Polly page loader retry options for the ScrapeAAS library.
Get Started
$ dotnet add package ScrapeAAS.PollyReadme
Scrape as a service
ScrapeAAS integrates existing packages and ASP.NET features into a toolstack enabling you, the developer, to design your scraping service using a fammilar environment.
Quickstart
Add ASP.NET Hosting, ScrapeAAS, a validator of your choice (here Dawn.Guard RIP), and a object mapper of your choice (here AutoMapper), and the database/messagequeue you feel most comftable with (here EFcore with SQLite).
dotnet add package Microsoft.Extensions.Hosting
dotnet add package ScrapeAAS
dotnet add package Dawn.Guard
dotnet add package AutoMapper.Extensions.Microsoft.DependencyInjection
Full example of scraping the r/dotnet subreddit.
Create a crawler, a that service periodically triggers scraping
var builder = Host.CreateApplicationBuilder(args);
builder.Services
.AddAutoMapper()
.AddScrapeAAS()
.AddHostedService<RedditSubredditCrawler>()
.AddDataflow<RedditPostSpider>()
.AddDataflow<RedditSqliteSink>()
sealed class RedditSubredditCrawler : BackgroundService {
private readonly IAngleSharpBrowserPageLoader _browserPageLoader;
private readonly IDataflowPublisher<RedditPost> _publisher;
...
protected override async Task ExecuteAsync(CancellationToken stoppingToken) {
... execute service scope periotically
}
private async Task CrawlAsync(IDataflowPublisher<RedditSubreddit> publisher, CancellationToken stoppingToken)
{
_logger.LogInformation("Crawling /r/dotnet");
await publisher.PublishAsync(new("dotnet", new("https://old.reddit.com/r/dotnet")), stoppingToken);
_logger.LogInformation("Crawling complete");
}
}
Implement your spiders, services that collect, and normalize data.
sealed class RedditPostSpider : IDataflowHandler<RedditSubreddit> {
private readonly IAngleSharpBrowserPageLoader _browserPageLoader;
private readonly IDataflowPublisher<RedditComment> _publisher;
...
private async Task ParseRedditTopLevelPosts(RedditSubreddit subreddit, CancellationToken stoppingToken)
{
Url root = new("https://old.reddit.com/");
_logger.LogInformation("Parsing top level posts from {RedditSubreddit}", subreddit);
var document = await _browserPageLoader.LoadAsync(subreddit.Url, stoppingToken);
_logger.LogInformation("Request complete");
var queriedContent = document
.QuerySelectorAll("div.thing")
.AsParallel()
.Select(div => new
{
PostUrl = div.QuerySelector("a.title")?.GetAttribute("href"),
Title = div.QuerySelector("a.title")?.TextContent,
Upvotes = div.QuerySelector("div.score.unvoted")?.GetAttribute("title"),
Comments = div.QuerySelector("a.comments")?.TextContent,
CommentsUrl = div.QuerySelector("a.comments")?.GetAttribute("href"),
PostedAt = div.QuerySelector("time")?.GetAttribute("datetime"),
PostedBy = div.QuerySelector("a.author")?.TextContent,
})
.Select(queried => new RedditPost(
new(root, Guard.Argument(queried.PostUrl).NotEmpty()),
Guard.Argument(queried.Title).NotEmpty(),
long.Parse(queried.Upvotes.AsSpan()),
Regex.Match(queried.Comments ?? "", "^\\d+") is { Success: true } commentCount ? long.Parse(commentCount.Value) : 0,
new(queried.CommentsUrl),
DateTimeOffset.Parse(queried.PostedAt.AsSpan()),
new(Guard.Argument(queried.PostedBy).NotEmpty())
), IExceptionHandler.Handle((ex, item) => _logger.LogInformation(ex, "Failed to parse {RedditTopLevelPostBrief}", item)));
foreach (var item in queriedContent)
{
await _publisher.PublishAsync(item, stoppingToken);
}
_logger.LogInformation("Parsing complete");
}
}