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<script type="text/javascript" src="_static/jquery.js"></script>
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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>In this tutorial, we will restructure 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>As before, this example is focused on a basic implementation of commercial paper (CP), which is essentially a simpler version of a corporate
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bond. A company issues commercial paper with a particular face value, say $100, but sells it for less, say $90. The paper can be redeemed
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for cash at a given future date. In our example, the commercial paper has a 10% interest rate, with a single repayment.
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The full Kotlin code can be found in <code class="docutils literal"><span class="pre">CommercialPaper.kt</span></code>.</p>
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<div class="section" id="what-are-clauses-and-why-use-them">
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<h2>What are clauses and why use them?<a class="headerlink" href="#what-are-clauses-and-why-use-them" title="Permalink to this headline">¶</a></h2>
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<p>Clauses are essentially micro-contracts which contain independent verification logic, and can be logically composed
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to form a complete contract. Clauses are designed to enable re-use of common verification parts. For example, issuing state objects
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is generally the same for all fungible contracts, so a common issuance clause can be used for each contract’s
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issue clause. This cuts down on scope for error, and improves consistency of behaviour. By splitting verification logic
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into smaller chunks, these can also be readily tested in isolation.</p>
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</div>
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<div class="section" id="how-do-clauses-work">
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<h2>How do clauses work?<a class="headerlink" href="#how-do-clauses-work" title="Permalink to this headline">¶</a></h2>
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<p>There are different types of clauses. The most basic are those that define the verification logic for a single command
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(e.g. <code class="docutils literal"><span class="pre">Move</span></code>, <code class="docutils literal"><span class="pre">Issue</span></code> and <code class="docutils literal"><span class="pre">Redeem</span></code>, in the case of commercial paper), or even run without any commands at all (e.g. <code class="docutils literal"><span class="pre">Timestamp</span></code>).</p>
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<p>These basic clauses can then be combined using a <code class="docutils literal"><span class="pre">CompositeClause</span></code>. The goal of composite clauses is to determine
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which individual clauses need to be matched and verified for a given transaction
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to be considered valid. We refer to a clause as being “matched” when the transaction has the required commands present for the clause
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in question to trigger. Meanwhile, we talk about a clause “verifying” when its <code class="docutils literal"><span class="pre">verify()</span></code> function returns <code class="docutils literal"><span class="pre">True</span></code>.</p>
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<p>As an example, let’s say we want a transaction to be valid only when every single one of its clauses matches and verifies. We implement this
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by wrapping the individual clauses into an <code class="docutils literal"><span class="pre">AllOf</span></code> composite clause, which ensures that a transaction is
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only considered valid if all of its clauses are both matched and verify.</p>
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<p>There are two other basic composite clauses that you should be aware of:</p>
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<blockquote>
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<div><ul class="simple">
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<li><code class="docutils literal"><span class="pre">AnyOf</span></code>, whereby 1 or more clauses may match, and every matched clause must verify</li>
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<li><code class="docutils literal"><span class="pre">FirstOf</span></code>, whereby at least one clause must match, and the first such clause must verify</li>
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</ul>
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</div></blockquote>
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<p>In turn, composite clauses are themselves <code class="docutils literal"><span class="pre">Clause</span></code> s, and can, for example, be wrapped in the special <code class="docutils literal"><span class="pre">GroupClauseVerifier</span></code> grouping clause.
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For <code class="docutils literal"><span class="pre">CommercialPaper</span></code>, this would look as follows:</p>
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<img alt="_images/commPaperClauses.png" src="_images/commPaperClauses.png" />
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<p>For this tutorial, we will be using <code class="docutils literal"><span class="pre">GroupClauseVerifier</span></code> and <code class="docutils literal"><span class="pre">AnyOf</span></code>. Since it’s important to understand how these work,
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charts showing their execution and other details can be found in <a class="reference internal" href="clauses.html"><span class="doc">Clauses</span></a>.</p>
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</div>
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<div class="section" id="commercial-paper-class">
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<span id="verify-ref"></span><h2>Commercial paper class<a class="headerlink" href="#commercial-paper-class" title="Permalink to this headline">¶</a></h2>
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<p>We start by defining the <code class="docutils literal"><span class="pre">CommercialPaper</span></code> class. As in the previous tutorial, we need some elementary parts: a <code class="docutils literal"><span class="pre">Commands</span></code> interface,
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<code class="docutils literal"><span class="pre">generateMove</span></code>, <code class="docutils literal"><span class="pre">generateIssue</span></code>, <code class="docutils literal"><span class="pre">generateRedeem</span></code>. So far, so good - these stay the same. The new part is verification and the
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<code class="docutils literal"><span class="pre">Clauses</span></code> interface (which we will see later in code). Let’s start from the basic structure:</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">Contract</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">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">verifyClause</span><span class="p">(</span><span class="n">tx</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">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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<span class="k">interface</span> <span class="nc">Commands</span> <span class="p">:</span> <span class="n">CommandData</span> <span class="p">{</span>
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<span class="k">data</span> <span class="k">class</span> <span class="nc">Move</span><span class="p">(</span><span class="k">override</span> <span class="k">val</span> <span class="py">contractHash</span><span class="p">:</span> <span class="n">SecureHash</span><span class="p">?</span> <span class="p">=</span> <span class="k">null</span><span class="p">)</span> <span class="p">:</span> <span class="n">FungibleAsset</span><span class="p">.</span><span class="n">Commands</span><span class="p">.</span><span class="n">Move</span><span class="p">,</span> <span class="n">Commands</span>
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<span class="k">class</span> <span class="nc">Redeem</span> <span class="p">:</span> <span class="n">TypeOnlyCommandData</span><span class="p">(),</span> <span class="n">Commands</span>
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<span class="k">data</span> <span class="k">class</span> <span class="nc">Issue</span><span class="p">(</span><span class="k">override</span> <span class="k">val</span> <span class="py">nonce</span><span class="p">:</span> <span class="n">Long</span> <span class="p">=</span> <span class="n">random63BitValue</span><span class="p">())</span> <span class="p">:</span> <span class="n">IssueCommand</span><span class="p">,</span> <span class="n">Commands</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">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>
|
|
<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">verifyClause</span><span class="o">(</span><span class="n">tx</span><span class="o">,</span> <span class="k">new</span> <span class="n">Clauses</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>
|
|
|
|
<span class="kd">public</span> <span class="kd">interface</span> <span class="nc">Commands</span> <span class="kd">extends</span> <span class="n">CommandData</span> <span class="o">{</span>
|
|
<span class="kd">class</span> <span class="nc">Move</span> <span class="kd">implements</span> <span class="n">Commands</span> <span class="o">{</span>
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">equals</span><span class="o">(</span><span class="n">Object</span> <span class="n">obj</span><span class="o">)</span> <span class="o">{</span> <span class="k">return</span> <span class="n">obj</span> <span class="k">instanceof</span> <span class="n">Move</span><span class="o">;</span> <span class="o">}</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="kd">class</span> <span class="nc">Redeem</span> <span class="kd">implements</span> <span class="n">Commands</span> <span class="o">{</span>
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">equals</span><span class="o">(</span><span class="n">Object</span> <span class="n">obj</span><span class="o">)</span> <span class="o">{</span> <span class="k">return</span> <span class="n">obj</span> <span class="k">instanceof</span> <span class="n">Redeem</span><span class="o">;</span> <span class="o">}</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="kd">class</span> <span class="nc">Issue</span> <span class="kd">implements</span> <span class="n">Commands</span> <span class="o">{</span>
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">equals</span><span class="o">(</span><span class="n">Object</span> <span class="n">obj</span><span class="o">)</span> <span class="o">{</span> <span class="k">return</span> <span class="n">obj</span> <span class="k">instanceof</span> <span class="n">Issue</span><span class="o">;</span> <span class="o">}</span>
|
|
<span class="o">}</span>
|
|
<span class="o">}</span>
|
|
</pre></div>
|
|
</div>
|
|
</div>
|
|
<p>As you can see, we used <code class="docutils literal"><span class="pre">verifyClause</span></code> function with <code class="docutils literal"><span class="pre">Clauses.Group()</span></code> in place of our previous verification logic.
|
|
It’s an entry point to running clause logic. <code class="docutils literal"><span class="pre">verifyClause</span></code> takes the transaction, a clause (usually a composite one)
|
|
to verify, and all of the commands the clause is expected to handle. This list of commands is important because
|
|
<code class="docutils literal"><span class="pre">verifyClause</span></code> checks that none of the commands are left unprocessed at the end, raising an error if they are.</p>
|
|
</div>
|
|
<div class="section" id="simple-clauses">
|
|
<h2>Simple Clauses<a class="headerlink" href="#simple-clauses" title="Permalink to this headline">¶</a></h2>
|
|
<p>Let’s move to constructing contract logic in terms of clauses. The commercial paper contract has three commands and
|
|
three corresponding behaviours: <code class="docutils literal"><span class="pre">Issue</span></code>, <code class="docutils literal"><span class="pre">Move</span></code> and <code class="docutils literal"><span class="pre">Redeem</span></code>. Each of them has a specific set of requirements that must be satisfied -
|
|
perfect material for defining clauses. For brevity, we will only show the <code class="docutils literal"><span class="pre">Move</span></code> clause. The rest is constructed in similar manner,
|
|
and is included in the <code class="docutils literal"><span class="pre">CommercialPaper.kt</span></code> code.</p>
|
|
<div class="codeset container">
|
|
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="k">interface</span> <span class="nc">Clauses</span> <span class="p">{</span>
|
|
<span class="k">class</span> <span class="nc">Move</span><span class="p">:</span> <span class="n">Clause</span><span class="p"><</span><span class="n">State</span><span class="p">,</span> <span class="n">Commands</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">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>
|
|
<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>
|
|
|
|
<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="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>
|
|
<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>
|
|
<span class="n">commands</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">Commands</span><span class="p">>>,</span>
|
|
<span class="n">groupingKey</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">Commands</span><span class="p">></span> <span class="p">{</span>
|
|
<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>
|
|
<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>
|
|
<span class="n">requireThat</span> <span class="p">{</span>
|
|
<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>
|
|
<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>
|
|
<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="p">}</span>
|
|
<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>
|
|
<span class="p">}</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">interface</span> <span class="nc">Clauses</span> <span class="o">{</span>
|
|
<span class="kd">class</span> <span class="nc">Move</span> <span class="kd">extends</span> <span class="n">Clause</span><span class="o"><</span><span class="n">State</span><span class="o">,</span> <span class="n">Commands</span><span class="o">,</span> <span class="n">State</span><span class="o">></span> <span class="o">{</span>
|
|
<span class="nd">@NotNull</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">@NotNull</span>
|
|
<span class="nd">@Override</span>
|
|
<span class="kd">public</span> <span class="n">Set</span><span class="o"><</span><span class="n">Commands</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">List</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">Commands</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">groupingKey</span><span class="o">)</span> <span class="o">{</span>
|
|
<span class="n">AuthenticatedObject</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="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">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="k">if</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="k">throw</span> <span class="k">new</span> <span class="n">IllegalStateException</span><span class="o">(</span><span class="s">"Failed requirement: the transaction is signed by the owner of the CP"</span><span class="o">);</span>
|
|
|
|
<span class="c1">// Check the output CP state is the same as the input state, ignoring the owner field.</span>
|
|
<span class="k">if</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="o">{</span>
|
|
<span class="k">throw</span> <span class="k">new</span> <span class="n">IllegalStateException</span><span class="o">(</span><span class="s">"the state is propagated"</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>
|
|
<span class="o">...</span>
|
|
</pre></div>
|
|
</div>
|
|
</div>
|
|
<p>We took part of the code for <code class="docutils literal"><span class="pre">Command.Move</span></code> verification from the previous tutorial and put it into the verify function
|
|
of <code class="docutils literal"><span class="pre">Move</span></code> class. Notice that this class must extend the <code class="docutils literal"><span class="pre">Clause</span></code> abstract class, which defines
|
|
the <code class="docutils literal"><span class="pre">verify</span></code> function and the <code class="docutils literal"><span class="pre">requiredCommands</span></code> property used to determine the conditions under which a clause
|
|
is triggered. In the above example, this means that the clause will run its verification logic when <code class="docutils literal"><span class="pre">Commands.Move</span></code> is present in a transaction.</p>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">Notice that commands refer to all input and output states in a transaction. For a clause to be executed, the transaction has
|
|
to include all commands from the <code class="docutils literal"><span class="pre">requiredCommands</span></code> set.</p>
|
|
</div>
|
|
<p>A few important changes:</p>
|
|
<ul class="simple">
|
|
<li>The <code class="docutils literal"><span class="pre">verify</span></code> function returns the set of commands which it has processed. Normally this set is identical to the
|
|
<code class="docutils literal"><span class="pre">requiredCommands</span></code> used to trigger the clause. However, in some cases, the clause may process further optional commands
|
|
which it needs to report that it has handled.</li>
|
|
<li>Verification takes new parameters. Usually inputs and outputs are some subset of the original transaction entries
|
|
passed to the clause by outer composite or grouping clause. <code class="docutils literal"><span class="pre">groupingKey</span></code> is a key used to group original states.</li>
|
|
</ul>
|
|
<p>As a simple example, imagine the following input states:</p>
|
|
<ol class="arabic simple">
|
|
<li>1000 GBP issued by Bank of England</li>
|
|
<li>500 GBP issued by Bank of England</li>
|
|
<li>1000 GBP issued by Bank of Scotland</li>
|
|
</ol>
|
|
<p>We will group states by Issuer, meaning that we have inputs 1 and 2 in one group, and input 3 in another group. The grouping keys are
|
|
‘GBP issued by Bank of England’ and ‘GBP issued by Bank of Scotland’.</p>
|
|
<p>How are the states grouped and passed in this form to the <code class="docutils literal"><span class="pre">Move</span></code> clause? Answering that question leads us to the concept of
|
|
<code class="docutils literal"><span class="pre">GroupClauseVerifier</span></code>.</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 may have a transaction with similar but unrelated state evolutions which need to be validated independently. It
|
|
makes sense to check the <code class="docutils literal"><span class="pre">Move</span></code> command on groups of related inputs and outputs (see example above). Thus, we need to collect
|
|
relevant states together.
|
|
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 top-level
|
|
clause to run on each group. In our example, the top level is a composite clause - <code class="docutils literal"><span class="pre">AnyCompostion</span></code> - that delegates verification to
|
|
its subclauses (wrapped move, issue, redeem). “Any” in this case means that it will take 0 or more clauses that match the transaction commands.</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">Commands</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">AnyOf</span><span class="p">(</span>
|
|
<span class="n">Redeem</span><span class="p">(),</span>
|
|
<span class="n">Move</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">groupStates</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">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">Commands</span><span class="o">,</span> <span class="n">State</span><span class="o">></span> <span class="o">{</span>
|
|
<span class="kd">public</span> <span class="nf">Group</span><span class="o">()</span> <span class="o">{</span>
|
|
<span class="kd">super</span><span class="o">(</span><span class="k">new</span> <span class="n">AnyOf</span><span class="o"><>(</span>
|
|
<span class="k">new</span> <span class="n">Clauses</span><span class="o">.</span><span class="na">Redeem</span><span class="o">(),</span>
|
|
<span class="k">new</span> <span class="n">Clauses</span><span class="o">.</span><span class="na">Move</span><span class="o">(),</span>
|
|
<span class="k">new</span> <span class="n">Clauses</span><span class="o">.</span><span class="na">Issue</span><span class="o">()</span>
|
|
<span class="o">));</span>
|
|
<span class="o">}</span>
|
|
|
|
<span class="nd">@NotNull</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">groupStates</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>For the <code class="docutils literal"><span class="pre">CommercialPaper</span></code> contract, <code class="docutils literal"><span class="pre">Group</span></code> is the main clause for the contract, and is passed directly into
|
|
<code class="docutils literal"><span class="pre">verifyClause</span></code> (see the example code at the top of this tutorial). We also used <code class="docutils literal"><span class="pre">groupStates</span></code> function here - it
|
|
may be worth reminding yourself how it works here: <a class="reference internal" href="tutorial-contract.html#state-ref"><span class="std std-ref">Using state groups</span></a>.</p>
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</div>
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<div class="section" id="summary">
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<h2>Summary<a class="headerlink" href="#summary" title="Permalink to this headline">¶</a></h2>
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<p>In summary, the top-level contract <code class="docutils literal"><span class="pre">CommercialPaper</span></code> specifies a single grouping clause of type
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<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
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(<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 verification flow: in order to verify <code class="docutils literal"><span class="pre">CommercialPaper</span></code>,
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we first group states, then we check which commands are specified, and finally we run command-specific verification logic accordingly.</p>
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<img alt="_images/commPaperExecution.png" src="_images/commPaperExecution.png" />
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</div>
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<div class="section" id="debugging">
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<h2>Debugging<a class="headerlink" href="#debugging" title="Permalink to this headline">¶</a></h2>
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<p>Debugging clauses which have been composed together can be complicated due to the difficulty in knowing which clauses
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have been matched, whether specific clauses failed to match or passed verification, etc. There is “trace” level
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logging code in the clause verifier which evaluates which clauses will be matched and logs them, before actually
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performing the validation. To enable this, ensure trace level logging is enabled on the <code class="docutils literal"><span class="pre">Clause</span></code> interface.</p>
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