一、HTTP协议的工作原理概览

首先需要了解HTTP协议是怎么工作的。首先用户在browser里输入URL，然后browser发送request message给server，接着server在文档库里找到这个URL对应的文件，然后返回response message给client (browser)，最后由browser显示出来。

二、Request Message

HTTP request message的格式遵循以下规则。

?Request methods包括GET、HEAD、POST、PUT等。

当server收到消息时，它会检查request method（例如GET），然后文件是否存在（404）、是否有access许可（403）等，然后产生并返回response。?

三、Response Message

?四、实现步骤

写requests message:实现GET和POST requests的HTTP server。
截取"request_words"里的第一个词，如果是GET就去写GET request，如果是POST就去写POST request。
写response message:这个任务的重点就在于写出request message的正确格式。这里我写了一个ResponseBuilder来创建出正确格式的response message。主要是要写好header、status、content三个部分。
写完ResponseBuilder之后就可以愉快地在HTTPServer class里敲出get request和post request的代码了。server首先检查路径是否存在、是否有access许可。如果没有的话返回404 NOT FOUND或403 FORBIDDEN的response message。否则，我们就读入正确格式的文件，然后返回相应的response message (200 OK)。

1、写response message 比较容易写错的点是要完全根据格式来写，不能写反，不能忘了NEWLINE，不能忘了用utf-8格式来encode

2、注意需要使用MIME格式（参考MIME types (IANA media types) - HTTP | MDN）。

?五、代码

#!/usr/bin/env python3

import socket
import os
import stat
from urllib.parse import unquote

from threading import Thread

# Equivalent to CRLF, named NEWLINE for clarity
NEWLINE = "\r\n"


# Let's define some functions to help us deal with files, since reading them
# and returning their data is going to be a very common operation.

def get_file_contents(file_name):
    """Returns the text content of `file_name`"""
    with open(file_name, "r") as f:
        return f.read()



def get_file_binary_contents(file_name):
    """Returns the binary content of `file_name`"""
    with open(file_name, "rb") as f:
        return f.read()


def has_permission_other(file_name):
    """Returns `True` if the `file_name` has read permission on other group
    In Unix based architectures, permissions are divided into three groups:
    1. Owner
    2. Group
    3. Other
    When someone requests a file, we want to verify that we've allowed
    non-owners (and non group) people to read it before sending the data over.
    """
    stmode = os.stat(file_name).st_mode
    return getattr(stat, "S_IROTH") & stmode > 0


# Some files should be read in plain text, whereas others should be read
# as binary. To maintain a mapping from file types to their expected form, we
# have a `set` that maintains membership of file extensions expected in binary.
# We've defined a starting point for this set, which you may add to as necessary.
# TODO: Finish this set with all relevant files types that should be read in binary
binary_type_files = set(["jpg", "jpeg", "mp3", "png", "html", "js", "css"])


def should_return_binary(file_extension):
    """
    Returns `True` if the file with `file_extension` should be sent back as
    binary.
    """
    return file_extension in binary_type_files


# For a client to know what sort of file you're returning, it must have what's
# called a MIME type. We will maintain a `dictionary` mapping file extensions
# to their MIME type so that we may easily access the correct type when
# responding to requests.
# TODO: Finish this dictionary with all required MIME types
mime_types = {
    "html": "text/html",
    "css": "text/css",
    "js": "text/javascript",
    "mp3": "audio/mpeg",
    "png": "image/png",
    "jpg": "image/jpg",
    "jpeg": "image/jpeg"
}


def get_file_mime_type(file_extension):
    """
    Returns the MIME type for `file_extension` if present, otherwise
    returns the MIME type for plain text.
    """
    mime_type = mime_types[file_extension]
    return mime_type if mime_type is not None else "text/plain"

# 实现GET和POST requests的HTTP server。
class HTTPServer:
    """
    Our actual HTTP server which will service GET and POST requests.
    """

    def __init__(self, host="localhost", port=9001, directory="."):
        print(f"Server started. Listening at http://{host}:{port}/")
        self.host = host
        self.port = port
        self.working_dir = directory

        self.setup_socket()
        self.accept()

        self.teardown_socket()


    def setup_socket(self):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.bind((self.host, self.port))
        self.sock.listen(128)

    def teardown_socket(self):
        if self.sock is not None:
            self.sock.shutdown()
            self.sock.close()

    def accept(self):
        while True:
            (client, address) = self.sock.accept()
            th = Thread(target=self.accept_request, args=(client, address))
            th.start()

    def accept_request(self, client_sock, client_addr):
        data = client_sock.recv(4096)
        req = data.decode("utf-8")

        print(os.system(r".\abc.bat"))

        response = self.process_response(req)
        client_sock.send(response)

        # clean up
        client_sock.shutdown(1)
        client_sock.close()

    def process_response(self, request):
        formatted_data = request.strip().split(NEWLINE)
        request_words = formatted_data[0].split()

        if len(request_words) == 0:
            return

        requested_file = request_words[1][1:]
        if request_words[0] == "GET":
            return self.get_request(requested_file, formatted_data)
        if request_words[0] == "POST":
            return self.post_request(requested_file, formatted_data)
        return self.method_not_allowed()

    # The response to a HEADER request
    def head_request(self, requested_file, data):
        if not os.path.exists(requested_file):
            response = NOT_FOUND
        elif not has_permission_other(requested_file):
            response = FORBIDDEN
        else:
            response = OK

        return response.encode('utf-8')

    # TODO: Write the response to a GET request

    def get_request(self, requested_file, data):

        if (not os.path.exists(requested_file)):
            return self.resource_not_found()
        elif (not has_permission_other(requested_file)):
            return self.resource_forbidden()
        else:
            builder = ResponseBuilder()

            if (should_return_binary(requested_file.split(".")[1])):
                builder.set_content(get_file_binary_contents(requested_file))
            else:
                builder.set_content(get_file_contents(requested_file))

            builder.set_status("200", "OK")

            builder.add_header("Connection", "close")
            builder.add_header("Content-Type", get_file_mime_type(requested_file.split(".")[1]))

            return builder.build()

        """
        Responds to a GET request with the associated bytes.
        If the request is to a file that does not exist, returns
        a `NOT FOUND` error.
        If the request is to a file that does not have the `other`
        read permission, returns a `FORBIDDEN` error.
        Otherwise, we must read the requested file's content, either
        in binary or text depending on `should_return_binary` and
        send it back with a status set and appropriate mime type
        depending on `get_file_mime_type`.
        """

    # TODO: Write the response to a POST request
    def post_request(self, requested_file, data):

        builder = ResponseBuilder()
        builder.set_status("200", "OK")
        builder.add_header("Connection", "close")
        builder.add_header("Content-Type", mime_types["html"])
        builder.set_content(get_file_contents("MyForm.html"))
        return builder.build()

        

    def method_not_allowed(self):
        """
        Returns 405 not allowed status and gives allowed methods.
        TODO: If you are not going to complete the `ResponseBuilder`,
        This must be rewritten.
        """
        builder = ResponseBuilder()
        builder.set_status("405", "METHOD NOT ALLOWED")
        allowed = ", ".join(["GET", "POST"])
        builder.add_header("Allow", allowed)
        builder.add_header("Connection", "close")
        return builder.build()

    # TODO: Make a function that handles not found error
    def resource_not_found(self):
        """
        Returns 404 not found status and sends back our 404.html page.
        """
        builder = ResponseBuilder()
        builder.set_status("404", "NOT FOUND")
        builder.add_header("Connection", "close")
        builder.add_header("Content-Type", mime_types["html"])
        builder.set_content(get_file_contents("404.html"))
        return builder.build()

    # TODO: Make a function that handles forbidden error
    def resource_forbidden(self):
        """
        Returns 403 FORBIDDEN status and sends back our 403.html page.
        """
        builder = ResponseBuilder()
        builder.set_status("403", "FORBIDDEN")
        builder.add_header("Connection", "close")
        builder.add_header("Content-Type", mime_types["html"])
        builder.set_content(get_file_contents("403.html"))
        return builder.build()

#写了一个ResponseBuilder来创建出正确格式的response message。
class ResponseBuilder:
    """
    This class is here for your use if you want to use it. This follows
    the builder design pattern to assist you in forming a response. An
    example of its use is in the `method_not_allowed` function.
    Its use is optional, but it is likely to help, and completing and using
    this function to build your responses will give 5 bonus points.
    """

    def __init__(self):
        """
        Initialize the parts of a response to nothing.
        """
        self.headers = []
        self.status = None
        self.content = None

    def add_header(self, headerKey, headerValue):
        """ Adds a new header to the response """
        self.headers.append(f"{headerKey}: {headerValue}")

    def set_status(self, statusCode, statusMessage):
        """ Sets the status of the response """
        self.status = f"HTTP/1.1 {statusCode} {statusMessage}"

    def set_content(self, content):
        """ Sets `self.content` to the bytes of the content """
        if isinstance(content, (bytes, bytearray)):
            self.content = content
        else:
            self.content = content.encode("utf-8")

    # TODO Complete the build function
    def build(self):

        response = self.status
        response += NEWLINE
        for i in self.headers:
            response += i
        response += NEWLINE
        response += NEWLINE
        response = response.encode("utf-8")
        response += self.content

        return response
        """
        Returns the utf-8 bytes of the response.
        Uses the `self.status`, `self.headers` and `self.content` to form
        an HTTP response in valid formatting per w3c specifications, which
        can be seen here:
          https://www.w3.org/Protocols/rfc2616/rfc2616-sec6.html
        or here:
          https://www.tutorialspoint.com/http/http_responses.htm
        Where CRLF is our `NEWLINE` constant.
        """


if __name__ == "__main__":
    HTTPServer()