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<a href="https://gitlab.com/nmav">Nikos Mavrogiannopoulos</a>
commented on a discussion
on <a href="https://gitlab.com/gnutls/gnutls/merge_requests/650#note_120070133">lib/auth/cert.c</a>:
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<pre style="margin: 0;">+<span id="LC643" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">int</span> <span class="n" style="color: #333;">ret</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC644" class="line" lang="c"> <span class="n" style="color: #333;">gnutls_pcert_st</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">apr_cert_list</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC645" class="line" lang="c"> <span class="n" style="color: #333;">gnutls_privkey_t</span> <span class="n" style="color: #333;">apr_pkey</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC646" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">int</span> <span class="n" style="color: #333;">apr_cert_list_length</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC647" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC648" class="line" lang="c"> <span class="c1" style="color: #998; font-style: italic;">// Retrieve the appropriate certificate</span></span>
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<pre style="margin: 0;">+<span id="LC649" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span><span class="p">((</span><span class="n" style="color: #333;">ret</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">_gnutls_get_selected_cert</span><span class="p">(</span><span class="n" style="color: #333;">session</span><span class="p">,</span> <span class="o" style="font-weight: 600;">&</span><span class="n" style="color: #333;">apr_cert_list</span><span class="p">,</span></span>
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650
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<pre style="margin: 0;">+<span id="LC650" class="line" lang="c"> <span class="o" style="font-weight: 600;">&</span><span class="n" style="color: #333;">apr_cert_list_length</span><span class="p">,</span> <span class="o" style="font-weight: 600;">&</span><span class="n" style="color: #333;">apr_pkey</span><span class="p">))</span> <span class="o" style="font-weight: 600;"><</span> <span class="mi" style="color: #099;">0</span><span class="p">)</span> <span class="p">{</span></span>
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<pre style="margin: 0;">+<span id="LC651" class="line" lang="c"> <span class="k" style="font-weight: 600;">return</span> <span class="n" style="color: #333;">gnutls_assert_val</span><span class="p">(</span><span class="n" style="color: #333;">ret</span><span class="p">);</span></span>
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<pre style="margin: 0;">+<span id="LC652" class="line" lang="c"> <span class="p">}</span></span>
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<pre style="margin: 0;">+<span id="LC653" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC654" class="line" lang="c"> <span class="cm" style="color: #998; font-style: italic;">/* Since we are transmitting a raw public key with no additional</span></span>
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<pre style="margin: 0;">+<span id="LC655" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * certificate credentials attached to it, it doesn't make sense to</span></span>
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<pre style="margin: 0;">+<span id="LC656" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * have more than one certificate set (i.e. to have a certificate chain).</span></span>
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<pre style="margin: 0;">+<span id="LC657" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> */</span></span>
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<pre style="margin: 0;">+<span id="LC658" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">apr_cert_list_length</span> <span class="o" style="font-weight: 600;">==</span> <span class="mi" style="color: #099;">1</span><span class="p">)</span> <span class="p">{</span></span>
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<blockquote dir="auto" style="color: #7f8fa4; border-left-width: 3px; border-left-color: #eaeaea; border-left-style: solid; margin: 0; padding: 0 0 0 15px;">
<p>Isn't that a matter of coding style? I'm used to check for the condition that I need and then act on that. All other scenario's are then falsy. I find it a good approach, especially within the field of security. What's the advantage of checking the inverse condition and directly returning an error? Just to get rid of the else-statement and one level of indentiation?</p>
</blockquote>
<p dir="auto">It is indeed, and it is best to be consistent through the code. Nevertheless we have discussed that in the past, but let me try to demonstrate with an extreme example why eliminating illegal values early makes for more readable code. The first checks for invalid values before and returns early while the other checks for invalid</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true" style="background-color: #fff; font-family: monospace; font-size: 90%; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0;"><code><span id="LC1" class="line" lang="plaintext">if (vara == 0 || varb == 1 || varc == 2)</span>
<span id="LC2" class="line" lang="plaintext"> return -1; /* our error condition */</span>
<span id="LC3" class="line" lang="plaintext"></span>
<span id="LC4" class="line" lang="plaintext">/* normal code flow */</span>
<span id="LC5" class="line" lang="plaintext">do_something();</span></code></pre>
<p dir="auto">The other approach, is checking within the code flow and does not worry about adding indentation for tests.</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true" style="background-color: #fff; font-family: monospace; font-size: 90%; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0;"><code><span id="LC1" class="line" lang="plaintext">if (vara == 0) {</span>
<span id="LC2" class="line" lang="plaintext"> return -1;</span>
<span id="LC3" class="line" lang="plaintext">} else {</span>
<span id="LC4" class="line" lang="plaintext"> if (varb == 1) {</span>
<span id="LC5" class="line" lang="plaintext"> return -1;</span>
<span id="LC6" class="line" lang="plaintext"> } else {</span>
<span id="LC7" class="line" lang="plaintext"> if (varc == 2)</span>
<span id="LC8" class="line" lang="plaintext"> return -1;</span>
<span id="LC9" class="line" lang="plaintext"> else</span>
<span id="LC10" class="line" lang="plaintext"> do_something();</span>
<span id="LC11" class="line" lang="plaintext"> }</span>
<span id="LC12" class="line" lang="plaintext">}</span></code></pre>
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