入门教程：用Go语言编写并发文件下载器

package main

import (
    "fmt"
    "io"
    "net/http"
    "os"
    "strconv"
    "sync"
)

func main() {
    url := "https://example.com/large_file.zip" // 替换为实际的下载链接
    numGoroutines := 5                           // 并发下载的goroutine数量

    fileSize, err := getFileSize(url)
    if err != nil {
        fmt.Println("获取文件大小失败:", err)
        return
    }

    chunkSize := fileSize / int64(numGoroutines)

    var wg sync.WaitGroup
    wg.Add(numGoroutines)

    for i := 0; i < numGoroutines; i++ {
        start := int64(i) * chunkSize
        end := start + chunkSize - 1
        if i == numGoroutines-1 {
            end = fileSize - 1 // 最后一个chunk下载剩余部分
        }

        go func(i int, start, end int64) {
            defer wg.Done()
            err := downloadChunk(url, "part_"+strconv.Itoa(i)+".tmp", start, end)
            if err != nil {
                fmt.Printf("Chunk %d 下载失败: %v\n", i, err)
            } else {
                fmt.Printf("Chunk %d 下载完成\n", i)
            }
        }(i, start, end)
    }

    wg.Wait()
    fmt.Println("所有chunk下载完成")

    // TODO: 合并所有chunk
    // ...
}

func getFileSize(url string) (int64, error) {
    resp, err := http.Head(url)
    if err != nil {
        return 0, err
    }
    defer resp.Body.Close()

    if resp.StatusCode != http.StatusOK {
        return 0, fmt.Errorf("HTTP status code: %d", resp.StatusCode)
    }

    fileSize, err := strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 64)
    if err != nil {
        return 0, err
    }

    return fileSize, nil
}

func downloadChunk(url, filename string, start, end int64) error {
    req, err := http.NewRequest("GET", url, nil)
    if err != nil {
        return err
    }

    rangeHeader := fmt.Sprintf("bytes=%d-%d", start, end)
    req.Header.Set("Range", rangeHeader)

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        return err
    }
    defer resp.Body.Close()

    if resp.StatusCode != http.StatusPartialContent {
        return fmt.Errorf("HTTP status code: %d", resp.StatusCode)
    }

    file, err := os.Create(filename)
    if err != nil {
        return err
    }
    defer file.Close()

    _, err = io.Copy(file, resp.Body)
    return err
}