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doc: add JSON-RPC: a tale of interfaces article
Originally published on The Go Programming Language Blog, Abril 27, 2010. http://blog.golang.org/2010/04/json-rpc-tale-of-interfaces.html R=adg, r CC=golang-dev https://golang.org/cl/5920044
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<!--{
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"Title": "JSON-RPC: a tale of interfaces"
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}-->
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<p>
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Here we present an example where Go's
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<a href="/doc/effective_go.html#interfaces_and_types">interfaces</a> made it
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easy to refactor some existing code to make it more flexible and extensible.
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Originally, the standard library's <a href="/pkg/net/rpc/">RPC package</a> used
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a custom wire format called <a href="/pkg/encoding/gob/">gob</a>. For a
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particular application, we wanted to use <a href="/pkg/encoding/json/">JSON</a>
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as an alternate wire format.
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</p>
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<p>
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We first defined a pair of interfaces to describe the functionality of the
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existing wire format, one for the client, and one for the server (depicted
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below).
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</p>
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<pre>
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type ServerCodec interface {
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ReadRequestHeader(*Request) error
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ReadRequestBody(interface{}) error
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WriteResponse(*Response, interface{}) error
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Close() error
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}
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</pre>
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<p>
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On the server side, we then changed two internal function signatures to accept
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the <code>ServerCodec</code> interface instead of our existing
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<code>gob.Encoder</code>. Here's one of them:
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</p>
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<pre>
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func sendResponse(sending *sync.Mutex, req *Request,
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reply interface{}, enc *gob.Encoder, errmsg string)
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</pre>
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<p>
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became
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</p>
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<pre>
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func sendResponse(sending *sync.Mutex, req *Request,
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reply interface{}, enc ServerCodec, errmsg string)
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</pre>
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<p>
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We then wrote a trivial <code>gobServerCodec</code> wrapper to reproduce the
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original functionality. From there it is simple to build a
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<code>jsonServerCodec</code>.
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</p>
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<p>
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After some similar changes to the client side, this was the full extent of the
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work we needed to do on the RPC package. This whole exercise took about 20
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minutes! After tidying up and testing the new code, the
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<a href="http://code.google.com/p/go/source/diff?spec=svn9daf796ebf1cae97b2fcf760a4ab682f1f063f29&r=9daf796ebf1cae97b2fcf760a4ab682f1f063f29&format=side&path=/src/pkg/rpc/server.go">final changeset</a>
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was submitted.
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</p>
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<p>
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In an inheritance-oriented language like Java or C++, the obvious path would be
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to generalize the RPC class, and create JsonRPC and GobRPC subclasses. However,
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this approach becomes tricky if you want to make a further generalization
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orthogonal to that hierarchy. (For example, if you were to implement an
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alternate RPC standard). In our Go package, we took a route that is both
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conceptually simpler and requires less code be written or changed.
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</p>
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<p>
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A vital quality for any codebase is maintainability. As needs change, it is
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essential to adapt your code easily and cleanly, lest it become unwieldy to work
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with. We believe Go's lightweight, composition-oriented type system provides a
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means of structuring code that scales.
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</p>
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@ -91,7 +91,7 @@ the Go team and guests.</p>
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<h4>Codewalks</h4>
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<p>
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Guided tours of Go programs.
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Guided tours of Go programs.
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</p>
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<ul>
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<li><a href="/doc/codewalk/functions">First-Class Functions in Go</a></li>
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@ -102,7 +102,7 @@ Guided tours of Go programs.
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<h4>Language</h4>
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<ul>
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<li><a href="http://blog.golang.org/2010/04/json-rpc-tale-of-interfaces.html">JSON-RPC: a tale of interfaces</a></li>
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<li><a href="/doc/articles/json_rpc_tale_of_interfaces.html">JSON-RPC: a tale of interfaces</a></li>
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<li><a href="/doc/articles/gos_declaration_syntax.html">Go's Declaration Syntax</a></li>
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<li><a href="/doc/articles/defer_panic_recover.html">Defer, Panic, and Recover</a></li>
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<li><a href="/doc/articles/concurrency_patterns.html">Go Concurrency Patterns: Timing out, moving on</a></li>
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@ -167,7 +167,7 @@ App Engine and renders images that it stores on Google Cloud Storage.
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A presentation delivered by Rob Pike and Russ Cox at Google I/O 2010. It
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illustrates how programming in Go differs from other languages through a set of
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examples demonstrating features particular to Go. These include concurrency,
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embedded types, methods on any type, and program construction using interfaces.
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embedded types, methods on any type, and program construction using interfaces.
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</p>
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<h3 id="practical_go_programming"><a href="http://www.youtube.com/watch?v=2-pPAvqyluI">Practical Go Programming</a><font color="red">*</font></h3>
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@ -188,7 +188,7 @@ more Go talks.
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<h2 id="nonenglish">Non-English Documentation</h2>
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<p>
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See the <a href="http://code.google.com/p/go-wiki/wiki/NonEnglish">NonEnglish</a> page
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See the <a href="http://code.google.com/p/go-wiki/wiki/NonEnglish">NonEnglish</a> page
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at the <a href="http://code.google.com/p/go-wiki/wiki">Go Wiki</a> for localized
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documentation.
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</p>
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@ -198,7 +198,7 @@ documentation.
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<img class="gopher" src="/doc/gopher/project.png"/>
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<h3 id="mailinglist"><a href="http://groups.google.com/group/golang-nuts">Go Nuts Mailing List</a></h3>
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<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a>
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<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a>
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mailing list is for general Go discussion.</p>
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<h3 id="projects"><a href="http://godashboard.appspot.com/project">Go Project Dashboard</a></h3>
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