cue语法

安装 cue:

go get -u cuelang.org/go/cmd/cue

常用命令

语法检查：

cue vet mpserver.cue

格式化：

cue fmt mpserver.cue

输出:

cue export mpserver.cue

输出指定参数：

cue export mpserver.cue  -e output

指定参数输出成YAML文件：

cue export mpserver.cue  -e output --out yaml

yaml 文件转换为 cue 文件:

cue import deployment.yaml

详细语法说明

导入golang包

cuelang 可以导入 golang 的包，比如可以导入 json包来处理 json 文件，导入strconv包做字符串和整型转换：

import (
    "strconv"
    "encoding/json"
)

test: {
    name: strconv.FormatInt(parameter.value, 10)
    test: json.Marshal(testvalue)
}

testvalue = {"value": 10}

parameter: {
    name: string
    value: int
}

# 设置值
parameter: {
    name: "test"
    value: 10
}

结果output:

$ cue export cue-test.cue
{
    "test": {
        "name": "10",
        "test": "{\"value\":10}"
    },
    "parameter": {
        "name": "test",
        "value": 10
    }
}

字符串拼接

cuelang 可以通过 \(变量) 将变量和字符串拼接：

import (
    "strconv"
    "encoding/json"
)

test: {
    name: strconv.FormatInt(parameter.value, 10)
    test: "example: \(json.Marshal(testvalue))"
}

testvalue = {"value": 10}

parameter: {
    name: string
    value: int
}

parameter: {
    name: "test"
    value: 10
}

结果output:

$ cue export cue-test.cue
{
    "test": {
        "name": "10",
        "test": "example: {\"value\":10}"
    },
    "parameter": {
        "name": "test",
        "value": 10
    }
}

参数定义为可选参考

cuelang 中 ? 表示参数可选：

import (
    "encoding/json"
)

test: {
    name: parameter.name
    value: json.Marshal(testvalue)
}

testvalue = {"value": 10}

parameter: {
    name: string
    value?: int
}

parameter: {
    name: "test"
}

结果output:

$ cue export cue-test.cue
{
    "test": {
        "name": "test",
        "value": "{\"value\":10}"
    },
    "parameter": {
        "name": "test"
    }
}

设置默认值

cuelang 用*表示默认值：

test: {
    name: *parameter.name | "test" //缺失就会用默认值代替
    value: *parameter.value | 0
}

parameter: {
    name: string
    value?: int
}

parameter: {
    name: "new"
}

结果output:

$ cue export cue-test.cue
{
    "test": {
        "name": "new",
        "value": 0
    },
    "parameter": {
        "name": "new"
    }
}

条件判断

cue 的条件判断也是用 if，语法和 golang一致，不过表示空对象用_|_表示：

test: {
    name: parameter["name"]
    if parameter.value != _|_ {
        value: parameter.value
    }
    
}

parameter: {
    name: string
    value?: int
}

parameter: {
    name: "test"
}

结果output:

$ cue export cue-test.cue
{
    "test": {
        "name": "new"
    },
    "parameter": {
        "name": "new"
    }
}

逻辑比较运算符

cuelang 提供了逻辑运算符，比如 | 和 &，用法如下：

test: {
    name: parameter["name"]
	value: parameter["value"]
}

parameter: {
    name: string
    value?: *0 | >=0 & < 10
}

parameter: {
    name: "test"
    value: 11
}

结果output:

$ cue export cue-test.cue
parameter.value: empty disjunction: conflicting values 0 and 11:
    .\cue-test.cue:8:14
    .\cue-test.cue:13:12
test.value: empty disjunction: conflicting values 0 and 11:
    .\cue-test.cue:8:14
    .\cue-test.cue:13:12
parameter.value: empty disjunction: invalid value 11 (out of bound <10):
    .\cue-test.cue:8:24
    .\cue-test.cue:13:12
test.value: empty disjunction: invalid value 11 (out of bound <10):
    .\cue-test.cue:8:24
    .\cue-test.cue:13:12

将 parameter 的值 value 改为 5:

$ cue export cue-test.cue
{
    "test": {
        "name": "test",
        "value": 5
    },
    "parameter": {
        "name": "test",
        "value": 5
    }
}

循环语句 for 和 数组

cuelang 里面的数组：

test: {
    name: parameter["name"]
	value: parameter["value"]
}

parameter: {
    name: [...string]
    value?: [... >=0 & < 10 & int]
}

parameter: {
    name: ["test1","test2"]
    value: [5]
}

output结果输出：

$ cue export cue-test.cue
{
    "test": {
        "name": [
            "test1",
            "test2"
        ],
        "value": [
            5
        ]
    },
    "parameter": {
        "name": [
            "test1",
            "test2"
        ],
        "value": [
            5
        ]
    }
}

循环：

test: {
    key: [
        for k,v in parameter["name"]{
            name: v
        }
    ]
}

parameter: {
    name: [...string]
}

parameter: {
    name: ["test1","test2"]
}

output 结果输出：

$ cue export cue-test.cue
{
    "test": {
        "key": [
            {
                "name": "test1"
            },
            {
                "name": "test2"
            }
        ]
    },
    "parameter": {
        "name": [
            "test1",
            "test2"
        ]
    }
}

vela 里面的 cuelang 模板

后面我们通过vela的模板文件进行 cue 语法学习：

output: {
	apiVersion: "apps/v1"
	kind:       "Deployment"
	spec: {
		selector: matchLabels: {
			"app.oam.dev/component": context.name
			"app":                   context.name
		}

		template: {
			metadata: labels: {
				"app.oam.dev/component": context.name
				"app":                   context.name
			}

			spec: {
				containers: [{
					name:  context.name
					image: parameter.image

					if parameter["cmd"] != _|_ {
						command: parameter.cmd
					}

					if parameter["env"] != _|_ {
						env: parameter.env
					}

					if context["config"] != _|_ {
						env: context.config
					}

					ports: [{
						containerPort: parameter.port
					}]

					if parameter["cpu"] != _|_ {
						resources: {
							limits:
								cpu: parameter.cpu
							memory: parameter.memory
							requests:
								cpu: parameter.cpu
							memory: parameter.memory
						}
					}

				}]
		}
		}
	}
}

parameter: {
	// +usage=Which image would you like to use for your service
	// +short=i
	image: string

	// +usage=Commands to run in the container
	cmd?: [...string]

	// +usage=Which port do you want customer traffic sent to
	// +short=p
	port: *80 | int
	// +usage=Define arguments by using environment variables
	env?: [...{
		// +usage=Environment variable name
		name: string
		// +usage=The value of the environment variable
		value?: string
		// +usage=Specifies a source the value of this var should come from
		valueFrom?: {
			// +usage=Selects a key of a secret in the pod's namespace
			secretKeyRef: {
				// +usage=The name of the secret in the pod's namespace to select from
				name: string
				// +usage=The key of the secret to select from. Must be a valid secret key
				key: string
			}
		}
	}]
	// +usage=Number of CPU units for the service, like `0.5` (0.5 CPU core), `1` (1 CPU core)
	cpu?: string
	// +usage=Number of CPU units for the service, like `0.5` (0.5 CPU core), `1` (1 CPU core)
	memory?: string
}

parameter: {
	image: "test"
	cmd: ["nginx"]
}

context: {
    name: "test"
}