# 21.22. `http.server` — HTTP 服务器

源代码： Lib/http/server.py

这个模块定义了实现 HTTP 服务器（ Web 服务器）的类。

警告

`http.server` is not recommended for production. It only implements only basic security checks.

`HTTPServer` 是 `socketserver.TCPServer` 的一个子类。它会创建和侦听 HTTP 套接字，并将请求调度给处理程序。用于创建和运行服务器的代码看起来像这样：

    def run(server_class=HTTPServer, handler_class=BaseHTTPRequestHandler):
        server_address = ('', 8000)
        httpd = server_class(server_address, handler_class)
        httpd.serve_forever()

class `http.server.``HTTPServer`(server_address, RequestHandlerClass)

  该类基于 `TCPServer` 类，并会将服务器地址存入名为 `server_name` 和 `server_port` 的实例变量中。服务器可被处理程序通过 `server` 实例变量访问。

The `HTTPServer` must be given a RequestHandlerClass on instantiation, of which this module provides three different variants:

class `http.server.``BaseHTTPRequestHandler`(request, client_address, server)

  这个类用于处理到达服务器的 HTTP 请求。 它本身无法响应任何实际的 HTTP 请求；它必须被子类化以处理每个请求方法（例如 GET 或 POST）。 `BaseHTTPRequestHandler` 提供了许多供子类使用的类和实例变量以及方法。

  这个处理程序将解析请求和标头，然后调用特定请求类型对应的方法。 方法名称将根据请求来构造。 例如，对于请求方法 `SPAM`，将不带参数地调用 `do_SPAM()` 方法。 所有相关信息会被保存在该处理程序的实际变量中。 子类不需要重载或扩展 `__init__()` 方法。

  `BaseHTTPRequestHandler` 具有下列实例变量:

  `client_address`

    包含 `(host, port)` 形式的指向客户端地址的元组。

  `server`

    包含服务器实例。

  `close_connection`

    应当在 `handle_one_request()` 返回之前设定的布尔值，指明是否要期待另一个请求，还是应当关闭连接。

  `requestline`

    包含 HTTP 请求行的字符串表示。 末尾的 CRLF 会被去除。 该属性应当由 `handle_one_request()` 来设定。 如果无有效请求行被处理，则它应当被设为空字符串。

  `command`

    包含具体的命令（请求类型）。 例如 `'GET'`。

  `path`

    包含请求路径。

  `request_version`

    包含请求的版本字符串。 例如 `'HTTP/1.0'`。

  `headers`

    Holds an instance of the class specified by the `MessageClass` class variable. This instance parses and manages the headers in the HTTP request. The `parse_headers()` function from `http.client` is used to parse the headers and it requires that the HTTP request provide a valid RFC 2822 style header.

  `rfile`

    An `io.BufferedIOBase` input stream, ready to read from the start of the optional input data.

  `wfile`

    Contains the output stream for writing a response back to the client. Proper adherence to the HTTP protocol must be used when writing to this stream in order to achieve successful interoperation with HTTP clients.

    3.6 版更變: This is an `io.BufferedIOBase` stream.

  `BaseHTTPRequestHandler` has the following attributes:

  `server_version`

    Specifies the server software version. You may want to override this. The format is multiple whitespace-separated strings, where each string is of the form name[/version]. For example, `'BaseHTTP/0.2'`.

  `sys_version`

    Contains the Python system version, in a form usable by the `version_string` method and the `server_version` class variable. For example, `'Python/1.4'`.

  `error_message_format`

    Specifies a format string that should be used by `send_error()` method for building an error response to the client. The string is filled by default with variables from `responses` based on the status code that passed to `send_error()`.

  `error_content_type`

    Specifies the Content-Type HTTP header of error responses sent to the client. The default value is `'text/html'`.

  `protocol_version`

    This specifies the HTTP protocol version used in responses. If set to `'HTTP/1.1'`, the server will permit HTTP persistent connections; however, your server must then include an accurate `Content-Length` header (using `send_header()`) in all of its responses to clients. For backwards compatibility, the setting defaults to `'HTTP/1.0'`.

  `MessageClass`

    Specifies an `email.message.Message`-like class to parse HTTP headers. Typically, this is not overridden, and it defaults to `http.client.HTTPMessage`.

  `responses`

    This attribute contains a mapping of error code integers to two-element tuples containing a short and long message. For example, `{code: (shortmessage, longmessage)}`. The shortmessage is usually used as the message key in an error response, and longmessage as the explain key. It is used by `send_response_only()` and `send_error()` methods.

  A `BaseHTTPRequestHandler` instance has the following methods:

  `handle`()

    Calls `handle_one_request()` once (or, if persistent connections are enabled, multiple times) to handle incoming HTTP requests. You should never need to override it; instead, implement appropriate `do_*()` methods.

  `handle_one_request`()

    This method will parse and dispatch the request to the appropriate `do_*()` method. You should never need to override it.

  `handle_expect_100`()

    When a HTTP/1.1 compliant server receives an `Expect: 100-continue` request header it responds back with a `100 Continue` followed by `200 OK` headers. This method can be overridden to raise an error if the server does not want the client to continue. For e.g. server can chose to send `417 Expectation Failed` as a response header and `return False`.

    3.2 版新加入.

  `send_error`(code, message=None, explain=None)

    Sends and logs a complete error reply to the client. The numeric code specifies the HTTP error code, with message as an optional, short, human readable description of the error. The explain argument can be used to provide more detailed information about the error; it will be formatted using the `error_message_format` attribute and emitted, after a complete set of headers, as the response body. The `responses` attribute holds the default values for message and explain that will be used if no value is provided; for unknown codes the default value for both is the string `???`. The body will be empty if the method is HEAD or the response code is one of the following: `1xx`, `204 No Content`, `205 Reset Content`, `304 Not Modified`.

    3.4 版更變: The error response includes a Content-Length header. Added the explain argument.

  `send_response`(code, message=None)

    Adds a response header to the headers buffer and logs the accepted request. The HTTP response line is written to the internal buffer, followed by Server and Date headers. The values for these two headers are picked up from the `version_string()` and `date_time_string()` methods, respectively. If the server does not intend to send any other headers using the `send_header()` method, then `send_response()` should be followed by an `end_headers()` call.

    3.3 版更變: Headers are stored to an internal buffer and `end_headers()` needs to be called explicitly.

  `send_header`(keyword, value)

    Adds the HTTP header to an internal buffer which will be written to the output stream when either `end_headers()` or `flush_headers()` is invoked. keyword should specify the header keyword, with value specifying its value. Note that, after the send_header calls are done, `end_headers()` MUST BE called in order to complete the operation.

    3.2 版更變: Headers are stored in an internal buffer.

  `send_response_only`(code, message=None)

    Sends the response header only, used for the purposes when `100 Continue` response is sent by the server to the client. The headers not buffered and sent directly the output stream.If the message is not specified, the HTTP message corresponding the response code is sent.

    3.2 版新加入.

  `end_headers`()

    Adds a blank line (indicating the end of the HTTP headers in the response) to the headers buffer and calls `flush_headers()`.

    3.2 版更變: The buffered headers are written to the output stream.

  `flush_headers`()

    Finally send the headers to the output stream and flush the internal headers buffer.

    3.3 版新加入.

  `log_request`(code='-', size='-')

    Logs an accepted (successful) request. code should specify the numeric HTTP code associated with the response. If a size of the response is available, then it should be passed as the size parameter.

  `log_error`(...)

    Logs an error when a request cannot be fulfilled. By default, it passes the message to `log_message()`, so it takes the same arguments (format and additional values).

  `log_message`(format, ...)

    Logs an arbitrary message to `sys.stderr`. This is typically overridden to create custom error logging mechanisms. The format argument is a standard printf-style format string, where the additional arguments to `log_message()` are applied as inputs to the formatting. The client ip address and current date and time are prefixed to every message logged.

  `version_string`()

    Returns the server software’s version string. This is a combination of the `server_version` and `sys_version` attributes.

  `date_time_string`(timestamp=None)

    Returns the date and time given by timestamp (which must be `None` or in the format returned by `time.time()`), formatted for a message header. If timestamp is omitted, it uses the current date and time.

    结果看起来像 `'Sun, 06 Nov 1994 08:49:37 GMT'`。

  `log_date_time_string`()

    返回当前的日期和时间，为日志格式化

  `address_string`()

    返回客户端的地址

    3.3 版更變: Previously, a name lookup was performed. To avoid name resolution delays, it now always returns the IP address.

class `http.server.``SimpleHTTPRequestHandler`(request, client_address, server)

  这个类为当前目录及以下的文件提供服务，直接映射目录结构到HTTP请求

  A lot of the work, such as parsing the request, is done by the base class `BaseHTTPRequestHandler`. This class implements the `do_GET()` and `do_HEAD()` functions.

  The following are defined as class-level attributes of `SimpleHTTPRequestHandler`:

  `server_version`

    This will be `"SimpleHTTP/" + __version__`, where `__version__` is defined at the module level.

  `extensions_map`

    A dictionary mapping suffixes into MIME types. The default is signified by an empty string, and is considered to be `application/octet-stream`. The mapping is used case-insensitively, and so should contain only lower-cased keys.

  The `SimpleHTTPRequestHandler` class defines the following methods:

  `do_HEAD`()

    This method serves the `'HEAD'` request type: it sends the headers it would send for the equivalent `GET` request. See the `do_GET()` method for a more complete explanation of the possible headers.

  `do_GET`()

    这一请求通过把其解释为当前工作目录的相对路径来映射到本地文件

    If the request was mapped to a directory, the directory is checked for a file named `index.html` or `index.htm` (in that order). If found, the file’s contents are returned; otherwise a directory listing is generated by calling the `list_directory()` method. This method uses `os.listdir()` to scan the directory, and returns a `404` error response if the `listdir()` fails.

    If the request was mapped to a file, it is opened and the contents are returned. Any `OSError` exception in opening the requested file is mapped to a `404`, `'File not found'` error. Otherwise, the content type is guessed by calling the `guess_type()` method, which in turn uses the extensions_map variable.

    A `'Content-type:'` header with the guessed content type is output, followed by a `'Content-Length:'` header with the file’s size and a `'Last-Modified:'` header with the file’s modification time.

    Then follows a blank line signifying the end of the headers, and then the contents of the file are output. If the file’s MIME type starts with `text/` the file is opened in text mode; otherwise binary mode is used.

    For example usage, see the implementation of the `test()` function invocation in the `http.server` module.

The `SimpleHTTPRequestHandler` class can be used in the following manner in order to create a very basic webserver serving files relative to the current directory:

    import http.server
    import socketserver

    PORT = 8000

    Handler = http.server.SimpleHTTPRequestHandler

    with socketserver.TCPServer(("", PORT), Handler) as httpd:
        print("serving at port", PORT)
        httpd.serve_forever()

`http.server` can also be invoked directly using the `-m` switch of the interpreter with a `port number` argument. Similar to the previous example, this serves files relative to the current directory:

    python -m http.server 8000

By default, server binds itself to all interfaces. The option `-b/--bind` specifies a specific address to which it should bind. For example, the following command causes the server to bind to localhost only:

    python -m http.server 8000 --bind 127.0.0.1

3.4 版新加入: `--bind` argument was introduced.

class `http.server.``CGIHTTPRequestHandler`(request, client_address, server)

  This class is used to serve either files or output of CGI scripts from the current directory and below. Note that mapping HTTP hierarchic structure to local directory structure is exactly as in `SimpleHTTPRequestHandler`.

  備註

  CGI scripts run by the `CGIHTTPRequestHandler` class cannot execute redirects (HTTP code 302), because code 200 (script output follows) is sent prior to execution of the CGI script. This pre-empts the status code.

  The class will however, run the CGI script, instead of serving it as a file, if it guesses it to be a CGI script. Only directory-based CGI are used — the other common server configuration is to treat special extensions as denoting CGI scripts.

  The `do_GET()` and `do_HEAD()` functions are modified to run CGI scripts and serve the output, instead of serving files, if the request leads to somewhere below the `cgi_directories` path.

  The `CGIHTTPRequestHandler` defines the following data member:

  `cgi_directories`

    This defaults to `['/cgi-bin', '/htbin']` and describes directories to treat as containing CGI scripts.

  The `CGIHTTPRequestHandler` defines the following method:

  `do_POST`()

    This method serves the `'POST'` request type, only allowed for CGI scripts. Error 501, 「Can only POST to CGI scripts」, is output when trying to POST to a non-CGI url.

  Note that CGI scripts will be run with UID of user nobody, for security reasons. Problems with the CGI script will be translated to error 403.

`CGIHTTPRequestHandler` can be enabled in the command line by passing the `--cgi` option:

    python -m http.server --cgi 8000