为什么大块在Erlang / ChicagoBoss中读取文件时返回一些代码 [英] Why chunk is returning some code while reading the file in Erlang/ChicagoBoss

问题描述

除了我的旧问题我们使用以下代码生成XML：

Further to my old question, We are generating XML using following code:

download_xml('GET', [])->
    Xml =generateXML(123445),
    %% generated Xml  data in string without any values 400,.etc
    Filename = export_xml:get_file_name(?SESSION_ID1, ?SESSION_ID2), 
    Filepath = "./priv/static/" ++ Filename,
    TotalSize = filelib:file_size(Filepath),
    {ok, FP} = file:open(Filepath, [read]),
    Generator = fun(FH) -> 
                        case file:read(FH, 1024) of %% But this line is causing something that we never wanted.
                            eof -> file:close(FH), 
                                   done; 
                            {ok, Data} -> 
                                {output, Data, FH} 
                        end 
                end,
{stream, Generator, FP, [
                             {"Content-Type", "application/force-download"},
                             {"Content-Disposition", "attachment; filename=" ++ Filename},
                             {"Content-length", TotalSize}
                            ]}.

我们正在使用文件读取块中的文件：read（FH，1024） 。但是，这一行还附加了一些数字 400 ， 400 ， 3b2 在每个块。我们已经观察到，这些代码只是每个块的十六进制值。
以下是示例XML：

We are reading files in chunks using file:read(FH, 1024) by this line. But this line is also appending some numbers 400, 400, 3b2 in each chunk. We have observed that those codes are nothing but the Hexadecimal values for each chunk. Here is the sample XML :

sample.xml

400
<?xml version="1.0" encoding="UTF-8"?>.....</info><inf
400
tel>4444</tel>...<address></address>
3b2
<name> Abc</name><surname>EFg</surname><city>XYZ</city>....
</DATA>
0

由于将块大小更改为 2048 从 1024 （即文件：读（FH，2048））值也被更改为 808 ， 365 ， 0 。

Since, on changing the chunk size to 2048 from 1024 (i.e file:read(FH, 2048)) values also get changed to 808, 365, 0.

我们不了解的是：
- 在以块为单位流传输文件内容时，每个块都附加，它的（chunk）尺寸在XML中，然后插入实际块

What we're not understanding is: - While streaming the file contents in chunks, each chunk is appending, it's (chunk's) size in the XML and then actual chunk is inserted.

这里是要生成的小型XML（ 93 Bytes ）：

Here is small XML wanted to generate has size (93 Bytes):

<?xml version="1.0">
<info>
<name> Abc</name>
<surname>EFg</surname>
<city>XYZ</city>
</info>

生成后，输出为：

5d
<?xml version="1.0">
<info>
<name> Abc</name>
<surname>EFg</surname>
<city>XYZ</city>
</info>
0 

5d = 93（Chunk size）在这种情况下文件大小。

5d = 93 (Chunk size) In this case file size.

问题是：

• 为什么大块在每个块之间追加大小，同时使用Generator流式传输文件？

注意 - 我们也尝试从代码中删除标题列表 {Content-length，TotalSize} ，但没有工作：（

NOTE - We also tried removing header list {"Content-length", TotalSize} from the code, but did not work :(

推荐答案

我在erlang bug邮件列表中看到一个与你的问题有关的交换：误导性的文档或文件的执行：读/ 2和朋友

I saw an exchange in the erlang bug mailing list which looks related to your problem : Misleading docs or implementation of file:read/2 and friends

似乎使用文件：读/ 2不是100％清洁与 utf8 选项，他们建议使用io：读/ 3，但我看看如何处理大块和潜在的新行。

It seems that the usage of file:read/2 is not 100% clean with the utf8 option. They recommend to use instead io:read/3, but I don't see how to deal with chunks and potential new line.

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