Blogument Go struct visibility for JSON

content/posts/2022-02-25-go-struct-json-case-gotcha.md

+---
+title: "Gotcha: Field casing is important when marshalling `struct`s to JSON in Go"
+description: "Why you may be missing fields from your `struct`s in your Go `json.Marshal` calls."
+tags:
+- blogumentation
+- go
+- json
+date: 2022-02-25T11:14:24+0000
+license_prose: CC-BY-NC-SA-4.0
+license_code: Apache-2.0
+slug: go-struct-json-case-gotcha
+image: https://media.jvt.me/b41202acf7.png
+syndication:
+- "https://brid.gy/publish/twitter"
+---
+I'm trying to learn a bit of Go, and while working through a few things, I spotted a little gotcha with marshalling JSON from `struct`s.
+
+In tutorials and example code, I've seen a mix of `struct`s with uppercase field names:
+
+```go
+type User struct {
+Name string
+}
+```
+
+But also some with lowercase field names:
+
+```go
+type User struct {
+name string
+}
+```
+
+Thinking that this didn't matter, I started using lowercase names, as I'm more used to lowercase, as a Java developer, and to my surprise, found that serialising this to JSON didn't work.
+
+The following code:
+
+```go
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+type User struct {
+  name string
+}
+
+func main() {
+	r, err := json.Marshal(User{name: "Bob"})
+	if err != nil {
+		panic(err)
+	}
+	fmt.Println(string(r))
+}
+```
+
+Would return me the following output:
+
+```json
+{}
+```
+
+It turns out that this is an expected case, because [according to this answer on StackOverflow](https://stackoverflow.com/a/24837507/2257038):
+
+> This is because only fields starting with a capital letter are exported, or in other words visible outside the curent package (and in the json package in this case).
+
+Therefore, the fix here was to make the following change, so the `Name` field would appear in the JSON as the `$.name` property:
+
+```diff
+ type User struct {
+-  name string
++  Name string `json:"name"`
+ }
+```