Environment Configuration – C#
It is often helpful to have different configurations based on the environment where the application is running. For example, you may wish to configure the scripts policy, override document style applying a custom user stylesheet, or handle any web requests from the application. Aspose.HTML provides the Configuration class that can be used exactly for these purposes.
Sandboxing
A sandboxing flag set is a set of zero or more of the flags, which are used to restrict the abilities that potentially untrusted resources. The sandbox attribute allows you to set a number of restrictions on the content loaded in the frame, for example, block forms and scripts. This improves the security of the current document, especially when a document is loaded into the frame from an unverified source.
The following example demonstrates how to mark ‘Scripts’ as an untrusted resource. As a result, ‘Scripts’ will be disabled during the application execution.
1using System.IO;
2using Aspose.Html;
3using Aspose.Html.Converters;
4using Aspose.Html.Saving;
5...
6 // Prepare HTML code and save it to a file
7 var code = "<span>Hello World!!</span> " +
8 "<script>document.write('Have a nice day!');</script>";
9
10 File.WriteAllText(Path.Combine(OutputDir, "sandboxing.html"), code);
11
12 // Create an instance of Configuration
13 using (var configuration = new Configuration())
14 {
15 // Mark 'scripts' as an untrusted resource
16 configuration.Security |= Sandbox.Scripts;
17
18 // Initialize an HTML document with specified configuration
19 using (var document = new HTMLDocument(Path.Combine(OutputDir, "sandboxing.html"), configuration))
20 {
21 // Convert HTML to PDF
22 Converter.ConvertHTML(document, new PdfSaveOptions(), Path.Combine(OutputDir, "sandboxing_out.pdf"));
23 }
24 }
Services
All important functional is grouped into separated services for usability purpose and located into Aspose.Html.Services namespace.
User Agent Service
The User Agent Service allows you to specify a custom user stylesheet, a primary character set for the document, language and fonts settings. You can specify your custom style information for a particular document and provide as little or as much environment configuration changes as needed. The IUserAgentService interface describes a user agent environment.
User Style Sheet
The user is able to specify a custom style information for a particular document. This information applies to the document according to the
cascading rules and may affect the presentation of the document. The next code snippet shows how to use the UserStyleSheet
property:
1using System.IO;
2using Aspose.Html;
3using Aspose.Html.Converters;
4using Aspose.Html.Saving;
5using Aspose.Html.Services;
6...
7 // Prepare HTML code and save it to a file
8 var code = "<h1>User Agent Service </h1>\r\n" +
9 "<p>The User Agent Service allows you to specify a custom user stylesheet, a primary character set for the document, language and fonts settings.</p>\r\n";
10
11 File.WriteAllText(Path.Combine(OutputDir, "user-agent-stylesheet.html"), code);
12
13 // Create an instance of Configuration
14 using (var configuration = new Configuration())
15 {
16 // Get the IUserAgentService
17 var userAgentService = configuration.GetService<IUserAgentService>();
18
19 // Set the custom style parameters for the "h1" and "p" elements
20 userAgentService.UserStyleSheet = "h1 { color:#a52a2a;; font-size:2em;}\r\n" +
21 "p { background-color:GhostWhite; color:SlateGrey; font-size:1.2em; }\r\n";
22
23 // Initialize the HTML document with specified configuration
24 using (var document = new HTMLDocument(Path.Combine(OutputDir, "user-agent-stylesheet.html"), configuration))
25 {
26 // Convert HTML to PDF
27 Converter.ConvertHTML(document, new PdfSaveOptions(), Path.Combine(OutputDir, "user-agent-stylesheet_out.pdf"));
28 }
29 }
Character Set
The CharSet
property sets the primary character-set for a document. In order to parse and display an HTML document correctly, the application must know what character-set (encoding) is used for the document. If the character encoding is not directly specified in the header of the document, Aspose.HTML uses UTF-8, which is defined as the default for HTML5 specification. However, if you are sure that your HTML document is written using different from UTF-8 encoding, you can specify it manually, as it follows.
1using System.IO;
2using Aspose.Html;
3using Aspose.Html.Converters;
4using Aspose.Html.Saving;
5using Aspose.Html.Services;
6...
7 // Prepare HTML code and save it to a file
8 var code = "<h1>Character Set</h1>\r\n" +
9 "<p>The <b>CharSet</b> property sets the primary character-set for a document.</p>\r\n";
10
11 File.WriteAllText(Path.Combine(OutputDir, "user-agent-charset.html"), code);
12
13 // Create an instance of Configuration
14 using (var configuration = new Configuration())
15 {
16 // Get the IUserAgentService
17 var userAgentService = configuration.GetService<IUserAgentService>();
18
19 // Set the custom style parameters for the "h1" and "p" elements
20 userAgentService.UserStyleSheet = "h1 { color:salmon; }\r\n" +
21 "p { background-color: #f0f0f0; color:DarkCyan; font-size:1.2em; }\r\n";
22
23 // Set ISO-8859-1 encoding to parse the document
24 userAgentService.CharSet = "ISO-8859-1";
25
26 // Initialize the HTML document with specified configuration
27 using (var document = new HTMLDocument(Path.Combine(OutputDir, "user-agent-charset.html"), configuration))
28 {
29 // Convert HTML to PDF
30 Converter.ConvertHTML(document, new PdfSaveOptions(), Path.Combine(OutputDir, "user-agent-charset_out.pdf"));
31 }
32 }
In the example above, we have used CharSet
and UserStyleSheet
properties for a setting of ISO-8859-1 encoding and a user style.
Install Font Folder
Aspose.HTML is a powerful library for working with HTML documents in .NET applications. It provides a wide range of features to enable developers to render HTML documents to various output formats, such as PDF, XPS, DOCX, and images. One of the key features of Aspose.HTML is its ability to work with custom fonts, enabling developers to add their own fonts to the rendering process.
The FontsSettings
property is used for configuration of fonts handling. For a situation when you need to use the custom fonts instead of the fonts installed on OS, you can set the path to your custom folder, as it is shown in the following code snippet:
1using System.IO;
2using Aspose.Html;
3using Aspose.Html.Converters;
4using Aspose.Html.Saving;
5using Aspose.Html.Services;
6...
7 // Prepare HTML code and save it to a file
8 var code = "<h1>FontsSettings property</h1>\r\n" +
9 "<p>The FontsSettings property is used for configuration of fonts handling.</p>\r\n";
10
11 File.WriteAllText(Path.Combine(OutputDir, "user-agent-fontsetting.html"), code);
12
13 // Create an instance of Configuration
14 using (var configuration = new Configuration())
15 {
16 // Get the IUserAgentService
17 var userAgentService = configuration.GetService<IUserAgentService>();
18
19 // Set the custom style parameters for the "h1" and "p" elements
20 userAgentService.UserStyleSheet = "h1 { color:#a52a2a; }\r\n" +
21 "p { color:grey; }\r\n";
22
23 // Set custom font folder path
24 userAgentService.FontsSettings.SetFontsLookupFolder(Path.Combine(DataDir + "fonts"));
25
26 // Initialize the HTML document with specified configuration
27 using (var document = new HTMLDocument(Path.Combine(OutputDir, "user-agent-fontsetting.html"), configuration))
28 {
29 // Convert HTML to PDF
30 Converter.ConvertHTML(document, new PdfSaveOptions(), Path.Combine(OutputDir, "user-agent-fontsetting_out.pdf"));
31 }
32 }
To set font folder using Aspose.HTML for .NET library, we use the SetFontsLookupFolder()
method of the
FontsSettings class. This method allows you to specify the folder where custom fonts are located. By setting the font folder, Aspose.HTML will look for fonts in the specified folder when rendering the HTML document.
The figure illustrates the result of the FontsSettings
and UserStyleSheet
properties applying (b) to the source “user-agent-fontsetting.html” file (a).
Runtime Service
This service gives you control over the lifetime of the internal processes. For instance, using IRuntimeService you can specify timeouts for JavaScripts. It is important to have such a timeout in case if a script contains an endless loop. The next code snippet demonstrates how to use timeouts.
1using System.IO;
2using Aspose.Html;
3using Aspose.Html.Converters;
4using Aspose.Html.Saving;
5using Aspose.Html.Services;
6...
7 // Prepare HTML code and save it to a file
8 var code = "<h1>Runtime Service</h1>\r\n" +
9 "<script> while(true) {} </script>\r\n" +
10 "<p>The Runtime Service optimizes your system by helping it start apps and programs faster.</p>\r\n";
11
12 File.WriteAllText(Path.Combine(OutputDir, "runtime-service.html"), code);
13
14 // Create an instance of Configuration
15 using (var configuration = new Configuration())
16 {
17 // Limit JS execution time to 5 seconds
18 var runtimeService = configuration.GetService<IRuntimeService>();
19 runtimeService.JavaScriptTimeout = TimeSpan.FromSeconds(5);
20
21 // Initialize an HTML document with specified configuration
22 using (var document = new HTMLDocument(Path.Combine(OutputDir, "runtime-service.html"), configuration))
23 {
24 // Convert HTML to PNG
25 Converter.ConvertHTML(document, new ImageSaveOptions(), Path.Combine(OutputDir, "runtime-service_out.png"));
26 }
27 }
Network Service
Aspose.HTML for .Net offers the INetworkService that allows you to control all incoming/outcoming traffic and implement your custom message handlers. It can be used for different purposes, such as: create custom caching mechanism, trace/logging request messages, etc.
Message Handlers
The following example demonstrates how to create a custom message handler – LogMessageHandler – to log information about unreachable resources:
1using System.IO;
2using Aspose.Html;
3using System.Net;
4using Aspose.Html.Net;
5using System.Collections.Generic;
6...
7 // This message handler logs all failed requests to the console
8 private class LogMessageHandler : MessageHandler
9 {
10 public List<string> ErrorMessages
11 {
12 get { return errors; }
13 }
14 public override void Invoke(INetworkOperationContext context)
15 {
16 // Check whether response is OK
17 if (context.Response.StatusCode != HttpStatusCode.OK)
18 {
19 // Set error information
20 errors.Add(string.Format("File '{0}' Not Found", context.Request.RequestUri));
21 }
22
23 // Invoke the next message handler in the chain
24 Next(context);
25 }
26 }
The next code snippet demonstrates how to use the LogMessageHandler class created in the previous example to log information about unavailable resources.
1using System;
2using System.IO;
3using Aspose.Html;
4using Aspose.Html.Converters;
5using Aspose.Html.Net;
6using Aspose.Html.Saving;
7using Aspose.Html.Services;
8...
9 // Prepare HTML code and save it to a file
10 var code = "<img src=\"https://docs.aspose.com/svg/net/drawing-basics/filters-and-gradients/park.jpg\" >\r\n" +
11 "<img src=\"https://docs.aspose.com/html/net/missing1.jpg\" >\r\n" +
12 "<img src=\"https://docs.aspose.com/html/net/missing2.jpg\" >\r\n";
13
14 File.WriteAllText(Path.Combine(OutputDir, "network-service.html"), code);
15
16 // Create an instance of Configuration
17 using (var configuration = new Configuration())
18 {
19 // Add the LogMessageHandler to the chain of existing message handlers
20 var networkService = configuration.GetService<INetworkService>();
21
22 var logHandler = new LogMessageHandler();
23 networkService.MessageHandlers.Add(logHandler);
24
25 // Initialize an HTML document with specified configuration
26 using (var document = new HTMLDocument(Path.Combine(OutputDir, "network-service.html"), configuration))
27 {
28 //Convert HTML to PNG
29 Converter.ConvertHTML(document, new ImageSaveOptions(), Path.Combine(OutputDir, "network-service_out.png"));
30
31 // Print the List of ErrorMessages
32 foreach (string errorMessage in logHandler.ErrorMessages)
33 {
34 Console.WriteLine(errorMessage);
35 }
36 }
37 }
After the example run:
- the created file “network-service.html” will be converted to PNG. Only one image is in the PNG file;
- the List of ErrorMessages will be printed:
File 'https://docs.aspose.com/html/net/missing1.jpg' Not Found
File 'https://docs.aspose.com/html/net/missing2.jpg' Not Found
You can download the complete examples and data files from GitHub.