Python 2 do_POST http.server multipart/formdata to Python 3

Question

Problem: Trying to translate instructor's python 2 code to python 3
Specific Problem: Cannot access message field from the form in python 3

Instructor's Code Snippet From Udacity Full-Stack Foundations Course

def do_POST(self):
            try:
                self.send_response(301)
                self.send_header('Content-type', 'text/html')
                self.end_headers()
                ctype, pdict = cgi.parse_header(
                    self.headers.getheader('content-type'))
                if ctype == 'multipart/form-data':
                    fields = cgi.parse_multipart(self.rfile, pdict)
                    messagecontent = fields.get('message')
                output = ""
                output += "<html><body>"
                output += " <h2> Okay, how about this: </h2>"
                output += "<h1> %s </h1>" % messagecontent[0]
                output += '''<form method='POST' enctype='multipart/form-data' action='/hello'><h2>What would you like me to say?</h2><input name="message" type="text" ><input type="submit" value="Submit"> </form>'''
                output += "</body></html>"
                self.wfile.write(output)
                print output
            except:
                pass

After looking up documentation, github repositories, stackoverflow posts, and spending countless hours... I could not figure out how to pull the messages field in python 3 like fields.get('message').

My attempt

def do_POST(self):
            try:
                length = int(self.headers['Content-Length'])
                print(self.headers['Content-Type'])
                self.send_response(301)
                self.send_header('Content-type', 'text/html')
                self.end_headers()
                post_data = parse_qs(self.rfile.read(length).decode('utf-8'))
                self.wfile.write("Lorem Ipsum".encode("utf-8"))
                ctype, pdict = cgi.parse_header(self.headers.getheader('content-type'))
                if ctype == 'multipart/form-data':
                    fields = cgi.parse_multipart(self.rfile, pdict)
                    messagecontent = fields.get('message')
    
                output = ''
                output += '<html><body>'
                output += '<h2> Okay, how about this: </h2>'
                output += '<h1> %s </h1>' % messagecontent[0]
                # You now have a dictionary of the post data
    
    
                output += "<form method='POST' enctype='multipart/form-data' action='/hello'><h2>What would you like me to say?</h2><input name='message' type='text'><input type='submit' value='Submit'></form>"
                output += '</html></body>'
                self.wfile.write(output.encode('utf-8'))
    
            except:
                print('Error!')

My post_data variable is a dictionary but I cannot find a way to pull out the 'hi' message that I typed into the form. I am also not sure if this is the right way to go about pulling the data from the form.

>>> post_data
{' name': ['"message"\r\n\r\nhi\r\n------WebKitFormBoundarygm0MsepKJXVrBubX--\r\n']}

Clever Programmer · Accepted Answer · 2016-05-21 23:29:11Z

My solution

def do_POST(self):
            try:
                length = int(self.headers['Content-Length'])
                self.send_response(301)
                self.send_header('Content-type', 'text/html')
                self.end_headers()
                post_data = parse_qs(self.rfile.read(length).decode('utf-8'))
                messagecontent = post_data.get(' name')[0].split('\n')[2]
                output = ''
                output += '<html><body>'
                output += '<h2> Okay, how about this: </h2>'
                output += '<h1> %s </h1>' % messagecontent
                output += "<form method='POST' enctype='multipart/form-data' action='/hello'><h2>What would you like me to say?</h2><input name='message' type='text'><input type='submit' value='Submit'></form>"
                output += '</html></body>'
                self.wfile.write(output.encode('utf-8'))
            except:
                pass

If there is a better way, I would like to know it! Not sure why I have to add a space before 'name' in post_data.get(' name'). But, hey! It works!

UPDATE: FINALLY FIGURED IT OUT

def do_POST(self):
        self.send_response(301)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        ctype, pdict = cgi.parse_header(self.headers['Content-Type'])
        if ctype == 'multipart/form-data':
            pdict['boundary'] = bytes(pdict['boundary'], 'utf-8')
            fields = cgi.parse_multipart(self.rfile, pdict)
            messagecontent = fields.get('message')[0].decode('utf-8')
        output = ''
        output += '<html><body>'
        output += '<h2> Okay, how about this: </h2>'
        output += '<h1> %s </h1>' % messagecontent
        output += "<form method='POST' enctype='multipart/form-data' action='/hello'><h2>What would you like me to say?</h2><input name='message' type='text'><input type='submit' value='Submit'></form>"
        output += '</html></body>'
        self.wfile.write(output.encode('utf-8'))

Use this to be unstuck on the Udacity Full Stack Foundations Course!!

Can you explain why you created a pdict['boundary'] and explain the other changes regarding the Python3 changes please?

Carlos Neto · Accepted Answer · 2019-11-13 12:26:55Z

I wasn't able to make your code work @ the time of posting (2019). Inspecting cgi module, parse_multipart tried to access pdict['CONTENT-LENGHT'].

My solution, working @ post time:

   def do_POST(self):
    try:
        self.send_response(301)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        # HEADERS are now in dict/json style container
        ctype, pdict = cgi.parse_header(
            self.headers.get('content-type'))
        # boundary data needs to be encoded in a binary format


        if ctype == 'multipart/form-data':
            pdict['boundary'] = bytes(pdict['boundary'], "utf-8")
            pdict['CONTENT-LENGTH'] = self.headers.get('content-length')
            fields = cgi.parse_multipart(self.rfile, pdict)
            messagecontent = fields.get('message')

        output = ""
        output += "<html><body>"
        output += " <h2> Okay, how about this: </h2>"
        # decode it back into a string rather than byte string(b'stuff')
        output += "<h1> {} </h1>".format(messagecontent[0])
        output += '''<form method='POST' enctype='multipart/form-data' action='/hello'><h2>What would you like me to say?</h2><input name="message" type="text" ><input type="submit" value="Submit"> </form>'''
        output += "</body></html>"
        self.wfile.write(output.encode())
        print(output)

    except:
        raise

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Python 2 do_POST http.server multipart/formdata to Python 3

Instructor's Code Snippet From Udacity Full-Stack Foundations Course

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UPDATE: FINALLY FIGURED IT OUT

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