fs.read(fd, buffer, offset, length, position, callback)

• fd <integer>

• buffer <Buffer> | <TypedArray> | <DataView> 数据将写入的缓冲区。

  ¥buffer <Buffer> | <TypedArray> | <DataView> The buffer that the data will be written to.

• offset <integer> 要写入数据的 buffer 中的位置。

  ¥offset <integer> The position in buffer to write the data to.

• length <integer> 读取的字节数。

  ¥length <integer> The number of bytes to read.

• position <integer> | <bigint> | <null> 指定从文件中开始读取的位置。如果 position 为 null 或 -1 ，则将从当前文件位置读取数据，并更新文件位置。如果 position 是整数，则文件位置将保持不变。

  ¥position <integer> | <bigint> | <null> Specifies where to begin reading from in the file. If position is null or -1 , data will be read from the current file position, and the file position will be updated. If position is an integer, the file position will be unchanged.

• callback <Function>

  • err <Error>

  • bytesRead <integer>

  • buffer <Buffer>

从 fd 指定的文件中读取数据。

¥Read data from the file specified by fd.

回调被赋予三个参数，(err, bytesRead, buffer)。

¥The callback is given the three arguments, (err, bytesRead, buffer).

如果未同时修改文件，当读取的字节数为零时，则到达文件末尾。

¥If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.

如果此方法作为其 util.promisify() 版本被调用，则返回具有 bytesRead 和 buffer 属性的 Object 的 promise。

¥If this method is invoked as its util.promisify()ed version, it returns a promise for an Object with bytesRead and buffer properties.

fs.read() 方法从文件描述符 (fd) 指定的文件中读取数据。length 参数指示 Node.js 将尝试从内核读取的最大字节数。然而，由于各种原因，实际读取的字节数 (bytesRead) 可能低于指定的 length。

¥The fs.read() method reads data from the file specified by the file descriptor (fd). The length argument indicates the maximum number of bytes that Node.js will attempt to read from the kernel. However, the actual number of bytes read (bytesRead) can be lower than the specified length for various reasons.

例如：

¥For example:

• 如果文件比指定的 length 短，bytesRead 将被设置为实际读取的字节数。

  ¥If the file is shorter than the specified length, bytesRead will be set to the actual number of bytes read.

• 如果文件在缓冲区被填充之前遇到 EOF（文件结束），Node.js 将读取所有可用字节，直到遇到 EOF，回调中的 bytesRead 参数将指示实际读取的字节数，该数可能会更少比指定的 length。

  ¥If the file encounters EOF (End of File) before the buffer could be filled, Node.js will read all available bytes until EOF is encountered, and the bytesRead parameter in the callback will indicate the actual number of bytes read, which may be less than the specified length.

• 如果文件位于慢速网络 filesystem 上或在读取过程中遇到任何其他问题，则 bytesRead 可以低于指定的 length。

  ¥If the file is on a slow network filesystem or encounters any other issue during reading, bytesRead can be lower than the specified length.

因此，在使用 fs.read() 时，检查 bytesRead 值以确定实际从文件中读取了多少字节非常重要。根据你的应用逻辑，你可能需要处理 bytesRead 低于指定的 length 的情况，例如，如果你需要最小数量的字节，则将读取调用封装在循环中。

¥Therefore, when using fs.read(), it's important to check the bytesRead value to determine how many bytes were actually read from the file. Depending on your application logic, you may need to handle cases where bytesRead is lower than the specified length, such as by wrapping the read call in a loop if you require a minimum amount of bytes.

此行为类似于 POSIX preadv2 函数。

¥This behavior is similar to the POSIX preadv2 function.