public static bool DownloadFile(HttpContext httpContext, string filePath, long speed)
{
bool ret = true;
try
{
#region-- Validation: HttpMethod , whether the requested file exists
switch (httpContext.Request.HttpMethod.ToUpper())
{ // Currently only supported GET and HEAD methods
case "GET":
case "HEAD":
break;
default:
httpContext.Response.StatusCode = 501;
return false;
}
if (!File.Exists(filePath))
{
httpContext.Response.StatusCode = 404;
return false;
}
#endregion
#region Define local variables
long startBytes = 0;
int packSize = 1024 * 10; // Read in blocks, each block 10K bytes
string fileName = Path.GetFileName(filePath);
FileStream myFile = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
BinaryReader br = new BinaryReader(myFile);
long fileLength = myFile.Length;
int sleep = (int)Math.Ceiling(1000.0 * packSize / speed);// Milliseconds: read down 1 The time interval of the data block
string lastUpdateTiemStr = File.GetLastWriteTimeUtc(filePath).ToString("r");
string eTag = HttpUtility.UrlEncode(fileName, Encoding.UTF8) + lastUpdateTiemStr;// It is easy to extract the request header when restoring the download ;
#endregion
#region-- Verify: whether the file is too large, whether it is retransmitted, and whether it has been fixed since the last requested date
if (myFile.Length > Int32.MaxValue)
{//------- The file is too big -------
httpContext.Response.StatusCode = 413;// The requesting entity is too large
return false;
}
if (httpContext.Request.Headers["If-Range"] != null)// Corresponding response header ETag : the name of the file + File last modified
{
//---------- The last requested date has been modified since --------------
if (httpContext.Request.Headers["If-Range"].Replace("\"", "") != eTag)
{// The file has been modified
httpContext.Response.StatusCode = 412;// Pretreatment failure
return false;
}
}
#endregion
try
{
#region ------- Add important response headers, parse request headers, and related validation -------------------
httpContext.Response.Clear();
httpContext.Response.Buffer = false;
httpContext.Response.AddHeader("Content-MD5", GetMD5Hash(myFile));// Used to validate files
httpContext.Response.AddHeader("Accept-Ranges", "bytes");// Important: must continue
httpContext.Response.AppendHeader("ETag", "\"" + eTag + "\"");// Important: must continue
httpContext.Response.AppendHeader("Last-Modified", lastUpdateTiemStr);// Write the last modified date to the response
httpContext.Response.ContentType = "application/octet-stream";//MIME Type: matches any file type
httpContext.Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(fileName, Encoding.UTF8).Replace("+", "%20"));
httpContext.Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
httpContext.Response.AddHeader("Connection", "Keep-Alive");
httpContext.Response.ContentEncoding = Encoding.UTF8;
if (httpContext.Request.Headers["Range"] != null)
{//------ If it is a continuation request, it gets the starting position of the continuation, that is, the number of bytes that have been downloaded to the client ------
httpContext.Response.StatusCode = 206;// Important: must continue the transmission, represents the local range response. Default at initial download 200
string[] range = httpContext.Request.Headers["Range"].Split(new char[] { '=', '-' });//"bytes=1474560-"
startBytes = Convert.ToInt64(range[1]);// The number of bytes that have been downloaded, where the download started
if (startBytes < 0 || startBytes >= fileLength)
{// Invalid start position
return false;
}
}
if (startBytes > 0)
{//------ If it is a continuation request, tell the client the starting number of bytes and the total length so that the client can append the continuation data to startBytes After the position ----------
httpContext.Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
}
#endregion
#region ------- Sends a block of data to the client -------------------
br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
int maxCount = (int)Math.Ceiling((fileLength - startBytes + 0.0) / packSize);// The number of blocks that can be divided into the remaining parts
for (int i = 0; i < maxCount && httpContext.Response.IsClientConnected; i++)
{// When the client breaks the connection, it is suspended
httpContext.Response.BinaryWrite(br.ReadBytes(packSize));
httpContext.Response.Flush();
if (sleep > 1) Thread.Sleep(sleep);
}
#endregion
}
catch
{
ret = false;
}
finally
{
br.Close();
myFile.Close();
}
}
catch
{
ret = false;
}
return ret;
}