backend/internal/pkg/tencent/client.go

package tencent

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"go.uber.org/zap"
)

const (
	host      = "tms.tencentcloudapi.com"
	service   = "tms"
	version   = "2020-12-29"
	action    = "TextModeration"
	algorithm = "TC3-HMAC-SHA256"
)

type Client interface {
	IsEnabled() bool
	TextModeration(ctx context.Context, content string) (*ModerationResponse, error)
}

type clientImpl struct {
	cfg        Config
	httpClient *http.Client
}

func NewClient(cfg Config) Client {
	timeout := cfg.Timeout
	if timeout <= 0 {
		timeout = 30
	}
	return &clientImpl{
		cfg: cfg,
		httpClient: &http.Client{
			Timeout: time.Duration(timeout) * time.Second,
		},
	}
}

func (c *clientImpl) IsEnabled() bool {
	return c.cfg.Enabled && c.cfg.SecretID != "" && c.cfg.SecretKey != ""
}

func (c *clientImpl) TextModeration(ctx context.Context, content string) (*ModerationResponse, error) {
	if !c.IsEnabled() {
		return nil, fmt.Errorf("tencent tms client is not enabled")
	}

	if strings.TrimSpace(content) == "" {
		return &ModerationResponse{Suggestion: SuggestionPass}, nil
	}

	encodedContent := base64.StdEncoding.EncodeToString([]byte(content))
	reqBody := textModerationRequest{
		Content: encodedContent,
		BizType: c.cfg.BizType,
	}
	payload, err := json.Marshal(reqBody)
	if err != nil {
		return nil, fmt.Errorf("marshal request: %w", err)
	}

	timestamp := time.Now().Unix()
	authorization, err := c.sign(string(payload), timestamp)
	if err != nil {
		return nil, fmt.Errorf("sign request: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, "https://"+host, strings.NewReader(string(payload)))
	if err != nil {
		return nil, fmt.Errorf("create request: %w", err)
	}

	req.Header.Set("Authorization", authorization)
	req.Header.Set("Content-Type", "application/json; charset=utf-8")
	req.Header.Set("Host", host)
	req.Header.Set("X-TC-Action", action)
	req.Header.Set("X-TC-Timestamp", strconv.FormatInt(timestamp, 10))
	req.Header.Set("X-TC-Version", version)
	req.Header.Set("X-TC-Region", c.cfg.Region)

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("request tencent tms: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("read response: %w", err)
	}

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("tencent tms error status=%d body=%s", resp.StatusCode, string(body))
	}

	var apiResp tencentAPIResponse
	if err := json.Unmarshal(body, &apiResp); err != nil {
		return nil, fmt.Errorf("unmarshal response: %w", err)
	}

	if apiResp.Response.Error != nil {
		return nil, fmt.Errorf("tencent tms api error: code=%s message=%s",
			apiResp.Response.Error.Code,
			apiResp.Response.Error.Message)
	}

	keywords := make([]string, 0, len(apiResp.Response.Keywords))
	for _, kw := range apiResp.Response.Keywords {
		keywords = append(keywords, kw.Word)
	}

	result := &ModerationResponse{
		Suggestion: ModerationSuggestion(apiResp.Response.Suggestion),
		Label:      apiResp.Response.Label,
		RiskLevel:  apiResp.Response.RiskLevel,
		Keywords:   keywords,
		RequestID:  apiResp.Response.RequestID,
	}

	zap.L().Debug("Tencent TMS moderation result",
		zap.String("suggestion", string(result.Suggestion)),
		zap.String("label", result.Label),
		zap.String("risk_level", result.RiskLevel),
		zap.Strings("keywords", result.Keywords),
		zap.String("request_id", result.RequestID),
	)

	return result, nil
}

func (c *clientImpl) sign(payload string, timestamp int64) (string, error) {
	date := time.Unix(timestamp, 0).UTC().Format("2006-01-02")

	canonicalHeaders := "content-type:application/json; charset=utf-8\n" + "host:" + host + "\n"
	signedHeaders := "content-type;host"
	hashedPayload := sha256hex(payload)

	canonicalRequest := fmt.Sprintf("%s\n%s\n%s\n%s\n%s\n%s",
		"POST",
		"/",
		"",
		canonicalHeaders,
		signedHeaders,
		hashedPayload,
	)

	credentialScope := fmt.Sprintf("%s/%s/tc3_request", date, service)
	hashedCanonicalRequest := sha256hex(canonicalRequest)
	string2sign := fmt.Sprintf("%s\n%d\n%s\n%s",
		algorithm,
		timestamp,
		credentialScope,
		hashedCanonicalRequest,
	)

	secretDate := hmacsha256(date, []byte("TC3"+c.cfg.SecretKey))
	secretService := hmacsha256(service, secretDate)
	secretSigning := hmacsha256("tc3_request", secretService)
	signature := hex.EncodeToString(hmacsha256(string2sign, secretSigning))

	authorization := fmt.Sprintf("%s Credential=%s/%s, SignedHeaders=%s, Signature=%s",
		algorithm,
		c.cfg.SecretID,
		credentialScope,
		signedHeaders,
		signature,
	)

	return authorization, nil
}

func sha256hex(s string) string {
	b := sha256.Sum256([]byte(s))
	return hex.EncodeToString(b[:])
}

func hmacsha256(s string, key []byte) []byte {
	h := hmac.New(sha256.New, key)
	h.Write([]byte(s))
	return h.Sum(nil)
}