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<script type="text/javascript" src="_static/codesets.js"></script><div class="section" id="writing-a-contract-using-clauses">
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<h1>Writing a contract using clauses<a class="headerlink" href="#writing-a-contract-using-clauses" title="Permalink to this headline">¶</a></h1>
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<p>This tutorial will take you through restructuring the commercial paper contract to use clauses. You should have
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already completed “<a class="reference internal" href="tutorial-contract.html"><span class="doc">Writing a contract</span></a>”.</p>
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<p>Clauses are essentially “mini-contracts” which contain verification logic, and are composed together to form
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a contract. With appropriate design, they can be made to be reusable, for example issuing contract state objects is
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generally the same for all fungible contracts, so a single issuance clause can be shared. This cuts down on scope for
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error, and improves consistency of behaviour.</p>
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<p>Clauses can be composed of subclauses, either to combine clauses in different ways, or to apply specialised clauses.
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In the case of commercial paper, we have a “Grouping” outermost clause, which will contain the “Issue”, “Move” and
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“Redeem” clauses. The result is a contract that looks something like this:</p>
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<blockquote>
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<div><ol class="arabic">
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<li><dl class="first docutils">
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<dt>Group input and output states together, and then apply the following clauses on each group:</dt>
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<dd><ol class="first last loweralpha simple">
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<li>If an Issue command is present, run appropriate tests and end processing this group.</li>
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<li>If a Move command is present, run appropriate tests and end processing this group.</li>
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<li>If a Redeem command is present, run appropriate tests and end processing this group.</li>
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</ol>
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</dd>
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</dl>
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</li>
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</ol>
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</div></blockquote>
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<div class="section" id="commercial-paper-class">
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<h2>Commercial paper class<a class="headerlink" href="#commercial-paper-class" title="Permalink to this headline">¶</a></h2>
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<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
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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,
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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
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<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
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examples are trimmed to the modified class definition and added elements, for brevity:</p>
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<div class="codeset container">
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<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>
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<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">"https://en.wikipedia.org/wiki/Commercial_paper"</span><span class="p">);</span>
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<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"><</span><span class="n">SingleClause</span><span class="p">></span>
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<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">"not implemented"</span><span class="p">)</span>
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<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"><</span><span class="n">AuthenticatedObject</span><span class="p"><</span><span class="n">CommandData</span><span class="p">>></span>
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<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"><</span><span class="n">Commands</span><span class="p">>()</span>
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</pre></div>
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</div>
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<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>
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<span class="nd">@Override</span>
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<span class="kd">public</span> <span class="n">SecureHash</span> <span class="nf">getLegalContractReference</span><span class="o">()</span> <span class="o">{</span>
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<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">"https://en.wikipedia.org/wiki/Commercial_paper"</span><span class="o">);</span>
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<span class="o">}</span>
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<span class="nd">@Override</span>
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<span class="kd">public</span> <span class="n">List</span><span class="o"><</span><span class="n">SingleClause</span><span class="o">></span> <span class="nf">getClauses</span><span class="o">()</span> <span class="o">{</span>
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<span class="k">throw</span> <span class="n">UnsupportedOperationException</span><span class="o">(</span><span class="s">"not implemented"</span><span class="o">);</span>
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<span class="o">}</span>
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<span class="nd">@Override</span>
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<span class="kd">public</span> <span class="n">Collection</span><span class="o"><</span><span class="n">AuthenticatedObject</span><span class="o"><</span><span class="n">CommandData</span><span class="o">>></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>
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<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">getCommands</span><span class="o">()</span>
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<span class="o">.</span><span class="na">stream</span><span class="o">()</span>
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<span class="o">.</span><span class="na">filter</span><span class="o">((</span><span class="n">AuthenticatedObject</span><span class="o"><</span><span class="n">CommandData</span><span class="o">></span> <span class="n">command</span><span class="o">)</span> <span class="o">-></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>
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<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>
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<span class="o">}</span>
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</pre></div>
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</div>
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</div>
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</div>
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<div class="section" id="clauses">
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<h2>Clauses<a class="headerlink" href="#clauses" title="Permalink to this headline">¶</a></h2>
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<p>We’ll tackle the inner clauses that contain the bulk of the verification logic, first, and the clause which handles
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grouping of input/output states later. The inner clauses need to implement the <code class="docutils literal"><span class="pre">GroupClause</span></code> interface, which defines
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the verify() function, and properties for key information on how the clause is processed. These properties specify the
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command(s) which must be present in order for the clause to be matched, and what to do after processing the clause
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depending on whether it was matched or not.</p>
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<p>The <code class="docutils literal"><span class="pre">verify()</span></code> functions defined in the <code class="docutils literal"><span class="pre">SingleClause</span></code> and <code class="docutils literal"><span class="pre">GroupClause</span></code> interfaces is similar to the conventional
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<code class="docutils literal"><span class="pre">Contract</span></code> verification function, although it adds new parameters and returns the set of commands which it has processed.
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Normally this returned set is identical to the commands matched in order to trigger the clause, however in some cases the
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clause may process optional commands which it needs to report that it has handled, or may by designed to only process
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the first (or otherwise) matched command.</p>
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<p>The Move clause for the commercial paper contract is relatively simple, so lets start there:</p>
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<div class="codeset container">
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<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Move</span><span class="p">:</span> <span class="n">GroupClause</span><span class="p"><</span><span class="n">State</span><span class="p">,</span> <span class="n">Issued</span><span class="p"><</span><span class="n">Terms</span><span class="p">>></span> <span class="p">{</span>
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<span class="k">override</span> <span class="k">val</span> <span class="py">ifNotMatched</span><span class="p">:</span> <span class="n">MatchBehaviour</span>
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<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">MatchBehaviour</span><span class="p">.</span><span class="n">CONTINUE</span>
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<span class="k">override</span> <span class="k">val</span> <span class="py">ifMatched</span><span class="p">:</span> <span class="n">MatchBehaviour</span>
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<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">MatchBehaviour</span><span class="p">.</span><span class="n">END</span>
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<span class="k">override</span> <span class="k">val</span> <span class="py">requiredCommands</span><span class="p">:</span> <span class="n">Set</span><span class="p"><</span><span class="n">Class</span><span class="p"><</span><span class="k">out</span> <span class="n">CommandData</span><span class="p">>></span>
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<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">setOf</span><span class="p">(</span><span class="n">Commands</span><span class="p">.</span><span class="n">Move</span><span class="o">::</span><span class="k">class</span><span class="p">.</span><span class="n">java</span><span class="p">)</span>
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<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>
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<span class="n">inputs</span><span class="p">:</span> <span class="n">List</span><span class="p"><</span><span class="n">State</span><span class="p">>,</span>
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<span class="n">outputs</span><span class="p">:</span> <span class="n">List</span><span class="p"><</span><span class="n">State</span><span class="p">>,</span>
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<span class="n">commands</span><span class="p">:</span> <span class="n">Collection</span><span class="p"><</span><span class="n">AuthenticatedObject</span><span class="p"><</span><span class="n">CommandData</span><span class="p">>>,</span>
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<span class="n">token</span><span class="p">:</span> <span class="n">Issued</span><span class="p"><</span><span class="n">Terms</span><span class="p">>):</span> <span class="n">Set</span><span class="p"><</span><span class="n">CommandData</span><span class="p">></span> <span class="p">{</span>
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<span class="k">val</span> <span class="py">command</span> <span class="p">=</span> <span class="n">commands</span><span class="p">.</span><span class="n">requireSingleCommand</span><span class="p"><</span><span class="n">Commands</span><span class="p">.</span><span class="n">Move</span><span class="p">>()</span>
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<span class="k">val</span> <span class="py">input</span> <span class="p">=</span> <span class="n">inputs</span><span class="p">.</span><span class="n">single</span><span class="p">()</span>
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<span class="n">requireThat</span> <span class="p">{</span>
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<span class="s">"the transaction is signed by the owner of the CP"</span> <span class="k">by</span> <span class="p">(</span><span class="n">input</span><span class="p">.</span><span class="n">owner</span> <span class="k">in</span> <span class="n">command</span><span class="p">.</span><span class="n">signers</span><span class="p">)</span>
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<span class="s">"the state is propagated"</span> <span class="k">by</span> <span class="p">(</span><span class="n">outputs</span><span class="p">.</span><span class="n">size</span> <span class="p">==</span> <span class="m">1</span><span class="p">)</span>
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<span class="c1">// Don't need to check anything else, as if outputs.size == 1 then the output is equal to</span>
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<span class="c1">// the input ignoring the owner field due to the grouping.</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="n">setOf</span><span class="p">(</span><span class="n">command</span><span class="p">.</span><span class="n">value</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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<div class="highlight-java"><div class="highlight"><pre><span></span><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Move</span> <span class="kd">implements</span> <span class="n">GroupClause</span><span class="o"><</span><span class="n">State</span><span class="o">,</span> <span class="n">State</span><span class="o">></span> <span class="o">{</span>
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<span class="nd">@Override</span>
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<span class="kd">public</span> <span class="n">MatchBehaviour</span> <span class="nf">getIfNotMatched</span><span class="o">()</span> <span class="o">{</span>
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<span class="k">return</span> <span class="n">MatchBehaviour</span><span class="o">.</span><span class="na">CONTINUE</span><span class="o">;</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">MatchBehaviour</span> <span class="nf">getIfMatched</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="k">return</span> <span class="n">MatchBehaviour</span><span class="o">.</span><span class="na">END</span><span class="o">;</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">Set</span><span class="o"><</span><span class="n">Class</span><span class="o"><?</span> <span class="kd">extends</span> <span class="n">CommandData</span><span class="o">>></span> <span class="nf">getRequiredCommands</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="k">return</span> <span class="n">Collections</span><span class="o">.</span><span class="na">singleton</span><span class="o">(</span><span class="n">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">Set</span><span class="o"><</span><span class="n">CommandData</span><span class="o">></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="nd">@NotNull</span> <span class="n">List</span><span class="o"><?</span> <span class="kd">extends</span> <span class="n">State</span><span class="o">></span> <span class="n">inputs</span><span class="o">,</span>
|
|
<span class="nd">@NotNull</span> <span class="n">List</span><span class="o"><?</span> <span class="kd">extends</span> <span class="n">State</span><span class="o">></span> <span class="n">outputs</span><span class="o">,</span>
|
|
<span class="nd">@NotNull</span> <span class="n">Collection</span><span class="o"><?</span> <span class="kd">extends</span> <span class="n">AuthenticatedObject</span><span class="o"><?</span> <span class="kd">extends</span> <span class="n">CommandData</span><span class="o">>></span> <span class="n">commands</span><span class="o">,</span>
|
|
<span class="nd">@NotNull</span> <span class="n">State</span> <span class="n">token</span><span class="o">)</span> <span class="o">{</span>
|
|
<span class="n">AuthenticatedObject</span><span class="o"><</span><span class="n">CommandData</span><span class="o">></span> <span class="n">cmd</span> <span class="o">=</span> <span class="n">requireSingleCommand</span><span class="o">(</span><span class="n">tx</span><span class="o">.</span><span class="na">getCommands</span><span class="o">(),</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
|
|
<span class="c1">// There should be only a single input due to aggregation above</span>
|
|
<span class="n">State</span> <span class="n">input</span> <span class="o">=</span> <span class="n">single</span><span class="o">(</span><span class="n">inputs</span><span class="o">);</span>
|
|
|
|
<span class="n">requireThat</span><span class="o">(</span><span class="n">require</span> <span class="o">-></span> <span class="o">{</span>
|
|
<span class="n">require</span><span class="o">.</span><span class="na">by</span><span class="o">(</span><span class="s">"the transaction is signed by the owner of the CP"</span><span class="o">,</span> <span class="n">cmd</span><span class="o">.</span><span class="na">getSigners</span><span class="o">().</span><span class="na">contains</span><span class="o">(</span><span class="n">input</span><span class="o">.</span><span class="na">getOwner</span><span class="o">()));</span>
|
|
<span class="n">require</span><span class="o">.</span><span class="na">by</span><span class="o">(</span><span class="s">"the state is propagated"</span><span class="o">,</span> <span class="n">outputs</span><span class="o">.</span><span class="na">size</span><span class="o">()</span> <span class="o">==</span> <span class="mi">1</span><span class="o">);</span>
|
|
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
|
|
<span class="o">});</span>
|
|
<span class="c1">// Don't need to check anything else, as if outputs.size == 1 then the output is equal to</span>
|
|
<span class="c1">// the input ignoring the owner field due to the grouping.</span>
|
|
<span class="k">return</span> <span class="n">Collections</span><span class="o">.</span><span class="na">singleton</span><span class="o">(</span><span class="n">cmd</span><span class="o">.</span><span class="na">getValue</span><span class="o">());</span>
|
|
<span class="o">}</span>
|
|
<span class="o">}</span>
|
|
</pre></div>
|
|
</div>
|
|
</div>
|
|
<dl class="docutils">
|
|
<dt>The post-processing <code class="docutils literal"><span class="pre">MatchBehaviour</span></code> options are:</dt>
|
|
<dd><ul class="first last simple">
|
|
<li>CONTINUE</li>
|
|
<li>END</li>
|
|
<li>ERROR</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<p>In this case we process commands against each group, until the first matching clause is found, so we <code class="docutils literal"><span class="pre">END</span></code> on a match
|
|
and <code class="docutils literal"><span class="pre">CONTINUE</span></code> otherwise. <code class="docutils literal"><span class="pre">ERROR</span></code> can be used as a part of a clause which must always/never be matched.</p>
|
|
</div>
|
|
<div class="section" id="group-clause">
|
|
<h2>Group Clause<a class="headerlink" href="#group-clause" title="Permalink to this headline">¶</a></h2>
|
|
<p>We need to wrap the move clause (as well as the issue and redeem clauses - see the relevant contract code for their
|
|
full specifications) in an outer clause. For this we extend the standard <code class="docutils literal"><span class="pre">GroupClauseVerifier</span></code> and specify how to
|
|
group input/output states, as well as the clauses to run on each group.</p>
|
|
<div class="codeset container">
|
|
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Group</span> <span class="p">:</span> <span class="n">GroupClauseVerifier</span><span class="p"><</span><span class="n">State</span><span class="p">,</span> <span class="n">Issued</span><span class="p"><</span><span class="n">Terms</span><span class="p">>>()</span> <span class="p">{</span>
|
|
<span class="k">override</span> <span class="k">val</span> <span class="py">ifNotMatched</span><span class="p">:</span> <span class="n">MatchBehaviour</span>
|
|
<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">MatchBehaviour</span><span class="p">.</span><span class="n">ERROR</span>
|
|
<span class="k">override</span> <span class="k">val</span> <span class="py">ifMatched</span><span class="p">:</span> <span class="n">MatchBehaviour</span>
|
|
<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">MatchBehaviour</span><span class="p">.</span><span class="n">END</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"><</span><span class="n">GroupClause</span><span class="p"><</span><span class="n">State</span><span class="p">,</span> <span class="n">Issued</span><span class="p"><</span><span class="n">Terms</span><span class="p">>>></span>
|
|
<span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">listOf</span><span class="p">(</span>
|
|
<span class="n">Clause</span><span class="p">.</span><span class="n">Redeem</span><span class="p">(),</span>
|
|
<span class="n">Clause</span><span class="p">.</span><span class="n">Move</span><span class="p">(),</span>
|
|
<span class="n">Clause</span><span class="p">.</span><span class="n">Issue</span><span class="p">()</span>
|
|
<span class="p">)</span>
|
|
|
|
<span class="k">override</span> <span class="k">fun</span> <span class="nf">extractGroups</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"><</span><span class="n">TransactionForContract</span><span class="p">.</span><span class="n">InOutGroup</span><span class="p"><</span><span class="n">State</span><span class="p">,</span> <span class="n">Issued</span><span class="p"><</span><span class="n">Terms</span><span class="p">>>></span>
|
|
<span class="p">=</span> <span class="n">tx</span><span class="p">.</span><span class="n">groupStates</span><span class="p"><</span><span class="n">State</span><span class="p">,</span> <span class="n">Issued</span><span class="p"><</span><span class="n">Terms</span><span class="p">>></span> <span class="p">{</span> <span class="n">it</span><span class="p">.</span><span class="n">token</span> <span class="p">}</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">Group</span> <span class="kd">extends</span> <span class="n">GroupClauseVerifier</span><span class="o"><</span><span class="n">State</span><span class="o">,</span> <span class="n">State</span><span class="o">></span> <span class="o">{</span>
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">MatchBehaviour</span> <span class="nf">getIfMatched</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="k">return</span> <span class="n">MatchBehaviour</span><span class="o">.</span><span class="na">END</span><span class="o">;</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">MatchBehaviour</span> <span class="nf">getIfNotMatched</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="k">return</span> <span class="n">MatchBehaviour</span><span class="o">.</span><span class="na">ERROR</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"><</span><span class="n">com</span><span class="o">.</span><span class="na">r3corda</span><span class="o">.</span><span class="na">core</span><span class="o">.</span><span class="na">contracts</span><span class="o">.</span><span class="na">clauses</span><span class="o">.</span><span class="na">GroupClause</span><span class="o"><</span><span class="n">State</span><span class="o">,</span> <span class="n">State</span><span class="o">>></span> <span class="nf">getClauses</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="kd">final</span> <span class="n">List</span><span class="o"><</span><span class="n">GroupClause</span><span class="o"><</span><span class="n">State</span><span class="o">,</span> <span class="n">State</span><span class="o">>></span> <span class="n">clauses</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o"><>();</span>
|
|
|
|
<span class="n">clauses</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">Clause</span><span class="o">.</span><span class="na">Redeem</span><span class="o">());</span>
|
|
<span class="n">clauses</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">Clause</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
|
|
<span class="n">clauses</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">Clause</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
|
|
|
|
<span class="k">return</span> <span class="n">clauses</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"><</span><span class="n">InOutGroup</span><span class="o"><</span><span class="n">State</span><span class="o">,</span> <span class="n">State</span><span class="o">>></span> <span class="nf">extractGroups</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">groupStates</span><span class="o">(</span><span class="n">State</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="n">State</span><span class="o">::</span><span class="n">withoutOwner</span><span class="o">);</span>
|
|
<span class="o">}</span>
|
|
<span class="o">}</span>
|
|
</pre></div>
|
|
</div>
|
|
</div>
|
|
<p>We then pass this clause into the outer <code class="docutils literal"><span class="pre">ClauseVerifier</span></code> contract by returning it from the <code class="docutils literal"><span class="pre">clauses</span></code> property. We
|
|
also implement the <code class="docutils literal"><span class="pre">extractCommands()</span></code> function, which filters commands on the transaction down to the set the
|
|
contained clauses must handle (any unmatched commands at the end of clause verification results in an exception to be
|
|
thrown).</p>
|
|
<div class="codeset container">
|
|
<div class="highlight-kotlin"><div class="highlight"><pre><span></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"><</span><span class="n">SingleClause</span><span class="p">></span>
|
|
<span class="k">get</span><span class="p">()</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="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"><</span><span class="n">AuthenticatedObject</span><span class="p"><</span><span class="n">CommandData</span><span class="p">>></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"><</span><span class="n">Commands</span><span class="p">>()</span>
|
|
</pre></div>
|
|
</div>
|
|
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">List</span><span class="o"><</span><span class="n">SingleClause</span><span class="o">></span> <span class="nf">getClauses</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="k">return</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="o">}</span>
|
|
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">Collection</span><span class="o"><</span><span class="n">AuthenticatedObject</span><span class="o"><</span><span class="n">CommandData</span><span class="o">>></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>
|
|
<span class="o">.</span><span class="na">stream</span><span class="o">()</span>
|
|
<span class="o">.</span><span class="na">filter</span><span class="o">((</span><span class="n">AuthenticatedObject</span><span class="o"><</span><span class="n">CommandData</span><span class="o">></span> <span class="n">command</span><span class="o">)</span> <span class="o">-></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>
|
|
</pre></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="section" id="summary">
|
|
<h2>Summary<a class="headerlink" href="#summary" title="Permalink to this headline">¶</a></h2>
|
|
<p>In summary the top level contract <code class="docutils literal"><span class="pre">CommercialPaper</span></code> specifies a single grouping clause of type
|
|
<code class="docutils literal"><span class="pre">CommercialPaper.Clauses.Group</span></code> which in turn specifies <code class="docutils literal"><span class="pre">GroupClause</span></code> implementations for each type of command
|
|
(<code class="docutils literal"><span class="pre">Redeem</span></code>, <code class="docutils literal"><span class="pre">Move</span></code> and <code class="docutils literal"><span class="pre">Issue</span></code>). This reflects the flow of verification: In order to verify a <code class="docutils literal"><span class="pre">CommercialPaper</span></code>
|
|
we first group states, check which commands are specified, and run command-specific verification logic accordingly.</p>
|
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