Where is mimetools.choose_boundary function in Python3?

httprequest, mime, multipartform-data, python, python-3.x

Solution

Well, I answer my question since no other available answer here.

Yes, I got the result finally, for more info about my work around the question, the below information may help.

1. What does `boundary` do in an `multipart/form-data` request?

In fact, to separate the different parts of data is such a request, we use a separator, here we call `boundary`, to divide the form data.

These parts may be field value (plain text), or uploading file contents.

2. First we put the boundary string in the request header.

To claim a request to be accepted as a `mulitipart/form-data` format, we first choose a special string, called `boundary`, and put it in the request header:

Content-Type: multipart/form-data; boundary=FORM-BOUNDARY

Seeing that we choose the boundary string to be `FORM-BOUNDARY` here, in fact we can choose any string we want.

Most time we may choose a long, randomly string, to prevent collision.

3. Use the chosen boundary in the request body.

In the request body (payload), we separate the data with the `boundary` separator, for example:

--FORM-BOUNDARY
Content-Disposition: form-data; name="template"; filename=".xls"
Content-Type: application/vnd.ms-excel

A654ADE5^%^#%@%$@ (BINARY DATA IN THIS SECTION)
--FORM-BOUNDARY
Content-Disposition: form-data; name="username"

admin
--FORM-BOUNDARY
Content-Disposition: form-data; name="password"

admin_password
--FORM-BOUNDARY--

Seeing that, we start one form-part with a separator, with the `boundary` after a single `--` symbol.

Then in that form-part, we export the header to claim the content type and the name of that posted field.

Then a single blank line is required.

Then we export the value(data) of that form-part.

After all form-parts, we ended the request body with a separator, with the `boundary` between two `--` symbol.

4. So what does `mimetools.choose_boundary` do then?

In fact, this function (deprecated since py3) generate a random boundary, with a specified format, see: https://docs.python.org/2.7/library/mimetools.html?highlight=choose_boundary#mimetools.choose_boundary

The format is:

'hostipaddr.uid.pid.timestamp.random'

Just that simple.

If we insist on getting the same result,

- we can write the functional by ourselves.

- Or call the `email.generator` module's `_make_boundary()` function.

But in fact, to make it work, no need to do that, just generate a random string to replace it!

Problem

I currently want to use the following piece of code in Python3, but found the function `mimetools.choose_boundary` to be deprecated, how to change the code and make it works? ``` import re from urllib.request import urlopen, Request import os import mimetypes import mimetools def get_content_type(filepath): return mimetypes.guess_type(filepath)[0] or 'application/octet-stream' def encode_multipart_formdata(fields, files=[]): """ fields is a sequence of (name, value) elements for regular form fields. files is a sequence of (name, filepath) elements for data to be uploaded as files Return (content_type, body) ready for httplib.HTTP instance """ BOUNDARY = mimetools.choose_boundary() CRLF = '\r\n' L = [] for (key, value) in fields: L.append('--' + BOUNDARY) L.append('Content-Disposition: form-data; name="%s"' % key) L.append('') L.append(value) for (key, filepath) in files: L.append('--' + BOUNDARY) L.append('Content-Disposition: form-data; name="%s"; filename="%s"' % (key, os.path.basename(filepath))) L.append('Content-Type: %s' % get_content_type(filepath)) L.append('') L.append(open(filepath, 'rb').read()) L.append('--' + BOUNDARY + '--') L.append('') body = CRLF.join(L) content_type = 'multipart/form-data; boundary=%s' % BOUNDARY return content_type, body ```

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