通过网络发送文件时如何指定文件结尾 [英] How to specify end of file when sending it over network

问题描述

我的servlet使用FileInputStream.read（）从二进制文件读取。如果到达文件末尾，则返回-1。然后，它通过响应流将文件的字节发送给客户端。

My servlet reads from a binary file using the FileInputStream.read(). This returns -1 if end of file is reached. It then sends the bytes of the file to the client over the response stream.

然后我想通过响应流发送文件的md5哈希的字节。我应该如何从文件的md5中拆分文件的末尾，以便客户端知道哪些字节是哪个？我无法发送-1字节，因为这样流就无法正常工作。

I want to then send the bytes of a md5 hash of the file over the response stream. How should i split the end of file from the md5 of the file so that the client knows which bytes are which? I can't send a -1 byte because then the stream stops working.

我是否可以发送其他任何字节来通知文件末尾，我知道不可能在实际文件中，因此也就不可能表明文件末尾

Are there any other bytes i can send to signal end of file that i know could not possibly be inside the actual file, and so not possibly signal the end of the file before it actually ends?

推荐答案

假设您可以依靠文件不进行更改，那么我将读取文件一次并计算MD5哈希，将其设置为标头，然后将文件写为完整正文。对于客户端来说，这比将主体分成两部分要容易得多。

Assuming you can rely on the file not to change, I would read the file once and compute the MD5 hash, set that as a header, and then write the file out as the complete body. That's likely to be easier for the client to handle than splitting the body into two parts.

如果文件足够小，则可以将其写入 ByteArrayOutputStream 在读取/哈希它时，避免不得不读取两次-但是，如果文件很大，则可能不想占用该内存。

If the file is small enough, you could write it into a ByteArrayOutputStream as you read/hash it, to avoid having to read it twice - but if the file is large, you probably don't want to take that memory hit.

另一种选择是将散列存储在文件系统中-首先进行负责文件散列的写入。这样，您只需要对其哈希一次即可；您可以随时对它进行哈希处理，以在必要时对它们进行 verify 验证。

Another option is to store the hash in the file system - make whatever's writing the file in the first place responsible for hashing it. That way you only need to hash it once; you could always hash it as you read it to verify the hash if necessary.

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