Convert file path to a file URI

Question

Does the  NET Framework have any methods for converting a path  e g   C  whatever txt   into a file URI  e g   file    C  whatever txt     The System Uri class has the reverse  from a file URI to absolute path   but nothing as far as I can find for converting to a file URI   Also  this is not an ASP NET application

User · Answer

What no-one seems to realize is that none of the System.Uri constructors correctly handles certain paths with percent signs in them.

new Uri(@"C:\%51.txt").AbsoluteUri;

This gives you "file:///C:/Q.txt" instead of "file:///C:/%2551.txt".

Neither values of the deprecated dontEscape argument makes any difference, and specifying the UriKind gives the same result too. Trying with the UriBuilder doesn't help either:

new UriBuilder() { Scheme = Uri.UriSchemeFile, Host = "", Path = @"C:\%51.txt" }.Uri.AbsoluteUri

This returns "file:///C:/Q.txt" as well.

As far as I can tell the framework is actually lacking any way of doing this correctly.

We can try to it by replacing the backslashes with forward slashes and feed the path to Uri.EscapeUriString - i.e.

new Uri(Uri.EscapeUriString(filePath.Replace(Path.DirectorySeparatorChar, '/'))).AbsoluteUri

This seems to work at first, but if you give it the path C:\a b.txt then you end up with file:///C:/a%2520b.txt instead of file:///C:/a%20b.txt - somehow it decides that some sequences should be decoded but not others. Now we could just prefix with "file:///" ourselves, however this fails to take UNC paths like \\remote\share\foo.txt into account - what seems to be generally accepted on Windows is to turn them into pseudo-urls of the form file://remote/share/foo.txt, so we should take that into account as well.

EscapeUriString also has the problem that it does not escape the '#' character. It would seem at this point that we have no other choice but making our own method from scratch. So this is what I suggest:

public static string FilePathToFileUrl(string filePath)
{
  StringBuilder uri = new StringBuilder();
  foreach (char v in filePath)
  {
    if ((v >= 'a' && v <= 'z') || (v >= 'A' && v <= 'Z') || (v >= '0' && v <= '9') ||
      v == '+' || v == '/' || v == ':' || v == '.' || v == '-' || v == '_' || v == '~' ||
      v > '\xFF')
    {
      uri.Append(v);
    }
    else if (v == Path.DirectorySeparatorChar || v == Path.AltDirectorySeparatorChar)
    {
      uri.Append('/');
    }
    else
    {
      uri.Append(String.Format("%{0:X2}", (int)v));
    }
  }
  if (uri.Length >= 2 && uri[0] == '/' && uri[1] == '/') // UNC path
    uri.Insert(0, "file:");
  else
    uri.Insert(0, "file:///");
  return uri.ToString();
}

This intentionally leaves + and : unencoded as that seems to be how it's usually done on Windows. It also only encodes latin1 as Internet Explorer can't understand unicode characters in file urls if they are encoded.

User · Answer

The System Uri constructor has the ability to parse full file paths and turn them into URI style paths   So you can just do the following   var uri   new System Uri  c   foo    var converted   uri AbsoluteUri

User · Answer

The solutions above do not work on Linux   Using  NET Core  attempting to execute new Uri   home foo README md   results in an exception   Unhandled Exception  System UriFormatException  Invalid URI  The format of the URI could not be determined     at System Uri CreateThis String uri  Boolean dontEscape  UriKind uriKind     at System Uri  ctor String uriString           You need to give the CLR some hints about what sort of URL you have   This works   Uri fileUri   new Uri new Uri  file        home foo README md         and the string returned by fileUri ToString   is  file    home foo README md   This works on Windows  too     new Uri new Uri  file         C  Users foo README md   ToString        emits  file    C  Users foo README md

User · Answer

The workaround is simple  Just use the Uri   ToString   method and percent-encode white-spaces  if any  afterwards   string path   new Uri  C  my example  txt   ToString   Replace        20      properly returns file    C  my 20example  txt

User · Answer

VB NET   Dim URI As New Uri  D  Development  AppFolder Att 1 gif     Different outputs    URI AbsolutePath   - gt   D  Development  AppFolder Att 1 gif   URI AbsoluteUri    - gt   file    D  Development  AppFolder Att 1 gif   URI OriginalString - gt   D  Development  AppFolder Att 1 gif   URI ToString       - gt   file    D  Development  AppFolder Att 1 gif   URI LocalPath      - gt   D  Development  AppFolder Att 1 gif   One liner   New Uri  D  Development  AppFolder Att 1 gif   AbsoluteUri      Output  file    D  Development  AppFolder Att 1 gif

User · Answer

UrlCreateFromPath to the rescue  Well  not entirely  as it doesn t support extended and UNC path formats  but that s not so hard to overcome   public static Uri FileUrlFromPath string path        const string prefix              const string extended                const string extendedUnc         UNC        const string device                const StringComparison comp   StringComparison Ordinal       if path StartsWith extendedUnc  comp                 path   prefix path Substring extendedUnc Length        else if path StartsWith extended  comp                 path   prefix path Substring extended Length        else if path StartsWith device  comp                 path   prefix path Substring device Length              int len   1      var buffer   new StringBuilder len       int result   UrlCreateFromPath path  buffer  ref len  0       if len    1  Marshal ThrowExceptionForHR result        buffer EnsureCapacity len       result   UrlCreateFromPath path  buffer  ref len  0       if result    1  throw new ArgumentException  Argument is not a valid path     path        Marshal ThrowExceptionForHR result       return new Uri buffer ToString         DllImport  shlwapi dll   CharSet CharSet Auto  SetLastError true   static extern int UrlCreateFromPath string path  StringBuilder url  ref int urlLength  int reserved     In case the path starts with with a special prefix  it gets removed  Although the documentation doesn t mention it  the function outputs the length of the URL even if the buffer is smaller  so I first obtain the length and then allocate the buffer   Some very interesting observation I had is that while    device path  is correctly transformed to  file   device path   specifically    localhost path  is transformed to just  file    path    The WinApi function managed to encode special characters  but leaves Unicode-specific characters unencoded  unlike the Uri construtor  In that case  AbsoluteUri contains the properly encoded URL  while OriginalString can be used to retain the Unicode characters

User · Answer

At least in  NET 4 5  you can also do   var uri   new System Uri  C   foo   UriKind Absolute

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