content: fix dead links in playground.article

Closes golang/go#40568

Change-Id: I95af7cc9f7a937e5593344b10c7257293da889f3
GitHub-Last-Rev: dc378b0
GitHub-Pull-Request: #45
Reviewed-on: https://go-review.googlesource.com/c/blog/+/258697
Reviewed-by: Andrew Bonventre <[email protected]>
Trust: Andrew Bonventre <[email protected]>
Run-TryBot: Andrew Bonventre <[email protected]>
TryBot-Result: Go Bot <[email protected]>

content/playground.article

@@ -5,6 +5,8 @@ Summary: How the Go playground works.
 
 Andrew Gerrand
 
+_NOTE: This article does not describe the current version of the Go Playground._
+
 ## Introduction
 
 In September 2010 we [introduced the Go Playground](https://blog.golang.org/introducing-go-playground),
@@ -208,17 +210,17 @@ with a set of files that can be used in documentation examples, blog posts, and
 the Go Tour.
 
 The implementation can be found in the
-[`fs_nacl.go`](https://github.com/golang/go/blob/master/src/syscall/fs_nacl.go) and
-[`fd_nacl.go`](https://github.com/golang/go/blob/master/src/syscall/fd_nacl.go) files
+[`fs_nacl.go`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fs_nacl.go) and
+[`fd_nacl.go`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fd_nacl.go) files
 (which, by virtue of their `_nacl` suffix, are built into package `syscall` only
 when `GOOS` is set to `nacl`).
 
 The file system itself is represented by the
-[`fsys` struct](https://github.com/golang/go/blob/master/src/syscall/fs_nacl.go#L26),
+[`fsys` struct](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fs_nacl.go#L26),
 of which a global instance (named `fs`) is created during init time.
 The various file-related functions then operate on `fs` instead of making the
 actual system call.
-For instance, here is the [`syscall.Open`](https://github.com/golang/go/blob/master/src/syscall/fs_nacl.go#L473) function:
+For instance, here is the [`syscall.Open`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fs_nacl.go#L473) function:
 
 	func Open(path string, openmode int, perm uint32) (fd int, err error) {
 		fs.mu.Lock()
@@ -231,13 +233,13 @@ For instance, here is the [`syscall.Open`](https://github.com/golang/go/blob/mas
 	}
 
 File descriptors are tracked by a global slice named
-[`files`](https://github.com/golang/go/blob/master/src/syscall/fd_nacl.go#L17).
-Each file descriptor corresponds to a [`file`](https://github.com/golang/go/blob/master/src/syscall/fd_nacl.go#L23)
-and each `file` provides a value that implements the [`fileImpl`](https://github.com/golang/go/blob/master/src/syscall/fd_nacl.go#L30) interface.
+[`files`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fd_nacl.go#L17).
+Each file descriptor corresponds to a [`file`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fd_nacl.go#L23)
+and each `file` provides a value that implements the [`fileImpl`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fd_nacl.go#L30) interface.
 There are several implementations of the interface:
 
-  - regular files and devices (such as `/dev/random`) are represented by [`fsysFile`](https://github.com/golang/go/blob/master/src/syscall/fs_nacl.go#L58),
-  - standard input, output, and error are instances of [`naclFile`](https://github.com/golang/go/blob/master/src/syscall/fd_nacl.go#L216),
+  - regular files and devices (such as `/dev/random`) are represented by [`fsysFile`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fs_nacl.go#L58),
+  - standard input, output, and error are instances of [`naclFile`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/fd_nacl.go#L216),
     which uses system calls to interact with the actual files (these are a playground
     program's only way to interact with the outside world),
   - network sockets have their own implementation, discussed in the next section.
@@ -260,8 +262,8 @@ implementation of the fake network is larger and more complex than the fake
 file system. It must simulate read and write timeouts, different address types
 and protocols, and so on.
 
-The implementation can be found in [`net_nacl.go`](https://github.com/golang/go/blob/master/src/syscall/net_nacl.go).
-A good place to start reading is [`netFile`](https://github.com/golang/go/blob/master/src/syscall/net_nacl.go#L461),
+The implementation can be found in [`net_nacl.go`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/net_nacl.go).
+A good place to start reading is [`netFile`](https://github.com/golang/go/blob/2197321db1dd997165c0091ba2bcb3b6be7633d0/src/syscall/net_nacl.go#L461),
 the network socket implementation of the `fileImpl` interface.
 
 ## The front end
@@ -292,24 +294,24 @@ code for setting up the user interface (the code and output boxes, the run
 button, and so on) and communicating with the playground front end.
 
 This implementation is in the file
-[`playground.js`](https://github.com/golang/tools/blob/master/godoc/static/playground.js)
+[`playground.js`](https://github.com/golang/tools/blob/f8e922be8efeabd06a510065ca5836b62fa10b9a/godoc/static/playground.js)
 in the `go.tools` repository, which can be imported from the
 [`golang.org/x/tools/godoc/static`](https://godoc.org/golang.org/x/tools/godoc/static) package.
 Some of it is clean and some is a bit crufty, as it is the result of
 consolidating several divergent implementations of the client code.
 
-The [`playground`](https://github.com/golang/tools/blob/master/godoc/static/playground.js#L227)
+The [`playground`](https://github.com/golang/tools/blob/f8e922be8efeabd06a510065ca5836b62fa10b9a/godoc/static/playground.js#L227)
 function takes some HTML elements and turns them into an interactive
 playground widget. You should use this function if you want to put the
 playground on your own site (see 'Other clients' below).
 
-The [`Transport`](https://github.com/golang/tools/blob/master/godoc/static/playground.js#L6)
+The [`Transport`](https://github.com/golang/tools/blob/f8e922be8efeabd06a510065ca5836b62fa10b9a/godoc/static/playground.js#L6)
 interface (not formally defined, this being JavaScript)
 abstracts the user interface from the means of talking to the web front end.
-[`HTTPTransport`](https://github.com/golang/tools/blob/master/godoc/static/playground.js#L43)
+[`HTTPTransport`](https://github.com/golang/tools/blob/f8e922be8efeabd06a510065ca5836b62fa10b9a/godoc/static/playground.js#L43)
 is an implementation of `Transport` that speaks the HTTP-based protocol
 described earlier.
-[`SocketTransport`](https://github.com/golang/tools/blob/master/godoc/static/playground.js#L115)
+[`SocketTransport`](https://github.com/golang/tools/blob/f8e922be8efeabd06a510065ca5836b62fa10b9a/godoc/static/playground.js#L115)
 is another implementation that speaks WebSocket (see 'Playing offline' below).
 
 To comply with the [same-origin policy](https://en.wikipedia.org/wiki/Same-origin_policy),