《使用Gin框架构建分布式应用》阅读笔记：p77-p87

《用Gin框架构建分布式应用》学习第5天，p77-p87总结，总计11页。

一、技术总结

1.Go知识点

(1)context

2.on-premises software

p80, A container is like a separate OS, but not virtualized; it only contains the dependencies needed for that one application, which makes the container portable and deployable on-premises or on the cloud。

premises的意思是“the land and buildings owned by someone, especially by a company or organization(归属于某人(尤指公司、组织)的土地或建筑物)”。简单来说 on-premises software 指的是运行在本地的服务(软件)。

wiki 对这个名称的定义很好，这里直接引用“On-premises software (abbreviated to on-prem, and often written as "on-premise") is installed and runs on computers on the premises of the person or organization using the software, rather than at a remote facility such as a server farm or cloud”。

3.openssl rand命令

openssl rand -base64 12 | docker secret create mongodb_password
-

rand 命令语法：

openssl rand [-help] [-out file] [-base64] [-hex] [-engine id] [-rand files] [-writerand file] [-provider name] [-provider-path path] [-propquery propq] num[K|M|G|T]

12对应 num参数。rand详细用法参考https://docs.openssl.org/3.4/man1/openssl-rand/。对于一个命令，我们需要掌握其有哪些参数及每个参数的含义。

4.查看docker latest tag对应的版本号

(1)未下载镜像

打开latest tag对应的页面，如：https://hub.docker.com/layers/library/mongo/latest/images/sha...，搜索 VERSION，然后找到版本号。

(2)已下载镜像

使用 docker inspect 命令进行查看。

# docker inspect d32 | grep -i version
        "DockerVersion": "",
                "GOSU_VERSION=1.17",
                "JSYAML_VERSION=3.13.1",
                "MONGO_VERSION=8.0.1",
                "org.opencontainers.image.version": "24.04"

5.mongo-go-driver示例

书上代码使用的mongo-go-driver v1.4.5，现在已经更新到了v2.0.0，导致有些代码无法运行，建议使用最新版。这里还得再吐槽下 Go 生态圈的文档写得太糟糕了。示例：

client, _ := mongo.Connect(options.Client().ApplyURI("mongodb://localhost:27017"))
ctx, cancel = context.WithTimeout(context.Background(), 2*time.Second)
defer cancel()

_ = client.Ping(ctx, readpref.Primary())

个人认为，上面的代码 err 就不应该忽略掉。而应该是：

package main

import (
    "context"
    "github.com/gin-gonic/gin"
    "github.com/rs/xid"
    "go.mongodb.org/mongo-driver/v2/mongo"
    "go.mongodb.org/mongo-driver/v2/mongo/options"
    "go.mongodb.org/mongo-driver/v2/mongo/readpref"
    "log"
    "net/http"
    "strings"
    "time"
)

type Recipe struct {
    ID           string    `json:"id"`
    Name         string    `json:"name"`
    Tags         []string  `json:"tags"`
    Ingredients  []string  `json:"ingredients"`
    Instructions []string  `json:"instructions"`
    PublishAt    time.Time `json:"publishAt"`
}

var recipes []Recipe

func init() {
    // 方式1：使用内存进行初始化
    // recipes = make([]Recipe, 0)
    // file, err := os.Open("recipes.json")
    // if err != nil {
    //     log.Fatal(err)
    //     return
    // }
    // defer file.Close()
    //
    // // 反序列化：将json转为slice
    // decoder := json.NewDecoder(file)
    // err = decoder.Decode(&recipes)
    // if err != nil {
    //     log.Fatal(err)
    //     return
    // }

    // 方式2：使用 MongoDB 存储数据
    ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
    defer cancel()
    // 创建连接,这里的 err 针对的是 URI 错误
    client, err := mongo.Connect(options.Client().ApplyURI("mongodb1://admin:admin@localhost:27017"))
    if err != nil {
        log.Fatal("MongoDB connect error: ", err)
    }

    // 判断连接是否成功
    if err := client.Ping(ctx, readpref.Primary()); err != nil {
        log.Fatal("MongoDB Ping error: ", err)
    }

    log.Println("Connected to MongoDB successfully.")

}

// swagger:route POST /recipes  createRecipe
//
// # Create a new recipe
//
// Responses:
//
//    200: recipeResponse
//
// NewRecipeHandler 新增recipe,是按照单个新增，所以这里名称这里用的是单数
func NewRecipeHandler(c *gin.Context) {
    var recipe Recipe
    if err := c.ShouldBindJSON(&recipe); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    recipe.ID = xid.New().String()
    recipe.PublishAt = time.Now()
    recipes = append(recipes, recipe)
    c.JSON(http.StatusOK, recipe)
}

// swagger:route GET /recipes  listRecipes
// Returns list of recipes
// ---
// produces:
// - application/json
// responses:
// '200':
// description: Successful operation
// ListRecipesHandler 差下recipes，因为是查询所有，所以名称这里用的是复数
func ListRecipesHandler(c *gin.Context) {
    c.JSON(http.StatusOK, recipes)
}

// UpdateRecipeHandler 更新 recipe，因为是单个，所以使用的是单数。
// id 从 path 获取，其它参数从 body 获取。
func UpdateRecipeHandler(c *gin.Context) {
    id := c.Param("id")

    // 数据解码
    var recipe Recipe
    if err := c.ShouldBindJSON(&recipe); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    // 判断 id 是否存在
    index := -1
    for i := 0; i < len(recipes); i++ {
        if recipes[i].ID == id {
            index = i
        }
    }

    // 如果 id 不存在
    if index == -1 {
        c.JSON(http.StatusNotFound, gin.H{"error": "recipe not found"})
        return
    }
    // 如果 id 存在则进行更新
    recipes[index] = recipe
    c.JSON(http.StatusOK, recipe)
}

// DeleteRecipeHandler 删除 recipe: 1.删除之前判断是否存在，存在就删除，不存在就提示不存在。
func DeleteRecipeHandler(c *gin.Context) {
    id := c.Param("id")
    index := -1
    for i := 0; i < len(recipes); i++ {
        if recipes[i].ID == id {
            index = i
        }
    }

    if index == -1 {
        c.JSON(http.StatusNotFound, gin.H{"message": "recipe not found"})
        return
    }
    recipes = append(recipes[:index], recipes[index+1:]...)
    c.JSON(http.StatusOK, gin.H{
        "message": "recipe deleted",
    })
}

// SearchRecipesHandler 查询 recipes
func SearchRecipesHandler(c *gin.Context) {
    tag := c.Query("tag")
    listOfRecipes := make([]Recipe, 0)

    for i := 0; i < len(recipes); i++ {
        found := false
        for _, t := range recipes[i].Tags {
            if strings.EqualFold(t, tag) {
                found = true
            }
            if found {
                listOfRecipes = append(listOfRecipes, recipes[i])
            }
        }
    }
    c.JSON(http.StatusOK, listOfRecipes)
}
func main() {
    router := gin.Default()
    router.POST("/recipes", NewRecipeHandler)
    router.GET("/recipes", ListRecipesHandler)
    router.PUT("/recipes/:id", UpdateRecipeHandler)
    router.DELETE("/recipes/:id", DeleteRecipeHandler)
    router.GET("/recipes/search", SearchRecipesHandler)
    err := router.Run()
    if err != nil {
        return
    }
}

二、英语总结

1.ephemeral

p79, I opted to go with Docker duce to its popularity and simplicity in runing ephermeral environment.

(1)ephemeral: ephemera + -al。

(2)ephemera: epi-("on") + hemera("day"), lasting one day , short-lived"。

三、其它

从目前的阅读体验来看，作者默认读者充分掌握Golang，丝毫不会展开介绍。

四、参考资料

1. 编程

(1) Mohamed Labouardy，《Building Distributed Applications in Gin》：https://book.douban.com/subject/35610349

2. 英语

(1) Etymology Dictionary：https://www.etymonline.com

(2) Cambridge Dictionary：https://dictionary.cambridge.org

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