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jamescarlyle
2016-09-06 17:56:01 +01:00
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docs/build/html/tutorial-contract-clauses.html vendored
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@ -174,7 +174,7 @@
<h1>Writing a contract using clauses<a class="headerlink" href="#writing-a-contract-using-clauses" title="Permalink to this headline"></a></h1>
<p>This tutorial will take you through restructuring the commercial paper contract to use clauses. You should have
already completed &#8220;<a class="reference internal" href="tutorial-contract.html"><span class="doc">Writing a contract</span></a>&#8221;.</p>
<p>Clauses are essentially &#8220;mini-contracts&#8221; which contain verification logic, and are composed together to form
<p>Clauses are essentially micro-contracts which contain independent verification logic, and are composed together to form
a contract. With appropriate design, they can be made to be reusable, for example issuing contract state objects is
generally the same for all fungible contracts, so a single issuance clause can be shared. This cuts down on scope for
error, and improves consistency of behaviour.</p>
@ -197,20 +197,19 @@ In the case of commercial paper, we have a &#8220;Grouping&#8221; outermost clau
</div></blockquote>
<div class="section" id="commercial-paper-class">
<h2>Commercial paper class<a class="headerlink" href="#commercial-paper-class" title="Permalink to this headline"></a></h2>
<p>First we need to change the class from implementing <code class="docutils literal"><span class="pre">Contract</span></code>, to extend <code class="docutils literal"><span class="pre">ClauseVerifier</span></code>. This is an abstract
class which provides a verify() function for us, and requires we provide a property (<code class="docutils literal"><span class="pre">clauses</span></code>) for the clauses to test,
and a function (<code class="docutils literal"><span class="pre">extractCommands</span></code>) to extract the applicable commands from the transaction. This is important because
<code class="docutils literal"><span class="pre">ClauseVerifier</span></code> checks that no commands applicable to the contract are left unprocessed at the end. The following
examples are trimmed to the modified class definition and added elements, for brevity:</p>
<p>To use the clause verification logic, the contract needs to call the <code class="docutils literal"><span class="pre">verifyClauses()</span></code> function, passing in the transaction,
a list of clauses to verify, and a collection of commands the clauses are expected to handle all of. This list of
commands is important because <code class="docutils literal"><span class="pre">verifyClauses()</span></code> checks that none of the commands are left unprocessed at the end, and
raises an error if they are. The following examples are trimmed to the modified class definition and added elements, for
brevity:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">CommercialPaper</span> <span class="p">:</span> <span class="n">ClauseVerifier</span> <span class="p">{</span>
<span class="k">override</span> <span class="k">val</span> <span class="py">legalContractReference</span><span class="p">:</span> <span class="n">SecureHash</span> <span class="p">=</span> <span class="n">SecureHash</span><span class="p">.</span><span class="n">sha256</span><span class="p">(</span><span class="s">&quot;https://en.wikipedia.org/wiki/Commercial_paper&quot;</span><span class="p">);</span>
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">CommercialPaper</span> <span class="p">:</span> <span class="n">Contract</span> <span class="p">{</span>
<span class="k">override</span> <span class="k">val</span> <span class="py">legalContractReference</span><span class="p">:</span> <span class="n">SecureHash</span> <span class="p">=</span> <span class="n">SecureHash</span><span class="p">.</span><span class="n">sha256</span><span class="p">(</span><span class="s">&quot;https://en.wikipedia.org/wiki/Commercial_paper&quot;</span><span class="p">)</span>
<span class="k">override</span> <span class="k">val</span> <span class="py">clauses</span><span class="p">:</span> <span class="n">List</span><span class="p">&lt;</span><span class="n">SingleClause</span><span class="p">&gt;</span>
<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="k">throw</span> <span class="n">UnsupportedOperationException</span><span class="p">(</span><span class="s">&quot;not implemented&quot;</span><span class="p">)</span>
<span class="k">override</span> <span class="k">fun</span> <span class="nf">extractCommands</span><span class="p">(</span><span class="n">tx</span><span class="p">:</span> <span class="n">TransactionForContract</span><span class="p">):</span> <span class="n">List</span><span class="p">&lt;</span><span class="n">AuthenticatedObject</span><span class="p">&lt;</span><span class="n">CommandData</span><span class="p">&gt;&gt;</span>
<span class="k">private</span> <span class="k">fun</span> <span class="nf">extractCommands</span><span class="p">(</span><span class="n">tx</span><span class="p">:</span> <span class="n">TransactionForContract</span><span class="p">):</span> <span class="n">List</span><span class="p">&lt;</span><span class="n">AuthenticatedObject</span><span class="p">&lt;</span><span class="n">CommandData</span><span class="p">&gt;&gt;</span>
<span class="p">=</span> <span class="n">tx</span><span class="p">.</span><span class="n">commands</span><span class="p">.</span><span class="n">select</span><span class="p">&lt;</span><span class="n">Commands</span><span class="p">&gt;()</span>
<span class="k">override</span> <span class="k">fun</span> <span class="nf">verify</span><span class="p">(</span><span class="n">tx</span><span class="p">:</span> <span class="n">TransactionForContract</span><span class="p">)</span> <span class="p">=</span> <span class="n">verifyClauses</span><span class="p">(</span><span class="n">tx</span><span class="p">,</span> <span class="n">listOf</span><span class="p">(</span><span class="n">Clauses</span><span class="p">.</span><span class="n">Group</span><span class="p">()),</span> <span class="n">extractCommands</span><span class="p">(</span><span class="n">tx</span><span class="p">))</span>
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="kd">public</span> <span class="kd">class</span> <span class="nc">CommercialPaper</span> <span class="kd">implements</span> <span class="n">Contract</span> <span class="o">{</span>
@ -219,11 +218,6 @@ examples are trimmed to the modified class definition and added elements, for br
<span class="k">return</span> <span class="n">SecureHash</span><span class="o">.</span><span class="na">Companion</span><span class="o">.</span><span class="na">sha256</span><span class="o">(</span><span class="s">&quot;https://en.wikipedia.org/wiki/Commercial_paper&quot;</span><span class="o">);</span>
<span class="o">}</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">SingleClause</span><span class="o">&gt;</span> <span class="nf">getClauses</span><span class="o">()</span> <span class="o">{</span>
<span class="k">throw</span> <span class="n">UnsupportedOperationException</span><span class="o">(</span><span class="s">&quot;not implemented&quot;</span><span class="o">);</span>
<span class="o">}</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="n">Collection</span><span class="o">&lt;</span><span class="n">AuthenticatedObject</span><span class="o">&lt;</span><span class="n">CommandData</span><span class="o">&gt;&gt;</span> <span class="nf">extractCommands</span><span class="o">(</span><span class="nd">@NotNull</span> <span class="n">TransactionForContract</span> <span class="n">tx</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">getCommands</span><span class="o">()</span>
@ -231,6 +225,11 @@ examples are trimmed to the modified class definition and added elements, for br
<span class="o">.</span><span class="na">filter</span><span class="o">((</span><span class="n">AuthenticatedObject</span><span class="o">&lt;</span><span class="n">CommandData</span><span class="o">&gt;</span> <span class="n">command</span><span class="o">)</span> <span class="o">-&gt;</span> <span class="o">{</span> <span class="k">return</span> <span class="n">command</span><span class="o">.</span><span class="na">getValue</span><span class="o">()</span> <span class="k">instanceof</span> <span class="n">Commands</span><span class="o">;</span> <span class="o">})</span>
<span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="n">Collectors</span><span class="o">.</span><span class="na">toList</span><span class="o">());</span>
<span class="o">}</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">verify</span><span class="o">(</span><span class="nd">@NotNull</span> <span class="n">TransactionForContract</span> <span class="n">tx</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">IllegalArgumentException</span> <span class="o">{</span>
<span class="n">ClauseVerifier</span><span class="o">.</span><span class="na">verifyClauses</span><span class="o">(</span><span class="n">tx</span><span class="o">,</span> <span class="n">Collections</span><span class="o">.</span><span class="na">singletonList</span><span class="o">(</span><span class="k">new</span> <span class="n">Clause</span><span class="o">.</span><span class="na">Group</span><span class="o">()),</span> <span class="n">extractCommands</span><span class="o">(</span><span class="n">tx</span><span class="o">));</span>
<span class="o">}</span>
</pre></div>
</div>
</div>