Pr/avatar (#319)

* feat: add avatar api
close #310

* chore: add description line

* fix: typo

* chore: reformat the json string to make it more readable and fix few bad indents

* fix: minimum go version

* feat: upload to Micro's CDN

* chore: delete redundant blank line

* chore: update README.md

avatar/handler/avatar.go

@@ -0,0 +1,98 @@
+package handler
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"fmt"
+	"image"
+	"image/jpeg"
+	"image/png"
+
+	"github.com/google/uuid"
+	"github.com/micro/micro/v3/service/errors"
+	"github.com/o1egl/govatar"
+
+	pb "github.com/micro/services/avatar/proto"
+	imagePb "github.com/micro/services/image/proto"
+)
+
+type avatar struct {
+	imageSvc imagePb.ImageService
+}
+
+func NewAvatar(service imagePb.ImageService) *avatar {
+	return &avatar{
+		imageSvc: service,
+	}
+}
+
+// Generate is used to generate a avatar
+func (e *avatar) Generate(ctx context.Context, req *pb.GenerateRequest, rsp *pb.GenerateResponse) error {
+	var gender govatar.Gender
+
+	// gender, default is `male`
+	if req.Gender == "male" {
+		gender = govatar.MALE
+	} else if req.Gender == "female" {
+		gender = govatar.FEMALE
+	} else {
+		gender = govatar.MALE
+	}
+
+	// generate avatar
+	var avatarImg image.Image
+	var err error
+
+	if req.Username == "" {
+		avatarImg, err = govatar.Generate(gender)
+	} else {
+		avatarImg, err = govatar.GenerateForUsername(gender, req.Username)
+	}
+	if err != nil {
+		return errors.InternalServerError("avatar.generate", "generate avatarImg error: %v", err)
+	}
+
+	// format avatar image, default is `jpeg`
+	format := req.Format
+	if format != "png" && format != "jpeg" {
+		format = "jpeg"
+	}
+
+	buf := bytes.NewBuffer(nil)
+	if format == "png" {
+		err = png.Encode(buf, avatarImg)
+	} else {
+		err = jpeg.Encode(buf, avatarImg, nil)
+	}
+	if err != nil {
+		return errors.InternalServerError("avatar.generate", "encode avatar image error: %v", err)
+	}
+
+	base64String := fmt.Sprintf("data:image/%s;base64,%s", format, base64.StdEncoding.EncodeToString(buf.Bytes()))
+
+	if !req.Upload {
+		rsp.Base64 = base64String
+		return nil
+	}
+
+	// upload to CDN
+	name := req.Username
+	if name == "" {
+		uid, _ := uuid.NewUUID()
+		name = uid.String()
+	}
+
+	uploadResp, err := e.imageSvc.Upload(ctx, &imagePb.UploadRequest{
+		Base64: base64String,
+		Name:   fmt.Sprintf("%s.%s", name, format),
+	})
+
+	if err != nil {
+		return errors.InternalServerError("avatar.generate", "upload avatar image error: %v", err)
+	}
+
+	rsp.Url = uploadResp.Url
+
+	return nil
+}