{"id":132,"date":"2011-10-15T22:23:10","date_gmt":"2011-10-15T14:23:10","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=132"},"modified":"2018-11-14T10:41:53","modified_gmt":"2018-11-14T02:41:53","slug":"downloading-a-file-from-via-http-post-and-http-get-in-c","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/downloading-a-file-from-via-http-post-and-http-get-in-c\/","title":{"rendered":"Downloading a file via HTTP post and HTTP get in C#"},"content":{"rendered":"

Previously, I had written two posts on how to upload files to a web server, one<\/a> for the case when the size of the HTTP request<\/a> is small, and the other<\/a> for the case when the size of the HTTP request is large. How about the downloading of files from a web server? In this post, I shall discuss how to download files from a HTTP server<\/a> via the System.Net.HttpWebRequest<\/a> class. <\/p>\n

Download a file via HTTP get<\/h3>\n

Downloading of a file from the web server via HTTP get in C# consists of three main steps:<\/p>\n

    \n
  1. Construct the HTTP get request to send to the web server.<\/li>\n
  2. Send the HTTP request and get the HTTP response<\/a> from the web server.<\/li>\n
  3. Save the contents in the HTTP response to a local file.<\/li>\n<\/ol>\n

    Construct the HTTP get request<\/h4>\n

    The following code segment prepares an instance of the System.Net.HttpWebRequest class to download my website logo<\/a>.<\/p>\n

    \r\n\/\/ Construct HTTP request to get the logo\r\nHttpWebRequest httpRequest = (HttpWebRequest)\r\n    WebRequest.Create("http:\/\/www.techcoil.com\/ph\/img\/logo.png");\r\nhttpRequest.Method = WebRequestMethods.Http.Get;\r\n<\/pre>\n
    Send the HTTP request and get the HTTP response from the web server.<\/h4>\n
    \r\n\/\/ Get back the HTTP response for web server\r\nHttpWebResponse httpResponse \r\n    = (HttpWebResponse)httpRequest.GetResponse();\r\nStream httpResponseStream = httpResponse.GetResponseStream();\r\n<\/pre>\n
    Save the file to your local disk<\/h4>\n
    \r\n\/\/ Define buffer and buffer size\r\nint bufferSize = 1024;\r\nbyte[] buffer = new byte[bufferSize];\r\nint bytesRead = 0;\r\n\r\n\/\/ Read from response and write to file\r\nFileStream fileStream = File.Create("techcoil-logo.png");\r\nwhile ((bytesRead = httpResponseStream.Read(buffer, 0, bufferSize)) != 0) \r\n{\r\n    fileStream.Write(buffer, 0, bytesRead);\r\n} \/\/ end while\r\n<\/pre>\n
    Download a file via HTTP post<\/h3>\n
    Sometimes, there is a need for the client to supply some information to the web server in order to download a file. This can be a case when we want to control how files are downloaded. We can refer to every file in our web server with a unique id and write a server script to serve the respective file based on the id received from the client. For the sake of demonstration, I had published a server script, \"\/poc\/downloadPng.php\", that will read a post variable labelled as id. If id is 1, it will write my website logo<\/a> to the client, else it will write my 404 icon image<\/a> to the client.     <\/p>\n
    As with HTTP get, downloading of a file from the web server via HTTP post in C# consists of three main steps:<\/p>\n
      \n
    1. Construct the HTTP post request to send to the web server.<\/li>\n
    2. Send the HTTP request and get the HTTP response from the web server.<\/li>\n
    3. Save the contents in the HTTP response to a local file.<\/li>\n<\/ol>\n
      Since step 2 and 3 are identical, I will just discuss step 1. <\/p>\n
      Construct the HTTP post request to send to the web server.<\/h4>\n
      \r\n\/\/ Construct HTTP request to get the file\r\nHttpWebRequest httpRequest = (HttpWebRequest)\r\n    WebRequest.Create("http:\/\/www.techcoil.com\/poc\/downloadPng.php");\r\nhttpRequest.Method = WebRequestMethods.Http.Post;\r\n\r\n\/\/ Include post data in the HTTP request\r\nstring postData = "id=1";\r\nhttpRequest.ContentLength = postData.Length;\r\nhttpRequest.ContentType = "application\/x-www-form-urlencoded";\r\n\/\/ Write the post data to the HTTP request\r\nStreamWriter requestWriter = new StreamWriter(\r\n    httpRequest.GetRequestStream(), \r\n    System.Text.Encoding.ASCII);\r\nrequestWriter.Write(postData);\r\nrequestWriter.Close();\r\n<\/pre>\n
      Namespaces to include<\/h3>\n
      The following namespaces need to be included in order for the above mentioned codes to compile.<\/p>\n