笨办法学C 练习45：一个简单的TCP/IP客户端

2016-06-22 17:44:00

练习45：一个简单的TCP/IP客户端

原文：Exercise 45: A Simple TCP/IP Client

译者：飞龙

我打算使用RingBuffer来创建一个非常简单的小型网络测试工具，叫做netclient。为此我需要向Makefile添加一些工具，来处理bin/目录下的小程序。

扩展Makefile

首先，为程序添加一些变量，就像单元测试的TESTS和TEST_SRC变量：

PROGRAMS_SRC=$(wildcard bin/*.c)PROGRAMS=$(patsubst %.c,%,$(PROGRAMS_SRC))

之后你可能想要添加PROGRAMS到所有目标中：

all: $(TARGET) $(SO_TARGET) tests $(PROGRAMS)

之后在clean目标中向rm那一行添加PROGRAMS：

rm -rf build $(OBJECTS) $(TESTS) $(PROGRAMS)

最后你还需要在最后添加一个目标来构建它们：

$(PROGRAMS): CFLAGS += $(TARGET)

做了这些修改你就能够将.c文件扔到bin中，并且编译它们以及为其链接库文件，就像测试那样。

netclient 代码

netclient的代码是这样的：

# undef NDEBUG# include # include # include # include # include # include # include # include # include # include # include # include struct tagbstring NL = bsStatic("\n");struct tagbstring CRLF = bsStatic("\r\n");int nonblock(int fd) {    int flags = fcntl(fd, F_GETFL, 0);    check(flags >= 0, "Invalid flags on nonblock.");    int rc = fcntl(fd, F_SETFL, flags | O_NONBLOCK);    check(rc == 0, "Can't set nonblocking.");    return 0;error:    return -1;}int client_connect(char *host, char *port){    int rc = 0;    struct addrinfo *addr = NULL;    rc = getaddrinfo(host, port, NULL, &addr);    check(rc == 0, "Failed to lookup %s:%s", host, port);    int sock = socket(AF_INET, SOCK_STREAM, 0);    check(sock >= 0, "Cannot create a socket.");    rc = connect(sock, addr->ai_addr, addr->ai_addrlen);    check(rc == 0, "Connect failed.");    rc = nonblock(sock);    check(rc == 0, "Can't set nonblocking.");    freeaddrinfo(addr);    return sock;error:    freeaddrinfo(addr);    return -1;}int read_some(RingBuffer *buffer, int fd, int is_socket){    int rc = 0;    if(RingBuffer_available_data(buffer) == 0) {        buffer->start = buffer->end = 0;    }    if(is_socket) {        rc = recv(fd, RingBuffer_starts_at(buffer), RingBuffer_available_space(buffer), 0);    } else {        rc = read(fd, RingBuffer_starts_at(buffer), RingBuffer_available_space(buffer));    }    check(rc >= 0, "Failed to read from fd: %d", fd);    RingBuffer_commit_write(buffer, rc);    return rc;error:    return -1;}int write_some(RingBuffer *buffer, int fd, int is_socket){    int rc = 0;    bstring data = RingBuffer_get_all(buffer);    check(data != NULL, "Failed to get from the buffer.");    check(bfindreplace(data, &NL, &CRLF, 0) == BSTR_OK, "Failed to replace NL.");    if(is_socket) {        rc = send(fd, bdata(data), blength(data), 0);    } else {        rc = write(fd, bdata(data), blength(data));    }    check(rc == blength(data), "Failed to write everything to fd: %d.", fd);    bdestroy(data);    return rc;error:    return -1;}int main(int argc, char *argv[]){    fd_set allreads;    fd_set readmask;    int socket = 0;    int rc = 0;    RingBuffer *in_rb = RingBuffer_create(1024 * 10);    RingBuffer *sock_rb = RingBuffer_create(1024 * 10);    check(argc == 3, "USAGE: netclient host port");    socket = client_connect(argv[1], argv[2]);    check(socket >= 0, "connect to %s:%s failed.", argv[1], argv[2]);    FD_ZERO(&allreads);    FD_SET(socket, &allreads);    FD_SET(0, &allreads);    while(1) {        readmask = allreads;        rc = select(socket + 1, &readmask, NULL, NULL, NULL);        check(rc >= 0, "select failed.");        if(FD_ISSET(0, &readmask)) {            rc = read_some(in_rb, 0, 0);            check_debug(rc != -1, "Failed to read from stdin.");        }        if(FD_ISSET(socket, &readmask)) {            rc = read_some(sock_rb, socket, 0);            check_debug(rc != -1, "Failed to read from socket.");        }        while(!RingBuffer_empty(sock_rb)) {            rc = write_some(sock_rb, 1, 0);            check_debug(rc != -1, "Failed to write to stdout.");        }        while(!RingBuffer_empty(in_rb)) {            rc = write_some(in_rb, socket, 1);            check_debug(rc != -1, "Failed to write to socket.");        }    }    return 0;error:    return -1;}

代码中使用了select来处理stdin（文件描述符0）和用于和服务器交互的socket中的事件。它使用了RingBuffer来储存和复制数据，并且你可以认为read_some和write_some函数都是RingBuffer中相似函数的原型。

在这一小段代码中，可能有一些你并不知道的网络函数。当你碰到不知道的函数时，在手册页上查询它来确保你理解了它。这一小段代码可能需要让你研究用于小型服务器编程的所有C语言API。

你会看到什么

如果你完成了所有构建，测试的最快方式就是看看你能否从learncodethehardway.org上得到一个特殊的文件：

$$ ./bin/netclient learncodethehardway.org 80GET /ex45.txt HTTP/1.1Host: learncodethehardway.orgHTTP/1.1 200 OKDate: Fri, 27 Apr 2012 00:41:25 GMTContent-Type: text/plainContent-Length: 41Last-Modified: Fri, 27 Apr 2012 00:42:11 GMTETag: 4f99eb63-29Server: Mongrel2/1.7.5Learn C The Hard Way, Exercise 45 works.^C$

这里我所做的事情是键入创建/ex45.txt的HTTP请求所需的语法，在Host:请求航之后，按下ENTER键来输入空行。接着我获取相应，包括响应头和内容。最后我按下CTRL-C来退出。