Building an Office Web Apps (OWA) WOPI Host

        /// <summary>
        /// Required for WOPI interface - on initial view
        /// </summary>
        /// <param name="name">file name</param>
        /// <param name="access_token">token that WOPI server will know</param>
        /// <returns></returns>
        public CheckFileInfo Get(string name, string access_token)
        {
            Validate(name, access_token);
        var fileInfo = _fileHelper.GetFileInfo(name);
        return fileInfo;
    }

  

 /// <summary>
 /// Required for View WOPI interface - returns stream of document.
 /// </summary>
 /// <param name="name">file name</param>
 /// <param name="access_token">token that WOPI server will know</param>
 /// <returns></returns>
 public HttpResponseMessage GetFile(string name, string access_token)
 {
     try
     {
         Validate(name, access_token);
         var file = HostingEnvironment.MapPath("~/App_Data/" + name);
         var rv = new HttpResponseMessage(HttpStatusCode.OK);
         var stream = new FileStream(file, FileMode.Open, FileAccess.Read);
     rv.Content = new StreamContent(stream);
     rv.Content.Headers.ContentType = new MediaTypeHeaderValue(&quot;application/octet-stream&quot;);
     return rv;

 }
 catch (Exception ex)
 {
     var rv = new HttpResponseMessage(HttpStatusCode.InternalServerError);
     var stream = new MemoryStream(UTF8Encoding.Default.GetBytes(ex.Message ?? &quot;&quot;));
     rv.Content = new StreamContent(stream);
     return rv;
 }

}

namespace MainWeb.Helpers
{
    public interface IKeyGen
    {
        string GetHash(string value);
    bool Validate(string name, string access_token);
}
public class KeyGen : IKeyGen
{
    byte[] _key;
    int _saltLength = 8;

    static RNGCryptoServiceProvider s_rngCsp = new RNGCryptoServiceProvider();

    public KeyGen()
    {
        var key = WebConfigurationManager.AppSettings["appHmacKey"];
        if (string.IsNullOrEmpty(key))
            throw new ArgumentNullException("must supply a HmacKey - check config");
        _key = Encoding.UTF8.GetBytes(key);
    }

    public string GetHash(string value)
    {
        byte[] salt = new byte[_saltLength];
        s_rngCsp.GetBytes(salt);

        var saltStr = Convert.ToBase64String(salt);
        return GetHash(value, saltStr);
    }

    private string GetHash(string value, string saltStr)
    {
        //Not really secure; must use random salt to ensure non-repeat....
        HMACSHA256 hmac = new HMACSHA256(_key);
        var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(saltStr + value));
        var rv = Convert.ToBase64String(hash);
        return saltStr + rv;
    }


    public bool Validate(string name, string access_token)
    {
        var targetHash = GetHash(name, access_token.Substring(0,_saltLength + 4));  //hack for base64 form
        return String.Equals(access_token, targetHash);
    }


}

}

public interface IFileHelper
{
    CheckFileInfo GetFileInfo(string name);
}
public class FileHelper : IFileHelper

{

public CheckFileInfo GetFileInfo(string name)

{

var fileName = GetFileName(name);

FileInfo info = new FileInfo(fileName);

string sha256 = "";
    using (FileStream stream = File.OpenRead(fileName))
    using (var sha = SHA256.Create())
    {
        byte[] checksum = sha.ComputeHash(stream);
        sha256 = Convert.ToBase64String(checksum);
    }

    var rv = new CheckFileInfo
    {
        BaseFileName = info.Name,
        OwnerId = "admin",
        Size = info.Length,
        SHA256 = sha256,
        Version = info.LastWriteTimeUtc.ToString("s")
    };

    return rv;
}


internal string GetFileName(string name)
{
    var file = HostingEnvironment.MapPath("~/App_Data/" + name);
    return file;
}

}

public class WopiAppHelper
{
    string _discoveryFile;
    WopiHost.wopidiscovery _wopiDiscovery;
public WopiAppHelper(string discoveryXml)
{
    _discoveryFile = discoveryXml;

    using (StreamReader file = new StreamReader(discoveryXml))
    {
        XmlSerializer reader = new XmlSerializer(typeof(WopiHost.wopidiscovery));
        var wopiDiscovery = reader.Deserialize(file) as WopiHost.wopidiscovery;
        _wopiDiscovery = wopiDiscovery;
    }
}


public WopiHost.wopidiscoveryNetzoneApp GetZone(string AppName)
{
    var rv = _wopiDiscovery.netzone.app.Where(c => c.name == AppName).FirstOrDefault();
    return rv;
}

public string  GetDocumentLink(string wopiHostandFile)
{
    var fileName = wopiHostandFile.Substring(wopiHostandFile.LastIndexOf('/') + 1);
    var accessToken = GetToken(fileName);
    var fileExt = fileName.Substring(fileName.LastIndexOf('.') + 1);
    var tt = _wopiDiscovery.netzone.app.AsEnumerable().Where(c => c.action.Where(d => d.ext == fileExt).Count() > 0);

    var appName = tt.FirstOrDefault();

    if (null == appName) throw new ArgumentException("invalid file extension " + fileExt);

    var rv = GetDocumentLink(appName.name, fileExt, wopiHostandFile, accessToken);

    return rv;
}

string GetToken(string fileName)
{
    KeyGen keyGen = new KeyGen();
    var rv = keyGen.GetHash(fileName);

    return HttpUtility.UrlEncode(rv);
}

const string s_WopiHostFormat = "{0}?WOPISrc={1}&access_token={2}";
public string GetDocumentLink(string appName, string fileExtension, string wopiHostAndFile, string accessToken)
{
    var wopiHostUrlsafe = HttpUtility.UrlEncode(wopiHostAndFile.Replace(" ", "%20"));
    var appStuff = _wopiDiscovery.netzone.app.Where(c => c.name == appName).FirstOrDefault();

    if (null == appStuff)
        throw new ApplicationException("Can't locate App: " + appName);


    var appAction = appStuff.action.Where(c => c.ext == fileExtension).FirstOrDefault();
                if (null == appAction)
        throw new ApplicationException("Can't locate UrlSrc for : " + appName);

    var endPoint = appAction.urlsrc.IndexOf('?');
    var fullPath = string.Format(s_WopiHostFormat, appAction.urlsrc.Substring(0, endPoint), wopiHostUrlsafe, accessToken); 

    return fullPath;
}

}