Question about the code

[YosefMac]

Hello! :)

I have this doubt about your code

In the file:line urldecode.c:15

  while(!d) {
    d = 1;
    int i; /* the counter for the string */

    for(i=0;i<strlen(dStr);++i) {
                           .
                           .
                           .

What is the purpose of have a nested loop ?
I thought that one is enough. Why perform another decode when you already did one ?
This is for achieve something of the standard rfc that I'm missing out ?

Thanks in advance!!!

[abejfehr]

Hey! This is a really good question.

I wrote this years ago so I had to look at my code again to see what I might have been thinking.

The code seems to be decoding the string until there's nothing left to decode, which could decode something that was doubly encoded. Try decoding the string %2524 for yourself and you'll see that the result is another percent-encoded string.

What I did here actually violates the spec, so that's too bad.

Implementations must not percent-encode or decode the same string more than once, as decoding an already decoded string might lead to misinterpreting a percent data octet as the beginning of a percent-encoding, or vice versa in the case of percent-encoding an already percent-encoded string.

I didn't actually know about that clause previously. I'll keep this issue open to represent the problem of continuously decoding strings. Feel free to submit a Pull Request that resolves this issue. Perhaps strings can be optionally decoded recursively?

I hope that helps!

[YosefMac]

Thanks for the clarification!! 😃

[bucanero]

Here's my simplified version, that:

• doesn't "doble decode" strings, following the spec
• doesn't use malloc (decodes over the same original string)
• returns 1 if it decoded some values (0 if nothing was decoded)

Note: since it's overwriting the original buffer, if you want to keep the original url you'll need to make a copy yourself

int urlDecode(char *dStr) {
	int i, j;
	char hex[] = "00"; /* for a hex code */

	for(i=0, j=0; dStr[i]; i++, j++)
	{
		if(dStr[i] != '%' || dStr[i+1] == 0)
		{
			dStr[j] = dStr[i];
			continue;
		}

		if(isxdigit(dStr[i+1]) && isxdigit(dStr[i+2]))
		{
			/* combine the next two numbers into one */
			hex[0] = dStr[i+1];
			hex[1] = dStr[i+2];

			/* convert it to decimal */
			dStr[j] = strtol(hex, NULL, 16);
			i += 2; /* move to the end of the hex */
		}
	}
	dStr[j] = 0; /* null terminate the string */

	return (i != j);
}