @@
+
+Google OAuth Setup (to send mails)
+==================================
+
+
+ - Login @ https://console.cloud.google.com
+
+ - GMail API akivieren: https://console.cloud.google.com/apis/library/gmail.googleapis.com?
+
+ - Create new Project (aka 'BackendMailAPI') @ https://console.cloud.google.com/projectcreate
+   User Type: Intern
+   Anwendungsname: 'BackendMailAPI'
+   Support-Email: ...
+   Authorisierte Domains: 'heydyno.de' (or project domain)
+   Kontakt-Email: ...
+   
+
+ - Unter "Anmeldedaten" neuer OAuth Client erstellen @ https://console.cloud.google.com/apis/credentials
+   Anwendungstyp: Web
+   Name: 'BackendMailOAuth'
+   Redirect-Uri: 'http://localhost/oauth'
+   Client-ID und Client-Key merken
+
+ - Open in Browser:
+   https://accounts.google.com/o/oauth2/v2/auth?redirect_uri=http://localhost/oauth&prompt=consent&response_type=code&client_id={...}&scope=https://www.googleapis.com/auth/gmail.send&access_type=offline
+   Code aus redirected URI merken
+
+ - Code via request einlösen (und refresh_roken merken):
+
+```
+curl --request POST \
+  --url https://oauth2.googleapis.com/token \
+  --data code={...} \
+  --data redirect_uri=http://localhost/oauth \
+  --data client_id={...} \
+  --data client_secret={...} \
+  --data grant_type=authorization_code \
+  --data scope=https://www.googleapis.com/auth/gmail.send
+```
+
+ - Fertig, mit `client_id`, `client_secret` und `refresh_token` kann das package benutzt werden
+
+
+
+
+
+
+
+
+
+
+
+
+

googleapi/attachment.go

@@ -0,0 +1,46 @@
+package googleapi
+
+import (
+	"encoding/base64"
+	"fmt"
+)
+
+type MailAttachment struct {
+	IsInline    bool
+	ContentType string
+	Filename    string
+	Data        []byte
+}
+
+func (a MailAttachment) dump() []string {
+	res := make([]string, 0, 4)
+
+	if a.ContentType != "" {
+		res = append(res, "Content-Type: "+a.ContentType+"; charset=UTF-8")
+	}
+
+	res = append(res, "Content-Transfer-Encoding: base64")
+
+	if a.IsInline {
+		if a.Filename != "" {
+			res = append(res, fmt.Sprintf("Content-Disposition: inline;filename=\"%s\"", a.Filename))
+		} else {
+			res = append(res, "Content-Disposition: inline")
+		}
+	} else {
+		if a.Filename != "" {
+			res = append(res, fmt.Sprintf("Content-Disposition: attachment;filename=\"%s\"", a.Filename))
+		} else {
+			res = append(res, "Content-Disposition: attachment")
+		}
+	}
+
+	b64 := base64.StdEncoding.EncodeToString(a.Data)
+	for i := 0; i < len(b64); i += 80 {
+		res = append(res, b64[i:min(i+80, len(b64))])
+	}
+
+	res = append(res)
+
+	return res
+}

googleapi/body.go

@@ -0,0 +1,6 @@
+package googleapi
+
+type MailBody struct {
+	Plain string
+	HTML  string
+}

googleapi/mimeMessage.go

@@ -0,0 +1,224 @@
+package googleapi
+
+import (
+	"gogs.mikescher.com/BlackForestBytes/goext/langext"
+	"mime"
+	"strings"
+	"time"
+)
+
+// https://datatracker.ietf.org/doc/html/rfc2822
+func encodeMimeMail(from string, recipients []string, cc []string, bcc []string, subject string, body MailBody, attachments []MailAttachment) string {
+
+	data := make([]string, 0, 32)
+
+	data = append(data, "Date: "+time.Now().Format(time.RFC1123Z))
+	data = append(data, "MIME-Version: 1.0")
+	data = append(data, "From: "+mime.QEncoding.Encode("UTF-8", from))
+	data = append(data, "To: "+strings.Join(langext.ArrMap(recipients, func(v string) string { return mime.QEncoding.Encode("UTF-8", v) }), ", "))
+	if len(cc) > 0 {
+		data = append(data, "To: "+strings.Join(langext.ArrMap(cc, func(v string) string { return mime.QEncoding.Encode("UTF-8", v) }), ", "))
+	}
+	if len(bcc) > 0 {
+		data = append(data, "Bcc: "+strings.Join(langext.ArrMap(bcc, func(v string) string { return mime.QEncoding.Encode("UTF-8", v) }), ", "))
+	}
+	data = append(data, "Subject: "+mime.QEncoding.Encode("UTF-8", subject))
+
+	hasInlineAttachments := langext.ArrAny(attachments, func(v MailAttachment) bool { return v.IsInline })
+	hasNormalAttachments := langext.ArrAny(attachments, func(v MailAttachment) bool { return !v.IsInline })
+	hasPlain := body.Plain != ""
+	hasHTML := body.HTML != ""
+
+	mixedBoundary := langext.MustRawHexUUID()
+	relatedBoundary := langext.MustRawHexUUID()
+	altBoundary := langext.MustRawHexUUID()
+
+	inlineAttachments := langext.ArrFilter(attachments, func(v MailAttachment) bool { return v.IsInline })
+	normalAttachments := langext.ArrFilter(attachments, func(v MailAttachment) bool { return !v.IsInline })
+
+	if hasInlineAttachments && hasNormalAttachments {
+		// "mixed+related"
+
+		data = append(data, "Content-Type: multipart/mixed; boundary="+mixedBoundary)
+		data = append(data, "")
+		data = append(data, "--"+mixedBoundary)
+
+		data = append(data, "Content-Type: multipart/related; boundary="+relatedBoundary)
+		data = append(data, "")
+
+		data = append(data, dumpMailBody(body, hasInlineAttachments, hasNormalAttachments, relatedBoundary, altBoundary)...)
+		data = append(data, "")
+
+		for i, attachment := range inlineAttachments {
+			data = append(data, "--"+relatedBoundary)
+			data = append(data, attachment.dump()...)
+
+			if i < len(inlineAttachments)-1 {
+				data = append(data, "")
+			}
+		}
+
+		data = append(data, "--"+relatedBoundary+"--")
+
+		for i, attachment := range normalAttachments {
+			data = append(data, "--"+mixedBoundary)
+			data = append(data, attachment.dump()...)
+
+			if i < len(normalAttachments)-1 {
+				data = append(data, "")
+			}
+		}
+
+		data = append(data, "--"+mixedBoundary+"--")
+
+	} else if hasNormalAttachments {
+		// "mixed"
+
+		data = append(data, "Content-Type: multipart/mixed; boundary="+mixedBoundary)
+		data = append(data, "")
+
+		data = append(data, dumpMailBody(body, hasInlineAttachments, hasNormalAttachments, mixedBoundary, altBoundary)...)
+		if hasPlain && hasHTML {
+			data = append(data, "")
+		}
+
+		for i, attachment := range normalAttachments {
+			data = append(data, "--"+mixedBoundary)
+			data = append(data, attachment.dump()...)
+
+			if i < len(normalAttachments)-1 {
+				data = append(data, "")
+			}
+		}
+
+		data = append(data, "--"+mixedBoundary+"--")
+
+	} else if hasInlineAttachments {
+		// "related"
+
+		data = append(data, "Content-Type: multipart/related; boundary="+relatedBoundary)
+		data = append(data, "")
+
+		data = append(data, dumpMailBody(body, hasInlineAttachments, hasNormalAttachments, relatedBoundary, altBoundary)...)
+		data = append(data, "")
+
+		for i, attachment := range inlineAttachments {
+			data = append(data, "--"+relatedBoundary)
+			data = append(data, attachment.dump()...)
+
+			if i < len(inlineAttachments)-1 {
+				data = append(data, "")
+			}
+		}
+
+		data = append(data, "--"+relatedBoundary+"--")
+
+	} else if hasPlain && hasHTML {
+		// "alternative"
+
+		data = append(data, "Content-Type: multipart/alternative; boundary="+altBoundary)
+		data = append(data, "")
+
+		data = append(data, dumpMailBody(body, hasInlineAttachments, hasNormalAttachments, altBoundary, altBoundary)...)
+		data = append(data, "")
+
+		data = append(data, "--"+altBoundary+"--")
+
+	} else if hasPlain {
+		// "plain"
+
+		data = append(data, "Content-Type: text/plain; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.Plain)
+
+	} else if hasHTML {
+		// "plain"
+
+		data = append(data, "Content-Type: text/html; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.HTML)
+
+	} else {
+		// "empty??"
+
+	}
+
+	return strings.Join(data, "\r\n")
+}
+
+func dumpMailBody(body MailBody, hasInlineAttachments bool, hasNormalAttachments bool, boundary string, boundaryAlt string) []string {
+
+	if body.HTML != "" && body.Plain != "" && !hasInlineAttachments && hasNormalAttachments {
+		data := make([]string, 0, 16)
+		data = append(data, "--"+boundary)
+		data = append(data, "Content-Type: multipart/alternative; boundary="+boundaryAlt)
+		data = append(data, "")
+		data = append(data, "--"+boundaryAlt)
+		data = append(data, "Content-Type: text/plain; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.Plain)
+		data = append(data, "")
+		data = append(data, "--"+boundaryAlt)
+		data = append(data, "Content-Type: text/html; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.HTML)
+		data = append(data, "")
+		data = append(data, "--"+boundaryAlt+"--")
+		return data
+	}
+
+	if body.HTML != "" && body.Plain != "" && hasInlineAttachments {
+		data := make([]string, 0, 2)
+		data = append(data, "--"+boundary)
+		data = append(data, body.HTML)
+		return data
+	}
+
+	if body.HTML != "" && body.Plain != "" {
+		data := make([]string, 0, 8)
+		data = append(data, "--"+boundary)
+		data = append(data, "Content-Type: text/plain; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.Plain)
+		data = append(data, "")
+		data = append(data, "--"+boundary)
+		data = append(data, "Content-Type: text/html; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.HTML)
+		return data
+	}
+
+	if body.HTML != "" {
+		data := make([]string, 0, 2)
+		data = append(data, "--"+boundary)
+		data = append(data, "Content-Type: text/html; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.HTML)
+		return data
+	}
+
+	if body.Plain != "" {
+		data := make([]string, 0, 2)
+		data = append(data, "--"+boundary)
+		data = append(data, "Content-Type: text/plain; charset=UTF-8")
+		data = append(data, "Content-Transfer-Encoding: 7bit")
+		data = append(data, "")
+		data = append(data, body.Plain)
+		return data
+	}
+
+	data := make([]string, 0, 16)
+	data = append(data, "--"+boundary)
+	data = append(data, "Content-Type: text/plain; charset=UTF-8")
+	data = append(data, "Content-Transfer-Encoding: 7bit")
+	data = append(data, "")
+	data = append(data, "") // no content ?!?
+	return data
+}

googleapi/mimeMessage_test.go

@@ -0,0 +1,77 @@
+package googleapi
+
+import (
+	"fmt"
+	"gogs.mikescher.com/BlackForestBytes/goext/tst"
+	"os"
+	"testing"
+)
+
+func TestEncodeMimeMail(t *testing.T) {
+
+	mail := encodeMimeMail(
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail",
+		MailBody{Plain: "Plain Text"},
+		nil)
+
+	fmt.Printf("%s\n\n", mail)
+}
+
+func TestEncodeMimeMail2(t *testing.T) {
+
+	mail := encodeMimeMail(
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail (alternative)",
+		MailBody{
+			Plain: "Plain Text",
+			HTML:  "<html><body><u>Non</u> Pl<i>ai</i>n T<b>ex</b>t</body></html>",
+		},
+		nil)
+
+	fmt.Printf("%s\n\n", mail)
+}
+
+func TestEncodeMimeMail3(t *testing.T) {
+
+	mail := encodeMimeMail(
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail (alternative)",
+		MailBody{
+			HTML: "<html><body><u>Non</u> Pl<i>ai</i>n T<b>ex</b>t</body></html>",
+		},
+		[]MailAttachment{
+			{Data: []byte("HelloWorld"), Filename: "test.txt", IsInline: false, ContentType: "text/plain"},
+		})
+
+	fmt.Printf("%s\n\n", mail)
+}
+
+func TestEncodeMimeMail4(t *testing.T) {
+
+	b := tst.Must(os.ReadFile("/home/mike/Pictures/Screenshot_20220706_190205.png"))(t)
+
+	mail := encodeMimeMail(
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail (inline)",
+		MailBody{
+			HTML: "<html><body><u>Non</u> Pl<i>ai</i>n T<b>ex</b>t</body></html>",
+		},
+		[]MailAttachment{
+			{Data: b, Filename: "img.png", IsInline: true, ContentType: "image/png"},
+		})
+
+	fmt.Printf("%s\n\n", mail)
+}

googleapi/oAuth.go

@@ -0,0 +1,91 @@
+package googleapi
+
+import (
+	"encoding/json"
+	"fmt"
+	"gogs.mikescher.com/BlackForestBytes/goext/exerr"
+	"gogs.mikescher.com/BlackForestBytes/goext/langext"
+	"gogs.mikescher.com/BlackForestBytes/goext/timeext"
+	"io"
+	"net/http"
+	"sync"
+	"time"
+)
+
+type GoogleOAuth interface {
+	AccessToken() (string, error)
+}
+
+type oauth struct {
+	clientID     string
+	clientSecret string
+	refreshToken string
+
+	lock        sync.RWMutex
+	accessToken *string
+	expiryDate  *time.Time
+}
+
+func NewGoogleOAuth(clientid string, clientsecret, refreshtoken string) GoogleOAuth {
+	return &oauth{
+		clientID:     clientid,
+		clientSecret: clientsecret,
+		refreshToken: refreshtoken,
+	}
+}
+
+func (c *oauth) AccessToken() (string, error) {
+	c.lock.RLock()
+	if c.accessToken != nil && c.expiryDate != nil && (*c.expiryDate).After(time.Now()) {
+		c.lock.RUnlock()
+		return *c.accessToken, nil // still valid
+	}
+	c.lock.RUnlock()
+
+	httpclient := http.Client{}
+
+	url := fmt.Sprintf("https://oauth2.googleapis.com/token?client_id=%s&client_secret=%s&grant_type=%s&refresh_token=%s",
+		c.clientID,
+		c.clientSecret,
+		"refresh_token",
+		c.refreshToken)
+
+	req, err := http.NewRequest(http.MethodPost, url, nil)
+	if err != nil {
+		return "", err
+	}
+
+	reqStartTime := time.Now()
+
+	res, err := httpclient.Do(req)
+
+	type response struct {
+		AccessToken string `json:"access_token"`
+		ExpiresIn   int    `json:"expires_in"`
+		Scope       string `json:"scope"`
+		TokenType   string `json:"token_type"`
+	}
+
+	var r response
+
+	data, err := io.ReadAll(res.Body)
+	if err != nil {
+		return "", err
+	}
+
+	err = json.Unmarshal(data, &r)
+	if err != nil {
+		return "", err
+	}
+
+	if r.ExpiresIn == 0 || r.AccessToken == "" {
+		return "", exerr.New(exerr.TypeGoogleResponse, "google oauth returned no response").Str("body", string(data)).Build()
+	}
+
+	c.lock.Lock()
+	c.expiryDate = langext.Ptr(reqStartTime.Add(timeext.FromSeconds(r.ExpiresIn - 10)))
+	c.accessToken = langext.Ptr(r.AccessToken)
+	c.lock.Unlock()
+
+	return r.AccessToken, nil
+}

googleapi/sendMail.go

@@ -0,0 +1,69 @@
+package googleapi
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"gogs.mikescher.com/BlackForestBytes/goext"
+	"gogs.mikescher.com/BlackForestBytes/goext/exerr"
+	"gogs.mikescher.com/BlackForestBytes/goext/langext"
+	"io"
+	"net/http"
+)
+
+type MailRef struct {
+	ID       string   `json:"id"`
+	ThreadID string   `json:"threadId"`
+	LabelIDs []string `json:"labelIds"`
+}
+
+func (c *client) SendMail(ctx context.Context, from string, recipients []string, cc []string, bcc []string, subject string, body MailBody, attachments []MailAttachment) (MailRef, error) {
+
+	mm := encodeMimeMail(from, recipients, cc, bcc, subject, body, attachments)
+
+	tok, err := c.oauth.AccessToken()
+	if err != nil {
+		return MailRef{}, exerr.Wrap(err, "").Build()
+	}
+
+	url := fmt.Sprintf("https://gmail.googleapis.com/gmail/v1/users/%s/messages/send?alt=json&prettyPrint=false", "me")
+
+	msgbody, err := json.Marshal(langext.H{"raw": base64.URLEncoding.EncodeToString([]byte(mm))})
+	if err != nil {
+		return MailRef{}, exerr.Wrap(err, "").Build()
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(msgbody))
+	if err != nil {
+		return MailRef{}, exerr.Wrap(err, "").Build()
+	}
+
+	req.Header.Add("Authorization", "Bearer "+tok)
+	req.Header.Add("X-Goog-Api-Client", "blackforestbytes-goext/"+goext.GoextVersion)
+	req.Header.Add("User-Agent", "blackforestbytes-goext/"+goext.GoextVersion)
+	req.Header.Add("Content-Type", "application/json")
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return MailRef{}, exerr.Wrap(err, "").Build()
+	}
+
+	respBody, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return MailRef{}, exerr.Wrap(err, "").Build()
+	}
+
+	if resp.StatusCode != 200 {
+		return MailRef{}, exerr.New(exerr.TypeGoogleStatuscode, "gmail returned non-200 statuscode").Int("sc", resp.StatusCode).Str("body", string(respBody)).Build()
+	}
+
+	var respObj MailRef
+	err = json.Unmarshal(respBody, &respObj)
+	if err != nil {
+		return MailRef{}, exerr.Wrap(err, "").Str("body", string(respBody)).Build()
+	}
+
+	return respObj, nil
+}

googleapi/sendMail_test.go

@@ -0,0 +1,151 @@
+package googleapi
+
+import (
+	"context"
+	"fmt"
+	"gogs.mikescher.com/BlackForestBytes/goext/exerr"
+	"gogs.mikescher.com/BlackForestBytes/goext/langext"
+	"gogs.mikescher.com/BlackForestBytes/goext/tst"
+	"os"
+	"testing"
+)
+
+func TestMain(m *testing.M) {
+	if !exerr.Initialized() {
+		exerr.Init(exerr.ErrorPackageConfigInit{ZeroLogErrTraces: langext.PFalse, ZeroLogAllTraces: langext.PFalse})
+	}
+	os.Exit(m.Run())
+}
+
+func TestSendMail1(t *testing.T) {
+	t.Skip()
+	return
+
+	auth := NewGoogleOAuth(
+		"554617284247-8di0j6s5dcmlk4lmk4hdf9kdn8scss54.apps.googleusercontent.com",
+		"TODO",
+		"TODO")
+
+	ctx := context.Background()
+
+	gclient := NewGoogleClient(auth)
+
+	mail, err := gclient.SendMail(
+		ctx,
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail",
+		MailBody{Plain: "Plain Text"},
+		nil)
+
+	tst.AssertNoErr(t, err)
+
+	fmt.Printf("mail.ID        := %s\n", mail.ID)
+	fmt.Printf("mail.ThreadID  := %s\n", mail.ThreadID)
+	fmt.Printf("mail.LabelIDs  := %v\n", mail.LabelIDs)
+}
+
+func TestSendMail2(t *testing.T) {
+	t.Skip()
+	return
+
+	auth := NewGoogleOAuth(
+		"554617284247-8di0j6s5dcmlk4lmk4hdf9kdn8scss54.apps.googleusercontent.com",
+		"TODO",
+		"TODO")
+
+	ctx := context.Background()
+
+	gclient := NewGoogleClient(auth)
+
+	mail, err := gclient.SendMail(
+		ctx,
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail (alternative)",
+		MailBody{
+			Plain: "Plain Text",
+			HTML:  "<html><body><u>Non</u> Pl<i>ai</i>n T<b>ex</b>t</body></html>",
+		},
+		nil)
+
+	tst.AssertNoErr(t, err)
+
+	fmt.Printf("mail.ID        := %s\n", mail.ID)
+	fmt.Printf("mail.ThreadID  := %s\n", mail.ThreadID)
+	fmt.Printf("mail.LabelIDs  := %v\n", mail.LabelIDs)
+}
+
+func TestSendMail3(t *testing.T) {
+	t.Skip()
+	return
+
+	auth := NewGoogleOAuth(
+		"554617284247-8di0j6s5dcmlk4lmk4hdf9kdn8scss54.apps.googleusercontent.com",
+		"TODO",
+		"TODO")
+
+	ctx := context.Background()
+
+	gclient := NewGoogleClient(auth)
+
+	mail, err := gclient.SendMail(
+		ctx,
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail (attach)",
+		MailBody{
+			HTML: "<html><body><u>Non</u> Pl<i>ai</i>n T<b>ex</b>t</body></html>",
+		},
+		[]MailAttachment{
+			{Data: []byte("HelloWorld"), Filename: "test.txt", IsInline: false, ContentType: "text/plain"},
+		})
+
+	tst.AssertNoErr(t, err)
+
+	fmt.Printf("mail.ID        := %s\n", mail.ID)
+	fmt.Printf("mail.ThreadID  := %s\n", mail.ThreadID)
+	fmt.Printf("mail.LabelIDs  := %v\n", mail.LabelIDs)
+}
+
+func TestSendMail4(t *testing.T) {
+	t.Skip()
+	return
+
+	auth := NewGoogleOAuth(
+		"554617284247-8di0j6s5dcmlk4lmk4hdf9kdn8scss54.apps.googleusercontent.com",
+		"TODO",
+		"TODO")
+
+	ctx := context.Background()
+
+	gclient := NewGoogleClient(auth)
+
+	b := tst.Must(os.ReadFile("/home/mike/Pictures/Screenshot_20220706_190205.png"))(t)
+
+	mail, err := gclient.SendMail(
+		ctx,
+		"noreply@heydyno.de",
+		[]string{"trash@mikescher.de"},
+		nil,
+		nil,
+		"Hello Test Mail (inline)",
+		MailBody{
+			HTML: "<html><body><u>Non</u> Pl<i>ai</i>n T<b>ex</b>t</body></html>",
+		},
+		[]MailAttachment{
+			{Data: b, Filename: "img.png", IsInline: true, ContentType: "image/png"},
+		})
+
+	tst.AssertNoErr(t, err)
+
+	fmt.Printf("mail.ID        := %s\n", mail.ID)
+	fmt.Printf("mail.ThreadID  := %s\n", mail.ThreadID)
+	fmt.Printf("mail.LabelIDs  := %v\n", mail.LabelIDs)
+}

googleapi/service.go

@@ -0,0 +1,22 @@
+package googleapi
+
+import (
+	"context"
+	"net/http"
+)
+
+type GoogleClient interface {
+	SendMail(ctx context.Context, from string, recipients []string, cc []string, bcc []string, subject string, body MailBody, attachments []MailAttachment) (MailRef, error)
+}
+
+type client struct {
+	oauth GoogleOAuth
+	http  http.Client
+}
+
+func NewGoogleClient(oauth GoogleOAuth) GoogleClient {
+	return &client{
+		oauth: oauth,
+		http:  http.Client{},
+	}
+}