Linker errors with current versions of libwebsockets

[timonsku]

Getting a lot of reference errors during linking. f.e.: server.c:10: undefined reference to 'lws_serve_http_file' server.c:33: undefined reference to 'lws_callback_on_writable_all_protocol'

[iamscottmoyers]

Hello! I just tried it out using the latest from the warmcat/libwebsockets project and it links fine for me. The functions you mentioned do exist in the latest libwebsockets library. The only difference I noticed was that lws_client_connect is now marked as deprecated so I've replaced it with lws_client_connect_via_info.

Try running pkg-config libwebsockets --libs --cflags and see what you get. I get -I/usr/local/include -L/usr/local/lib -lwebsockets. Maybe pkg-config isn't pointing to your libwebsockets install?

The Makefile is pretty simple, if you've installed libwebsockets somewhere pkg-config doesn't know about you can compile the client / server with: gcc -I/usr/local/include -L/usr/local/lib -lwebsockets client.c -o client gcc -I/usr/local/include -L/usr/local/lib -lwebsockets server.c -o server ...replacing the /usr/local paths with your libwebsockets install paths.

[timonsku]

Weird, I also tried the latest git version as well as 2.3 stable, same issue on two different platforms. pkgconfig resolves to these same paths for me. Maybe I need libwebsockets compiled with specific flags? It does seem to find it, I also got the deprecation message for lws_client_connect. It seems there is an issue with library binary itself.

[iamscottmoyers]

If it's compiling but not linking then yeah it sounds like your headers are installed ok but the library binary isn't. My libwebsockets build has ssl disabled, but I doubt that's the problem. I'm build on a mac, the commands I ran to install libwebsockets were: git clone https://github.com/warmcat/libwebsockets.git cd libwebsockets mkdir build cd build cmake -DLWS_WITH_SSL=0 .. make sudo make install

I guess you can check the library has been updated by looking at the timestamp of /usr/local/lib/libwebsockets.a. Also nm /usr/local/lib/libwebsockets.a | grep lws_serve_http_file should output something only if the symbol exists in the library.

[timonsku]

Right, I totally forgot about nm. That does output the symbol. My build procedure was exactly the same. I tried again without SSL but same outcome if I run gcc -I/usr/local/include -L/usr/local/lib -lwebsockets client.c -o client

Output: `` /tmp/ccCR0TMo.o: In functioncallback_example': client.c:(.text+0x5c): undefined reference to lws_callback_on_writable' client.c:(.text+0xa8): undefined reference tolws_write' /tmp/ccCR0TMo.o: In function main': client.c:(.text+0x154): undefined reference tolws_create_context' client.c:(.text+0x210): undefined reference to lws_canonical_hostname' client.c:(.text+0x238): undefined reference tolws_client_connect_via_info' client.c:(.text+0x268): undefined reference to lws_callback_on_writable' client.c:(.text+0x27c): undefined reference tolws_service' collect2: error: ld returned 1 exit status

[timonsku]

Ugh ok this seems to be a difference in Linux and MacOS. Reading this https://stackoverflow.com/questions/11112318/linked-cannot-find-symbols-but-libraries-are-read-and-symbols-exist I tried gcc -o client client.c -I/usr/local/include -L/usr/local/lib -lwebsockets and compiled without any issues, seems to be a Linux thing. Maybe you could try if that works as well on Mac? Might be worthwhile to update the make file if that works on both platforms.

[iamscottmoyers]

I just tried it in my Linux VM and I can reproduce the same problem as you. Your fix works on Mac and Linux. I'll update the Makefile! Thanks for debugging it! I've never run into that GCC quirk before.

[timonsku]

Great! Also thanks for these examples, they help a lot.