Embedding graphic images in http/html

Ev Conrad · January 28, 2003

I have a web application written in ASP.NET that allows users to select records from a database. Some of these records include image data. I would like to deliver the image content to the user without having to write them to the disk. Is there a way to 'stream' the images via http without requiring them to be written to disk? Thanks!

Everett

Robby · January 28, 2003

Here's something that I have used in the past, I stripped it down to only what you may need. (I did it for something other than images, but this should work)

   Private Function GetAttach(ByVal nID As Integer) As Byte()
       Dim oImage() As Byte

       'use nID in the WHERE clause of the SQL statement

       oImage = CType(yourDataReader.Item("SomeImageField"), Byte())


       Return oImage
   End Function

   Private Sub GetDownload(ByVal nID As Integer)
       Try
           Dim sFile As String = "SomeDefaultName" 'you can use a function to acquire the name

           Response.Clear()
           Response.ContentType = "image/JPEG"
           Response.AppendHeader("Content-Disposition", "filename=" & sFile & ".jpg")

           Dim oImage() As Byte = GetAttach(nID)
           Response.BinaryWrite(oImage)

       Catch
           Response.Clear()
       Finally
           Response.Flush()
           Response.Close()
       End Try

   End Sub

Ev Conrad · January 28, 2003

Thanks. A couple of questions:

Since this will be binary data, can I use any name as a file name?

If I want the image to be on the page in addition to normal text data, can I switch the content type back & forth?

I couldn't make my first pass work, but I'll try again tonight or tomorrow morning and see how it goes. Thanks again.

Everett

Robby · January 28, 2003

I use the above code to allow users to download files from a database, AppendHeader is to give a default name to the file as the user is saving in a SaveAs situation... I don't know how it will act while displaying images as I haven't tried it. (for images)

Robby · January 28, 2003

I tested it and it works, I used almost the same method, here's the complete code....

'ASPX code.....
<%@ Page Language="vb" AutoEventWireup="false" Codebehind="WebForm1.aspx.vb" Inherits="TestImageFromDatabaseSQL.WebForm1"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
	<title>WebForm1</title>
	<meta content="Microsoft Visual Studio.NET 7.0" name="GENERATOR">
	<meta content="Visual Basic 7.0" name="CODE_LANGUAGE">
	<meta content="JavaScript" name="vs_defaultClientScript">
	<meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
</HEAD>
<body MS_POSITIONING="GridLayout">
	<form id="Form1" method="post" runat="server">
		<asp:placeholder id="PlaceHolder1" runat="server"></asp:placeholder></form>
</body>
</HTML>

'ASP code

Imports System.Data.SqlClient

Public Class WebForm1
   Inherits System.Web.UI.Page
   Protected WithEvents PlaceHolder1 As System.Web.UI.WebControls.PlaceHolder
   Protected WithEvents Button1 As New System.Web.UI.WebControls.Button()

#Region " Web Form Designer Generated Code "
   <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

   End Sub

   Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
       InitializeComponent()
   End Sub

#End Region

   Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

       Try
           PlaceHolder1.Controls.Add(Button1)
           Button1.Text = "Display Image"

           Dim nid As Integer = Convert.ToInt32(Request.QueryString("id"))
           Dim con As New SqlConnection("server=127.0.0.1;Trusted_Connection=yes;database=NorthWind")
           Dim cmd As New SqlClient.SqlCommand("SELECT Image FROM Images WHERE ID = " & nid, con)
           If con.State = ConnectionState.Closed Then con.Open()
           Dim dr As SqlClient.SqlDataReader = cmd.ExecuteReader()

           If dr.Read() Then
               Response.ContentType = "image/JPEG"
               Response.BinaryWrite(CType(dr("Image"), Byte()))
           End If
           If Not con.State = ConnectionState.Closed Then con.Close()
           If Not dr.IsClosed Then dr.Close()
           If Not cmd Is Nothing Then cmd.Dispose()
       Catch ex As Exception
           Response.Write(ex.ToString)

       End Try
   End Sub

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
       Response.Redirect("http://localhost/TestImageFromDatabaseSQL/WebForm1.aspx?id=6")
   End Sub
End Class

Ev Conrad · January 28, 2003

Sucks for me. I can't make the above work after cutting and pasting (after changing the query and connection string). I'm using C#, but the same concepts apply. I also tried to run it in VB - it runs, but not with the expected result. Any other ideas are appreciated.

Robby · January 28, 2003

Oh, I thought you were using VB, I think I have something in C#, I'll check...

Ev Conrad · January 29, 2003

Thanks again!

I have been able to bring up the image - the only problem is that I am using a sqlDataReader item to do so, and if I attempt to give a byte buffer anything other than a size of constant value, I get an error. My code looks something like this (hopefully it formats ok):


// Code that works
reader = cmd.ExecuteReader(CommandBehavior.SequentialAccess);
if (reader.Read())
{	
	imageLength = 9672; // reader[0].Length;
	imageData = new byte[imageLength];
	Response.ClearContent();
	Response.ContentType = "image/gif";
	Response.AppendHeader("Content-Disposition", "filename=foo.gif");
	retval = reader.GetBytes(0, 0, imageData, 0, 9672);
	Response.BinaryWrite(imageData);
	Response.Flush();
}

When I attempt to do the below, it chokes:

reader = cmd.ExecuteReader(CommandBehavior.SequentialAccess);
if (reader.Read())
{	
	imageLength = reader[0].Length;
	imageData = new byte[imageLength];
	Response.ClearContent();
	Response.ContentType = "image/gif";
	Response.AppendHeader("Content-Disposition", "filename=foo.gif");
	retval = reader.GetBytes(0, 0, imageData, 0, imageLength);
	Response.BinaryWrite(imageData);
	Response.Flush();
}

Any insight is appreciated.

Everett

Sign In

Embedding graphic images in http/html

Recommended Posts

Ev Conrad

Robby

Ev Conrad

Robby

Robby

Ev Conrad

Robby

Ev Conrad

Join the conversation

Browse

Activity