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POdecode a file stream using UTF-8
 

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    <p>I have a XML document, which is very big (about 120M), and I do not want to load it into memory at once. My purpose is to check whether this file is using valid UTF-8 encoding. </p> <p>Any ideas to have a quick check without reading the whole file into memory in the form of <code>byte[]</code>?</p> <p>I am using VSTS 2008 and C#.</p> <p>When using <code>XMLDocument</code> to load an XML document, which contains invalid byte sequences, there is an exception, but when reading all content into a byte array and then checking against UTF-8, there is no exception, any ideas?</p> <p>Here is a screenshot showing the content of my XML file, or you can download a copy of the file from <a href="http://www.filefactory.com/file/ag00da3/n/a_xml" rel="nofollow noreferrer">here</a></p> <p><a href="https://i.stack.imgur.com/cPlhO.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cPlhO.jpg" alt="enter image description here"></a></p> <p><strong>EDIT 1:</strong></p> <pre><code>class Program { public static byte[] RawReadingTest(string fileName) { byte[] buff = null; try { FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read); BinaryReader br = new BinaryReader(fs); long numBytes = new FileInfo(fileName).Length; buff = br.ReadBytes((int)numBytes); } catch (Exception ex) { Console.WriteLine(ex.Message); } return buff; } static void XMLTest() { try { XmlDocument xDoc = new XmlDocument(); xDoc.Load("c:\\abc.xml"); } catch (Exception ex) { Console.WriteLine(ex.Message); } } static void Main() { try { XMLTest(); Encoding ae = Encoding.GetEncoding("utf-8"); string filename = "c:\\abc.xml"; ae.GetString(RawReadingTest(filename)); } catch (Exception ex) { Console.WriteLine(ex.Message); } return; } } </code></pre> <p><strong>EDIT 2:</strong> When using <code>new UTF8Encoding(true, true)</code> there will be an exception, but when using <code>new UTF8Encoding(false, true)</code>, there is no exception thrown. I am confused, because it should be the 2nd parameter which controls whether an exception is thrown (if there are invalid byte sequences), why the 1st parameter matters?</p> <pre><code> public static void TestTextReader2() { try { // Create an instance of StreamReader to read from a file. // The using statement also closes the StreamReader. using (StreamReader sr = new StreamReader( "c:\\a.xml", new UTF8Encoding(true, true) )) { int bufferSize = 10 * 1024 * 1024; //could be anything char[] buffer = new char[bufferSize]; // Read from the file until the end of the file is reached. int actualsize = sr.Read(buffer, 0, bufferSize); while (actualsize &gt; 0) { actualsize = sr.Read(buffer, 0, bufferSize); } } } catch (Exception e) { // Let the user know what went wrong. Console.WriteLine("The file could not be read:"); Console.WriteLine(e.Message); } } </code></pre>
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    1. COIsn't almost any sequence of bytes, even random byte values, valid UTF8? Or are there some byte value sequences that are not valid UTF8?
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    2. CONot all of them, there are some exceptions, please refer here, http://en.wikipedia.org/wiki/UTF-8#Invalid_code_points
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    3. CO@ChrisW: Absolutely not; UTF-8 has specific encoding rules.
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