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<a href="https://gitlab.com/createyourpersonalaccount" style="color: #1068bf;">Nikolaos Chatzikonstantinou</a>
commented on a
<a href="https://gitlab.com/gnutls/gnutls/-/merge_requests/1622#note_1053063594" style="color: #1068bf;">discussion</a>:
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<p dir="auto" style="color: #303030; margin: 0 0 16px;" align="initial">I can come up with two solutions, but first let me summarize the current situation:</p>
<p dir="auto" style="color: #303030; margin: 0 0 16px;" align="initial">In the first commit, I included <code style='font-size: 90%; color: #1f1f1f; word-wrap: break-word; background-color: #f0f0f0; border-radius: 4px; margin-top: 0; font-weight: inherit; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'><config.h></code> in the header. This is wrong. In the second commit, I removed <code style='font-size: 90%; color: #1f1f1f; word-wrap: break-word; background-color: #f0f0f0; border-radius: 4px; font-weight: inherit; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'><config.h></code> from the header, and placed it in the <code style='font-size: 90%; color: #1f1f1f; word-wrap: break-word; background-color: #f0f0f0; border-radius: 4px; font-weight: inherit; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'>gnutlsx.cpp</code> file instead. But now the header has no support for extra features configured during the build process, even if the C library supports them.</p>
<p dir="auto" style="color: #303030; margin: 0 0 16px;" align="initial">The two solutions: One is a generated header that includes only the definitions of enabled features, that is included by <code style='font-size: 90%; color: #1f1f1f; word-wrap: break-word; background-color: #f0f0f0; border-radius: 4px; margin-top: 0; font-weight: inherit; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'><gnutlsxx.h></code>. This again ties the header to the C library, since a differently-built C library (say, less features) may be missing symbols. The other option is to add functions in the C++ header-only library, such as:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" lang="plaintext" data-canonical-lang="" v-pre="true" style='display: block; font-size: 13px; color: #303030; line-height: 1.6em; overflow-x: auto; border-radius: 2px; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: #fafafa; margin: 0 0 16px; padding: 12px; border: 1px solid #dbdbdb;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: 4px; white-space: pre; margin-top: 0; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">bool have_X_feature(void) {</span>
<span id="LC2" class="line" lang="plaintext">#ifdef GNUTLS_X_FEATURE</span>
<span id="LC3" class="line" lang="plaintext"> return true;</span>
<span id="LC4" class="line" lang="plaintext">#else</span>
<span id="LC5" class="line" lang="plaintext"> return false;</span>
<span id="LC6" class="line" lang="plaintext">#endif</span>
<span id="LC7" class="line" lang="plaintext">}</span></code></pre>
<copy-code></copy-code>
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<p dir="auto" style="color: #303030; margin: 0 0 16px;" align="initial">The user would check that <code style='font-size: 90%; color: #1f1f1f; word-wrap: break-word; background-color: #f0f0f0; border-radius: 4px; margin-top: 0; font-weight: inherit; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'>have_X_feature()</code> is true before using said feature. Note that <code style='font-size: 90%; color: #1f1f1f; word-wrap: break-word; background-color: #f0f0f0; border-radius: 4px; font-weight: inherit; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'>have_X_feature()</code> is a function in the C library. This decouples the C++ header from the C library and allows the user to have a choice of which C library to link to, using the same C++ header.</p>
<p dir="auto" style="color: #303030; margin: 0;" align="initial">Yet another behavior of the C++ wrapper would be to throw an exception if the feature is missing in an invoked function. Again the underlying C library function as above would be required. I'm leaning towards providing a C function that lets the user know at runtime whether a feature was enabled or disabled, but I wanted to ask for your opinion.</p>
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