Difference in encoded and decoded string

Question

I used a zlib compression to return a string.

void StatsClientImpl::sendToServer(std::stringstream &sstr) // to include an update interval version
{
    std::string error_msg = "";
    std::stringstream temp(AppState::getPid() + "," + AppState::getInstallOS());
    temp << sstr.str();
    std::string s = zlib_compress(temp.str());
.......

zlib_compress was as defined in : https://panthema.net/2007/0328-ZLibString.html

Then I did : std::cout << s.size() <<"\n";

The size of the string was shown to be 18.

Then I did:

CURL *handle = curl_easy_init();
char* o = curl_easy_escape(handle, s.data(), s.size());
        std::string bin(o);
        std::cout << o <<"\n";
        char* i= curl_easy_unescape(handle, bin.data(), bin.size(), NULL);
        std::string in(i);
        std::cout << i << in.size() <<"\n";

This gave me the following output:

x%DA%D3%D1%81%80%E2%92%D2%B44%1D%03%00%1BW%03%E5
x??с??Ҵ413
x%DA%D3%D1%81%80%E2%92%D2%B44%1D%03

I was passing this as the input string:

,,,,,,stuff,0

Why is there a difference in the decoded and encoded strings? How do I fix this?

Matteo Italia · Accepted Answer · 2015-07-03 23:23:18Z

1

    std::string in(i);

The problem lies here; this std::string constructor expects a null-terminated string, so it truncates the data to the first 0 byte it finds (which is found early in the gzip output). You want to ask to curl_easy_unescape how long is the unescaped data and construct in accordingly:

    int sz=0;
    char* i= curl_easy_unescape(handle, bin.data(), bin.size(), &sz);
    std::string in(i, i+sz);

But I have a question.Why doesn't this happen in bin(o) ?

Because o points to an URL-encoded string, which doesn't include null bytes besides the terminator.

edited Jul 3, 2015 at 23:23

answered Jul 3, 2015 at 15:48

Matteo Italia

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5 Comments

V Shreyas Over a year ago

Saviour! :) I just need to run some tests on my server side then I'll accept your answer!

V Shreyas Over a year ago

But I have a question.Why doesn't this happen in bin(o) ?

V Shreyas Over a year ago

Also, If I try to decode this string in javascript, what function should i use?

V Shreyas Over a year ago

when I try to use unescape in javascript, and then use zlib inflate, it doesn't work

Matteo Italia Over a year ago

@VShreyas: added reply to the first question in answer body; for the other problems, that's material for another question (I don't know much about JavaScript).

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