get_header_value should not compile with unknown types

[kiwixz]

Currently an empty function gets called but doesn't return a value so at best it segfaults. See here.

One solution in recent standards would be to have some kind of static_assert; but in C++11 I don't know... Maybe to not define it so we get a linker error ?

[yhirose]

@kiwixz this is for making sure that only `detail::get_header_value<uint64_t> is allowed in httplib.h. This function is only for internal use anyway. So you don't have to worry about. :)

[kiwixz]

I linked the underlying function, but it happened to me when calling the public one here.

[yhirose]

You can see the calling example of the public method of Response object:

cpp-httplib/test/test.cc

Line 1019 in 67f6ff7

EXPECT_EQ(18527U, res->get_header_value<uint64_t>("Content-Length"));

As I mentioned for the internal one, this public method also allows only uint64_t type. If we put a different type, the code won't be compiled. Hope it helps.

[kiwixz]

Thanks for looking into it!

I opened this issue because unfortunately the code does actually compile with other types, and then lead to segfaults. (godbolt)

#include <cassert>
#include <httplib.h>

int main() {
    httplib::Client client{"example.com"};
    httplib::Result res = client.Get("/");
    assert(res);
    res->get_header_value<int>("some_header");
}

I'm including httplib as a system header, so I didn't even get the helpful warning in my project!

[yhirose]

@kiwixz thanks for the information. I'll take a look at it when I have time. Thanks!

[yhirose]

@kiwixz, I removed the template functions and added get_header_value_u64 instead. So there is now no ambiguity.