derive/
derive.rs

1//! Derive-macro workflow — `Serialize` and `Deserialize`.
2//!
3//! Annotate your structs and enums and get serialize/deserialize for free.
4//! Rename fields with `#[nanojson(rename = "...")]`.
5//!
6//! Shows both API tiers:
7//!
8//! **`std` tier**: `nanojson::stringify` / `nanojson::parse` — one-liners,
9//! no buffer choices.
10//!
11//! **`no_std` tier**: `nanojson::stringify_sized::<N, _>` / `nanojson::parse_sized::<STR_BUF, _>` —
12//! all memory on the stack, caller picks sizes.
13
14extern crate std;
15
16use nanojson::{Serialize, Deserialize};
17
18// ---- Domain types ----
19
20#[derive(Serialize, Deserialize, Debug, PartialEq)]
21struct Vec2 {
22    x: i64,
23    y: i64,
24}
25
26#[derive(Serialize, Deserialize, Debug, PartialEq)]
27struct Entity {
28    id: i64,
29    #[nanojson(rename = "is_active")]
30    active: bool,
31    position: Vec2,
32    health: i64,
33}
34
35// Unit enums serialize to/from JSON strings.
36#[derive(Serialize, Deserialize, Debug, PartialEq)]
37enum Team {
38    Red,
39    Blue,
40    #[nanojson(rename = "spectator")]
41    Spectator,
42}
43
44// Enums with data use externally-tagged format: {"VariantName": {...}}.
45#[derive(Serialize, Deserialize, Debug, PartialEq)]
46enum Event {
47    Spawn { entity_id: i64, x: i64, y: i64 },
48    Death { entity_id: i64 },
49}
50
51fn main() {
52    let entity = Entity {
53        id: 42,
54        active: true,
55        position: Vec2 { x: 100, y: -50 },
56        health: 80,
57    };
58
59    // ----------------------------------------------------------------
60    // std tier — String in, String out, no buffer choices
61    // ----------------------------------------------------------------
62
63    let json = nanojson::stringify(&entity).unwrap();
64    std::println!("Entity JSON (std): {json}");
65
66    let entity2: Entity = nanojson::parse(&json).unwrap();
67    std::println!("Decoded (std):     {:?}", entity2);
68    assert_eq!(entity, entity2);
69
70    // ----------------------------------------------------------------
71    // no_std tier — stack-allocated buffers, explicit sizes
72    //
73    // stringify_sized::<N, _>  — N bytes for the output JSON.
74    // parse_sized::<S, _> — S bytes for the string-decode scratch buffer;
75    //                     only needs to fit the longest single field value.
76    // ----------------------------------------------------------------
77
78    let (buf, len) = nanojson::stringify_sized::<256, _>(&entity).unwrap();
79    std::println!("\nEntity JSON (no_std, {len} bytes): {}", core::str::from_utf8(&buf[..len]).unwrap());
80
81    let entity3: Entity = nanojson::parse_sized::<64, _>(&buf[..len]).unwrap();
82    std::println!("Decoded (no_std):  {:?}", entity3);
83    assert_eq!(entity, entity3);
84
85    // ----------------------------------------------------------------
86    // Unit enum — std and no_std
87    // ----------------------------------------------------------------
88
89    let team = Team::Spectator;
90
91    let json = nanojson::stringify(&team).unwrap();
92    std::println!("\nTeam JSON (std):    {json}");
93    let team2: Team = nanojson::parse(&json).unwrap();
94    assert_eq!(team, team2);
95
96    let (buf, len) = nanojson::stringify_sized::<16, _>(&team).unwrap();
97    std::println!("Team JSON (no_std): {}", core::str::from_utf8(&buf[..len]).unwrap());
98    let team3: Team = nanojson::parse_sized::<16, _>(&buf[..len]).unwrap();
99    assert_eq!(team, team3);
100
101    // ----------------------------------------------------------------
102    // Data enum
103    // ----------------------------------------------------------------
104
105    let events: [Event; 2] = [
106        Event::Spawn { entity_id: 1, x: 0, y: 0 },
107        Event::Death { entity_id: 1 },
108    ];
109
110    for ev in &events {
111        // std
112        let json = nanojson::stringify(ev).unwrap();
113        std::println!("\nEvent JSON (std):    {json}");
114        let ev2: Event = nanojson::parse(&json).unwrap();
115        assert_eq!(*ev, ev2);
116
117        // no_std
118        let (buf, len) = nanojson::stringify_sized::<128, _>(ev).unwrap();
119        std::println!("Event JSON (no_std): {}", core::str::from_utf8(&buf[..len]).unwrap());
120        let ev3: Event = nanojson::parse_sized::<32, _>(&buf[..len]).unwrap();
121        assert_eq!(*ev, ev3);
122    }
123
124    // ----------------------------------------------------------------
125    // Error handling — unknown field, missing field
126    // ----------------------------------------------------------------
127
128    let bad = r#"{"id":1,"is_active":true,"position":{"x":0,"y":0},"health":100,"unknown":999}"#;
129    match nanojson::parse::<Entity>(bad) {
130        Err(e) => std::println!("\nExpected error (unknown field): {:?} at offset {}", e.kind, e.offset),
131        Ok(_)  => panic!("should have failed"),
132    }
133
134    let incomplete = r#"{"id":2,"is_active":false,"position":{"x":1,"y":2}}"#;
135    match nanojson::parse::<Entity>(incomplete) {
136        Err(e) => std::println!("Expected error (missing field): {:?} at offset {}", e.kind, e.offset),
137        Ok(_)  => panic!("should have failed"),
138    }
139
140    // ----------------------------------------------------------------
141    // Size estimation — measure before picking N
142    // ----------------------------------------------------------------
143
144    let n = nanojson::measure(|s| entity.serialize(s));
145    std::println!("\nEntity serializes to {n} bytes — use stringify_sized::<{n}, _> or larger.");
146}
derive/derive.rs

derive/
derive.rs
