Project: Parallel Downloader

Project Goals

Build a concurrent file downloader:

Accept list of URLs from file or stdin
Download files in parallel (configurable workers)
Show progress bar for each download
Handle errors gracefully (retry failed downloads)
Support cancellation with Ctrl+C

Components to Use

sync.WaitGroup — coordinate workers
context.Context — for cancellation
channels — for progress updates
semaphore pattern — limit concurrent downloads

Suggested Structure

Worker pattern

func worker(ctx context.Context, urls chan string, results chan Result) {
    for url := range urls {
        select {
        case <-ctx.Done():
            return
        default:
            result := download(ctx, url)
            results <- result
        }
    }
}

func download(ctx context.Context, url string) Result {
    req, _ := http.NewRequestWithContext(ctx, "GET", url, nil)
    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return Result{URL: url, Err: err}
    }
    defer resp.Body.Close()
    
    // Download and track progress...
    return Result{URL: url, Size: size}
}

Example Usage

Terminal

$ cat urls.txt | downloader -workers 5
Downloading 10 files with 5 workers...
[████████████████████] 100% file1.zip (15 MB)
[████████████░░░░░░░░]  60% file2.tar.gz (8/13 MB)
[████░░░░░░░░░░░░░░░░]  20% file3.iso (200/1000 MB)
...

Skills Used: Goroutines, channels, WaitGroups, context cancellation, HTTP streaming, progress tracking.