Episode 19 - Parsing Arbitrary JSON (#145)

* Episode 19 - consuming unknown JSON input

* dropping use of go-simplejson

* updating docs to reflect not using go-simplejson

* bare link to simplejson

* Adding web page for parsing arbitrary JSON

.gitignore

@@ -28,4 +28,6 @@ glide-v0.12.0-linux-amd64.tar.gz
 *.prof
 episode*/vendor
 episode*/episode*
+episode*/gifm
 www/public
+episode19/vendor

episode19/Makefile

@@ -0,0 +1,4 @@
+build:
+	go build -o gifm
+run:
+	./gifm

episode19/README.md

@@ -0,0 +1,18 @@
+# Consuming Unknown JSON Input
+
+Go in 5 Minutes, episode 19, as requested by [@tmcarr](https://github.com/tmcarr)!
+
+This screencast teaches how to consume some unknown JSON. We don't know what it looks like
+ahead of time, and we have to handle anything that comes our way.
+
+We'll be using only the standard library for this, although we could also use some wonderful 
+packages out there to help. My favorite so far is Bitly's 
+[go-simplejson](https://godoc.org/github.com/bitly/go-simplejson).
+I've always done this type of parsing myself, but I've started using `go-simplejson` and really
+like it. It's well designed and very easy to use!
+
+# Outline
+
+1. Basics of JSON Parsing in Go
+2. Handling different types with recursion :)
+3. Let's see an example!

episode19/init.go

@@ -0,0 +1,8 @@
+package main
+
+import (
+	"log"
+	"os"
+)
+
+var logger = log.New(os.Stdout, "", log.Lshortfile)

episode19/main.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+func main() {
+	if js, err := unmarshal(aDict); err != nil {
+		logger.Fatalf("error decoding (%s)", err)
+	} else {
+		if str, err := ifaceToString(js); err != nil {
+			logger.Fatalf("error converting js (%s)", err)
+		} else {
+			logger.Println(str)
+		}
+	}
+
+	if js, err := unmarshal(aList); err != nil {
+		logger.Fatalf("error decoding (%s)", err)
+	} else {
+		if str, err := ifaceToString(js); err != nil {
+			logger.Fatalf("error converting js (%s)", err)
+		} else {
+			logger.Println(str)
+		}
+	}
+
+	if js, err := unmarshal(anInt); err != nil {
+		logger.Fatalf("error decoding (%s)", err)
+	} else {
+		if str, err := ifaceToString(js); err != nil {
+			logger.Fatalf("error converting js (%s)", err)
+		} else {
+			logger.Println(str)
+		}
+	}
+
+	if js, err := unmarshal(aString); err != nil {
+		logger.Fatalf("error decoding (%s)", err)
+	} else {
+		if str, err := ifaceToString(js); err != nil {
+			logger.Fatalf("error converting js (%s)", err)
+		} else {
+			logger.Println(str)
+		}
+	}
+}
+
+func unmarshal(str string) (interface{}, error) {
+	var iface interface{}
+	decoder := json.NewDecoder(strings.NewReader(str))
+	decoder.UseNumber()
+	if err := decoder.Decode(&iface); err != nil {
+		return nil, err
+	}
+	return iface, nil
+}
+
+func ifaceToString(iface interface{}) (string, error) {
+	switch t := iface.(type) {
+	case map[string]interface{}:
+		strs := make([]string, len(t))
+		i := 0
+		for key, val := range t {
+			str, err := ifaceToString(val)
+			if err != nil {
+				return "", err
+			}
+			strs[i] = fmt.Sprintf("%s: %s", key, str)
+			i++
+		}
+		return "{" + strings.Join(strs, ", ") + "}", nil
+	case []interface{}:
+		strs := make([]string, len(t))
+		i := 0
+		for _, val := range t {
+			str, err := ifaceToString(val)
+			if err != nil {
+				return "", err
+			}
+			strs[i] = str
+			i++
+		}
+		return "[" + strings.Join(strs, ", ") + "]", nil
+	case int:
+		return fmt.Sprintf("%d", t), nil
+	case json.Number:
+		return fmt.Sprintf("%s", t), nil
+	case string:
+		return fmt.Sprintf(`"%s"`, t), nil
+	}
+	return "", fmt.Errorf("unsupported value %#v (%T)", iface, iface)
+}

episode19/unknown_json.go

@@ -0,0 +1,13 @@
+package main
+
+const (
+	aDict = `{
+		"an_int": 1,
+		"a_string": "abc",
+		"an_array": [1, 2, "3"],
+		"a_dict": {"a": 1, "b": 2}
+	}`
+	aList   = `[1, "2", 3, {"four": 4}]`
+	anInt   = `1`
+	aString = `"1"`
+)

www/content/screencast/episode_19_parsing_arbitrary_json.md

@@ -0,0 +1,29 @@
++++
+date = "2018-02-19T11:44:01-08:00"
+title = "Parsing Arbitrary JSON"
+type = "screencast"
+
++++
+
+_Episode 19_
+
+[@tmcarr](https://github.com/tmcarr) requested in 
+[#125](https://github.com/arschles/go-in-5-minutes/issues/125) that I do a screencast
+on how to consume json with unknown fields.
+
+This screencast shows how to exactly that! I'll show how to parse JSON using just the standard
+library, and also point folks to a package that will help if you don't want to steal my code
+(which is totally fine by the way!)
+
+Here ya go [@tmcarr](https://github.com/tmcarr)!
+
+<!--more-->
+
+If you like what you see here, consider 
+[subscribing to the GIFM newsletter](https://www.goin5minutes.com/subscribe/).
+
+Keep on rockin', Gophers!
+
+<iframe width="560" height="315" src="https://www.youtube.com/embed/52yMK6p_cAg" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
+
+Check out the example code [on Github](https://github.com/arschles/go-in-5-minutes/tree/master/episode19).