/// <summary>
/// Writes the file stored in the filesystem to the response stream without buffering in memory, ideal for large files. Supports resumable downloads.
/// </summary>
/// <param name="filename">The name of the file to write to the HTTP output.</param>
/// <param name="etag">A unique identifier for the content. Required for IE9 resumable downloads, must be a strong etag which means begins and ends in a quote i.e. "\"6c132-941-ad7e3080\""</param>
public static void TransmitFile(this HttpResponse response, string filename, string etag)
{
var request = HttpContext.Current.Request;
var fileInfo = new FileInfo(filename);
var responseLength = fileInfo.Exists ? fileInfo.Length : 0;
var buffer = new byte[4096];
var startIndex = 0;
//if the "If-Match" exists and is different to etag (or is equal to any "*" with no resource) then return 412 precondition failed
if (request.Headers["If-Match"] == "*" && !fileInfo.Exists ||
request.Headers["If-Match"] != null && request.Headers["If-Match"] != "*" && request.Headers["If-Match"] != etag)
{
response.StatusCode = (int)HttpStatusCode.PreconditionFailed;
response.End();
}
if (!fileInfo.Exists)
{
response.StatusCode = (int)HttpStatusCode.NotFound;
response.End();
}
if (request.Headers["If-None-Match"] == etag)
{
response.StatusCode = (int)HttpStatusCode.NotModified;
response.End();
}
if (request.Headers["Range"] != null && (request.Headers["If-Range"] == null || request.Headers["IF-Range"] == etag))
{
var match = Regex.Match(request.Headers["Range"], @"bytes=(\d*)-(\d*)");
startIndex = Parse<int>(match.Groups[1].Value);
responseLength = (Parse<int?>(match.Groups[2].Value) + 1 ?? fileInfo.Length) - startIndex;
response.StatusCode = (int)HttpStatusCode.PartialContent;
response.Headers["Content-Range"] = "bytes " + startIndex + "-" + (startIndex + responseLength - 1) + "/" + fileInfo.Length;
}
response.Headers["Accept-Ranges"] = "bytes";
response.Headers["Content-Length"] = responseLength.ToString();
response.Cache.SetCacheability(HttpCacheability.Public); //required for etag output
response.Cache.SetETag(etag); //required for IE9 resumable downloads
response.TransmitFile(filename, startIndex, responseLength);
}
public void ProcessRequest(HttpContext context)
{
var id = Parse<int>(context.Request.QueryString["id"]);
var version = context.Request.QueryString["v"];
var db = new DataClassesDataContext();
var filePath = db.Documents.Where(d => d.ID == id).Select(d => d.Fullpath).FirstOrDefault();
if (String.IsNullOfEmpty(filePath) || !File.Exists(filePath))
{
context.Response.StatusCode = (int)HttpStatusCode.NotFound;
context.Response.End();
}
context.Response.AddHeader("content-disposition", "filename=" + Path.GetFileName(filePath));
context.Response.ContentType = GetMimeType(filePath);
context.Response.TransmitFile(filePath, version);
}
数据库示例
/// <summary>
/// Writes the file stored in the database to the response stream without buffering in memory, ideal for large files. Supports resumable downloads.
/// </summary>
/// <param name="retrieveBinarySql">The sql to retrieve the binary data of the file from the database to be transmitted to the client. Parameters can be reffered to by {0} the index in the supplied parameter array.</param>
/// <param name="retrieveBinarySqlParameters">The parameters used in the sql query. Specify null if no parameters are required.</param>
/// <param name="connectionString">The connectring string for the sql database.</param>
/// <param name="contentLength">The length of the content in bytes.</param>
/// <param name="etag">A unique identifier for the content. Required for IE9 resumable downloads, must be a strong etag which means begins and ends in a quote i.e. "\"6c132-941-ad7e3080\""</param>
/// <param name="useFilestream">If the binary data is stored using Sql's Filestream feature set this to true to stream the file directly.</param>
public static void TransmitFile(this HttpResponse response, string retrieveBinarySql, object[] retrieveBinarySqlParameters, string connectionString, int contentLength, string etag, bool useFilestream)
{
var request = HttpContext.Current.Request;
var responseLength = contentLength;
var buffer = new byte[4096];
var startIndex = 0;
//if the "If-Match" exists and is different to etag (or is equal to any "*" with no resource) then return 412 precondition failed
if (request.Headers["If-Match"] == "*" && contentLength == 0 ||
request.Headers["If-Match"] != null && request.Headers["If-Match"] != "*" && request.Headers["If-Match"] != etag)
{
response.StatusCode = (int)HttpStatusCode.PreconditionFailed;
response.End();
}
if (contentLength == 0)
{
response.StatusCode = (int)HttpStatusCode.NotFound;
response.End();
}
if (request.Headers["If-None-Match"] == etag)
{
response.StatusCode = (int)HttpStatusCode.NotModified;
response.End();
}
if (request.Headers["Range"] != null && (request.Headers["If-Range"] == null || request.Headers["IF-Range"] == etag))
{
var match = Regex.Match(request.Headers["Range"], @"bytes=(\d*)-(\d*)");
startIndex = Parse<int>(match.Groups[1].Value);
responseLength = (Parse<int?>(match.Groups[2].Value) + 1 ?? contentLength) - startIndex;
response.StatusCode = (int)HttpStatusCode.PartialContent;
response.Headers["Content-Range"] = "bytes " + startIndex + "-" + (startIndex + responseLength - 1) + "/" + contentLength;
}
response.Headers["Accept-Ranges"] = "bytes";
response.Headers["Content-Length"] = responseLength.ToString();
response.Cache.SetCacheability(HttpCacheability.Public); //required for etag output
response.Cache.SetETag(etag); //required for IE9 resumable downloads
response.BufferOutput = false; //don't load entire data into memory (buffer) before sending
if (!useFilestream)
{
using (var connection = new SqlConnection(connectionString))
{
connection.Open();
var command = new SqlCommand(retrieveBinarySql, connection);
for (var i = 0; retrieveBinarySqlParameters != null && i < retrieveBinarySqlParameters.Length; i++)
{
command.Parameters.AddWithValue("p" + i, retrieveBinarySqlParameters[i]);
command.CommandText = command.CommandText.Replace("{" + i + "}", "@p" + i);
}
var reader = command.ExecuteReader(CommandBehavior.SequentialAccess);
if (!reader.Read())
{
response.StatusCode = (int)HttpStatusCode.NotFound;
response.End();
}
for (var i = startIndex; i < contentLength; i += buffer.Length)
{
var bytesRead = (int)reader.GetBytes(0, i, buffer, 0, buffer.Length);
response.OutputStream.Write(buffer, 0, bytesRead);
}
}
}
else
{
using (var connection = new SqlConnection(connectionString))
{
connection.Open();
var tran = connection.BeginTransaction(IsolationLevel.ReadCommitted);
var command = new SqlCommand(Regex.Replace(retrieveBinarySql, @"select \w+ ", v => v.Value.TrimEnd() + ".PathName(), GET_FILESTREAM_TRANSACTION_CONTEXT() "), connection);
command.Transaction = tran;
for (var i = 0; retrieveBinarySqlParameters != null && i < retrieveBinarySqlParameters.Length; i++)
{
command.Parameters.AddWithValue("p" + i, retrieveBinarySqlParameters[i]);
command.CommandText = command.CommandText.Replace("{" + i + "}", "@p" + i);
}
var reader = command.ExecuteReader();
if (!reader.Read())
{
response.StatusCode = (int)HttpStatusCode.NotFound;
response.End();
}
var path = reader.GetString(0);
var transactionContext = (byte[])reader.GetValue(1);
using (var fileStream = new SqlFileStream(path, transactionContext, FileAccess.Read, FileOptions.SequentialScan, 0))
{
fileStream.Seek(startIndex, SeekOrigin.Begin);
int bytesRead;
do
{
bytesRead = fileStream.Read(buffer, 0, buffer.Length);
response.OutputStream.Write(buffer, 0, bytesRead);
}
while (bytesRead == buffer.Length);
}
tran.Commit();
}
}
}
public void ProcessRequest(HttpContext context)
{
var id = Parse<int>(context.Request.QueryString["id"]);
var db = new DataClassesDataContext();
var doc = db.Documents.Where(d => d.ID == id).Select(d => new { d.Data.Length, d.Filename, d.Version }).FirstOrDefault();
if (doc == null)
{
context.Response.StatusCode = (int)HttpStatusCode.NotFound;
context.Response.End();
}
context.Response.AddHeader("content-disposition", "filename=" + doc.Filename);
context.Response.ContentType = GetMimeType(doc.Filename);
context.Response.TransmitFile("select data from documents where id = {0}", new[] { id }, db.Connection.ConnectionString, doc.Length, doc.Version, false);
}
辅助方法
public static T Parse<T>(object value)
{
//convert value to string to allow conversion from types like float to int
//converter.IsValid only works since .NET4 but still returns invalid values for a few cases like NULL for Unit and not respecting locale for date validation
try { return (T)System.ComponentModel.TypeDescriptor.GetConverter(typeof(T)).ConvertFrom(value.ToString()); }
catch (Exception) { return default(T); }
}
public string GetMimeType(string fileName)
{
//note use version 2.0.0.0 if .NET 4 is not installed, in .NET 4.5 this method has now been made public, this method apparently stores a list of mime types which would be more complete then using registry
return (string)Assembly.Load("System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")
.GetType("System.Web.MimeMapping")
.GetMethod("GetMimeMapping", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static)
.Invoke(null, new object[] { fileName });
}
恢复下载通常通过HTTP Range头字段实现。例如，如果客户端只需要文件的第二个千字节，它可能会发送头字段Range: bytes=1024-2048。
您可以查看HTTP/1.1 RFC文档的第139页获取更多信息。