这是一个很棒的初学者项目！让我来分析一下你的爬虫搜索引擎实现，并提供一些专业的代码改进建议。

1. 并发处理优化

你的爬虫可以更好地利用Go的并发特性。当前版本可能没有充分利用goroutine：

// 改进的并发爬取示例
func crawlConcurrently(urls []string, maxWorkers int) []string {
    results := make(chan string, len(urls))
    sem := make(chan struct{}, maxWorkers) // 控制并发数
    
    var wg sync.WaitGroup
    
    for _, url := range urls {
        wg.Add(1)
        go func(u string) {
            defer wg.Done()
            sem <- struct{}{}        // 获取信号量
            defer func() { <-sem }() // 释放信号量
            
            if content, err := fetchURL(u); err == nil {
                results <- content
            }
        }(url)
    }
    
    go func() {
        wg.Wait()
        close(results)
    }()
    
    var allResults []string
    for result := range results {
        allResults = append(allResults, result)
    }
    
    return allResults
}

2. 请求限速与礼貌爬取

避免被网站封禁，实现礼貌爬取：

type RateLimiter struct {
    interval time.Duration
    ticker   *time.Ticker
}

func NewRateLimiter(ratePerSecond int) *RateLimiter {
    interval := time.Second / time.Duration(ratePerSecond)
    return &RateLimiter{
        interval: interval,
        ticker:   time.NewTicker(interval),
    }
}

func (rl *RateLimiter) Wait() {
    <-rl.ticker.C
}

// 使用示例
func politeCrawl(url string, limiter *RateLimiter) (string, error) {
    limiter.Wait()
    return fetchURL(url)
}

3. 改进的HTML解析与数据提取

使用更健壮的解析库：

import "github.com/PuerkitoBio/goquery"

func extractContent(html string) (title, body string, links []string) {
    doc, err := goquery.NewDocumentFromReader(strings.NewReader(html))
    if err != nil {
        return "", "", nil
    }
    
    // 提取标题
    title = doc.Find("title").Text()
    
    // 提取正文内容（排除脚本和样式）
    doc.Find("script, style").Remove()
    body = doc.Find("body").Text()
    
    // 提取所有链接
    doc.Find("a[href]").Each(func(i int, s *goquery.Selection) {
        if href, exists := s.Attr("href"); exists {
            links = append(links, href)
        }
    })
    
    return title, body, links
}

4. 简单的倒排索引实现

对于搜索引擎功能，需要建立索引：

type SearchEngine struct {
    index map[string][]IndexEntry
    mu    sync.RWMutex
}

type IndexEntry struct {
    URL   string
    Title string
    Score float64
}

func (se *SearchEngine) IndexPage(url, title, content string) {
    se.mu.Lock()
    defer se.mu.Unlock()
    
    words := tokenize(content)
    for _, word := range words {
        if se.index[word] == nil {
            se.index[word] = make([]IndexEntry, 0)
        }
        se.index[word] = append(se.index[word], IndexEntry{
            URL:   url,
            Title: title,
            Score: calculateTFIDF(word, content),
        })
    }
}

func (se *SearchEngine) Search(query string) []IndexEntry {
    se.mu.RLock()
    defer se.mu.RUnlock()
    
    queryWords := tokenize(query)
    results := make(map[string]IndexEntry)
    
    for _, word := range queryWords {
        if entries, exists := se.index[word]; exists {
            for _, entry := range entries {
                if existing, ok := results[entry.URL]; ok {
                    existing.Score += entry.Score
                    results[entry.URL] = existing
                } else {
                    results[entry.URL] = entry
                }
            }
        }
    }
    
    // 按分数排序
    sortedResults := make([]IndexEntry, 0, len(results))
    for _, entry := range results {
        sortedResults = append(sortedResults, entry)
    }
    
    sort.Slice(sortedResults, func(i, j int) bool {
        return sortedResults[i].Score > sortedResults[j].Score
    })
    
    return sortedResults
}

5. 错误处理与重试机制

func fetchWithRetry(url string, maxRetries int) (string, error) {
    var lastErr error
    
    for i := 0; i < maxRetries; i++ {
        if i > 0 {
            time.Sleep(time.Duration(i*i) * time.Second) // 指数退避
        }
        
        content, err := fetchURL(url)
        if err == nil {
            return content, nil
        }
        lastErr = err
        
        if shouldRetry(err) {
            continue
        }
        break
    }
    
    return "", fmt.Errorf("failed after %d retries: %v", maxRetries, lastErr)
}

func shouldRetry(err error) bool {
    if err == nil {
        return false
    }
    
    // 检查是否为网络错误或5xx服务器错误
    if strings.Contains(err.Error(), "timeout") ||
       strings.Contains(err.Error(), "connection refused") ||
       strings.Contains(err.Error(), "5") {
        return true
    }
    
    return false
}

6. 配置管理与上下文传递

type Config struct {
    MaxConcurrent int           `yaml:"max_concurrent"`
    RequestDelay  time.Duration `yaml:"request_delay"`
    UserAgent     string        `yaml:"user_agent"`
    Timeout       time.Duration `yaml:"timeout"`
}

type Crawler struct {
    config     *Config
    httpClient *http.Client
    limiter    *RateLimiter
    index      *SearchEngine
}

func NewCrawler(cfg *Config) *Crawler {
    return &Crawler{
        config: cfg,
        httpClient: &http.Client{
            Timeout: cfg.Timeout,
        },
        limiter: NewRateLimiter(int(time.Second / cfg.RequestDelay)),
        index:   &SearchEngine{index: make(map[string][]IndexEntry)},
    }
}

func (c *Crawler) Crawl(ctx context.Context, startURL string) error {
    // 使用上下文控制爬取过程
    select {
    case <-ctx.Done():
        return ctx.Err()
    default:
        c.limiter.Wait()
        return c.crawlPage(ctx, startURL)
    }
}

这些改进可以让你的爬虫搜索引擎更加健壮、高效和可维护。每个组件都可以独立测试和扩展，这是生产级爬虫系统的基础架构。