数据格式演进史（五）：配置文件简史，从混沌到秩序

XML → JSON → Protobuf → FlatBuffers → Parquet/Arrow

[database]
host = localhost
port = 5432
name = myapp

[server]
host = 0.0.0.0
port = 8080
debug = true

; 想表达这样的结构？
; database:
;   primary:
;     host: localhost
;   replica:
;     host: replica.local

; INI 只能这样：
[database.primary]
host = localhost

[database.replica]
host = replica.local

; 但这只是命名约定，解析器不理解层级关系

; 想表达多个服务器？
; servers: [server1, server2, server3]

; INI 只能这样：
servers = server1,server2,server3
; 或者
server1 = xxx
server2 = xxx
server3 = xxx

; 但逗号分隔的解析全靠应用程序自己

port = 8080      ; 这是字符串 "8080" 还是整数 8080？
debug = true     ; 这是字符串 "true" 还是布尔值 true？
timeout = 30.5   ; 这是字符串还是浮点数？

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <database>
        <primary>
            <host>localhost</host>
            <port>5432</port>
        </primary>
        <replica>
            <host>replica.local</host>
            <port>5432</port>
        </replica>
    </database>
    <servers>
        <server>server1</server>
        <server>server2</server>
        <server>server3</server>
    </servers>
</configuration>

database:
  primary:
    host: localhost
    port: 5432
  replica:
    host: replica.local
    port: 5432

servers:
  - server1
  - server2
  - server3

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

# 正确
database:
  host: localhost
  port: 5432

# 错误（缩进不一致）
database:
  host: localhost
   port: 5432  # 多了一个空格，解析失败或语义错误

# 你以为是这样：
server:
  host: localhost
  port: 8080

# 但因为缩进错误，实际是：
server:
  host: localhost
port: 8080  # 这变成了顶层 key！

countries:
  - US    # 字符串 "US"
  - FR    # 字符串 "FR"
  - NO    # 布尔值 false！！！

countries:
  - "NO"  # 强制为字符串

port: 0123  # 这是 83，不是 123！

version: 1.0   # 浮点数 1.0
version: 1.10  # 浮点数 1.1（末尾的 0 被吃掉）
version: "1.10"  # 字符串 "1.10"

# 方式 1：保留换行符
description: |
  This is line 1
  This is line 2

# 方式 2：折叠换行符
description: >
  This is line 1
  This is line 2

# 方式 3：引号
description: "This is line 1\nThis is line 2"

# 方式 4：块标量（带缩进控制）
description: |2
  This is line 1
  This is line 2

# 方式 5：保留末尾换行
description: |+
  Text

# 方式 6：删除末尾换行
description: |-
  Text

# 运维工程师以为的配置：
resources:
  limits:
    memory: "128Mi"
    cpu: "500m"

# 实际的配置（缩进错误）：
resources:
  limits:
    memory: "128Mi"
  cpu: "500m"  # 这变成了 resources.cpu，不是 limits.cpu！

[database.primary]
host = "localhost"
port = 5432

[database.replica]
host = "replica.local"
port = 5432

servers = ["server1", "server2", "server3"]

# 这是注释

# 基本类型
string = "hello"
integer = 42
float = 3.14
boolean = true
datetime = 2025-01-01T10:00:00Z

# 数组
ports = [8080, 8081, 8082]

# 嵌套表
[database]
host = "localhost"
port = 5432

# 嵌套表的另一种写法
[database.connection]
timeout = 30
max_pool = 10

# 表数组（数组里的每个元素是表）
[[servers]]
name = "alpha"
ip = "10.0.0.1"

[[servers]]
name = "beta"
ip = "10.0.0.2"

database:
  primary:
    host: localhost
    port: 5432
    options:
      timeout: 30
      pool_size: 10
  replicas:
    - host: replica1.local
      port: 5432
    - host: replica2.local
      port: 5432

[database.primary]
host = "localhost"
port = 5432

[database.primary.options]
timeout = 30
pool_size = 10

[[database.replicas]]
host = "replica1.local"
port = 5432

[[database.replicas]]
host = "replica2.local"
port = 5432

# 使用 JSON Schema 验证 YAML
# schema.json
{
  "type": "object",
  "properties": {
    "database": {
      "type": "object",
      "properties": {
        "host": { "type": "string" },
        "port": { "type": "integer", "minimum": 1, "maximum": 65535 }
      },
      "required": ["host", "port"]
    }
  }
}

# config.example.yaml
database:
  host: localhost        # 数据库主机
  port: 5432            # 数据库端口
  # password: secret    # 取消注释并填入密码

// Rust 使用 serde 进行强类型解析
#[derive(Deserialize)]
struct Config {
    database: DatabaseConfig,
}

#[derive(Deserialize)]
struct DatabaseConfig {
    host: String,
    port: u16,  // 明确是整数
}

# 总是给可能有歧义的值加引号
version: "1.10"    # 不是 1.1
country: "NO"      # 不是 false
port: 8080         # 不要写成 08080

# 使用 linter
# yamllint .

INI（简单但有限）
  ↓ 需要嵌套和数组
XML（强大但啰嗦）
  ↓ 需要更简洁
YAML（简洁但有坑）
  ↓ 需要更安全
TOML（简单且明确）