Develop Reference

"Stream not Writable" error when using StreamWriter in loop

I'm trying to write a tool in C# to help QA some network issues, and am running into a problem. The program is supposed to send a query in JSON format to the server every second.
Currently, it works once, but on the second attempt to send the query, I get an exception because the
"Stream was not writable."
Here's my code:
public partial class Form1 : Form
{
Timer timer1;
String query;
String result;
HttpWebRequest request;
StreamWriter writeData;
StreamReader readData;
HttpWebResponse response;
public Form1()
{
InitializeComponent();
timer1 = new Timer();
timer1.Tick += new EventHandler(timer1_Tick);
timer1.Interval = 1000;
File.Delete(AppDomain.CurrentDomain.BaseDirectory + "log.txt");
logOutput.ReadOnly = true;
request = (HttpWebRequest)WebRequest.Create("a URL goes here");
request.ContentType = "application/json";
request.Method = "POST";
query = "{some json stuff goes here}";
}
private void startButton_Click(object sender, EventArgs e)
{
if (!timer1.Enabled)
{
timer1.Start();
startButton.Text = "Stop";
}
else
{
timer1.Stop();
startButton.Text = "Start";
}
}
private void timer1_Tick(object sender, EventArgs e)
{
writeData = new StreamWriter(request.GetRequestStream());
writeData.Write(query);
writeData.Flush();
writeData.Close();
response = (HttpWebResponse)request.GetResponse();
readData = new StreamReader(response.GetResponseStream());
result = readData.ReadToEnd();
logOutput.Text = result;
File.AppendAllText(AppDomain.CurrentDomain.BaseDirectory + "log.txt", result + "\r\n");
}
}
}
Anyone know what I'm doing wrong?

First off, Stop with the global variables. Move the streamwriter, streamreader, httpwebresponse etc into the actual tick method.
Anything that implements IDisposable, which most of that stuff does, should be very local variables that aren't hanging around and are wrapped up in using clauses.
Basically your request object is closed out once your method has finished.
Something like this will work a LOT better:
private void timer1_Tick( object sender, EventArgs e ) {
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("a URL goes here");
request.ContentType = "application/json";
request.Method = "POST";
String query = "{some json stuff goes here}";
String result = String.Empty;
using ( StreamWriter writeData = new StreamWriter(request.GetRequestStream()) ) {
writeData.Write(query);
writeData.Flush();
using ( HttpWebResponse response = (HttpWebResponse)request.GetResponse() ) {
using ( StreamReader readData = new StreamReader(response.GetResponseStream()) ) {
result = readData.ReadToEnd();
}
}
}
logOutput.Text = result;
File.AppendAllText(AppDomain.CurrentDomain.BaseDirectory + "log.txt", result + "\r\n");
}
}

So I presume it's the writeData.Write(query) that's throwing? request.GetRequestStream() should only be writeable until the request is actually sent, which I believe is done when you call request.GetResponse(). So it works on the first tick, but then sends the request and can't write the second time.
Are you trying to send the request multiple times? You would need to reinitialize the request object.

Similar issue causes if you do not reinitialize the request. As mentioned by ryachza i have pushed request initialization inside loop and it worked for me.
foreach (String item in DATA)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
request.Method = "POST";
request.ContentType = "application/json";
using (Stream webStream = request.GetRequestStream())
using (StreamWriter requestWriter = new StreamWriter(webStream, System.Text.Encoding.ASCII))
{
JavaScriptSerializer json_serializer = new JavaScriptSerializer();
Object routes_list =
json_serializer.DeserializeObject(item);
requestWriter.Write(item);
}
WebResponse webResponse = request.GetResponse();
using (Stream webStream = webResponse.GetResponseStream() ?? Stream.Null)
using (StreamReader responseReader = new StreamReader(webStream))
{
response.Add(responseReader.ReadToEnd());
}
}

WebException when loading rss feed

I am attempting to load a page I've received from an RSS feed and I receive the following WebException:
Cannot handle redirect from HTTP/HTTPS protocols to other dissimilar ones.
with an inner exception:
Invalid URI: The hostname could not be parsed.
I wrote a code that would attempt loading the url via an HttpWebRequest. Due to some suggestions I received, when the HttpWebRequest fails I then set the AllowAutoRedirect to false and basically manually loop through the iterations of redirect until I find out what ultimately fails. Here's the code I'm using, please forgive the gratuitous Console.Write/Writeline calls:
Uri url = new Uri(val);
bool result = true;
System.Net.HttpWebRequest req = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url);
string source = String.Empty;
Uri responseURI;
try
{
using (System.Net.WebResponse webResponse = req.GetResponse())
{
using (HttpWebResponse httpWebResponse = webResponse as HttpWebResponse)
{
responseURI = httpWebResponse.ResponseUri;
StreamReader reader;
if (httpWebResponse.ContentEncoding.ToLower().Contains("gzip"))
{
reader = new StreamReader(new GZipStream(httpWebResponse.GetResponseStream(), CompressionMode.Decompress));
}
else if (httpWebResponse.ContentEncoding.ToLower().Contains("deflate"))
{
reader = new StreamReader(new DeflateStream(httpWebResponse.GetResponseStream(), CompressionMode.Decompress));
}
else
{
reader = new StreamReader(httpWebResponse.GetResponseStream());
}
source = reader.ReadToEnd();
reader.Close();
}
}
req.Abort();
HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(source);
result = true;
}
catch (ArgumentException ae)
{
Console.WriteLine(url + "\n--\n" + ae.Message);
result = false;
}
catch (WebException we)
{
Console.WriteLine(url + "\n--\n" + we.Message);
result = false;
string urlValue = url.ToString();
try
{
bool cont = true;
int count = 0;
do
{
req = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(urlValue);
req.Headers.Add("Accept-Language", "en-us,en;q=0.5");
req.AllowAutoRedirect = false;
using (System.Net.WebResponse webResponse = req.GetResponse())
{
using (HttpWebResponse httpWebResponse = webResponse as HttpWebResponse)
{
responseURI = httpWebResponse.ResponseUri;
StreamReader reader;
if (httpWebResponse.ContentEncoding.ToLower().Contains("gzip"))
{
reader = new StreamReader(new GZipStream(httpWebResponse.GetResponseStream(), CompressionMode.Decompress));
}
else if (httpWebResponse.ContentEncoding.ToLower().Contains("deflate"))
{
reader = new StreamReader(new DeflateStream(httpWebResponse.GetResponseStream(), CompressionMode.Decompress));
}
else
{
reader = new StreamReader(httpWebResponse.GetResponseStream());
}
source = reader.ReadToEnd();
if (string.IsNullOrEmpty(source))
{
urlValue = httpWebResponse.Headers["Location"].ToString();
count++;
reader.Close();
}
else
{
cont = false;
}
}
}
} while (cont);
}
catch (UriFormatException uriEx)
{
Console.WriteLine(urlValue + "\n--\n" + uriEx.Message + "\r\n");
result = false;
}
catch (WebException innerWE)
{
Console.WriteLine(urlValue + "\n--\n" + innerWE.Message+"\r\n");
result = false;
}
}
if (result)
Console.WriteLine("testing successful");
else
Console.WriteLine("testing unsuccessful");
Since this is currently just test code I hardcode val as http://rss.nytimes.com/c/34625/f/642557/s/3d072012/sc/38/l/0Lartsbeat0Bblogs0Bnytimes0N0C20A140C0A70C30A0Csarah0Ekane0Eplay0Eamong0Eofferings0Eat0Est0Eanns0Ewarehouse0C0Dpartner0Frss0Gemc0Frss/story01.htm
the ending url that gives the UriFormatException is: http:////www-nc.nytimes.com/2014/07/30/sarah-kane-play-among-offerings-at-st-anns-warehouse/?=_php=true&_type=blogs&_php=true&_type=blogs&_php=true&_type=blogs&_php=true&_type=blogs&_php=true&_type=blogs&_php=true&_type=blogs&_php=true&_type=blogs&partner=rss&emc=rss&_r=6&
Now I'm sure if I'm missing something or if I'm doing the looping wrong, but if I take val and just put that into a browser the page loads fine, and if I take the url that causes the exception and put it in a browser I get taken to an account login for nytimes.
I have a number of these rss feed urls that are resulting in this problem. I also have a large number of these rss feed urls that have no problem loading at all. Let me know if there is any more information needed to help resolve this. Any help with this would be greatly appreciated.
Could it be that I need to have some sort of cookie capability enabled?

You need to keep track of the cookies while doing all your requests. You can use an instance of the CookieContainer class to achieve that.
At the top of your method I made the following changes:
Uri url = new Uri(val);
bool result = true;
// keep all our cookies for the duration of our calls
var cookies = new CookieContainer();
System.Net.HttpWebRequest req = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url);
// assign our CookieContainer to the new request
req.CookieContainer = cookies;
string source = String.Empty;
Uri responseURI;
try
{
And in the exception handler where you create a new HttpWebRequest, you do the assignment from our CookieContainer again:
do
{
req = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(urlValue);
// reuse our cookies!
req.CookieContainer = cookies;
req.Headers.Add("Accept-Language", "en-us,en;q=0.5");
req.AllowAutoRedirect = false;
using (System.Net.WebResponse webResponse = req.GetResponse())
{
This makes sure that on each successive call the already present cookies are resend again in the next request. If you leave this out, no cookies are sent and therefore the site you try to visit assumes you are a fresh/new/unseen user and gives you a kind of authentication path.
If you want to store/keep cookies beyond this method you could move the cookie instance variable to a static public property so you can use all those cookies program-wide like so:
public static class Cookies
{
static readonly CookieContainer _cookies = new CookieContainer();
public static CookieContainer All
{
get
{
return _cookies;
}
}
}
And to use it in a WebRequest:
var req = (System.Net.HttpWebRequest) WebRequest.Create(url);
req.CookieContainer = Cookies.All;

Getting data back from an HttpWebRequest.BeginGetResponse callback

I am writing a Windows Phone 8 app that is supposed to send an GET+POST request to a server and parse the answer.
The code I am using to send the request and to get a response back is the following (it is written in a separate static class):
// server to POST to
string url = "http://myserver.com/?page=hello&param2=val2";
// HTTP web request
var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
httpWebRequest.ContentType = "application/x-www-form-urlencoded";
httpWebRequest.Method = "POST";
// Write the request Asynchronously
using (var stream = await Task.Factory.FromAsync<Stream>(httpWebRequest.BeginGetRequestStream,
httpWebRequest.EndGetRequestStream, null))
{
// Create the post data
string postData = "pseudo=pseudo&titre=test&texte=\"Contenu du message\"";
byte[] byteArray = Encoding.UTF8.GetBytes(postData);
// Write the bytes to the stream
await stream.WriteAsync(byteArray, 0, byteArray.Length);
stream.Close();
IAsyncResult ar = httpWebRequest.BeginGetResponse(new AsyncCallback(GetResponsetStreamCallback), httpWebRequest);
}
}
private static void GetResponsetStreamCallback(IAsyncResult callbackResult)
{
HttpWebRequest request = (HttpWebRequest)callbackResult.AsyncState;
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(callbackResult);
using (StreamReader httpWebStreamReader = new StreamReader(response.GetResponseStream()))
{
string result = httpWebStreamReader.ReadToEnd();
//For debug: show results
System.Diagnostics.Debug.WriteLine(result);
}
My problem is : I have no idea how to get this answer (the string result) back in my behind-code in my app (or any other method in my app to be honest).
How could I do that?

You can try the following code,
string url = "http://myserver.com/?page=hello&param2=val2";
// HTTP web request
var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
httpWebRequest.ContentType = "application/x-www-form-urlencoded";
httpWebRequest.Method = "POST";
httpWebRequest.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), webRequest);
}
private void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest webRequest = (HttpWebRequest)asynchronousResult.AsyncState;
using (var postStream = webRequest.EndGetRequestStream(asynchronousResult))
{
//send yoour data here
}
webRequest.BeginGetResponse(new AsyncCallback(GetResponseCallback), webRequest);
}
void GetResponseCallback(IAsyncResult asynchronousResult)
{
try
{
HttpWebRequest myrequest = (HttpWebRequest)asynchronousResult.AsyncState;
using (HttpWebResponse response = (HttpWebResponse)myrequest.EndGetResponse(asynchronousResult))
{
System.IO.Stream responseStream = response.GetResponseStream();
using (var reader = new System.IO.StreamReader(responseStream))
{
data = reader.ReadToEnd();
}
responseStream.Close();
}
}
catch (Exception e)
{
//Handle Exception
}
else
throw;
}
}

public static string GetPageAsString(Uri address)
{
string result = "";
// Create the web request
HttpWebRequest request = WebRequest.Create(address) as HttpWebRequest;
// Get response
using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
{
// Get the response stream
StreamReader reader = new StreamReader(response.GetResponseStream(), Constants.EncodingType);
// Read the whole contents and return as a string
result = reader.ReadToEnd();
}
return result;
}

Does it have to be a static class? Because if you have a new webrequest object for each request, then each response will come back into it's own object.v
You need to put the result somewhere that you can access it from the place you want to use it.
e.g. if you put it into another public static variable member then you can read it off where you need to. But you probably need to signal the UI to action it, or bind it to the UI.
If you use a static place to store it, then you will only have one active at a time. Unless you add it to a static list of items or results that you are working with
See also: http://blogs.msdn.com/b/devfish/archive/2011/04/07/httpwebrequest-fundamentals-windows-phone-services-consumption-part-2.aspx

You can: make a global variable in App.xaml.cs:
public string result;
In code use it as
(App.Current as App).result = httpWebStreamReader.ReadToEnd();
If you will need to get notified in your current active page when the result is updated - use delegates after you get the response which will signal to your page.

Why do I receive this error: The remote server returned an error: (417) Expectation Failed

A friend show me this sample code to implement HTTP POST in C# and did work out in a WINFORM App:
http://www.terminally-incoherent.com/blog/2008/05/05/send-a-https-post-request-with-c/
And implemented in a METRO APP:
// this is what we are sending
string post_data = "user=user#example.com&pass=example123";
// this is where we will send it
string uri = "http://app.proceso.com.mx/win8/login";
// create a request
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = "POST";
// turn our request string into a byte stream
byte[] postBytes = Encoding.UTF8.GetBytes(post_data);
// this is important - make sure you specify type this way
request.ContentType = "application/x-www-form-urlencoded";
Stream requestStream = await request.GetRequestStreamAsync();
// now send it
requestStream.Write(postBytes, 0, postBytes.Length);
// grab te response and print it out to the console along with the status code
WebResponse response = await request.GetResponseAsync();
//var a = new StreamReader(response.GetResponseStream()).ReadToEnd();
StreamReader requestReader = new StreamReader(response.GetResponseStream());
String webResponse = requestReader.ReadToEnd();
I realized, HttpWebRequest does not contain ProtocolVersion and is throwing me this error in this line:
WebResponse response = await request.GetResponseAsync();
// ERROR: The remote server returned an error: (417) Expectation Failed.
I guess the last property is the solution. How can I solve this problem?
Thanks in advance

I recently wrote a small function to handle the posting of trivial data to a server.
private struct HttpPostParam
{
private string _key;
private string _value;
public string Key { get { return HttpUtility.UrlEncode(this._key); } set { this._key = value; } }
public string Value { get { return HttpUtility.UrlEncode(this._value); } set { this._value = value; } }
public HttpPostParam(string key, string value)
{
this._key = key;
this._value = value;
}
};
private static string PostTrivialData(Uri page, HttpPostParam[] parameters)
{
string pageResponse = string.Empty;
try
{
var request = (HttpWebRequest)WebRequest.Create(page); //create the initial request.
request.Method = WebRequestMethods.Http.Post; //set the method
request.AllowAutoRedirect = true; //couple of settings I personally prefer.
request.KeepAlive = true;
request.ContentType = "application/x-www-form-urlencoded";
//create the post data.
byte[] bData = Encoding.UTF8.GetBytes(string.Join("&", Array.ConvertAll(parameters, kvp => string.Format("{0}={1}", kvp.Key, kvp.Value))));
using (var reqStream = request.GetRequestStream())
reqStream.Write(bData, 0, bData.Length); //write the data to the request.
using (var response = (HttpWebResponse)request.GetResponse()) //attempt to get the response.
if (response.StatusCode == HttpStatusCode.OK || response.StatusCode == HttpStatusCode.NotModified) //check for a valid status (should only return 200 if successful)
using (var reader = new System.IO.StreamReader(response.GetResponseStream()))
pageResponse = reader.ReadToEnd();
}
catch (Exception e)
{
/* todo: any error handling, for my use case failing gracefully was all that was needed. */
}
return pageResponse;
}
Essentially it posts the value pairs defined in the "parameters" argument. Will require a reference and import of the System.Web namespace to compile.
I just tested it with your website and got a response back:
HttpPostParam[] httpparams = {
new HttpPostParam("user", "censored#email.com"),
new HttpPostParam("pass", "example123")
};
string response = PostTrivialData(new Uri("http://app.proceso.com.mx/win8/login"), httpparams);
Let me know if there's any issues.

Google Translate V2 cannot hanlde large text translations from C#

I've implemented C# code using the Google Translation V2 api with the GET Method.
It successfully translates small texts but when increasing the text length and it takes 1,800 characters long ( including URI parameters ) I'm getting the "URI too large" error.
Ok, I burned down all the paths and investigated the issue across multiple pages posted on Internet. All of them clearly says the GET method should be overriden to simulate a POST method ( which is meant to provide support to 5,000 character URIs ) but there is no way to find out a code example to of it.
Does anyone has any example or can provide some information?
[EDIT] Here is the code I'm using:
String apiUrl = "https://www.googleapis.com/language/translate/v2?key={0}&source={1}&target={2}&q={3}";
String url = String.Format(apiUrl, Constants.apiKey, sourceLanguage, targetLanguage, text);
Stream outputStream = null;
byte[] bytes = Encoding.ASCII.GetBytes(url);
// create the http web request
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
webRequest.KeepAlive = true;
webRequest.Method = "POST";
// Overrride the GET method as documented on Google's docu.
webRequest.Headers.Add("X-HTTP-Method-Override: GET");
webRequest.ContentType = "application/x-www-form-urlencoded";
// send POST
try
{
webRequest.ContentLength = bytes.Length;
outputStream = webRequest.GetRequestStream();
outputStream.Write(bytes, 0, bytes.Length);
outputStream.Close();
}
catch (HttpException e)
{
/*...*/
}
try
{
// get the response
HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse();
if (webResponse.StatusCode == HttpStatusCode.OK && webRequest != null)
{
// read response stream
using (StreamReader sr = new StreamReader(webResponse.GetResponseStream(), Encoding.UTF8))
{
string lista = sr.ReadToEnd();
DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(TranslationRootObject));
MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(lista));
TranslationRootObject tRootObject = (TranslationRootObject)serializer.ReadObject(stream);
string previousTranslation = string.Empty;
//deserialize
for (int i = 0; i < tRootObject.Data.Detections.Count; i++)
{
string translatedText = tRootObject.Data.Detections[i].TranslatedText.ToString();
if (i == 0)
{
text = translatedText;
}
else
{
if (!text.Contains(translatedText))
{
text = text + " " + translatedText;
}
}
}
return text;
}
}
}
catch (HttpException e)
{
/*...*/
}
return text;
}

Apparently using WebClient won't work as you cannot alter the headers as needed, per the documentation:
Note: You can also use POST to invoke the API if you want to send more data in a single request. The q parameter in the POST body must be less than 5K characters. To use POST, you must use the X-HTTP-Method-Override header to tell the Translate API to treat the request as a GET (use X-HTTP-Method-Override: GET).
You can use WebRequest, but you'll need to add the X-HTTP-Method-Override header:
var request = WebRequest.Create (uri);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.Headers.Add("X-HTTP-Method-Override", "GET");
var body = new StringBuilder();
body.Append("key=SECRET");
body.AppendFormat("&source={0}", HttpUtility.UrlEncode(source));
body.AppendFormat("&target={0}", HttpUtility.UrlEncode(target));
//--
body.AppendFormat("&q={0}", HttpUtility.UrlEncode(text));
var bytes = Encoding.ASCII.GetBytes(body.ToString());
if (bytes.Length > 5120) throw new ArgumentOutOfRangeException("text");
request.ContentLength = bytes.Length;
using (var output = request.GetRequestStream())
{
output.Write(bytes, 0, bytes.Length);
}

The accepted answer appears to be out of date. You can now use the WebClient (.net 4.5) successfully to POST to the google translate API making sure to set the X-HTTP-Method-Override header.
Here is some code to show you how.
using (var webClient = new WebClient())
{
webClient.Headers.Add("X-HTTP-Method-Override", "GET");
var data = new NameValueCollection()
{
{ "key", GoogleTranslateApiKey },
{ "source", "en" },
{ "target", "fr"},
{ "q", "<p>Hello World</p>" }
};
try
{
var responseBytes = webClient.UploadValues(GoogleTranslateApiUrl, "POST", data);
var json = Encoding.UTF8.GetString(responseBytes);
var result = JsonConvert.DeserializeObject<dynamic>(json);
var translation = result.data.translations[0].translatedText;
}
catch (Exception ex)
{
loggingService.Error(ex.Message);
}
}

? What? it is trivial to post using C# - it is right there in the documentation.
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
{
// Set type to POST
request.Method = "POST";
From there on you bascially put the data into fom fields into the content stream.
This is not "simulate a post meethod", it is fully doing a post request as per specifications.
Btw. hwhere does json enter here? You say "in C#". There is no need to use json?