编译Go代码时遇rego.ReadFile未定义错误求助

错误信息 #

编译时触发如下错误：

-bash-4.2$ go build main.go 
# command-line-arguments
./main.go:20:26: undefined: rego.ReadFile

相关代码 #

discount_policy.rego #

package discounts

rule "Bronze Discount"
    salience 10
    when
        Customer loyaltyLevel == "Bronze"
    then
        Discount.percent = 5;
        Discount.message = "You have earned a 5% discount!";
end

rule "Default Discount"
    salience 0
    then
        Discount.percent = 0;
        Discount.message = "Sorry, no discount available.";
end

main.go（原错误代码） #

package main

import (
        "context"
        "fmt"

        "github.com/open-policy-agent/opa/rego"
)

type Customer struct {
        LoyaltyLevel string `json:"loyaltyLevel"`
}

type Discount struct {
        Percent int    `json:"percent"`
        Message string `json:"message"`
}

func LoadPolicy() (*rego.Rego, error) {
        regoPolicy, err := rego.ReadFile("discount_policy.rego")
        if err != nil {
                return nil, fmt.Errorf("failed to load policy file: %w", err)
        }

        return rego.New(
                rego.Query("data.discounts.Discount"),
                rego.Compiler(regoPolicy),
        ), nil
}        

func main() {
        // Load the GRules policy
        r, err := LoadPolicy()
        if err != nil {
                fmt.Println("Policy loading error:", err)
                return
        }
}

解决方法 #

rego.ReadFile并非OPA rego包的标准公开API，该函数不存在导致编译失败。正确的策略加载方式有两种：

方法一：直接通过rego.File指定文件路径 #

由OPA SDK内部处理文件读取与编译逻辑，代码更简洁：

func LoadPolicy() (*rego.Rego, error) {
        return rego.New(
                rego.Query("data.discounts.Discount"),
                rego.File("discount_policy.rego"), // 直接传入策略文件路径
        ), nil
}

方法二：手动读取文件后通过rego.Module传入 #

若需要对文件内容做预处理，可使用标准库os.ReadFile读取内容，再传递给SDK：

import "os"

func LoadPolicy() (*rego.Rego, error) {
        policyContent, err := os.ReadFile("discount_policy.rego")
        if err != nil {
                return nil, fmt.Errorf("failed to load policy file: %w", err)
        }

        return rego.New(
                rego.Query("data.discounts.Discount"),
                rego.Module("discount_policy.rego", string(policyContent)),
        ), nil
}

修改代码后重新编译即可解决该错误。

内容的提问来源于stack exchange，提问作者van neilsen