Showing posts from March, 2010

CodeSnip problems, problems, problems

Arrgh!I've been having a lot of problems with the CodeSnip program's database update code - it's been working for some and not for others. All this has happened since I converted the program to Unicode and compiled with Delphi 2010.I'm posting this for two reasons:To try to explain to long suffering users what has been going on with program lately - it's not usually this flaky.To forewarn anyone about to fall down the same hole as I have.The problem never raised its head on my system, but did on some that don't use the Windows-1252 code page. The problem was caused by a checksum failure, which in turn was caused by the downloaded data being converted to the wrong code page before the checksum got calculated: result - bang - bad checksum.My code relies on Indy components to translate downloaded content into text - and Indy and I make different assumptions about how this should be done. And I'm not sure either of us was correct, but they are a much more exper…

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URL Decoding revisited

Time to complete the set. So far in this series I have presented URIEncode, URIDecode and URIEncodeQueryString. So here's the missing piece of the jigsaw: URIDecodeQueryString. This routine decodes a query string that has been "query-string-encoded".If you look at URL Encoding revisited you'll see that a query string is encoded with normal URI encoding, except that space characters are encoded using '+' characters instead of '%20'.So, to decode a query string we first need to replace literal '+' characters with spaces. Because the string is still URI encoded we should replace ocurrences of '+' with '%20', not the actual space character. Once this is done we are left with a standard URI encoded string which we decode as normal. Here's the code:functionURIDecodeQueryString(constStr:string):string;beginResult:=URIDecode(ReplaceStr(Str,'+','%20'));end; The URIDecode routine was presented in my URL Decoding post.U…

URL Decoding

To complement the code of my URL Encoding post, I've now developed a URIDecode routine.It attempts to decode URIs that were percent-encoded according to RFC 3986. It also allows for some malformed percent-encoded URIs, i.e. those that contain characters outside the RFC's "unreserved" character set.Here's the code. An explanation follows.functionURIDecode(constStr:string):string;// Counts number of '%' characters in a UTF8 stringfunctionCountPercent(constS:UTF8String):Integer;varIdx:Integer;// loops thru all octets of SbeginResult:=0;forIdx:=1toLength(S)doifS[Idx]=cPercentthenInc(Result);end;varSrcUTF8:UTF8String;// input string as UTF-8SrcIdx:Integer;// index into source UTF-8 stringResUTF8:UTF8String;// output string as UTF-8ResIdx:Integer;// index into result UTF-8 stringHex:string;// hex component of % encodingChValue:Integer;// character ordinal value from a % encodingbegin// Convert input string to UTF-8SrcUTF8:=UTF8Encode(Str);// Size the decoded UT…

URL Encoding revisited

In my previous post I covered URI encoding part of a URI or URL. What I didn't cover was the almost trivial case of encoding a query string. The only difference is that spaces in a query string are converted to reserved '+' characters that are not then percent encoded.The only complication arises when the query string to be encoded already contains '+' symbols. They must be percent-encoded so they are not confused with the symbols that are used to replace spaces.In the original version of this post I completely misunderstood this and presented code that percent-encoded both literal and space-replacement '+' symbols.Unfortunately percent-encoding at this stage also encodes spaces as %20. We fix this by simply replacing each occurence of %20 with a '+' symbol. Here's the code: it's a very simple function that encodes a query string value passed as a UTF-8 string parameter:functionURIEncodeQueryString(constS:UTF8String):string;beginResult:=Rep…

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