C How can I check if a URL exists is valid

Question

I am making a simple program in visual c  2005 that looks up a stock symbol on Yahoo  Finance  downloads the historical data  and then plots the price history for the specified ticker symbol   I know the exact URL that I need to acquire the data  and if the user inputs an existing ticker symbol  or at least one with data on Yahoo  Finance  it works perfectly fine  However  I have a run-time error if the user makes up a ticker symbol  as the program tries to pull data from a non-existent web page   I am using the WebClient class  and using the DownloadString function  I looked through all the other member functions of the WebClient class  but didn t see anything I could use to test a URL   How can I do this

User · Answer

This solution seems easy to follow   public static bool isValidURL string url        WebRequest webRequest   WebRequest Create url       WebResponse webResponse      try               webResponse   webRequest GetResponse              catch   If exception thrown then couldn t get response from address               return false             return true

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I have always found Exceptions are much slower to be handled   Perhaps a less intensive way would yeild a better  faster  result   public bool IsValidUri Uri uri         using  HttpClient Client   new HttpClient               HttpResponseMessage result   Client GetAsync uri  Result      HttpStatusCode StatusCode   result StatusCode       switch  StatusCode                 case HttpStatusCode Accepted              return true          case HttpStatusCode OK              return true           default              return false                      Then just use   IsValidUri new Uri  http   www google com censorship algorithm

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You could issue a  HEAD  request rather than a  GET     edit  - lol  Looks like I ve done this before   changed to wiki to avoid accusations of rep-garnering  So to test a URL without the cost of downloading the content      using MyClient from linked post using var client   new MyClient          client HeadOnly   true         fine  no content downloaded     string s1   client DownloadString  http   google com           throws 404     string s2   client DownloadString  http   google com silly        You would try catch around the DownloadString to check for errors  no error  It exists       With C  2 0  VS2005    private bool headOnly  public bool HeadOnly       get  return headOnly       set  headOnly   value       and  using WebClient client   new MyClient             code as before

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Web servers respond with a HTTP status code indicating the outcome of the request e g  200  sometimes 202  means success  404 - not found etc  see here   Assuming the server address part of the URL is correct and you are not getting a socket timeout  the exception is most likely telling you the HTTP status code was other than 200  I would suggest checking the class of the exception and seeing if the exception carries the HTTP status code   IIRC - The call in question throws a WebException or a descendant  Check the class name to see which one and wrap the call in a try block to trap the condition

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WebRequest request   WebRequest Create  http   www google com    try        request GetResponse      catch   If exception thrown then couldn t get response from address        MessageBox Show  The URL is incorrect

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Here is another option  public static bool UrlIsValid string url        bool br   false      try           IPHostEntry ipHost   Dns Resolve url           br   true            catch  SocketException se            br   false            return br

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These solutions are pretty good  but they are forgetting that there may be other status codes than 200 OK  This is a solution that I ve used on production environments for status monitoring and such    If there is a url redirect or some other condition on the target page  the return will be true using this method  Also  GetResponse   will throw an exception and hence you will not get a StatusCode for it  You need to trap the exception and check for a ProtocolError   Any 400 or 500 status code will return false  All others return true   This code is easily modified to suit your needs for specific status codes        lt summary gt      This method will check a url to see that it does not return server or protocol errors      lt  summary gt       lt param name  url  gt The path to check lt  param gt       lt returns gt  lt  returns gt  public bool UrlIsValid string url        try               HttpWebRequest request   HttpWebRequest Create url  as HttpWebRequest          request Timeout   5000    set the timeout to 5 seconds to keep the user from waiting too long for the page to load         request Method    HEAD     Get only the header information -- no need to download any content          using  HttpWebResponse response   request GetResponse   as HttpWebResponse                        int statusCode    int response StatusCode              if  statusCode  gt   100  amp  amp  statusCode  lt  400    Good requests                               return true                            else if  statusCode  gt   500  amp  amp  statusCode  lt   510    Server Errors                                 log Warn String Format  The remote server has thrown an internal error  Url is not valid   0    url                    Debug WriteLine String Format  The remote server has thrown an internal error  Url is not valid   0    url                    return false                                    catch  WebException ex                if  ex Status    WebExceptionStatus ProtocolError    400 errors                       return false                    else                       log Warn String Format  Unhandled status   0   returned for url   1    ex Status  url   ex                       catch  Exception ex                log Error String Format  Could not test url  0     url   ex             return false

User · Answer

If I understand your question correctly  you could use a small method like this to give you the results of your URL test   WebRequest webRequest   WebRequest Create url     WebResponse webResponse  try      webResponse   webRequest GetResponse      catch   If exception thrown then couldn t get response from address     return 0     return 1    You could wrap the above code in a method and use it to perform validation  I hope this answers the question you were asking

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Try this  Make sure you use System Net    public bool checkWebsite string URL       try         WebClient wc   new WebClient          string HTMLSource   wc DownloadString URL         return true          catch  Exception          return false           When the checkWebsite   function gets called  it tries to get the source code of the URL passed into it  If it gets the source code  it returns true  If not  it returns false   Code Example     The checkWebsite command will return true  bool websiteExists   this checkWebsite  https   www google com       The checkWebsite command will return false  bool websiteExists   this checkWebsite  https   www thisisnotarealwebsite com fakepage html

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Here is another implementation of this solution   using System Net           Checks the file exists or not          The URL of the remote file      True   If the file exits  False if file not exists private bool RemoteFileExists string url        try                 Creating the HttpWebRequest         HttpWebRequest request   WebRequest Create url  as HttpWebRequest            Setting the Request method HEAD  you can also use GET too          request Method    HEAD             Getting the Web Response          HttpWebResponse response   request GetResponse   as HttpWebResponse            Returns TRUE if the Status code    200         response Close            return  response StatusCode    HttpStatusCode OK             catch                 Any exception will returns false          return false            From  http   www dotnetthoughts net 2009 10 14 how-to-check-remote-file-exists-using-c

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i have a more simple way to determine weather a url is valid   if  Uri IsWellFormedUriString uriString  UriKind RelativeOrAbsolute

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Following on from the examples already given  I d say  it s best practice to also wrap the response in a using like this      public bool IsValidUrl string url                 try                         var request   WebRequest Create url                request Timeout   5000               request Method    HEAD                 using  var response    HttpWebResponse request GetResponse                                   response Close                    return response StatusCode    HttpStatusCode OK                                  catch  Exception exception                         return false

[c#] C# How can I check if a URL exists/is valid?

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