URL Encoding

I've being reviewing the URI encoding code from the Code Snippets Database and I realised that it doesn't comply with RFC 3986.

So here's my first attempt at some compliant code.

According to the RFC:

"the data should first be encoded as octets according to the UTF-8 character encoding [STD63]; then only those octets that do not correspond to characters in the unreserved set should be percent-encoded."

So, we define the URIEncode function to operate on the UTF8String type. It's easy to encode UnicodeString and AnsiString into UTF using the System unit's UTF8Encode overloaded functions. You can overload URIEncode to do the UTF8 conversion, but I haven't done here.

There's a nice shortcut we can take when url encoding. Remember only unreserved characters are percent-encoded. The set of unreserved characters is:

const
  cURLUnreservedChars = [
    'A'..'Z', 'a'..'z', '0'..'9', '-', '_', '.', '~'
  ];

All other characters are percent encoded. But what about any UTF-8 continuation bytes? Well, by definition these have value > $80. And all the unreserved characters have ordinal value < $80. This means that no legal continuation character can be an unreserved character.

Therefore any byte in the UTF-8 string can be treated the same regardless of whether it's a lead or continuation character: i.e. we percent encode it if it's not an unreserved character.

Here's the function:

// Assumes Defined(UNICODE)
function URIEncode(const S: UTF8String): string; overload;
var
  Ch: AnsiChar;
begin
  // Just scan the string an octet at a time looking for chars to encode
  Result := '';
  for Ch in S do
    if CharInSet(Ch,  cURLUnreservedChars) then
      Result := Result + WideChar(Ch)
    else
      Result := Result + '%' + IntToHex(Ord(Ch), 2);
end;

This, and more similar routines, are available (and may even be evolving) in my Delphi Doodlings repo. View the code (see UURIEncode.pas).

Source code highlighting by DelphiDabbler PasHi.

Comments

Post a Comment

Comments are very welcome, but please don't comment here if:

1) You have a query about, or a bug report for, one of my programs or libraries. Most of my posts contain a link to the relevant repository where there will be an issue tracker you can use.

2) You have a query about any 3rd party programs I feature, please address them to the developer(s) - there will be a link in the post.

3) You're one of the tiny, tiny minority who are aggressive or abusive - in the bin you go and reported you will be!

Thanks

Popular posts from this blog

Deleting elements from a dynamic array

In my blog " Initialising Dynamic Arrays " I mentioned I have been writing some unit tests that needed numerous repetative array initialisation operations. Well, one of the other common operations I found myself writing was the deletion of items from dynamic arrays. So I decided to find a generic way of doing this. Assuming we know the index of the item to be deleted we need the equivalent of Delphi's built-in Delete procedure for strings. If you read the previous post you won't be surprised to learn that I decided to further extend the Generics.Collections.TArray class by adding to the TArrayEx class I introduced there. My first attempt emulates Delphi's Delete procedure by deleting the array element in-place: i.e. it updates the array passed as a parameter. Unsurprisingly the method is called DeleteInPlace . Here's how it goes: type TArrayEx = class ( TArray ) public .. . class procedure DeleteInPlace < T > ( var A :
Read more

Initialising dynamic arrays

When writing some unit tests a while ago I found myself needing to initialise some dynamic arrays with test data. It would be nice if we could do something like this: var A : array of Integer ; begin A := ( 1 , 2 , 3 , 4 ) ; // !! WRONG end ; but we can't. So I decided to write some functions to initialise dynamic arrays to the contents of another array, be it a constant, a literal or another dynamic array. The result was a set of overloaded routines, one for each data type I needed to handle, for example for Integer and string arrays I had: function CloneArray ( const A : array of Integer ) : TIntegerDynArray ; overload ; var Idx : Integer ; begin SetLength ( Result , Length ( A ) ) ; for Idx := Low ( A ) to High ( A ) do Result [ Idx - Low ( A ) ] := A [ Idx ] ; end ; function CloneArray ( const A : array of string ) : TStringDynArray ; overload ; var Idx : Integer ; begin SetLength ( Result , Len
Read more

New String Property Editor Planned For RAD Studio 12 Yukon 🤞

Image
This blog post is based on a pre-release version of the RAD Studio software and it has been written with specific permission by Embarcadero. No feature is committed until the product GA release. It seems I'm getting very excited about multi-line strings of late. My previous post was about multi-line string literals for Delphi  and this time I'm talking about the new multi-line string property editor being slated for the RAD Studio 12 IDE. For more years than I care to remember, I've been frustrated by the inability to enter multi-line strings in the Delphi IDE object inspector. That meant having to resort to code to initialise some multi-line labels. So frustrated was I that I wrote a little property editor of my own ( stringpe ), way back in 2004. It's still around and on GitHub. Here's what it (sometimes) looks like: Yeah, I know this is Vista - I used an old screenshot Sometimes? Well it looked like that until it got installed on DPI aware Delphis, and then it sh
Read more