Use CURL library for the network test instead of external tools.

[SunBlack]

We are currently still using a relatively old version of PROJ and are about to upgrade. We are using a Dockerfile for our project that is still based on Ubuntu 22.04, so CURL is not preinstalled, which is why I installed libcurl4-openssl-dev. However, when building I get the message:

Cannot establish if network is available - 'curl' or 'ping' not found

This is technically correct, as libcurl4-openssl-dev does not install curl itself. However, I think it would make more sense to test the ping with libcurl4-openssl-dev itself. You could do it via try_compile + execute_progress:

Since I have thus far not worked with the CURL API, I used AI to generate an example that shows the direction in which I was thinking.

# Make sure we have the helper module for checking C++ source compilation
include(CheckCXXSourceCompiles)

# 1. Write a temporary C++ source file that attempts to ping Google using libcurl
set(TEST_SOURCE "${CMAKE_BINARY_DIR}/curl_test.cpp")
file(WRITE ${TEST_SOURCE} "
#include <curl/curl.h>
#include <iostream>
int main() {
    CURL* curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, \"https://www.google.com\");
        curl_easy_setopt(curl, CURLOPT_NOBODY, 1L); // Request headers only
        CURLcode res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
        return res == CURLE_OK ? 0 : 1;
    }
    return 1;
}
")

# 2. Compile the test program with libcurl
try_compile(CURL_TEST_OK
    ${CMAKE_BINARY_DIR}/curl_test_build
    ${TEST_SOURCE}
    LINK_LIBRARIES curl
)

if(CURL_TEST_OK)
    message(STATUS "Compilation successful.")

    # 3. Attempt to execute the compiled test binary
    execute_process(
        COMMAND ${CMAKE_BINARY_DIR}/curl_test_build/cmTC_*/cmTC_*
        RESULT_VARIABLE EXITCODE
        OUTPUT_VARIABLE STDOUT
        ERROR_VARIABLE STDERR
        OUTPUT_STRIP_TRAILING_WHITESPACE
        ERROR_STRIP_TRAILING_WHITESPACE
    )

    if(EXITCODE EQUAL 0)
        message(STATUS "Google is reachable (libcurl appears to work).")
    else()
        message(WARNING "Ping failed. libcurl compiled, but could not reach Google.\n${STDERR}")
    endif()
else()
    message(WARNING "Compilation failed. libcurl may be missing or misconfigured.")
endif

I think a change to this would be good, as it would make it easier to recognize whether there are really network issues (for proj) or not when building.

[rouault]

That looks a bit like a complication... You may just want to build PROJ with -DBUILD_TESTING=OFF

[SunBlack]

Indeed, I've already noticed that too. However, I currently find the message unfortunate, as you can't directly see that it is being executed when building the tests and is actually only of limited impact. That this is part of the test in particular is not easy to see by the fact that the message appears before the search for GTest:

#13 36.70 -- BUILD_SHARED_LIBS              = ON
#13 36.70 -- PROJ_LIBRARIES                 = proj
#13 36.71 -- Checking if network is available
#13 36.71 -- Checking if network is available - no; skipping network-dependent tests.
#13 36.71 CMake Warning at test/CMakeLists.txt:39 (message):
#13 36.71   Cannot establish if network is available - 'curl' or 'ping' not found
#13 36.71 
#13 36.71 
#13 36.81 -- Looking for GTest
#13 36.82 -- Looking for GTest - not found
#13 36.82 CMake Warning at test/unit/CMakeLists.txt:94 (message):
#13 36.82   Tests that require GTest will be skipped; install GTest dependency

I think it would also okay to improve the message:

Cannot establish if network is available - 'curl' or 'ping' not found. The network functionality may still work because the CURL library was found. This check is part of the testing and can be deactivated with the CMake option BUILD_TESTING.

I don't have it in my head right now, but if the CURL library is only optional, the current message may also be wrong, because at least at first glance the test only seems to test for curl or ping, but not whether the library is missing and in that case to say: I don't care if CURL or ping are installed, it won't work at runtime anyway.

BTW: I think this should be also not CMake warning, but a CMake status message (I think the stack trace of CMake is not necessary)

[mwtoews]

The network detection tests uses curl or ping commands here.

For Ubuntu, these can be installed with either curl or iputils-ping packages. (The curl library package does not have the curl command.)

These tests/messages can be switched off with either -DBUILD_TESTING=OFF or -DTESTING_USE_NETWORK=OFF.

[SunBlack]

the fact that the message is currently somewhat misleading:

• It appears before the message about searching for GTest => you don't immediately think that cURL is only needed for the tests
• If you pass the curl library, the message still appears because the executable is used here. It's easy to overlook the difference. Therefore, it would be helpful if the message clarified in some way that the library is not being used here.

Based on this, the two suggestions above were:

• More detailed message
• Optionally use the library instead of the executable (even if it means more effort) – but the improved message alone would suffice.