从Blob Storage通过Download to Buffer获取PDF出现空白问题求助

最初遇到大量错误，首个错误为：Content-Length mismatch: too many bytes written (216523 of 215706)。修复该错误后，PDF可成功下载，但文件内容为空白（原PDF应有内容）。相关代码如下：

let blobUrl = fileUrl;

if (!blobUrl) {
    req.context.log(`Skipping attachment, URL is not yet ready.`, new Date().toString());
    return res.status(400).send({ message: 'Attachment is not ready.' });
} else {
    let sharedKeyCredential = new StorageSharedKeyCredential(utility.dec(client.storageName), utility.dec(client.storageKey));
    let blobServiceClient = new BlobServiceClient(
        `https://${utility.dec(client.storageName)}.blob.core.windows.net`,
        sharedKeyCredential
    );

    let urlParts = new URL(blobUrl);
    let pathParts = urlParts.pathname.split('/');
    let blobName = pathParts.slice(2).join('/'); 

    let sourceBlob = blobServiceClient.getContainerClient(constants.BLOB_CONTAINER_ATTACHMENT).getBlobClient(blobName);

    req.context.log('Downloading blob:', blobName);

    const pdfFile = await sourceBlob.downloadToBuffer({
        onProgress: (progress) => {
          req.context.log(`Downloaded ${progress.loadedBytes} bytes`);
        }
      });
    
    res.setHeader('Content-Type', 'application/pdf');
    res.setHeader('Content-Disposition', `attachment; filename="${blobName}"`);
    res.set('Transfer-Encoding', 'identity');
    res.send(pdfFile);

1. 移除Transfer-Encoding手动设置 #

Express会根据响应内容自动处理Content-Length和编码方式，手动设置Transfer-Encoding: identity会和自动计算的内容长度冲突，既会引发Content-Length mismatch错误，也可能导致内容传输异常。

2. 修正文件名转义问题 #

Content-Disposition中的文件名使用了HTML实体"，这会导致文件名解析异常，应直接使用单引号或正确转义的双引号。

3. 验证Blob内容有效性 #

在发送响应前添加日志，确认下载的buffer长度，避免因路径解析错误下载了空文件。

修改后的代码 #

let blobUrl = fileUrl;

if (!blobUrl) {
    req.context.log(`Skipping attachment, URL is not yet ready.`, new Date().toString());
    return res.status(400).send({ message: 'Attachment is not ready.' });
} else {
    let sharedKeyCredential = new StorageSharedKeyCredential(utility.dec(client.storageName), utility.dec(client.storageKey));
    let blobServiceClient = new BlobServiceClient(
        `https://${utility.dec(client.storageName)}.blob.core.windows.net`,
        sharedKeyCredential
    );

    let urlParts = new URL(blobUrl);
    let pathParts = urlParts.pathname.split('/');
    let blobName = pathParts.slice(2).join('/'); 

    let sourceBlob = blobServiceClient.getContainerClient(constants.BLOB_CONTAINER_ATTACHMENT).getBlobClient(blobName);

    req.context.log('Downloading blob:', blobName);

    const pdfFile = await sourceBlob.downloadToBuffer({
        onProgress: (progress) => {
          req.context.log(`Downloaded ${progress.loadedBytes} bytes`);
        }
      });
    
    // 验证buffer是否有效
    req.context.log(`Downloaded buffer length: ${pdfFile.length}`);
    if (pdfFile.length === 0) {
        return res.status(500).send({ message: 'Downloaded blob is empty.' });
    }

    res.setHeader('Content-Type', 'application/pdf');
    // 修正文件名转义，使用单引号避免转义问题
    res.setHeader('Content-Disposition', `attachment; filename='${blobName}'`);
    // 移除手动设置的Transfer-Encoding
    res.send(pdfFile);
}

额外排查点 #

• 确认blobName解析是否正确：打印blobName值，验证是否和存储中的Blob路径一致，避免因路径错误下载了不存在或空的Blob。
• 检查Azure Blob存储中的目标PDF是否确实有内容：直接在Azure Portal中查看Blob的大小和内容，排除源文件本身为空的可能。

内容的提问来源于stack exchange，提问作者hellblazer