Carica HTML in Excel con StreamProvider

Quando si caricano file html che contengono risorse esterne, ci imbattiamo spesso nei seguenti due problemi:

1. Quando lo stream html viene caricato, le immagini e le risorse esterne referenziate dal file html non possono essere ottenute tramite percorsi relativi.
2. I percorsi delle risorse esterne referenziate nei file html devono essere mappati

Questo articolo spiega come implementare l’interfaccia IStreamProvider per impostare la proprietà HtmlLoadOptions.StreamProvider. Implementando questa interfaccia, sarà possibile caricare le risorse esterne durante il caricamento degli stream Html o queste risorse esterne sono relative.

Questo è il codice principale che mostra l’uso della proprietà HtmlLoadOptions.StreamProvider

internal class HtmlAttachedStreamProvider : Aspose.Cells.IStreamProvider
{
    internal static bool IsHRef(string picPath)
    {
        //This handles http://,https:// file:// and probably ftp://.
        if (picPath.StartsWith("http://")
            || picPath.StartsWith("https://")
            || picPath.StartsWith("file://")
            || picPath.StartsWith("ftp://"))
        {
            return true;
        }
        return false;
    }
    internal static Stream GetStreamFromHref(string href)
    {
        try
        {
            WebRequest request = WebRequest.Create(href);
            WebResponse response = request.GetResponse();

            // FIX: Do not specify capacity since the length of the response is sometimes not known.
            MemoryStream dstStream = new MemoryStream();
            using (Stream responseStream = response.GetResponseStream())
            {
                byte[] buf = new byte[4096];
                while (true)
                {
                    int bytesRead = responseStream.Read(buf, 0, buf.Length);
                    // Read returns 0 when reached end of stream. Checking for negative too to make it conceptually close to Java.
                    if (bytesRead <= 0)
                        break;
                    else
                        dstStream.Write(buf, 0, bytesRead);
                }
            }


            dstStream.Position = 0;
            return dstStream;
        }
        catch
        {
            //ignored
        }
        return null;

    }
    public void InitStream(StreamProviderOptions options)
    {
        string absolutePath = null;
        switch (options.DefaultPath)
        {
            case "/Files/Image1.png":
                absolutePath = @"D:/filetemp/G1.png";
                break;
             case "/Files/Image2.png":
                absolutePath = @"D:/filetemp/E1.png";
                break;
            case "https://www.aspose.com/templates/aspose/img/products/cells/aspose_cells-for-net.svg":
                absolutePath = @"D:/filetemp/F1.png";
                break;
            default:
                break;

        }
        if(absolutePath == null)
        {
            if(IsHRef(options.DefaultPath))
            {
                options.Stream = GetStreamFromHref(options.DefaultPath);
            }
            else if(File.Exists(options.DefaultPath))
            {
                options.Stream = File.OpenRead(options.DefaultPath);
            }
            return;
        }
        options.Stream = File.OpenRead(absolutePath);

    }

    public void CloseStream(StreamProviderOptions options)
    {
        if(options.Stream != null)
        {

            options.Stream.Close();
        }

    }
}

static void Main(string[] args)
{
		HtmlAttachedStreamProvider attachedStreamProvider = new HtmlAttachedStreamProvider();
		HtmlLoadOptions options = new HtmlLoadOptions();
		options.StreamProvider = attachedStreamProvider;
		var workbook = new Workbook(@"html1.html", options);
		workbook.Save("dest.xlsx");
}