玩转iPhone网络通讯之BSD Socket篇(手把手教你iphone开发 - 基础篇)

作
者：孙东风 2009-11-11（请尊重作者劳动成果，转载务必注明出处）

在进行iPhone网络通讯程序的开发中，不可避免的要利用Socket套接字。iPhone提供了Socket网络编程的接口CFSocket，不过笔者更喜欢使用BSD Socket。

iPhone BSD Socket进行编程所需要的头文件基本都位于/Xcode3.1.4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk/usr/include/sys下，既然本篇文章作为基础篇，
那么笔者就从最基本的知识讲解开始。

首先，Socket是进行程序间通讯(IPC, Internet Process Connection)的BSD方法，这意味着Socket是用来让一个进程和其他的进程互相通讯的，就像我们用电话来和其他人交流一样。

既然说Socket像个电话，那么如果要打电话首先就要安装一部电话，“安装电话”这个动作对BSD Socket来说就是初始化一个Socket，方法如下：

int socket(int,
int, int);

第一个int参数为Socket的地址方式，既然要“安装电话”，那么就要首先确认所要安装的电话是音频的还是脉冲的。而如果要给BSD Socket安装电话，有两种类型可供读者选择：AF_UNIX和AF_INET，它们代表Socket的地址格式。如果选择AF_UNIX，意味着需要为Socket提供一个类似Unix路径的名称，这个选项主要用于本地程序之间的socket通讯；本文主要讲解网络通讯，所以需要选择参数AF_INET。

第二个int参数为Socket的类型，“安装电话”需要首先确定是装有线的还是装无线的，安装Socket也一样，在Socket中提供了两种类型：SOCK_STREAM和SOCK_DGRAM。SOCK_STREAM表明数据像字符流一样通过Socket；而SOCK_DGRAM则表明数据以数据报（Datagrams）的形式通过Socket，本文主要讲解SOCK_STREAM，因为它的使用更为广泛。

第三个int参数为所使用的协议，本文里使用0即可。

“安装电话”的代码如下：

if((sockfd
= socket(AF_INET, SOCK_STREAM, 0)) == -1)

{

perror("socket");

exit(1);

}

到现在为止，怎么安装电话已经清
楚了。因为本文主要演示如何在iPhone上使用BSD Socket获取内容，更多的功能是“打电话”而不是“接电话”，所以下面主要讲解BSD Socket扮演“客户端”角色的操作。

既然要“打电话”，那么首先要有
打电话的对象，更确切的说需要一个“电话号码”，BSD Socket中的“电话号码”就是IP地址。更糟糕的情况是，如果只知道联系人的名字而不知道电话号码，那么还需要程序查找相应联系人的电
话号码，根据联系人姓名查找电话号码的过程在BSD Socket中叫做DNS解析，代码如下：

-
(NSString*)getIpAddressForHost:(NSString*) theHost

{

struct
hostent *host = gethostbyname([theHost UTF8String]);

if(!host)

{

herror("resolv");

return
NULL;

}

struct
in_addr **list = (struct in_addr **)host->h_addr_list;

NSString
*addressString = [NSString stringWithCString:inet_ntoa(*list[0])];

return
addressString;

}

hostent是个结构体，使用它需要#import <netdb.h>，通过这个方法得到theHost域名的第一个有效的IP地址并返回。

正确的“找到电话号码”后，就需
要“拨打电话”了，代码如下：

their_addr.sin_family
= AF_INET;

their_addr.sin_addr.s_addr
= inet_addr([[self getIpAddressForHost:hostName] UTF8String]);

NSLog(@"getIpAddressForHost
:%@",[self getIpAddressForHost:hostName]);

their_addr.sin_port
= htons(80);

bzero(&(their_addr.sin_zero),
8);

int
conn = connect(sockfd, (struct sockaddr*)&their_addr, sizeof(struct
sockaddr));

NSLog(@"Connect errno is :%d",conn);

笔者最初试图采用NHost进行主机域名的解析，奈何iPhone的这个类为private的，在application的开发中不可使用。

如果“电话”能顺利的接通，那么
就可以进行“讲话”了，反之则会断开“电话连接”，如果友好的话，最好能给个提示，诸如“您所拨打的电话不在服务区之类”：）

if(conn
!= -1)

{

NSLog(@"Then
the conn is not -1!");

NSMutableString*
httpContent = [self makeHttpHeader:hostName];

NSLog(@"httpCotent
is :%@",httpContent);

if(contentSended
!= nil)

[httpContent appendFormat:contentSended];

NSLog(@"Sended
content is :%@",httpContent);

NSData
*data = [httpContent dataUsingEncoding:NSISOLatin1StringEncoding];

ssize_t
dataSended = send(sockfd, [data bytes], [data length], 0);

if(dataSended
== [data length])

{

NSLog(@"Datas have been sended over!");

}

printf("send
%d bytes to %s\n",dataSended,inet_ntoa(their_addr.sin_addr));

NSMutableString*
readString = [[NSMutableString alloc] init];

char
readBuffer[512];

int
br = 0;

while((br
= recv(sockfd, readBuffer, sizeof(readBuffer), 0)) <
sizeof(readBuffer))

{

NSLog(@"read datas length is :%d",br);

[readString appendFormat:[NSString stringWithCString:readBuffer
length:br]];

NSLog(@"Hava received datas is :%@",readString);

}

close(sockfd);

}else
{

UIAlertView
*alert = [[UIAlertView alloc] initWithTitle:[@"Connection failed to
host " stringByAppendingString:hostName] message:@"Please check the
hostname in the preferences." delegate:self cancelButtonTitle:@"OK"
otherButtonTitles:nil];

[alert
show];

[alert
release];

}

“讲话”通过send()，“听话”通过recv()，这个两个函数的原型如下：

int send(int sockfd, const void *msg,
int len, int flags);

int recv(int sockfd,void *buf,int
len,unsigned int flags);

可以看出，这两个函数的参数基本
相同。

第一个参数为套接字的句柄。

第二个参数为数据缓冲区。

第三个参数为数据长度。

最后一个参数有点特殊，这个参数
是为了让BSD Socket能支持“带外数
据”，何谓“带外数据”？顾名思义，就是“带内以外的数据”，而带内数据就是常规的按照Socket字节流顺序进行传递的数据。通常情况下，数据由连接的一端流到接收的一端，并且认为数据的所有字节都
是精确排序的，晚写入的字节绝不会早于先写入的字节到达。但是如果我们“挂断了电话”，而接收方还有大量已经被接收的缓冲数据，这些数据还没被程序读取，
那么接收方需要在读取这些缓冲的“带内数据”之前先读取一个标识取消的请求，这个请求就可以利用带外请求的方法进行传送。请求带外数据传送需要把标识位置
为MSG_OOB，如下：

char buf[64];

int len;

int s;

…

send(s,buf,len,MSG_OOB);

至此，一个完整的“通话过程”已
经结束，最后别忘记调用close(sockfd)“挂断电
话”。

下面笔者尝试请求www.baidu.com的首页，并把请求的页面内容打印到控制台，所以需要对请求进行封装，以支持HTTP协议。很简单，只需要在请求的内容前面加上相应的HTTP头信息即可，如下：

#define HTTPMETHOD @"GET"

#define HTTPVERSION
@"HTTP/1.1"

#define HTTPHOST @"Host"

#define KENTER @"\r\n"

#define
KBLANK @" "

- (NSMutableString*)
makeHttpHeader:(NSString*) hostName

{

NSMutableString
*header = [[NSMutableString alloc] init];

[header
appendFormat:HTTPMETHOD];

[header
appendFormat:KBLANK];

[header
appendFormat:@"/index.html"];

[header
appendFormat:KBLANK];

[header
appendFormat:HTTPVERSION];

[header
appendFormat:KENTER];

[header
appendFormat:HTTPHOST];

[header
appendFormat:@":"];

[header
appendFormat:hostName];

[header
appendFormat:KENTER];

[header
appendFormat:KENTER];

return
header;

}

在上面的方法中，笔者封装了HTTP头信息，对HTTP不熟悉的同学可以先熟悉熟悉HTTP的格式，请求到的内容打印如下：

[Session
started at 2009-11-12 15:40:02 +0800.]
2009-11-12 15:40:04.691
BSDHttpExample[3483:207] getIpAddressForHost :119.75.216.30
2009-11-12
15:40:04.725 BSDHttpExample[3483:207] Connect errno is :0
2009-11-12
15:40:04.727 BSDHttpExample[3483:207] Then the conn is not -1!
2009-11-12
15:40:04.735 BSDHttpExample[3483:207] httpCotent is :GET /index.html
HTTP/1.1
Host:www.baidu.com

2009-11-12 15:40:04.736
BSDHttpExample[3483:207] Sended content is :GET /index.html HTTP/1.1
Host:www.baidu.com

2009-11-12
15:40:04.736 BSDHttpExample[3483:207] Datas have been sended over!
send
48 bytes to 119.75.216.30
2009-11-12 15:40:04.764
BSDHttpExample[3483:207] read datas length is :363
2009-11-12
15:40:04.765 BSDHttpExample[3483:207] Hava received datas is :HTTP/1.1
200 OK
Date: Thu, 12 Nov 2009 07:40:05 GMT
Server: BWS/1.0
Content-Length:
3520
Content-Type: text/html;charset=gb2312
Cache-Control:
private
Expires: Thu, 12 Nov 2009 07:40:05 GMT
Set-Cookie:
BAIDUID=9B024266ADD3B52AC8367A2BDD1676E5:FG=1; expires=Thu, 12-Nov-39
07:40:05 GMT; path=/; domain=.baidu.com
P3P: CP=" OTI DSP COR IVA OUR
IND COM "

2009-11-12 15:40:04.766 BSDHttpExample[3483:207] view
has been loaded!

最后为了造福大家，笔者附上完整
的代码，头文件如下：

//

// BSDHttpExampleViewController.h

// BSDHttpExample

//

// Created
by sun dfsun2009 on 09-11-12.

// Copyright
__MyCompanyName__ 2009. All rights reserved.

//

#import <UIKit/UIKit.h>

#define MYPORT 4880

#import <stdio.h>

#import <stdlib.h>

#import <unistd.h>

#import <arpa/inet.h>

#import <sys/types.h>

#import <sys/socket.h>

#import <netdb.h>

@interface
BSDHttpExampleViewController : UIViewController {

int
sockfd;

struct
sockaddr_in their_addr;

}

@end

实现文件如下：

//

// BSDHttpExampleViewController.m

// BSDHttpExample

//

// Created
by sun dfsun2009 on 09-11-12.

// Copyright
__MyCompanyName__ 2009. All rights reserved.

//

#import
"BSDHttpExampleViewController.h"

@implementation
BSDHttpExampleViewController

#define HTTPMETHOD @"GET"

#define HTTPVERSION
@"HTTP/1.1"

#define HTTPHOST @"Host"

#define KENTER @"\r\n"

#define KBLANK @" "

/*

// The
designated initializer. Override to perform setup that is required
before the view is loaded.

-
(id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle
*)nibBundleOrNil {

if
(self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {

//
Custom initialization

}

return
self;

}

*/

/*

//
Implement loadView to create a view hierarchy programmatically, without
using a nib.

-
(void)loadView {

}

*/

void error_handle(char
*errorMsg)

{

fputs(errorMsg,
stderr);

fputc('\n',stderr);

exit(1);

}

- (NSMutableString*)
makeHttpHeader:(NSString*) hostName

{

NSMutableString
*header = [[NSMutableString alloc] init];

[header
appendFormat:HTTPMETHOD];

[header
appendFormat:KBLANK];

[header
appendFormat:@"/index.html"];

[header
appendFormat:KBLANK];

[header
appendFormat:HTTPVERSION];

[header
appendFormat:KENTER];

[header
appendFormat:HTTPHOST];

[header
appendFormat:@":"];

[header
appendFormat:hostName];

[header
appendFormat:KENTER];

[header
appendFormat:KENTER];

return
header;

}

-
(NSString*)getIpAddressForHost:(NSString*) theHost

{

struct
hostent *host = gethostbyname([theHost UTF8String]);

if(!host)

{

herror("resolv");

return
NULL;

}

struct
in_addr **list = (struct in_addr **)host->h_addr_list;

NSString
*addressString = [NSString stringWithCString:inet_ntoa(*list[0])];

return
addressString;

}

- (void)Connect:(NSString
*)hostName content:(NSString *)contentSended

{

if((sockfd
= socket(AF_INET, SOCK_STREAM, 0)) == -1)

{

perror("socket");

exit(1);

}

//NSHost
*host = [NSHost hostWithName:hostName];

//if(host)

//{

their_addr.sin_family
= AF_INET;

//their_addr.sin_addr.s_addr
= inet_addr([[host address] UTF8String]);

their_addr.sin_addr.s_addr
= inet_addr([[self getIpAddressForHost:hostName] UTF8String]);

NSLog(@"getIpAddressForHost
:%@",[self getIpAddressForHost:hostName]);

their_addr.sin_port
= htons(80);

bzero(&(their_addr.sin_zero),
8);

int
conn = connect(sockfd, (struct sockaddr*)&their_addr, sizeof(struct
sockaddr));

NSLog(@"Connect
errno is :%d",conn);

if(conn
!= -1)

{

NSLog(@"Then
the conn is not -1!");

NSMutableString*
httpContent = [self makeHttpHeader:hostName];

NSLog(@"httpCotent
is :%@",httpContent);

if(contentSended
!= nil)

[httpContent appendFormat:contentSended];

NSLog(@"Sended
content is :%@",httpContent);

NSData
*data = [httpContent dataUsingEncoding:NSISOLatin1StringEncoding];

ssize_t
dataSended = send(sockfd, [data bytes], [data length], 0);

if(dataSended
== [data length])

{

NSLog(@"Datas have been sended over!");

}

printf("send
%d bytes to %s\n",dataSended,inet_ntoa(their_addr.sin_addr));

NSMutableString*
readString = [[NSMutableString alloc] init];

char
readBuffer[512];

int
br = 0;

while((br
= recv(sockfd, readBuffer, sizeof(readBuffer), 0)) <
sizeof(readBuffer))

{

NSLog(@"read datas length is :%d",br);

[readString appendFormat:[NSString stringWithCString:readBuffer
length:br]];

NSLog(@"Hava received datas is :%@",readString);

}

close(sockfd);

}else
{

UIAlertView
*alert = [[UIAlertView alloc] initWithTitle:[@"Connection failed to
host " stringByAppendingString:hostName] message:@"Please check the
hostname in the preferences." delegate:self cancelButtonTitle:@"OK"
otherButtonTitles:nil];

[alert
show];

[alert
release];

}

/*

}

else

{

UIAlertView
*alert = [[UIAlertView alloc] initWithTitle:[@"Could not look up host "
stringByAppendingString:hostName] message:@"Please check the hostname
in the preferences." delegate:self cancelButtonTitle:@"OK"
otherButtonTitles:nil];

[alert
show];

[alert
release];

}

**/

}

- (void)Send:(id)sender

{

char
message[7] = "aaag";

send(sockfd,message,sizeof(message),0);

NSLog(@"%s",message);

}

// Implement viewDidLoad to do
additional setup after loading the view, typically from a nib.

- (void)viewDidLoad {

[self
Connect:@"www.baidu.com" content:nil];

[super
viewDidLoad];

NSLog(@"view
has been loaded!");

}

/*

//
Override to allow orientations other than the default portrait
orientation.

-
(BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{

//
Return YES for supported orientations

return
(interfaceOrientation == UIInterfaceOrientationPortrait);

}

*/

-
(void)didReceiveMemoryWarning {

//
Releases the view if it doesn't have a superview.

[super
didReceiveMemoryWarning];

//
Release any cached data, images, etc that aren't in use.

}

- (void)viewDidUnload {

//
Release any retained subviews of the main view.

//
e.g. self.myOutlet = nil;

}

- (void)dealloc {

[super
dealloc];

}

@end