字符串流中可能被获取的元素的计数

Question

我想写一个程序，应该发送http请求，并从服务器接收整个响应。我还想在Ada流的帮助下做到这一点(不是Send_Socket/Receive_Socket和Stream_Element_Vector和String之间的数据转换)。

我的问题是:如何检测流是否为空?我想这样做是因为当我试图读取比流包含的数据更多的数据时，操作String'Read会自己挂起。我无法确定响应的大小。

目前我的代码是这样的:

with Ada.Text_IO;
with GNAT.Sockets;
with Ada.Strings.Unbounded;
procedure sockets is
    package to renames Ada.Text_IO;
    package s renames GNAT.Sockets;
    package su renames Ada.Strings.Unbounded;
    host      : constant String      := "www.google.pl";
    HTTP_PORT : constant s.PORT_TYPE := 80;
    task ping is
        entry start;
        entry stop;
    end ping;
    task body ping is
        query    : su.Unbounded_String := su.To_Unbounded_String("");
        host2    : su.Unbounded_String;
        Address  : s.Sock_Addr_Type;
        Socket   : s.Socket_Type;
        Channel  : s.Stream_Access;
        cr       : constant Character := Character'Val(13);
        lf       : constant Character := Character'Val(10);
        new_line : constant String := (cr, lf);
        output   : String (1 .. 4096);
    begin
        to.Put("Ala");
        to.Put(new_line);
        to.Put("Kot");
        accept start;
        Address.Addr := s.Addresses (s.Get_Host_By_Name (host), 1);
        Address.Port := HTTP_PORT;
        s.Create_Socket (Socket);
        s.Set_Socket_Option (
            Socket,
            s.Socket_Level,
            (s.Reuse_Address, True));
        delay 0.2;
        to.Put_Line("Lacze z hostem");
        s.Connect_Socket(Socket, Address);
        Channel := s.Stream (Socket);
        to.Put_Line("Wysylam dane");
        su.Append(query, "GET / HTTP/1.1");
        su.Append(query, new_line);
        su.Append(query, "Host: ");
        su.Append(query, host);
        su.Append(query, new_Line);
        su.Append(query, new_line);
        String'Write (Channel, su.To_String(query));
        to.Put_Line("Odbieram dane");
        String'Read (Channel, output);
        to.Put(output);
        to.Put_Line("Zamykam gniazdo");
        s.Close_Socket(Socket);
        accept stop;
        to.Put_Line("ping stopped");
    end ping;

begin
    to.Put_Line("Hello World!!!");
    ping.start;
    ping.stop;
end sockets;

Answer 1

XML/Ada已经包含了从http流中读取文件的实现。看一下input_sources-http文件。

Answer 2

Ada流根据定义是阻塞的。如果你想使用流属性，你必须知道有多少数据到达流。

PS: Black是另一个讨论HTTP的库。