服务器没有收到我通过 TCP 发送的内容

Question

我目前正在为 iOS 编写一个客户端-服务器应用程序。客户端是 Objective-C/CocoaTouch，服务器后端是用 C++ 编写的。现在我正在努力处理 TCP 通信——具体来说，是通过文件发送到服务器。

所有其他数据包发送/接收都有效，但对于这个数据包，服务器似乎接收到“坏”数据。服务器和客户端都是小端，所以端不是问题。

这是发件人代码：

- (void) sendGameUpdateWithFile:(NSString*)filePath gameID:(NSInteger)gameID {
    NSMutableData* data = [[NSMutableData alloc] init];
    data = [NSMutableData dataWithContentsOfFile:filePath];

    fileheadPacket head;

    head.msgtype = 0x12;
    strncpy(head.data1, [myUsername cStringUsingEncoding:NSUTF8StringEncoding], [myUsername length]);
    head.data1[[myUsername length]] = '\0';
    int followingPackets = 1;
    if([data length] % 1024 == 0){
        if([data length] > 1024){
            followingPackets = (int)[data length]/1024;
        }
    } else {
        followingPackets = (int)([data length]/1024)+1;
    }
    head.following = followingPackets;
    head.fileid = (int)gameID;
    head.size = sizeof(fileheadPacket);

    [mySock writeData:[NSData dataWithBytes:&head length:sizeof(fileheadPacket)] withTimeout:-1 tag:8];

    NSRange thisRange;
    thisRange.length = 1024;

    for(int i = 0; i < followingPackets; i++){
        thisRange.location = i*1024;

        if(thisRange.location + thisRange.length > [data length]){
            thisRange.length = [data length] - thisRange.location;
        }

        filePacket tmp;
        tmp.extra = (int)thisRange.length;
        tmp.msgtype = 0x13;
        tmp.size = sizeof(filePacket);
        tmp.following = (int)gameID;
        [data getBytes:tmp.fileBuffer range:thisRange];

        [mySock writeData:[NSData dataWithBytes:&tmp length:sizeof(filePacket)] withTimeout:-1 tag:8];

        NSLog(@"Wrote packet of type 0x%02x, size %d", tmp.msgtype, tmp.size);
    }
}

请原谅那段代码的混乱，它仍处于早期开发阶段，将得到改进。

这是接收者的代码：

std::vector<filePacket> PacketInterpreter::readPacket(filePacket* inPacket, int FD){
    //The returned vector contains stuff to return to the socket. If it's empty, there's nothing to return (and thus, the client on that FD shouldn't be listening)

    packetsToSend.clear();
    packetsToSend.reserve(1024);

    std::cout << "Received a packet of type " << inPacket->msgtype << " with size " << inPacket->size << std::endl;

    switch (inPacket->msgtype){
        case 0x12:
        {
            fileheadPacket* ptr = (fileheadPacket*) inPacket;
            assembleFile(ptr->following, ptr->fileid);
            break;
        }
        case 0x13:
            concatFilePart(inPacket->extra, inPacket->following, inPacket->fileBuffer);
            break;
    }

    return packetsToSend;

}

void PacketInterpreter::assembleFile(int following, int gameID){
    std::cout << "assembleFile with following: " << following << " and gameid " << gameID << std::endl;
    char* s = (char*)malloc(sizeof(char)*(following+1)*1024);
    inAssembly.insert(std::make_pair(gameID, s));
    inAssemblyCountdown.insert(std::make_pair(gameID, following+1));
    inAssemblyCountup.insert(std::make_pair(gameID, 0));
}

void PacketInterpreter::concatFilePart(int readLen, int gameID, unsigned char* data){

    for(int i = 0; i < readLen; i++){
        inAssembly[gameID][inAssemblyCountup[gameID]] = data[i];
        inAssemblyCountup[gameID]++;
    }

    inAssemblyCountdown[gameID]--;
    if(readLen != 1024 || inAssemblyCountdown[gameID] == 0){
        makeFile(gameID, inAssembly[gameID]);
        delete inAssembly[gameID];
        inAssembly.erase(gameID);
        inAssemblyCountdown.erase(gameID);

    }
}

void PacketInterpreter::makeFile(int gameID, char* buffer){
    std::string rmgameIDdir = ("rm -r " + std::to_string(gameID));
    system(rmgameIDdir.c_str());
    std::string gameIDdir = "mkdir " + std::to_string(gameID);
    std::string constructedPath = std::to_string(gameID);
    constructedPath += "/";

    std::system(gameIDdir.c_str());
    std::cout << gameIDdir.c_str() << std::endl;

    std::ofstream thisFile;
    thisFile.open(constructedPath+"sound.caf");

    std::cout << "opened " << constructedPath+"sound.caf" << " is open? " << thisFile.is_open() << std::endl;


    std::string temp = "";
    for(int i = 0; i < inAssemblyCountup[gameID]; i++){
        thisFile << std::hex << buffer[i];
    }
    thisFile.close();

    std::cout << "File assembled at " << constructedPath << "sound.caf" << std::endl;
}

void PacketInterpreter::assembleFile(int following, int gameID){
    std::cout << "assembleFile with following: " << following << " and gameid " << gameID << std::endl;
    char* s = (char*)malloc(sizeof(char)*(following+1)*1024);
    inAssembly.insert(std::make_pair(gameID, s));
    inAssemblyCountdown.insert(std::make_pair(gameID, following+1));
    inAssemblyCountup.insert(std::make_pair(gameID, 0));
}

void PacketInterpreter::concatFilePart(int readLen, int gameID, unsigned char* data){

    for(int i = 0; i < readLen; i++){
        inAssembly[gameID][inAssemblyCountup[gameID]] = data[i];
        inAssemblyCountup[gameID]++;
    }

    inAssemblyCountdown[gameID]--;
    if(readLen != 1024 || inAssemblyCountdown[gameID] == 0){
        makeFile(gameID, inAssembly[gameID]);
        delete inAssembly[gameID];
        inAssembly.erase(gameID);
        inAssemblyCountdown.erase(gameID);

    }
}

我在连接两端使用的结构如下所示：

//Packet used for small stuff
typedef struct small_packet {
    int msgtype;
    int size;
    int extra;
    int following;
    char data1[64];
    char data2[64];
} packet;

//Packet used for files
typedef struct file_packet {
    int msgtype; //For partial file packet this should be 0x02
    int size;
    int extra;
    int following;
    char data1[64];
    unsigned char fileBuffer[1024];
} filePacket;

//Used for file headers
typedef struct filehead_packet {
    int msgtype;
    int size;
    int extra;
    int following;
    char data1[64];
    int fileid;
    char rest[60];
} fileheadPacket;

我肯定知道两个单元上的结构以相同的方式打包，因为所有其他消息都使用相同的数据包，并且它们可以正常工作。当我尝试从客户端->服务器发送文件时，这是一个典型的日志：

Received a packet of type 18 with size 144
assembleFile with following: 367 and gameid 109
Received a packet of type 19 with size 1104
Received a packet of type 19 with size 1104
Received a packet of type 19 with size 1104
Received a packet of type 19 with size 1104
Checking for new games
Received a packet of type 0 with size 0
Received a packet of type -262149 with size -196612
Received a packet of type -131075 with size -196612
Received a packet of type -1 with size -1
Received a packet of type 327685 with size 327685
Received a packet of type 131074 with size 196611
Received a packet of type 65537 with size 65537
Received a packet of type -65538 with size -65538
Received a packet of type 131074 with size 196611
Received a packet of type 196611 with size 65537
Received a packet of type 131074 with size 196611
Received a packet of type 393222 with size 196611
Received a packet of type 0 with size 0
... many packets which make no sense, although the total number of packets is correct (367 in this case) ...
Received a packet of type -196612 with size -196612
Received a packet of type 131074 with size 131074
Received a packet of type 65537 with size 131074
Received a packet of type -196612 with size -196612
Received a packet of type 0 with size 65537
Received a packet of type -393223 with size -327686
Received a packet of type 131074 with size 131074
Received a packet of type 393222 with size 393222
Received a packet of type 0 with size 0
Received a packet of type 19 with size 1104
Received a packet of type 19 with size 1104
Received a packet of type 19 with size 1104
mkdir 109
opened 109/sound.caf is open? 1
File assembled at 109/sound.caf

这让我很生气，因为我不知道出了什么问题。如果您需要更多代码示例（例如发送和接收数据包的 main() 中的 select() 块，请告诉我。非常感谢您的帮助。提前致谢！

Answer 1

我实际上已经发现这里出了什么问题。服务器读取的速度比 iPhone 发送数据包的速度快，这意味着当服务器尝试读取完整大小的 (filePacket) 时，只有从 iPhone 传输的数据包的前半部分到达服务器文件描述符的行尾。

由于两台机器都是小端，数据包的“尾部”首先由服务器读取，在这种情况下，每个数据包中包含的元信息都存储在当前可用数据的“末尾”文件描述符。当我们尝试读取 1140 个字节并且只说...其中一半实际到达时，元数据从数据包的 fileBuffer 字段中获取随机值。

我通过“减慢”服务器端的读取速度快速解决了这个问题，但我认为我必须减少 filePacket 结构的总大小才能使其正常运行而不会以编程方式减慢速度。

那么我今天学到了什么？不要通过 TCP 发送太大的数据包并期望服务器将其全部读取。一次发送 1K 太多了。