Request for improvements: URL decoder

Saturday, September 24. 2005

Request for improvements: URL decoder

As the observing readers of my weblog already I know, I'm working on an HTTP stack as part of a high-performance Ruby servlet container that I want to implement. This weekend, I finished the work on the HTTP stack, and the tests so far look good, so everything seems quite stable. That means: refactoring. Currently, there's only one piece of code that doesn't look to good in my eyes, as it is to "un-C++-ish", but as I'm not a regular user of the C++ language and especially its standard library, and have no good ideas how.

That piece of code is an URL decoder, and looks like the following:

static inline int h2c(char hi, char lo) {
std::string s;
int value = util::PARSE_FAILED;
s += hi;
s += lo;
std::istringstream is(s);
is >> std::hex >> value;
return value;
}
std::string util::url_decode(const std::string& s) {
std::string result;
std::istringstream iss(s);
char c;
for (iss >> c;!iss.eof();iss >> c) {
if ('+' == c) {
result += ' ';
} else if ('%' == c) {
char c1 = 0, c2 = 0;
iss >> c1;
iss >> c2;
if (!iss.eof()) {
int r = h2c(c1,c2);
if (r != PARSE_FAILED) {
result += static_cast<char>(r);
}
}
} else {
result += c;
}
}
return result;
}

Any recommendations?

Posted by admin at 19:16 | Comments (3) | Trackbacks (0)

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I don't have std::string's concatenation operator implementation at hand right now, but appending character by character might trigger N re-allocations on the string's internal buffer. Consider resizing the target string to an appropriate size first.

#1 Arno (Homepage) on 2005-09-25 21:53 (Reply)

Some suggestions:
- I would use the iterators of std::string instead of the stringstream to iterate over the chars of the string.
- Take a look at the replace member functions of std::string and from #include <algorithm>
- There must be a better way than h2c to get the char from two hex digits, you could try to read them directly from the substring: stringstream(str.substring(...)) >> intValue (don't know if that really works)

Hope that helps,
Cheers,
David.

#2 struppi (Homepage) on 2005-09-26 21:02 (Reply)

Grusel, das sieht ja furchtbar ineffizient aus. Über C++ Strings mußt du wissen, daß sie zumindest bei gcc nicht etwa ein Vector von char ist, sondern ein AVL-Baum aus Teilstring-Klassen. Um C++-Strings einen weiten Bogen machen!

Wenn du wirklich bloß nen URL-Decoder suchst, nimm halt den aus libowfat/textcode

#3 Fefe on 2005-09-27 12:34 (Reply)

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