[racket-users] Re: Sending a file via HTML request.

[George Neuner]

On Tue, 23 Aug 2016 02:09:24 -0700 (PDT), Normal Loone
 wrote:

>Yeah, my main problem is how do I pack the file into a JSON Object
>and then send it?

Just FYI: JSON is a printable coding, so any non-printable characters
in a binary file must be escaped - making the transfer larger.

The read-json and write-json functions take care of escaping, but if
you are sending large files, the overhead may be significant.


>With (require net/http-client) I could already establish a connection
>with (http-conn-sendrecv! hc uri), but All I can send is the empty
>header of the http request. 
>
>How do I add the HTML code or the file in the json object within it?

If I understand correctly, you're trying to send the file to a server
via HTTP from a Racket client.

If the file is JSON encoded, you can send it as a simple HTTP
parameter: e.g.,

(require net/http-client
 net/uri-codec)

(let [
  (params 
   (alist->form-urlencoded
(list (cons 'file (write-bytes  your-file-data ))
  )))
  (headers
   (list "Content-Type: application/x-www-form-urlencoded")
   )
 ]

  (let-values
  [
   ((resp-code resp-hdrs port)
(http-sendrecv host
   url
   #:method #"POST"
   #:data params
   #:headers headers 
   ))
  ]  
(printf "~s~n~s~n~s~n"
resp-code
resp-hdrs
(port->bytes port))
   ))


Sending binary file data or extremely long files (that can't be loaded
fully into memory) requires an HTTP multipart form. 

Multipart forms are complex to encode: they have opening headers,
boundary markers enclosing and sometimes interspersed with the data,
and closing footers after the data.  I don't have a ready example.
For more information see http://www.rfc-base.org/rfc-1867.html

Hope this helps,
George

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Re: [racket-users] Re: Sending a file via HTML request.

[George Neuner]

I posted to this thread yesterday through Gmane, but I see it hasn't yet 
appeared.  Posting through Gmane has been flaky lately - I'm sending 
this updated version via email.Not sure what's happening with 
Gmane.  Apologies if you see things multiple times.


George




On 8/24/2016 7:36 AM, Normal Loone wrote:

Sorry, I should have been clearer:

I want to send a file directly from DrRacket to a server. I have submit button 
as a plugin in DrRacket and it then should take the file and send it to the 
server (the file is known, doesnt need to be selected from user).

I tried the code from HTH Stephen, but problem is that the web application 
starts on DrRacket start and not when I press the button, how I wanted it.

So if someone could tell me a way to just directly send a file with DrRacket as 
an HTML request, I'd really appreciate that.



On Tue, 23 Aug 2016 02:09:24 -0700 (PDT), Normal Loone
 wrote:

>Yeah, my main problem is how do I pack the file into a JSON Object
>and then send it?

Just FYI: JSON is a printable coding, so any non-printable characters
in a binary file must be escaped - making the transfer larger.

The read-json and write-json functions take care of escaping, but if
you are sending large files, the conversion overhead may be significant.

Note that converting an arbitrary binary file to JSON is convoluted -
JSON is meant to handle character strings, not bytes.  You have
to do something like:

(string->jsexpr  (bytes->string/utf-8  file-bytes))

which is a problem if the file is very large as the file data and converted
string both need to be in memory.  It's possible to send a file in pieces
and reassemble it at the receiver, but that can get quite complicated.


>With (require net/http-client) I could already establish a connection
>with (http-conn-sendrecv! hc uri), but All I can send is the empty
>header of the http request.
>
>How do I add the HTML code or the file in the json object within it?

If the data is JSON encoded, you can send it as an HTTP string
parameter: e.g.,

(require net/http-client
 net/uri-codec)

(let [
  (params
   (alist->form-urlencoded
(list (cons 'file  json-encoded-data ))
  )))
  (headers
   (list "Content-Type: application/x-www-form-urlencoded")
   )
 ]

  (let-values
  [
   ((resp-code resp-hdrs port)
(http-sendrecv host
   url
   #:method #"POST"
   #:data params
   #:headers headers
   ))
  ]
(printf "~s~n~s~n~s~n"
resp-code
resp-hdrs
(port->bytes port))
   ))

The print at the end is displaying the server's response.


There is a limit  - which I can't recall at the moment - to the size of
simple upload forms, so you might have trouble sending a long
file this way.

Large uploads, binary data uploads, and piecemeal incremental
uploads are meant to be done using multipart forms.

Multipart forms are complex to encode: they have opening headers,
boundary markers enclosing and sometimes interspersed with the
data, and closing footers after the data.

I don't have a ready example. For more information see
http://www.rfc-base.org/rfc-1867.html

Hope this helps,
George


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Re: [racket-users] Re: Sending a file via HTML request.

[Stephen Chang]

Vishesh Yadav wrote a DrRacket plugin that automatically compiles a
program to JS via whalesong and uploads it to a server. It sounds
related to what you are describing so you may want to take a look at
his code.

The plugin code is here: https://github.com/vishesh/drracket-whalesong
in particular these lines may be of interest:
https://github.com/vishesh/drracket-whalesong/blob/master/tool.rkt#L62-L74

and the server code is here: https://github.com/vishesh/whalebin

If you want to try it out, the server is running at
bigbang.ccs.neu.edu (but seems to be experiencing temporary problems
at the moment).

On Wed, Aug 24, 2016 at 7:36 AM, Normal Loone  wrote:
> Sorry, I should have been clearer:
>
> I want to send a file directly from DrRacket to a server. I have submit 
> button as a plugin in DrRacket and it then should take the file and send it 
> to the server (the file is known, doesnt need to be selected from user).
>
> I tried the code from HTH Stephen, but problem is that the web application 
> starts on DrRacket start and not when I press the button, how I wanted it.
>
> So if someone could tell me a way to just directly send a file with DrRacket 
> as an HTML request, I'd really appreciate that.
>
> --
> You received this message because you are subscribed to the Google Groups 
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.

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[racket-users] Re: Sending a file via HTML request.

[Normal Loone]

Sorry, I should have been clearer:

I want to send a file directly from DrRacket to a server. I have submit button 
as a plugin in DrRacket and it then should take the file and send it to the 
server (the file is known, doesnt need to be selected from user).

I tried the code from HTH Stephen, but problem is that the web application 
starts on DrRacket start and not when I press the button, how I wanted it.

So if someone could tell me a way to just directly send a file with DrRacket as 
an HTML request, I'd really appreciate that.

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[racket-users] Re: Sending a file via HTML request.

[Jack Firth]

You could base64 encode the file bytes and stick that into a field in the JSON 
you send. Why not just send the file directly though? For instance, instead of 
sending this:

POST /somewhere
Content-Type: application/json
{
  filename: "foo"
  content: "Zm9vLGJhcixiYXoNCjEsMSwxDQoyLDIsMg0KMywzLDM="
}

Send this:

POST /somewhere
Content-Type: text/csv
foo,bar,baz
1,1,1
2,2,2
3,3,3

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