I do not know if you can control this directly in libcurl. But even if you cannot, not all hope is lost. Your code can hijack curl_easy_escape to get the behavior you want. This is a hack, but you could use it as a last resort, I guess.
The here is a simple example that highjacks the double sin(double) function from the math library. First the main file which uses sin:
sin_test.c:
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char ** argv)
{
double x = atof(argv[1]);
printf("sin(%f) = %f\n", x, sin(x));
return 0;
}
Compile this file: gcc -o sin_test sin_test.c -lm, and check that it works
./sin_test 1
sin(1.000000) = 0.841471
We will now take this as given, and try to override its behavior without changing its source code. To do this, we define a shared library sin_override.so as follows. Create the file sin_override.c with the contents:
#include <math.h>
#include <stdlib.h>
#define __USE_GNU
#include <dlfcn.h>
double sin(double x)
{
double (*real_sin)(double) = NULL;
if(!real_sin) real_sin = dlsym(RTLD_NEXT,"sin");
return real_sin(x)/10;
}
And compile it with `gcc -fPIC -shared -o sin_override.so sin_override.c -ldl. Now tell the system to load this shared library before the program itself:
LD_PRELOAD=/full/path/to/sin_override.so ./sin_test 1
sin(1.000000) = 0.084147
The answer is now 10 times smaller than before, confirming that we have overridden the default sin.
In your case, you would be overriding curl_easy_escape instead, by first calling the real curl_easy_escape, and then running through the resulting string, replacing %23 with #, and then returning the modified string. I haven't tested this for libcurl, but something like this should work, though it is a bit cumbersome.
