# 机器翻译niutrans API 文档

    package main
    import (
        "crypto/hmac"
        "crypto/sha256"
        "encoding/base64"
        "fmt"
        "time"
        "github.com/valyala/fasthttp"
    )
    const (
        // 支持的算法
        Algorithm = "hmac-sha256"
        // 版本协议
        HttpProto = "HTTP/1.1"
        // 假定的secret
        Secret = "12345"
    )
    func assemblyRequestHeader(req *fasthttp.Request, apiKey, host, uri string, body []byte) {
        req.Header.Set("Content-Type", "application/json")
        // 设置请求头 其中Host Date 必须有
        req.Header.Set("Host", host)
        // date必须是utc时区，且不能和服务器时间相差300s
        currentTime := time.Now().UTC().Format(time.RFC1123)
        req.Header.Set("Date", currentTime)
        // 对body进行sha256签名,生成digest头部，POST请求必须对body验证
        digest := "SHA-256=" + signBody(body)
        req.Header.Set("Digest", digest)
        // 根据请求头部内容，生成签名
        sign := generateSignature(host, currentTime,"POST", uri, HttpProto, digest,Secret)
        // 组装Authorization头部
        authHeader := fmt.Sprintf(`api_key="%s", algorithm="%s", headers="host date request-line digest", signature="%s"`, apiKey, Algorithm, sign)
        req.Header.Set("Authorization", authHeader)
    }
    func generateSignature(host, date, httpMethod, requestUri, httpProto, digest string, secret string) string {
        // 不是request-line的话，则以header名称,后跟ASCII冒号:和ASCII空格，再附加header值
        var signatureStr string
        if len(host) != 0 {
            signatureStr = "host: " + host + "\n"
        }
        signatureStr += "date: " + date + "\n"
        // 如果是request-line的话，则以 http_method request_uri http_proto
        signatureStr += httpMethod + " " + requestUri + " " + httpProto + "\n"
        signatureStr += "digest: " + digest
        return hmacsign(signatureStr, secret)
    }
    func hmacsign(data, secret string) string {
        mac := hmac.New(sha256.New, []byte(secret))
        mac.Write([]byte(data))
        encodeData := mac.Sum(nil)
        return base64.StdEncoding.EncodeToString(encodeData)
    }
    func signBody(data []byte) string {
        // 进行sha256签名
        sha := sha256.New()
        sha.Write(data)
        encodeData := sha.Sum(nil)
        // 经过base64转换
        return base64.StdEncoding.EncodeToString(encodeData)
    }