本文用python在TCP的基础上实现一个HTTP客户端, 该客户端能够复用TCP连接, 使用HTTP1.1协议.
一. 创建HTTP请求
HTTP是基于TCP连接的, 它的请求报文格式如下:
因此, 我们只需要创建一个到服务器的TCP连接, 然后按照上面的格式写好报文并发给服务器, 就实现了一个HTTP请求.
1. HTTPConnection类
基于以上的分析, 我们首先定义一个HTTPConnection类来管理连接和请求内容:
class HTTPConnection:
default_port = 80
_http_vsn = 11
_http_vsn_str = 'HTTP/1.1'
def __init__(self, host: str, port: int = None) -> None:
self.sock = None
self._buffer = []
self.host = host
self.port = port if port is not None else self.default_port
self._state = _CS_IDLE
self._response = None
self._method = None
self.block_size = 8192
def _output(self, s: Union[str, bytes]) -> None:
if hasattr(s, 'encode'):
s = s.encode('latin-1')
self._buffer.append(s)
def connect(self) -> None:
self.sock = socket.create_connection((self.host, self.port))
对于这个HTTPConnection对象, 我们只需要创建TCP连接, 然后按照HTTP协议的格式把请求数据写入buffer中, 最后把buffer中的数据发送出去就行了.
2. 编写请求行
请求行的内容比较简单, 就是说明请求方法, 请求路径和HTTP协议. 使用下面的方法来编写一个请求行:
def put_request(self, method: str, url: str) -> None:
self._method = method
url = url or '/'
request = f'{method} {url} {self._http_vsn_str}'
self._output(request)
3. 添加请求头
HTTP请求头和python的字典类似, 每行都是一个字段名与值的映射关系. HTTP协议并不要求设置所有合法的请求头的值, 我们只需要按照需要, 设置特定的请求头即可. 使用如下代码添加请求头:
def put_header(self, header: Union[bytes, str], value: Union[bytes, str, int]) -> None:
if hasattr(header, 'encode'):
header = header.encode('ascii')
if hasattr(value, 'encode'):
value = value.encode('latin-1')
elif isinstance(value, int):
value = str(value).encode('ascii')
header = header + b': ' + value
self._output(header)
此外, 在HTTP请求中, Host请求头字段是必须的, 否则网站可能会拒绝响应. 因此, 如果用户没有设置这个字段, 这里就应该主动把它加上去:
def _add_host(self, url: str) -> None:
# 所有HTTP / 1.1请求报文中必须包含一个Host头字段
# 如果用户没给,就调用这个函数来生成
netloc = ''
if url.startswith('http'):
nil, netloc, nil, nil, nil = urllib.parse.urlsplit(url)
if netloc:
try:
netloc_enc = netloc.encode('ascii')
except UnicodeEncodeError:
netloc_enc = netloc.encode('idna')
self.put_header('Host', netloc_enc)
else:
host = self.host
port = self.port
try:
host_enc = host.encode('ascii')
except UnicodeEncodeError:
host_enc = host.encode('idna')
# 对IPv6的地址进行额外处理
if host.find(':') >= 0:
host_enc = b'[' + host_enc + b']'
if port == self.default_port:
self.put_header('Host', host_enc)
else:
host_enc = host_enc.decode('ascii')
self.put_header('Host', f'{host_enc}:{port}')
4. 发送请求正文
我们接受两种形式的body数据: 一个基于io.IOBase的可读文件对象, 或者是一个能通过迭代得到数据的对象. 在传输数据之前, 我们首先要确定数据是否采用分块传输:
def request(self, method: str, url: str, headers: dict = None, body: Union[io.IOBase, Iterable] = None,
encode_chunked: bool = False) -> None:
...
if 'content-length' not in header_names:
if 'transfer-encoding' not in header_names:
encode_chunked = False
content_length = self._get_content_length(body, method)
if content_length is None:
if body is not None:
# 在这种情况下, body一般是个生成器或者可读文件之类的东西,应该分块传输
encode_chunked = True
self.put_header('Transfer-Encoding', 'chunked')
else:
self.put_header('Content-Length', str(content_length))
else:
# 如果设置了transfer-encoding,则根据用户给的encode_chunked参数决定是否分块
pass
else:
# 只要给了content-length,那么一定不是分块传输
encode_chunked = False
...
@staticmethod
def _get_content_length(body: Union[str, bytes, bytearray, Iterable, io.IOBase], method: str) -> Optional[int]:
if body is None:
# PUT,POST,PATCH三个方法默认是有body的
if method.upper() in _METHODS_EXPECTING_BODY:
return 0
else:
return None
if hasattr(body, 'read'):
return None
try:
# 对于bytes或者bytearray格式的数据,通过memoryview获取它的长度
return memoryview(body).nbytes
except TypeError:
pass
if isinstance(body, str):
return len(body)
return None
在确定了是否分块之后, 就可以把正文发出去了. 如果body是一个可读文件的话, 就调用_read_readable方法把它封装为一个生成器:
def _send_body(self, message_body: Union[str, bytes, bytearray, Iterable, io.IOBase], encode_chunked: bool) -> None:
if hasattr(message_body, 'read'):
chunks = self._read_readable(message_body)
else:
try:
memoryview(message_body)
except TypeError:
try:
chunks = iter(message_body)
except TypeError:
raise TypeError(
f'message_body should be a bytes-like object or an iterable, got {repr(type(message_body))}')
else:
# 如果是字节类型的,通过一次迭代把它发出去
chunks = (message_body,)
for chunk in chunks:
if not chunk:
continue
if encode_chunked:
chunk = f'{len(chunk):X}\r\n'.encode('ascii') + chunk + b'\r\n'
self.send(chunk)
if encode_chunked:
self.send(b'0\r\n\r\n')
def _read_readable(self, readable: io.IOBase) -> Generator[bytes, None, None]:
need_encode = False
if isinstance(readable, io.TextIOBase):
need_encode = True
while True:
data_block = readable.read(self.block_size)
if not data_block:
break
if need_encode:
data_block = data_block.encode('utf-8')
yield data_block
二. 获取响应数据
HTTP响应报文的格式与请求报文大同小异, 它大致是这样的:
因此, 我们只要用HTTPConnection的socket对象读取服务器发送的数据, 然后按照上面的格式对数据进行解析就行了.
1. HTTPResponse类
我们首先定义一个简单的HTTPResponse类. 它的属性大致上就是socket的文件对象以及一些请求的信息等等, 调用它的begin方法来解析响应行和响应头的数据, 然后调用read方法读取响应正文:
class HTTPResponse:
def __init__(self, sock: socket.socket, method: str = None) -> None:
self.fp = sock.makefile('rb')
self._method = method
self.headers = None
self.version = _UNKNOWN
self.status = _UNKNOWN
self.reason = _UNKNOWN
self.chunked = _UNKNOWN
self.chunk_left = _UNKNOWN
self.length = _UNKNOWN
self.will_close = _UNKNOWN
def begin(self) -> None:
...
def read(self, amount: int = None) -> bytes:
...
2. 解析状态行
状态行的解析比较简单, 我们只需要读取响应的第一行数据, 然后把它解析为HTTP协议版本,状态码和原因短语三部分就行了:
def _read_status(self) -> Tuple[str, int, str]:
line = str(self._read_line(), 'latin-1')
if not line:
raise RemoteDisconnected('Remote end closed connection without response')
try:
version, status, reason = line.split(None, 2)
except ValueError:
# reason只是给人看的, 一般和status对应, 所以它有可能不存在
try:
version, status = line.split(None, 1)
reason = ''
except ValueError:
version, status, reason = '', '', ''
if not version.startswith('HTTP/'):
self._close_conn()
raise BadStatusLine(line)
try:
status = int(status)
if status < 100 or status > 999:
raise BadStatusLine(line)
except ValueError:
raise BadStatusLine(line)
return version, status, reason.strip()
如果状态码为100, 则客户端需要解析多个响应状态行. 它的原理是这样的: 在请求数据过大的时候, 有的客户端会先不发送请求数据, 而是先在header中添加一个Expect: 100-continue, 如果服务器愿意接收数据, 会返回100的状态码, 这时候客户端再把数据发过去. 因此, 如果读取到100的状态码, 那么后面往往还会收到一个正式的响应数据, 应该继续读取响应头. 这部分的代码如下:
def begin(self) -> None:
while True:
version, status, reason = self._read_status()
if status != HTTPStatus.CONTINUE:
break
# 跳过100状态码部分的响应头
while True:
skip = self._read_line().strip()
if not skip:
breakself.status = status
self.reason = reason
if version in ('HTTP/1.0', 'HTTP/0.9'):
self.version = 10
elif version.startswith('HTTP/1.'):
self.version = 11
else:
# HTTP2还没研究, 这里就不写了
raise UnknownProtocol(version)
...
3. 解析响应头
解析响应头比响应行还要简单. 因为每个header字段占一行, 我们只需要一直调用read_line方法读取字段, 直到读完header为止就行了.
def _parse_header(self) -> None:
headers = {}
while True:
line = self._read_line()
if len(headers) > _MAX_HEADERS:
raise HTTPException('got more than %d headers' % _MAX_HEADERS)
if line in _EMPTY_LINE:
break
line = line.decode('latin-1')
i = line.find(':')
if i == -1:
raise BadHeaderLine(line)
# 这里默认没有重名的情况
key, value = line[:i].lower(), line[i + 1:].strip()
headers[key] = value
self.headers = headers
4. 接收响应正文
在接收响应正文之前, 首先要确定它的传输方式和长度:
def _set_chunk(self) -> None:
transfer_encoding = self.get_header('transfer-encoding')
if transfer_encoding and transfer_encoding.lower() == 'chunked':
self.chunked = True
self.chunk_left = None
else:
self.chunked = False
def _set_length(self) -> None:
# 首先要知道数据是否是分块传输的
if self.chunked == _UNKNOWN:
self._set_chunk()
# 如果状态码是1xx或者204(无响应内容)或者304(使用上次缓存的内容),则没有响应正文
# 如果这是个HEAD请求,那么也不能有响应正文
if (self.status == HTTPStatus.NO_CONTENT or
self.status == HTTPStatus.NOT_MODIFIED or
100 <= self.status < 200 or
self._method == 'HEAD'):
self.length = 0
return
length = self.get_header('content-length')
if length and not self.chunked:
try:
self.length = int(length)
except ValueError:
self.length = None
else:
if self.length < 0:
self.length = None
else:
self.length = None
然后, 我们实现一个read方法, 从body中读取指定大小的数据:
def read(self, amount: int = None) -> bytes:
if self.is_closed():
return b''
if self._method == 'HEAD':
self.close()
return b''
if amount is None:
return self._read_all()
return self._read_amount(amount)
如果没有指定需要的数据大小, 就默认读取所有数据:
def _read_all(self) -> bytes:
if self.chunked:
return self._read_all_chunk()
if self.length is None:
s = self.fp.read()
else:
try:
s = self._read_bytes(self.length)
except IncompleteRead:
self.close()
raise
self.length = 0
self.close()
return s
def _read_all_chunk(self) -> bytes:
assert self.chunked != _UNKNOWN
value = []
try:
while True:
chunk = self._read_chunk()
if chunk is None:
break
value.append(chunk)
return b''.join(value)
except IncompleteRead:
raise IncompleteRead(b''.join(value))
def _read_chunk(self) -> Optional[bytes]:
try:
chunk_size = self._read_chunk_size()
except ValueError:
raise IncompleteRead(b'')
if chunk_size == 0:
self._read_and_discard_trailer()
self.close()
return None
chunk = self._read_bytes(chunk_size)
# 每块的结尾会有一个\r\n,这里把它读掉
self._read_bytes(2)
return chunk
def _read_chunk_size(self) -> int:
line = self._read_line(error_message='chunk size')
i = line.find(b';')
if i >= 0:
line = line[:i]
try:
return int(line, 16)
except ValueError:
self.close()
raise
def _read_and_discard_trailer(self) -> None:
# chunk的尾部可能会挂一些额外的信息,比如MD5值,过期时间等等,一般会在header中用trailer字段说明
# 当chunk读完之后调用这个函数, 这些信息就先舍弃掉得了
while True:
line = self._read_line(error_message='chunk size')
if line in _EMPTY_LINE:
break
否则的话, 就读取部分数据, 如果正好是分块数据的话, 就比较复杂了. 简单来说, 就是用bytearray制造一个所需大小的数组, 然后依次读取chunk把数据往里面填, 直到填满或者没数据为止. 然后用chunk_left记录下当前块剩余的量, 以便下次读取.
def _read_amount(self, amount: int) -> bytes:
if self.chunked:
return self._read_amount_chunk(amount)
if isinstance(self.length, int) and amount > self.length:
amount = self.length
container = bytearray(amount)
n = self.fp.readinto(container)
if not n and container:
# 如果读不到字节了,也就可以关了
self.close()
elif self.length is not None:
self.length -= n
if not self.length:
self.close()
return memoryview(container)[:n].tobytes()
def _read_amount_chunk(self, amount: int) -> bytes:
# 调用这个方法,读取amount大小的chunk类型数据,不足就全部读取
assert self.chunked != _UNKNOWN
total_bytes = 0
container = bytearray(amount)
mvb = memoryview(container)
try:
while True:
# mvb可以理解为容器的空的那一部分
# 这里一直调用_full_readinto把数据填进去,让mvb越来越小,同时记录填入的量
# 等没数据或者当前数据足够把mvb填满之后,跳出循环
chunk_left = self._get_chunk_left()
if chunk_left is None:
break
if len(mvb) <= chunk_left:
n = self._full_readinto(mvb)
self.chunk_left = chunk_left - n
total_bytes += n
break
temp_mvb = mvb[:chunk_left]
n = self._full_readinto(temp_mvb)
mvb = mvb[n:]
total_bytes += n
self.chunk_left = 0
except IncompleteRead:
raise IncompleteRead(bytes(container[:total_bytes]))
return memoryview(container)[:total_bytes].tobytes()
def _full_readinto(self, container: memoryview) -> int:
# 返回读取的量.如果没能读满,这个方法会报警
amount = len(container)
n = self.fp.readinto(container)
if n < amount:
raise IncompleteRead(bytes(container[:n]), amount - n)
return n
def _get_chunk_left(self) -> Optional[int]:
# 如果当前块读了一半,那么直接返回self.chunk_left就行了
# 否则,有三种情况
# 1). chunk_left为None,说明body压根没开始读,于是返回当前这一整块的长度
# 2). chunk_left为0,说明这块读完了,于是返回下一块的长度
# 3). body数据读完了,返回None,顺便做好善后工作
chunk_left = self.chunk_left
if not chunk_left:
if chunk_left == 0:
# 如果剩余零,说明上一块已经读完了,这里把\r\n读掉
# 如果是None,就说明chunk压根没开始读
self._read_bytes(2)
try:
chunk_left = self._read_chunk_size()
except ValueError:
raise IncompleteRead(b'')
if chunk_left == 0:
self._read_and_discard_trailer()
self.close()
chunk_left = None
self.chunk_left = chunk_left
return chunk_left
三. 复用TCP连接
HTTP通信本质上是基于TCP连接发送和接收HTTP请求和响应, 因此, 只要TCP连接不断开, 我们就可以继续用它进行HTTP请求, 这样就避免了创建和销毁TCP连接产生的消耗.
1. 判断连接是否会断开
在下面几种情况中, 服务端会自动断开连接:
HTTP协议小于1.1且没有在头部设置了keep-alive
HTTP协议大于等于1.1但是在头部设置了connection: close
数据没有分块传输, 也没有说明数据的长度, 这种情况下, 服务器一般会在发送完成后断开连接, 让客户端知道数据发完了
根据上面列出来的几种情况, 通过下面的代码来判断连接是否会断开:
def _check_close(self) -> bool:
conn = self.get_header('connection')
if not self.chunked and self.length is None:
return True
if self.version == 11:
if conn and 'close' in conn.lower():
return True
return False
else:
if self.headers.get('keep-alive'):
return False
if conn and 'keep-alive' in conn.lower():
return False
return True
2. 正确地关闭HTTPResponse对象
由于TCP连接的复用, 一个HTTPConnection可以产生多个HTTPResponse对象, 而这些对象在同一个TCP连接上, 会共用这个连接的读缓冲区. 这就导致, 如果上一个HTTPResponse对象没有把它的那部分数据读完, 就会对下一个响应产生影响.
另一方面来看, 我们也需要及时地关闭与这个TCP关联的文件对象来避免占用资源. 因此, 我们定义如下的close方法关闭一个HTTPResponse对象:
def close(self) -> None:
if self.is_closed():
return
fp = self.fp
self.fp = None
fp.close()
def is_closed(self) -> bool:
return self.fp is None
用户调用HTTPResponse对象的read方法, 把缓冲区数据读完之后, 就会自动调用close方法(具体实现见上一章的第四节: 读取响应数据这部分). 因此, 在获取下一个响应数据之前, 我们只需要调用这个对象的is_closed方法, 就能判断读缓冲区是否已经读完, 能否继续接收响应了.
3. HTTP请求的生命周期
不使用管道机制的话, 不同的HTTP请求必须按次序进行, 相互之间不能重叠. 基于这个原因, 我们为HTTPConnection对象设置IDLE, REQ_STARTED和REQ_SENT三种状态, 一个完整的请求应该经历这几种状态:
根据上面的流程, 对HTTPConnection中对应的方法进行修改:
def get_response(self) -> HTTPResponse:
if self._response and self._response.is_closed():
self._response = None
if self._state != _CS_REQ_SENT or self._response:
raise ResponseNotReady(self._state)
response = HTTPResponse(self.sock, method=self._method)
try:
try:
response.begin()
except ConnectionError:
self.close()
raise
assert response.will_close != _UNKNOWN
self._state = _CS_IDLE
if response.will_close:
self.close()
else:
self._response = response
return response
except Exception as _:
response.close()
raise
def put_request(self, method: str, url: str) -> None:
# 调用这个函数开始新一轮的请求,它负责写好请求行输出到缓存里面去
# 调用它的前提是当前处于空闲状态
# 如果之前的response还在并且已结束,会自动把它消除掉
if self._response and self._response.is_closed():
self._response = None
if self._state == _CS_IDLE:
self._state = _CS_REQ_STARTED
else:
raise CannotSendRequest(self._state)
...
def put_header(self, header: Union[bytes, str], value: Union[bytes, str, int]) -> None:
if self._state != _CS_REQ_STARTED:
raise CannotSendHeader()
...
def end_headers(self, message_body=None, encode_chunked=False) -> None:
if self._state == _CS_REQ_STARTED:
self._state = _CS_REQ_SENT
else:
raise CannotSendHeader()
...
需要注意的是, 如果第二个请求已经进入到获取响应的阶段了, 而上一个请求的响应还没关闭, 那么就应该直接报错, 否则读取到的会是上一个请求剩余的响应部分数据, 导致解析响应出现问题.
事实上, HTTP1.1开始支持管道化技术, 也就是一次提交多个HTTP请求, 然后等待响应, 而不是在接收到上一个请求的响应后, 才发送后面的请求.
基于这种处理模式, 管道化技术理论上可以减少IO时间的损耗, 提升效率, 不过, 需要服务端的支持, 而且会增加程序的复杂程度, 这里就不实现了.
四. 总结
1. 完整代码
HTTPConnection的完整代码如下:
class HTTPConnection:
default_port = 80
_http_vsn = 11
_http_vsn_str = 'HTTP/1.1'
def __init__(self, host: str, port: int = None) -> None:
self.sock = None
self._buffer = []
self.host = host
self.port = port if port is not None else self.default_port
self._state = _CS_IDLE
self._response = None
self._method = None
self.block_size = 8192
def request(self, method: str, url: str, headers: dict = None, body: Union[io.IOBase, Iterable] = None,
encode_chunked: bool = False) -> None:
self.put_request(method, url)
headers = headers or {}
header_names = frozenset(k.lower() for k in headers.keys())
if 'host' not in header_names:
self._add_host(url)
if 'content-length' not in header_names:
if 'transfer-encoding' not in header_names:
encode_chunked = False
content_length = self._get_content_length(body, method)
if content_length is None:
if body is not None:
encode_chunked = True
self.put_header('Transfer-Encoding', 'chunked')
else:
self.put_header('Content-Length', str(content_length))
else:
# 如果设置了transfer-encoding,则根据用户给的encode_chunked参数决定是否分块
pass
else:
# 只要给了content-length,那么一定不是分块传输
encode_chunked = False
for hdr, value in headers.items():
self.put_header(hdr, value)
if isinstance(body, str):
body = _encode(body)
self.end_headers(body, encode_chunked=encode_chunked)
def send(self, data: bytes) -> None:
if self.sock is None:
self.connect()
self.sock.sendall(data)
def get_response(self) -> HTTPResponse:
if self._response and self._response.is_closed():
self._response = None
if self._state != _CS_REQ_SENT or self._response:
raise ResponseNotReady(self._state)
response = HTTPResponse(self.sock, method=self._method)
try:
try:
response.begin()
except ConnectionError:
self.close()
raise
assert response.will_close != _UNKNOWN
self._state = _CS_IDLE
if response.will_close:
self.close()
else:
self._response = response
return response
except Exception as _:
response.close()
raise
def connect(self) -> None:
self.sock = socket.create_connection((self.host, self.port))
def close(self) -> None:
self._state = _CS_IDLE
try:
sock = self.sock
if sock:
self.sock = None
sock.close()
finally:
response = self._response
if response:
self._response = None
response.close()
def put_request(self, method: str, url: str) -> None:
# 调用这个函数开始新一轮的请求,它负责写好请求行输出到缓存里面去
# 调用它的前提是当前处于空闲状态
# 如果之前的response还在并且已结束,会自动把它消除掉
if self._response and self._response.is_closed():
self._response = None
if self._state == _CS_IDLE:
self._state = _CS_REQ_STARTED
else:
raise CannotSendRequest(self._state)
self._method = method
url = url or '/'
request = f'{method} {url} {self._http_vsn_str}'
self._output(request)
def put_header(self, header: Union[bytes, str], value: Union[bytes, str, int]) -> None:
if self._state != _CS_REQ_STARTED:
raise CannotSendHeader()
if hasattr(header, 'encode'):
header = header.encode('ascii')
if hasattr(value, 'encode'):
value = value.encode('latin-1')
elif isinstance(value, int):
value = str(value).encode('ascii')
header = header + b': ' + value
self._output(header)
def end_headers(self, message_body=None, encode_chunked=False) -> None:
if self._state == _CS_REQ_STARTED:
self._state = _CS_REQ_SENT
else:
raise CannotSendHeader()
self._send_output(message_body, encode_chunked=encode_chunked)
def _add_host(self, url: str) -> None:
# 所有HTTP / 1.1请求报文中必须包含一个Host头字段
# 如果用户没给,就调用这个函数来生成
netloc = ''
if url.startswith('http'):
nil, netloc, nil, nil, nil = urlsplit(url)
if netloc:
try:
netloc_enc = netloc.encode('ascii')
except UnicodeEncodeError:
netloc_enc = netloc.encode('idna')
self.put_header('Host', netloc_enc)
else:
host = self.host
port = self.port
try:
host_enc = host.encode('ascii')
except UnicodeEncodeError:
host_enc = host.encode('idna')
# 对IPv6的地址进行额外处理
if host.find(':') >= 0:
host_enc = b'[' + host_enc + b']'
if port == self.default_port:
self.put_header('Host', host_enc)
else:
host_enc = host_enc.decode('ascii')
self.put_header('Host', f'{host_enc}:{port}')
def _output(self, s: Union[str, bytes]) -> None:
# 将数据添加到缓冲区
if hasattr(s, 'encode'):
s = s.encode('latin-1')
self._buffer.append(s)
def _send_output(self, message_body=None, encode_chunked=False) -> None:
# 发送并清空缓冲数据.然后,如果有请求正文,就也顺便发送
self._buffer.extend((b'', b''))
msg = b'\r\n'.join(self._buffer)
self._buffer.clear()
self.send(msg)
if message_body is not None:
self._send_body(message_body, encode_chunked)
def _send_body(self, message_body: Union[bytes, str, bytearray, Iterable, io.IOBase], encode_chunked: bool) -> None:
if hasattr(message_body, 'read'):
chunks = self._read_readable(message_body)
else:
try:
memoryview(message_body)
except TypeError:
try:
chunks = iter(message_body)
except TypeError:
raise TypeError(
f'message_body should be a bytes-like object or an iterable, got {repr(type(message_body))}')
else:
# 如果是字节类型的,通过一次迭代把它发出去
chunks = (message_body,)
for chunk in chunks:
if not chunk:
continue
if encode_chunked:
chunk = f'{len(chunk):X}\r\n'.encode('ascii') + chunk + b'\r\n'
self.send(chunk)
if encode_chunked:
self.send(b'0\r\n\r\n')
def _read_readable(self, readable: io.IOBase) -> Generator[bytes, None, None]:
need_encode = False
if isinstance(readable, io.TextIOBase):
need_encode = True
while True:
data_block = readable.read(self.block_size)
if not data_block:
break
if need_encode:
data_block = data_block.encode('utf-8')
yield data_block
@staticmethod
def _get_content_length(body: Union[str, bytes, bytearray, Iterable, io.IOBase], method: str) -> Optional[int]:
if body is None:
# PUT,POST,PATCH三个方法默认是有body的
if method.upper() in _METHODS_EXPECTING_BODY:
return 0
else:
return None
if hasattr(body, 'read'):
return None
try:
# 对于bytes或者bytearray格式的数据,通过memoryview获取它的长度
return memoryview(body).nbytes
except TypeError:
pass
if isinstance(body, str):
return len(body)
return None
HTTPResponse的完整代码如下:
class HTTPResponse:
def __init__(self, sock: socket.socket, method: str = None) -> None:
self.fp = sock.makefile('rb')
self._method = method
self.headers = None
self.version = _UNKNOWN
self.status = _UNKNOWN
self.reason = _UNKNOWN
self.chunked = _UNKNOWN
self.chunk_left = _UNKNOWN
self.length = _UNKNOWN
self.will_close = _UNKNOWN
def begin(self) -> None:
if self.headers is not None:
return
self._parse_status_line()
self._parse_header()
self._set_chunk()
self._set_length()
self.will_close = self._check_close()
def _read_line(self, limit: int = _MAX_LINE + 1, error_message: str = '') -> bytes:
# 注意,这个方法默认不去除line尾部的\r\n
line = self.fp.readline(limit)
if len(line) > _MAX_LINE:
raise LineTooLong(error_message)
return line
def _read_bytes(self, amount: int) -> bytes:
data = self.fp.read(amount)
if len(data) < amount:
raise IncompleteRead(data, amount - len(data))
return data
def _parse_status_line(self) -> None:
while True:
version, status, reason = self._read_status()
if status != HTTPStatus.CONTINUE:
break
while True:
skip = self._read_line(error_message='header line').strip()
if not skip:
break
self.status = status
self.reason = reason
if version in ('HTTP/1.0', 'HTTP/0.9'):
self.version = 10
elif version.startswith('HTTP/1.'):
self.version = 11
else:
raise UnknownProtocol(version)
def _read_status(self) -> Tuple[str, int, str]:
line = str(self._read_line(error_message='status line'), 'latin-1')
if not line:
raise RemoteDisconnected('Remote end closed connection without response')
try:
version, status, reason = line.split(None, 2)
except ValueError:
# reason只是给人看的, 和status对应, 所以它有可能不存在
try:
version, status = line.split(None, 1)
reason = ''
except ValueError:
version, status, reason = '', '', ''
if not version.startswith('HTTP/'):
self.close()
raise BadStatusLine(line)
try:
status = int(status)
if status < 100 or status > 999:
raise BadStatusLine(line)
except ValueError:
raise BadStatusLine(line)
return version, status, reason.strip()
def _parse_header(self) -> None:
headers = {}
while True:
line = self._read_line(error_message='header line')
if len(headers) > _MAX_HEADERS:
raise HTTPException('got more than %d headers' % _MAX_HEADERS)
if line in _EMPTY_LINE:
break
line = line.decode('latin-1')
i = line.find(':')
if i == -1:
raise BadHeaderLine(line)
# 这里默认没有重名的情况
key, value = line[:i].lower(), line[i + 1:].strip()
headers[key] = value
self.headers = headers
def _set_chunk(self) -> None:
transfer_encoding = self.get_header('transfer-encoding')
if transfer_encoding and transfer_encoding.lower() == 'chunked':
self.chunked = True
self.chunk_left = None
else:
self.chunked = False
def _set_length(self) -> None:
# 首先要知道数据是否是分块传输的
if self.chunked == _UNKNOWN:
self._set_chunk()
# 如果状态码是1xx或者204(无响应内容)或者304(使用上次缓存的内容),则没有响应正文
# 如果这是个HEAD请求,那么也不能有响应正文
assert isinstance(self.status, int)
if (self.status == HTTPStatus.NO_CONTENT or
self.status == HTTPStatus.NOT_MODIFIED or
100 <= self.status < 200 or
self._method == 'HEAD'):
self.length = 0
return
length = self.get_header('content-length')
if length and not self.chunked:
try:
self.length = int(length)
except ValueError:
self.length = None
else:
if self.length < 0:
self.length = None
else:
self.length = None
def _check_close(self) -> bool:
conn = self.get_header('connection')
if not self.chunked and self.length is None:
return True
if self.version == 11:
if conn and 'close' in conn.lower():
return True
return False
else:
if self.headers.get('keep-alive'):
return False
if conn and 'keep-alive' in conn.lower():
return False
return True
def close(self) -> None:
if self.is_closed():
return
fp = self.fp
self.fp = None
fp.close()
def is_closed(self) -> bool:
return self.fp is None
def read(self, amount: int = None) -> bytes:
if self.is_closed():
return b''
if self._method == 'HEAD':
self.close()
return b''
if amount is None:
return self._read_all()
print(amount, amount is None)
return self._read_amount(amount)
def _read_all(self) -> bytes:
if self.chunked:
return self._read_all_chunk()
if self.length is None:
s = self.fp.read()
else:
try:
s = self._read_bytes(self.length)
except IncompleteRead:
self.close()
raise
self.length = 0
self.close()
return s
def _read_all_chunk(self) -> bytes:
assert self.chunked != _UNKNOWN
value = []
try:
while True:
chunk = self._read_chunk()
if chunk is None:
break
value.append(chunk)
return b''.join(value)
except IncompleteRead:
raise IncompleteRead(b''.join(value))
def _read_chunk(self) -> Optional[bytes]:
try:
chunk_size = self._read_chunk_size()
except ValueError:
raise IncompleteRead(b'')
if chunk_size == 0:
self._read_and_discard_trailer()
self.close()
return None
chunk = self._read_bytes(chunk_size)
# 每块的结尾会有一个\r\n,这里把它读掉
self._read_bytes(2)
return chunk
def _read_chunk_size(self) -> int:
line = self._read_line(error_message='chunk size')
i = line.find(b';')
if i >= 0:
line = line[:i]
try:
return int(line, 16)
except ValueError:
self.close()
raise
def _read_and_discard_trailer(self) -> None:
# chunk的尾部可能会挂一些额外的信息,比如MD5值,过期时间等等,一般会在header中用trailer字段说明
# 当chunk读完之后调用这个函数, 这些信息就先舍弃掉得了
while True:
line = self._read_line(error_message='chunk size')
if line in _EMPTY_LINE:
break
def _read_amount(self, amount: int) -> bytes:
if self.chunked:
return self._read_amount_chunk(amount)
if isinstance(self.length, int) and amount > self.length:
amount = self.length
container = bytearray(amount)
n = self.fp.readinto(container)
if not n and container:
# 如果读不到字节了,也就可以关了
self.close()
elif self.length is not None:
self.length -= n
if not self.length:
self.close()
return memoryview(container)[:n].tobytes()
def _read_amount_chunk(self, amount: int) -> bytes:
# 调用这个方法,读取amount大小的chunk类型数据,不足就全部读取
assert self.chunked != _UNKNOWN
total_bytes = 0
container = bytearray(amount)
mvb = memoryview(container)
try:
while True:
# mvb可以理解为容器的空的那一部分
# 这里一直调用_full_readinto把数据填进去,让mvb越来越小,同时记录填入的量
# 等没数据或者当前数据足够把mvb填满之后,跳出循环
chunk_left = self._get_chunk_left()
if chunk_left is None:
break
if len(mvb) <= chunk_left:
n = self._full_readinto(mvb)
self.chunk_left = chunk_left - n
total_bytes += n
break
temp_mvb = mvb[:chunk_left]
n = self._full_readinto(temp_mvb)
mvb = mvb[n:]
total_bytes += n
self.chunk_left = 0
except IncompleteRead:
raise IncompleteRead(bytes(container[:total_bytes]))
return memoryview(container)[:total_bytes].tobytes()
def _full_readinto(self, container: memoryview) -> int:
# 返回读取的量.如果没能读满,这个方法会报警
amount = len(container)
n = self.fp.readinto(container)
if n < amount:
raise IncompleteRead(bytes(container[:n]), amount - n)
return n
def _get_chunk_left(self) -> Optional[int]:
# 如果当前块读了一半,那么直接返回self.chunk_left就行了
# 否则,有三种情况
# 1). chunk_left为None,说明body压根没开始读,于是返回当前这一整块的长度
# 2). chunk_left为0,说明这块读完了,于是返回下一块的长度
# 3). body数据读完了,返回None,顺便做好善后工作
chunk_left = self.chunk_left
if not chunk_left:
if chunk_left == 0:
# 如果剩余零,说明上一块已经读完了,这里把\r\n读掉
# 如果是None,就说明chunk压根没开始读
self._read_bytes(2)
try:
chunk_left = self._read_chunk_size()
except ValueError:
raise IncompleteRead(b'')
if chunk_left == 0:
self._read_and_discard_trailer()
self.close()
chunk_left = None
self.chunk_left = chunk_left
return chunk_left
def get_header(self, name, default: str = None) -> Optional[str]:
if self.headers is None:
raise ResponseNotReady()
return self.headers.get(name, default)
@property
def info(self) -> str:
return repr(self.headers)
这两个类应该放到同一个py文件中, 同时这个文件内还有其他一些辅助性质的代码:
import io
import socket
from typing import Generator, Iterable, Optional, Tuple, Union
from urllib.parse import urlsplit
_CS_IDLE = 'Idle'
_CS_REQ_STARTED = 'Request-started'
_CS_REQ_SENT = 'Request-sent'
_METHODS_EXPECTING_BODY = {'PATCH', 'POST', 'PUT'}
_UNKNOWN = 'UNKNOWN'
_MAX_LINE = 65536
_MAX_HEADERS = 100
_EMPTY_LINE = (b'\r\n', b'\n', b'')
class HTTPStatus:
CONTINUE = 100
SWITCHING_PROTOCOLS = 101
PROCESSING = 102
OK = 200
CREATED = 201
ACCEPTED = 202
NON_AUTHORITATIVE_INFORMATION = 203
NO_CONTENT = 204
RESET_CONTENT = 205
PARTIAL_CONTENT = 206
MULTI_STATUS = 207
ALREADY_REPORTED = 208
IM_USED = 226
MULTIPLE_CHOICES = 300
MOVED_PERMANENTLY = 301
FOUND = 302
SEE_OTHER = 303
NOT_MODIFIED = 304
USE_PROXY = 305
TEMPORARY_REDIRECT = 307
PERMANENT_REDIRECT = 308
BAD_REQUEST = 400
UNAUTHORIZED = 401
PAYMENT_REQUIRED = 402
FORBIDDEN = 403
NOT_FOUND = 404
METHOD_NOT_ALLOWED = 405
NOT_ACCEPTABLE = 406
PROXY_AUTHENTICATION_REQUIRED = 407
REQUEST_TIMEOUT = 408
CONFLICT = 409
GONE = 410
LENGTH_REQUIRED = 411
PRECONDITION_FAILED = 412
REQUEST_ENTITY_TOO_LARGE = 413
REQUEST_URI_TOO_LONG = 414
UNSUPPORTED_MEDIA_TYPE = 415
REQUESTED_RANGE_NOT_SATISFIABLE = 416
EXPECTATION_FAILED = 417
MISDIRECTED_REQUEST = 421
UNPROCESSABLE_ENTITY = 422
LOCKED = 423
FAILED_DEPENDENCY = 424
UPGRADE_REQUIRED = 426
PRECONDITION_REQUIRED = 428
TOO_MANY_REQUESTS = 429
REQUEST_HEADER_FIELDS_TOO_LARGE = 431
UNAVAILABLE_FOR_LEGAL_REASONS = 451
INTERNAL_SERVER_ERROR = 500
NOT_IMPLEMENTED = 501
BAD_GATEWAY = 502
SERVICE_UNAVAILABLE = 503
GATEWAY_TIMEOUT = 504
HTTP_VERSION_NOT_SUPPORTED = 505
VARIANT_ALSO_NEGOTIATES = 506
INSUFFICIENT_STORAGE = 507
LOOP_DETECTED = 508
NOT_EXTENDED = 510
NETWORK_AUTHENTICATION_REQUIRED = 511
class HTTPResponse:
...
class HTTPConnection:
...
def _encode(data: str, encoding: str = 'latin-1', name: str = 'data') -> bytes:
# 给请求正文等不知道能怎么转码的东西转码时用这个,默认使用latin-1编码
# 它的好处是,转码失败后能抛出详细的错误信息,一目了然
try:
return data.encode(encoding)
except UnicodeEncodeError as err:
raise UnicodeEncodeError(
err.encoding,
err.object,
err.start,
err.end,
"{} ({:.20!r}) is not valid {}. Use {}.encode('utf-8') if you want to send it encoded in UTF-8.".format(
name.title(), data[err.start:err.end], encoding, name)
) from None
class HTTPException(Exception):
pass
class ImproperConnectionState(HTTPException):
pass
class CannotSendRequest(ImproperConnectionState):
pass
class CannotSendHeader(ImproperConnectionState):
pass
class CannotCloseStream(ImproperConnectionState):
pass
class ResponseNotReady(ImproperConnectionState):
pass
class LineTooLong(HTTPException):
def __init__(self, line_type):
HTTPException.__init__(self, 'got more than %d bytes when reading %s'
% (_MAX_LINE, line_type))
class BadStatusLine(HTTPException):
def __init__(self, line):
if not line:
line = repr(line)
self.args = line,
self.line = line
class BadHeaderLine(HTTPException):
def __init__(self, line):
if not line:
line = repr(line)
self.args = line,
self.line = line
class RemoteDisconnected(ConnectionResetError, BadStatusLine):
def __init__(self, *args, **kwargs):
BadStatusLine.__init__(self, '')
ConnectionResetError.__init__(self, *args, **kwargs)
class UnknownProtocol(HTTPException):
def __init__(self, version):
self.args = version,
self.version = version
class UnknownTransferEncoding(HTTPException):
pass
class IncompleteRead(HTTPException):
def __init__(self, partial, expected=None):
self.args = partial,
self.partial = partial
self.expected = expected
def __repr__(self):
if self.expected is not None:
e = f', {self.expected} more expected'
else:
e = ''
return f'{self.__class__.__name__}({len(self.partial)} bytes read{e})'
__str__ = object.__str__
2. 需要注意的点
总的来说, 本文的内容不算复杂, 毕竟HTTP属于不难理解, 但知识点很多很杂的类型. 这里把本文中一些需要注意的点总结一下:
请求和响应数据的结构大致相同, 都是状态行+头部+正文, 状态行和头部的每个字段都用一个\r\n分割, 与正文之间用两个分割;
状态行是必须的, 请求头则最少需要host这个字段, 同时为了大家的方便, 你最好也设置一下Accept-encoding和Accept来限制服务器返回给你的数据内容和格式;
正文不是必须的, 特别是对于除了3P(PATCH, POST, PUT)之外的方法来说. 如果你有正文, 你最好在header中使用Content-Length说明正文的长度, 如果是分块发送, 则使用Transfer-Encoding字段说明;
如果对正文使用分块传输, 每块的格式是: 16进制的数据长度+\r\n+数据+\r\n, 使用0\r\n\r\n来收尾. 收尾之后, 你还可以放一个trailer, 里面放数据的MD5值或者过期时间什么的, 这时候最好在header中设置trailer字段;
在一个请求的生命周期完成后, TCP连接是否会断开取决于三点: 响应数据的HTTP版本, 响应头中的Connection和Keep-Alive字段, 是否知道响应正文的长度;
最最重要的一点, HTTP协议只是一个约定而非限制, 这就和矿泉水的建议零售价差不多, 你可以选择遵守, 也可以不遵守, 后果自负.
3. 结果测试
首先, 我们用tornado写一个简单的服务器, 它会显示客户端的地址和接口;
import tornado.web
import tornado.ioloop
class IndexHandler(tornado.web.RequestHandler):
def get(self) -> None:
print(f'new connection from {self.request.connection.context.address}')
self.write('hello world')
app = tornado.web.Application([(r'/', IndexHandler)])
app.listen(8888)
tornado.ioloop.IOLoop.current().start()
然后, 使用我们刚写好的客户端进行测试:
from client import HTTPConnection
def fetch(conn: HTTPConnection, url: str = '') -> None:
conn.request('GET', url)
res = conn.get_response()
print(res.read())
connection = HTTPConnection('127.0.0.1', 8888)
for i in range(10):
fetch(connection)
结果如下:
以上就是python用700行代码实现http客户端的详细内容，更多关于python http客户端的资料请关注WEB开发者其它相关文章！
