video-compliance-ai/backend/app/services/oss.py

"""
火山引擎 TOS (Volcengine Object Storage) 服务 — 表单直传签名 (V4)
"""
import time
import hmac
import base64
import hashlib
import json
from typing import Optional
from datetime import datetime, timezone
from app.config import settings


def generate_upload_policy(
    max_size_mb: int = 500,
    expire_seconds: int = 3600,
    upload_dir: Optional[str] = None,
) -> dict:
    """
    生成前端直传 TOS 所需的 Policy 和签名 (V4 HMAC-SHA256)

    TOS 表单直传签名流程 (PostObject):
    1. 构建 policy JSON → Base64 编码
    2. 派生签名密钥: kDate → kRegion → kService → kSigning
    3. signature = HMAC-SHA256(kSigning, policy_base64)

    Returns:
        {
            "x_tos_algorithm": "TOS4-HMAC-SHA256",
            "x_tos_credential": "AKIDxxxx/20260210/cn-beijing/tos/request",
            "x_tos_date": "20260210T120000Z",
            "x_tos_signature": "...",
            "policy": "base64 encoded policy",
            "host": "https://bucket.tos-cn-beijing.volces.com",
            "dir": "uploads/2026/02/",
            "expire": 1234567890,
        }
    """
    if not settings.TOS_ACCESS_KEY_ID or not settings.TOS_SECRET_ACCESS_KEY:
        raise ValueError("TOS 配置未设置")

    # 计算时间
    now_utc = datetime.now(timezone.utc)
    date_stamp = now_utc.strftime("%Y%m%d")  # 20260210
    tos_date = now_utc.strftime("%Y%m%dT%H%M%SZ")  # 20260210T120000Z
    expire_time = int(time.time()) + expire_seconds
    expiration = datetime.fromtimestamp(expire_time, tz=timezone.utc).strftime(
        "%Y-%m-%dT%H:%M:%S.000Z"
    )

    # Credential scope
    region = settings.TOS_REGION
    credential = f"{settings.TOS_ACCESS_KEY_ID}/{date_stamp}/{region}/tos/request"

    # 默认上传目录：uploads/年/月/
    if upload_dir is None:
        now = datetime.now()
        upload_dir = f"uploads/{now.year}/{now.month:02d}/"

    # 1. 构建 Policy
    policy_dict = {
        "expiration": expiration,
        "conditions": [
            {"bucket": settings.TOS_BUCKET_NAME},
            ["starts-with", "$key", upload_dir],
            {"x-tos-algorithm": "TOS4-HMAC-SHA256"},
            {"x-tos-credential": credential},
            {"x-tos-date": tos_date},
            ["content-length-range", 0, max_size_mb * 1024 * 1024],
        ],
    }

    # 2. Base64 编码 Policy
    policy_json = json.dumps(policy_dict)
    policy_base64 = base64.b64encode(policy_json.encode()).decode()

    # 3. 派生签名密钥 (V4 Signing Key)
    k_date = hmac.new(
        f"TOS4{settings.TOS_SECRET_ACCESS_KEY}".encode(),
        date_stamp.encode(),
        hashlib.sha256,
    ).digest()

    k_region = hmac.new(k_date, region.encode(), hashlib.sha256).digest()
    k_service = hmac.new(k_region, b"tos", hashlib.sha256).digest()
    k_signing = hmac.new(k_service, b"request", hashlib.sha256).digest()

    # 4. signature = HMAC-SHA256(kSigning, policy_base64)
    signature = hmac.new(
        k_signing,
        policy_base64.encode(),
        hashlib.sha256,
    ).hexdigest()

    # 构建 Host
    endpoint = settings.TOS_ENDPOINT or f"tos-cn-{region}.volces.com"
    host = f"https://{settings.TOS_BUCKET_NAME}.{endpoint}"

    return {
        "x_tos_algorithm": "TOS4-HMAC-SHA256",
        "x_tos_credential": credential,
        "x_tos_date": tos_date,
        "x_tos_signature": signature,
        "policy": policy_base64,
        "host": host,
        "dir": upload_dir,
        "expire": expire_time,
    }


def get_file_url(file_key: str) -> str:
    """
    获取文件的访问 URL

    优先使用 CDN 域名，否则用 TOS 源站域名。

    Args:
        file_key: 文件在 TOS 中的 key，如 "uploads/2026/02/video.mp4"

    Returns:
        完整的访问 URL
    """
    if settings.TOS_CDN_DOMAIN:
        host = settings.TOS_CDN_DOMAIN
    else:
        endpoint = settings.TOS_ENDPOINT or f"tos-cn-{settings.TOS_REGION}.volces.com"
        host = f"https://{settings.TOS_BUCKET_NAME}.{endpoint}"

    # 确保 host 以 https:// 开头
    if not host.startswith("http"):
        host = f"https://{host}"

    # 确保 host 不以 / 结尾
    host = host.rstrip("/")

    # 确保 file_key 不以 / 开头
    file_key = file_key.lstrip("/")

    return f"{host}/{file_key}"


def parse_file_key_from_url(url: str) -> str:
    """
    从完整 URL 解析出文件 key

    Args:
        url: 完整的 TOS URL

    Returns:
        文件 key
    """
    # 尝试移除 CDN 域名
    if settings.TOS_CDN_DOMAIN:
        cdn = settings.TOS_CDN_DOMAIN.rstrip("/")
        if not cdn.startswith("http"):
            cdn = f"https://{cdn}"
        if url.startswith(cdn):
            return url[len(cdn):].lstrip("/")

    # 尝试移除 TOS 源站域名
    endpoint = settings.TOS_ENDPOINT or f"tos-cn-{settings.TOS_REGION}.volces.com"
    tos_host = f"https://{settings.TOS_BUCKET_NAME}.{endpoint}"
    if url.startswith(tos_host):
        return url[len(tos_host):].lstrip("/")

    return url