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

3 files changed, 84 insertions, 5 deletions

diff --git a/doc/Makefile b/doc/Makefile
index da29e600b3..37deecab3e 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -12,6 +12,7 @@ RAWHTML=\
 	articles/godoc_documenting_go_code.rawhtml\
 	articles/gobs_of_data.rawhtml\
 	articles/json_and_go.rawhtml\
+	articles/json_rpc_tale_of_interfaces.rawhtml\
 	articles/image_draw.rawhtml\
 	effective_go.rawhtml\
 	go1.rawhtml\
diff --git a/doc/articles/json_rpc_tale_of_interfaces.html b/doc/articles/json_rpc_tale_of_interfaces.html
new file mode 100644
index 0000000000..a545f55f61
--- /dev/null
+++ b/doc/articles/json_rpc_tale_of_interfaces.html
@@ -0,0 +1,78 @@
+<!--{
+"Title": "JSON-RPC: a tale of interfaces"
+}-->
+
+<p>
+Here we present an example where Go's
+<a href="/doc/effective_go.html#interfaces_and_types">interfaces</a> made it
+easy to refactor some existing code to make it more flexible and extensible.
+Originally, the standard library's <a href="/pkg/net/rpc/">RPC package</a> used
+a custom wire format called <a href="/pkg/encoding/gob/">gob</a>. For a
+particular application, we wanted to use <a href="/pkg/encoding/json/">JSON</a>
+as an alternate wire format.
+</p>
+
+<p>
+We first defined a pair of interfaces to describe the functionality of the
+existing wire format, one for the client, and one for the server (depicted
+below).
+</p>
+
+<pre>
+type ServerCodec interface {
+	ReadRequestHeader(*Request) error
+	ReadRequestBody(interface{}) error
+	WriteResponse(*Response, interface{}) error
+	Close() error
+}
+</pre>
+
+<p>
+On the server side, we then changed two internal function signatures to accept
+the <code>ServerCodec</code> interface instead of our existing
+<code>gob.Encoder</code>. Here's one of them:
+</p>
+
+<pre>
+func sendResponse(sending *sync.Mutex, req *Request,
+	reply interface{}, enc *gob.Encoder, errmsg string)
+</pre>
+
+<p>
+became
+</p>
+
+<pre>
+func sendResponse(sending *sync.Mutex, req *Request,
+		reply interface{}, enc ServerCodec, errmsg string)
+</pre>
+
+<p>
+We then wrote a trivial <code>gobServerCodec</code> wrapper to reproduce the
+original functionality. From there it is simple to build a
+<code>jsonServerCodec</code>.
+</p>
+
+<p>
+After some similar changes to the client side, this was the full extent of the
+work we needed to do on the RPC package. This whole exercise took about 20
+minutes! After tidying up and testing the new code, the
+<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>
+was submitted.
+</p>
+
+<p>
+In an inheritance-oriented language like Java or C++, the obvious path would be
+to generalize the RPC class, and create JsonRPC and GobRPC subclasses. However,
+this approach becomes tricky if you want to make a further generalization
+orthogonal to that hierarchy. (For example, if you were to implement an
+alternate RPC standard). In our Go package, we took a route that is both
+conceptually simpler and requires less code be written or changed.
+</p>
+
+<p>
+A vital quality for any codebase is maintainability. As needs change, it is
+essential to adapt your code easily and cleanly, lest it become unwieldy to work
+with. We believe Go's lightweight, composition-oriented type system provides a
+means of structuring code that scales.
+</p>
diff --git a/doc/docs.html b/doc/docs.html
index d94962845b..577166e15c 100644
--- a/doc/docs.html
+++ b/doc/docs.html
@@ -91,7 +91,7 @@ the Go team and guests.</p>
 
 <h4>Codewalks</h4>
 <p>
-Guided tours of Go programs. 
+Guided tours of Go programs.
 </p>
 <ul>
 <li><a href="/doc/codewalk/functions">First-Class Functions in Go</a></li>
@@ -102,7 +102,7 @@ Guided tours of Go programs.
 
 <h4>Language</h4>
 <ul>
-<li><a href="http://blog.golang.org/2010/04/json-rpc-tale-of-interfaces.html">JSON-RPC: a tale of interfaces</a></li>
+<li><a href="/doc/articles/json_rpc_tale_of_interfaces.html">JSON-RPC: a tale of interfaces</a></li>
 <li><a href="/doc/articles/gos_declaration_syntax.html">Go's Declaration Syntax</a></li>
 <li><a href="/doc/articles/defer_panic_recover.html">Defer, Panic, and Recover</a></li>
 <li><a href="/doc/articles/concurrency_patterns.html">Go Concurrency Patterns: Timing out, moving on</a></li>
@@ -167,7 +167,7 @@ App Engine and renders images that it stores on Google Cloud Storage.
 A presentation delivered by Rob Pike and Russ Cox at Google I/O 2010.  It
 illustrates how programming in Go differs from other languages through a set of
 examples demonstrating features particular to Go.  These include concurrency,
-embedded types, methods on any type, and program construction using interfaces. 
+embedded types, methods on any type, and program construction using interfaces.
 </p>
 
 <h3 id="practical_go_programming"><a href="http://www.youtube.com/watch?v=2-pPAvqyluI">Practical Go Programming</a><font color="red">*</font></h3>
@@ -188,7 +188,7 @@ more Go talks.
 <h2 id="nonenglish">Non-English Documentation</h2>
 
 <p>
-See the <a href="http://code.google.com/p/go-wiki/wiki/NonEnglish">NonEnglish</a> page 
+See the <a href="http://code.google.com/p/go-wiki/wiki/NonEnglish">NonEnglish</a> page
 at the <a href="http://code.google.com/p/go-wiki/wiki">Go Wiki</a> for localized
 documentation.
 </p>
@@ -198,7 +198,7 @@ documentation.
 <img class="gopher" src="/doc/gopher/project.png"/>
 
 <h3 id="mailinglist"><a href="http://groups.google.com/group/golang-nuts">Go Nuts Mailing List</a></h3>
-<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a> 
+<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a>
 mailing list is for general Go discussion.</p>
 
 <h3 id="projects"><a href="http://godashboard.appspot.com/project">Go Project Dashboard</a></h3>