《互联网产品的服务端架构·内容、社交与实时互动》10.2 通知聚合与频控

// file: internal/push/template.go
// tier: L1
// verify: go test ./internal/push/

package push

import (
	"fmt"
	"regexp"
	"unicode/utf8"
)

// Template 是运营配置的原始文案。Vars 必须列出标题和正文里
// 允许出现的全部占位符，Render 不接受未声明的变量。
type Template struct {
	ID    string
	Title string
	Body  string
	Vars  []string
}

// Message 是完成变量替换后的最终文案。
type Message struct {
	Title string
	Body  string
}

const (
	maxTitleRunes = 64
	maxBodyRunes  = 200
)

var placeholder = regexp.MustCompile(`\{\{([a-zA-Z0-9_]+)\}\}`)

// Render 用 vars 替换 {{name}} 占位符，并检查声明、缺参和长度。
// 错误信息里带占位符名字，运营可以直接定位是哪一条文案配置错了。
func Render(t Template, vars map[string]string) (Message, error) {
	declared := make(map[string]bool, len(t.Vars))
	for _, name := range t.Vars {
		declared[name] = true
	}
	for _, field := range []string{t.Title, t.Body} {
		for _, m := range placeholder.FindAllStringSubmatch(field, -1) {
			name := m[1]
			if !declared[name] {
				return Message{}, fmt.Errorf("push: template %q uses undeclared placeholder %q", t.ID, name)
			}
		}
	}

	title, err := fill("title", t.ID, t.Title, vars)
	if err != nil {
		return Message{}, err
	}
	body, err := fill("body", t.ID, t.Body, vars)
	if err != nil {
		return Message{}, err
	}

	if n := utf8.RuneCountInString(title); n > maxTitleRunes {
		return Message{}, fmt.Errorf("push: template %q title is %d chars, limit %d", t.ID, n, maxTitleRunes)
	}
	if n := utf8.RuneCountInString(body); n > maxBodyRunes {
		return Message{}, fmt.Errorf("push: template %q body is %d chars, limit %d", t.ID, n, maxBodyRunes)
	}
	return Message{Title: title, Body: body}, nil
}

func fill(part, id, text string, vars map[string]string) (string, error) {
	var missing string
	out := placeholder.ReplaceAllStringFunc(text, func(m string) string {
		name := m[2 : len(m)-2]
		v, ok := vars[name]
		if !ok {
			if missing == "" {
				missing = name
			}
			return m
		}
		return v
	})
	if missing != "" {
		return "", fmt.Errorf("push: template %q missing %s variable %q", id, part, missing)
	}
	return out, nil
}

// file: internal/push/template_test.go
// tier: L1
// verify: go test ./internal/push/

package push

import (
	"strings"
	"testing"
)

func TestRenderReplacesDeclaredVars(t *testing.T) {
	tpl := Template{
		ID:    "comment-reply",
		Title: "{{actor}} 回复了你",
		Body:  "在《{{title}}》下：{{excerpt}}",
		Vars:  []string{"actor", "title", "excerpt"},
	}
	got, err := Render(tpl, map[string]string{
		"actor":   "小林",
		"title":   "周末骑行路线",
		"excerpt": "这段路我也走过",
	})
	if err != nil {
		t.Fatal(err)
	}
	if got.Title != "小林 回复了你" {
		t.Fatalf("title = %q", got.Title)
	}
	if got.Body != "在《周末骑行路线》下：这段路我也走过" {
		t.Fatalf("body = %q", got.Body)
	}
}

func TestRenderRejectsMissingVariable(t *testing.T) {
	tpl := Template{
		ID:    "order-paid",
		Title: "订单已支付",
		Body:  "金额 {{amount}} 元",
		Vars:  []string{"amount"},
	}
	_, err := Render(tpl, map[string]string{})
	if err == nil {
		t.Fatal("want error for missing variable")
	}
	if !strings.Contains(err.Error(), "amount") {
		t.Fatalf("error %q does not name the missing variable", err)
	}
}

func TestRenderRejectsUndeclaredPlaceholder(t *testing.T) {
	tpl := Template{
		ID:    "promo",
		Title: "限时活动",
		Body:  "{{discount}} 折",
		Vars:  []string{"amount"},
	}
	_, err := Render(tpl, map[string]string{"discount": "8"})
	if err == nil {
		t.Fatal("want error for undeclared placeholder")
	}
	if !strings.Contains(err.Error(), "discount") {
		t.Fatalf("error %q does not name the undeclared placeholder", err)
	}
}

func TestRenderEnforcesLengthLimits(t *testing.T) {
	vars := map[string]string{}
	base := Template{ID: "length", Title: "标题", Body: "正文"}

	ok := base
	ok.Title = strings.Repeat("标", maxTitleRunes)
	ok.Body = strings.Repeat("文", maxBodyRunes)
	if _, err := Render(ok, vars); err != nil {
		t.Fatalf("boundary values should pass: %v", err)
	}

	longTitle := base
	longTitle.Title = strings.Repeat("标", maxTitleRunes+1)
	if _, err := Render(longTitle, vars); err == nil {
		t.Fatal("want error for overlong title")
	}

	longBody := base
	longBody.Body = strings.Repeat("文", maxBodyRunes+1)
	if _, err := Render(longBody, vars); err == nil {
		t.Fatal("want error for overlong body")
	}
}

cd .local/checks/webapp-lab && go test ./internal/push/ -run 'TestRender' -count=1 -v

=== RUN   TestRenderReplacesDeclaredVars
--- PASS: TestRenderReplacesDeclaredVars (0.00s)
=== RUN   TestRenderRejectsMissingVariable
--- PASS: TestRenderRejectsMissingVariable (0.00s)
=== RUN   TestRenderRejectsUndeclaredPlaceholder
--- PASS: TestRenderRejectsUndeclaredPlaceholder (0.00s)
=== RUN   TestRenderEnforcesLengthLimits
--- PASS: TestRenderEnforcesLengthLimits (0.00s)
PASS
ok  	webapp/internal/push	0.271s