能否从Cloud Storage触发函数返回图片URL这类值？

我想知道是否可以从Cloud Storage触发的云函数中返回存储桶里的图片URL。以下是我当前的实现代码：

const bucket = admin.storage().bucket(fileBucket);

const metadata = {
  contentType: contentType,
};

const downloadResponse = await bucket.file(filePath).download();

const imageBuffer = downloadResponse[0];

functions.logger.log("Image downloaded!");

// Generate a thumbnail using sharp.

const thumbnailBuffer = await sharp(imageBuffer).resize({
  width: 200,
  height: 200,
  withoutEnlargement: true,
}).toBuffer();

functions.logger.log("Thumbnail created");

// Upload the thumbnail with a 'thumb_' prefix.
const thumbFileName = `thumb_${fileName}`;

const thumbFilePath = path.join(path.dirname(filePath), thumbFileName);

await bucket.file(thumbFilePath).save(thumbnailBuffer, {
  metadata: metadata,
});

return functions.logger.log("Thumbnail uploaded!");
});

我尝试修改代码，希望能返回存储桶中的图片URL：

// Download file from bucket.
const bucket = admin.storage().bucket(fileBucket);
const metadata = {
  contentType: contentType,
};
const downloadResponse = await bucket.file(filePath).download();
const imageBuffer = downloadResponse[0];
functions.logger.log("Image downloaded!");

// Generate a thumbnail using sharp.
const thumbnailBuffer = await sharp(imageBuffer).resize({
  width: 200,
  height: 200,
  withoutEnlargement: true,
}).toBuffer();
functions.logger.log("Thumbnail created");

// Upload the thumbnail with a 'thumb_' prefix.
const thumbFileName = `thumb_${fileName}`;
const thumbFilePath = path.join(path.dirname(filePath), thumbFileName);
await bucket.file(thumbFilePath).save(thumbnailBuffer, {
  metadata: metadata,
});
return // potential bucket file image url;

当然可以返回图片URL，根据文件权限需求，有两种实现方式：

1. 文件设为公开可读 #

如果缩略图允许公开访问，可直接构造公开URL：

// 上传完成后获取文件实例
const thumbFile = bucket.file(thumbFilePath);
// 构造公开URL
const publicUrl = `https://storage.googleapis.com/${bucket.name}/${thumbFile.name}`;
// 返回URL
return publicUrl;

注意：需要在上传时设置文件为公开可读权限：

await bucket.file(thumbFilePath).save(thumbnailBuffer, {
  metadata: metadata,
  predefinedAcl: 'publicRead' // 添加此行设置公开权限
});

2. 文件保持私有（生成签名URL） #

如果文件需要私有访问，可生成带过期时间的签名URL：

const thumbFile = bucket.file(thumbFilePath);
// 生成签名URL，设置1小时过期
const [signedUrl] = await thumbFile.getSignedUrl({
  action: 'read',
  expires: '1h' // 支持自定义过期时间，如'2024-12-31'
});
return signedUrl;

完整修改后的代码示例 #

const bucket = admin.storage().bucket(fileBucket);
const metadata = {
  contentType: contentType,
};
const downloadResponse = await bucket.file(filePath).download();
const imageBuffer = downloadResponse[0];
functions.logger.log("Image downloaded!");

// Generate a thumbnail using sharp.
const thumbnailBuffer = await sharp(imageBuffer).resize({
  width: 200,
  height: 200,
  withoutEnlargement: true,
}).toBuffer();
functions.logger.log("Thumbnail created");

// Upload the thumbnail with a 'thumb_' prefix.
const thumbFileName = `thumb_${fileName}`;
const thumbFilePath = path.join(path.dirname(filePath), thumbFileName);
// 设置文件为公开可读
await bucket.file(thumbFilePath).save(thumbnailBuffer, {
  metadata: metadata,
  predefinedAcl: 'publicRead'
});

// 构造并返回公开URL
const publicUrl = `https://storage.googleapis.com/${bucket.name}/${thumbFilePath}`;
functions.logger.log("Thumbnail uploaded! URL:", publicUrl);
return publicUrl;

内容的提问来源于stack exchange，提问作者Samuel Airadion