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Inside the "present" tool |
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Andrew Gerrand |
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Google |
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@enneff |
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adg@golang.org |
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https://go.dev |
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* The Playground API |
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The API used by the Playground (and the Tour) is a simple HTTP POST request |
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that returns a JSON-encoded response. |
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Request: |
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POST /compile HTTP/1.1 |
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Host:play.golang.org |
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Content-Length:113 |
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Content-Type:application/x-www-form-urlencoded; charset=UTF-8 |
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body=package+main%0A%0Aimport+%22fmt%22%0A%0Afunc+main()+%7B%0A%09fmt.Println(%22Hello%2C+playground%22)%0A%7D%0A |
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Response body: |
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{"compile_errors":"","output":"Hello, playground\n"} |
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* Playground drawbacks |
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The compile service has no concept of time. (Necessary to limit resource use.) |
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The API reflects this; output is sent in one blob, not streamed. |
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Even when running locally, the API is bad for demonstrating code that uses time. |
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Rob needed to use time in his _Go_Concurrency_Patterns_ talk. |
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* Enter WebSockets |
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WebSockets are a bi-directional communication channel between a JavaScript program running in a web browser and a web server. They are part of HTML 5. |
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The `websocket` package in Go's `go.net` sub-repository provides a WebSocket client and server. |
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I thought I could use WebSockets to stream program output to a running |
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presentation. |
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And thus the `present` tool was born. |
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* Hello, WebSocket |
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.code insidepresent/websocket.js |
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.play insidepresent/websocket.go |
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* Messages |
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The client (browser) and server (present) communicate with JSON-encoded messages. |
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.code insidepresent/socket.go /Message is/,/^}/ |
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Go's `encoding/json` format can convert these `Message` values to and from JSON. |
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Go: |
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Message{Id: "0", Kind: "run", Body: `package main; func main() { print("hello"); }`} |
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JSON: |
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{"Id":"0","Kind":"run","Body":"package main; func main() { print(\"hello\"); }"} |
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* On the wire |
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.play insidepresent/hello.go |
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.html insidepresent/wire.html |
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* Implementation |
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* socketHandler (1/3) |
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First, register the handler with the `net/http` package: |
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http.Handle("/socket", websocket.Handler(socketHandler)) |
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Implementation: |
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.code insidepresent/socket.go /func socketHandler/,/errc/ |
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* socketHandler (2/3) |
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.code insidepresent/socket.go /Decode messages/,/END/ |
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* socketHandler (3/3) |
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.code insidepresent/socket-simple.go /Start and kill/,/^}/ |
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* Process |
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.code insidepresent/socket.go /Process represents/,/^}/ |
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* StartProcess |
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.code insidepresent/socket.go /StartProcess builds/,/^}/ |
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* Process.start (1/2) |
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.code insidepresent/socket.go /start builds/,/END/ |
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* Process.start (2/2) |
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.code insidepresent/socket.go /build x\.go/,/^}/ |
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* Process.cmd |
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.code insidepresent/socket.go /cmd builds/,/^}/ |
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.code insidepresent/socket.go /messageWriter is/,/END/ |
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* Process.wait and Process.end |
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.code insidepresent/socket.go /wait waits/,/^}/ |
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.code insidepresent/socket.go /end sends/,/^}/ |
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* Process.Kill |
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.code insidepresent/socket.go /Kill stops/,/^}/ |
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* One more thing |
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* Limiting output (1/2) |
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.code insidepresent/socket.go /switch m\.Kind/,/^ }/ |
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* Limiting output (2/2) |
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.code insidepresent/socket.go /limiter returns/,/^}/ |
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