How do I handle file downloads with Pholcus?

Pholcus is a distributed, high-concurrency and powerful web crawler software written in Go. Handling file downloads with Pholcus involves setting up your crawler task to target the specific files you want to download and then processing the response to save the files to disk.

Here's a general approach to handling file downloads with Pholcus:

1. Identify the file URLs: You must first identify the URLs of the files you wish to download. This can typically be done by crawling the website and extracting the relevant <a href="..."> tags that link to the files.

2. Create a Pholcus spider: You need to define a spider that will handle the crawling process. This spider should be configured to target the URLs of the files you want to download.

3. Handle the response: Once Pholcus fetches the file from the URL, you will need to process the response and write the file contents to disk.

Here's an example of how you might set up a spider to download files using Pholcus:

package main

import (
    "github.com/henrylee2cn/pholcus/exec"
    "github.com/henrylee2cn/pholcus/logs"
    // Import the Pholcus web spider package
    _ "github.com/henrylee2cn/pholcus_lib"
    // Import the file output package (for saving files)
    _ "github.com/henrylee2cn/pholcus_lib/output"
    // Import the HTTP downloader
    _ "github.com/henrylee2cn/pholcus_lib/net/http"
)

func main() {
    // Initialize Pholcus with default settings
    exec.DefaultRun("web")

    // Define your spider here
    spider := &Spider{
        Name: "FileDownloader",
        Description: "A spider to download files",
        // Define the Parsers for handling different types of pages or files
        Parsers: []Parser{
            {
                // Parser name
                Name: "DownloadFile",
                // Parse function will be called when the parser is executed
                ParseFunc: func(ctx *Context) {
                    // The URL of the file to download
                    fileURL := ctx.GetTemp("fileUrl", "").(string)
                    // The name of the file to save
                    fileName := "downloaded_file"

                    // Get the response body as a byte slice
                    fileBytes := ctx.GetResponse().Body

                    // Save the file to disk
                    err := ioutil.WriteFile(fileName, fileBytes, 0644)
                    if err != nil {
                        logs.Log.Error("Error saving file: %v", err)
                    } else {
                        logs.Log.Informational("File saved successfully: %s", fileName)
                    }
                },
            },
        },
    }
    // Add the spider to Pholcus
    exec.AddSpider(spider)

    // Start the crawler
    exec.Run()
}

In this example, we define a spider named FileDownloader with a single parser named DownloadFile. The ParseFunc function is responsible for handling the download. It reads the URL of the file to be downloaded from a temporary context variable, fetches the response body, and saves it to a file on disk.

Please note that this example is a high-level and simplified illustration. You may need to adjust the code and add error handling, configure output directories, and set up the appropriate spider rules to target the correct URLs for your specific use case.

To actually run a Pholcus spider, you would typically use the command line interface provided by Pholcus or integrate it into your Go application, as shown in the example.

Remember that when downloading files from the internet, you should always be respectful of the website's terms of service and copyright laws. Additionally, make sure to handle the load on the server you are scraping from by limiting the rate of your requests and using appropriate user-agent strings.