Add joke api exercise

content/en/docs/exercises/lab_joke_api/_index.md

@@ -0,0 +1,42 @@
+---
+title: "Joke API"
+weight: 9151
+---
+
+Try and solve the following. Every task has links to relevant documentation.
+
+### Request an API
+1. Begin with the following [main.go](main.txt) which requests a joke from https://official-joke-api.appspot.com/random_joke and decodes it into a Go struct.
+2. Refactor the HTTP request into another [function](/docs/basics/functions/) that returns `joke, error`
+3. Update the code to also [decode](/docs/standard-library/json/) and print the punchline
+4. [Delay](https://pkg.go.dev/time#Sleep) the punchline by a few seconds
+5. Make the delay configurable with a `--delay 10` [flag](https://pkg.go.dev/flag)
+
+### Build an API
+6. Write another program that [reads](https://pkg.go.dev/os#ReadFile) a [json file](https://github.com/15Dkatz/official_joke_api/blob/master/jokes/index.json) and picks a [random](https://pkg.go.dev/math/rand#Intn) joke
+7. Implement a [HTTP Server](/docs/standard-library/http-server/) that serves the picked joke
+8. Add a new endpoint that expects a joke and [persists](/docs/standard-library/io/) it
+
+### Use an API
+9. Write another program that asks the user to enter a joke on the command line (standard input) and [sends](/docs/standard-library/http-client/) it to your own API.
+
+
+## Tips
+
+{{%details title="Project structure"%}}
+You cannot have multiple `main` functions in a single directory. If you want to create multiple binaries, these must be separated into different directories. By convention the directory equals the binary name and is located under `cmd/` (e.g. `cmd/request-joke/main.go`).
+{{%/details%}}
+
+{{%details title="Prompt for input on the command line (standard input)"%}}
+With the [bufio](https://pkg.go.dev/bufio) package we can read from the standard input ([os.Stdin](https://pkg.go.dev/os#Stdin)) until a certain character occurs:
+
+```golang
+line, err := bufio.NewReader(os.Stdin).ReadString('\n')
+```
+
+The [strings](https://pkg.go.dev/strings) package contains various functions to work with strings. For example [strings.TrimSpace](https://pkg.go.dev/strings#TrimSpace) to remove whithspace characters (spaces, newlines, etc.) from strings.
+
+```golang
+line = strings.TrimSpace(line)
+```
+{{%/details%}}

content/en/docs/exercises/lab_joke_api/main.txt

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+// If you want to create an executable binary,
+// you must name your package `main`.
+// By using another name, you create a library.
+package main
+
+// Import external modules that you would like to use
+import (
+	"encoding/json" // JSON encoding and decoding
+	"fmt"           // Formatting
+	"io"            // Input/Output
+	"net/http"      // HTTP requests
+	"os"            // Operating System
+)
+
+type joke struct {
+	Type string
+	// The json key can be overridden
+	Message string `json:"setup"`
+}
+
+// The main function is called when executing the binary
+func main() {
+	// Variables are declared using `:=`
+	// The type is automatically evaluated and cannot be modified
+	url := "https://official-joke-api.appspot.com/random_joke"
+	// The following will not work:
+	// url = 9
+
+	// Output a string to the terminal
+	// %v detects the variable type. You may also use %s for strings and %d for digits
+	fmt.Printf("Requesting joke from %v\n", url)
+	// The following would also work:
+	// fmt.Println("Requesting joke from", url)
+
+	// Functions can return multiple results!
+	// The variable names can be freely modified,
+	// but using `err` for the error result is a convention.
+	res, err := http.Get(url)
+	// If the error is not nil, it means an error has occurred
+	if err != nil {
+		fmt.Printf("Error making http request: %v\n", err)
+		// Exit the program with statuscode 1
+		os.Exit(1)
+	}
+	body, err := io.ReadAll(res.Body)
+	if err != nil {
+		fmt.Printf("Error reading response body: %v\n", err)
+		os.Exit(1)
+	}
+	fmt.Printf("Body: %s\n", body)
+
+	// Initialize a new instance of the joke struct
+	j := joke{}
+	// Pass a pointer of j to json.Unmarshal
+	err = json.Unmarshal(body, &j)
+	if err != nil {
+		fmt.Printf("Error decoding body: %v\n", err)
+		os.Exit(1)
+	}
+	fmt.Printf("%+v", j)
+}