【发布时间】：2018-03-11 03:03:31
【问题描述】：
我正在尝试通过 websocket 从一个 javascript/html 客户端向另一个客户端发送图像。问题是服务器错误地接收图像。我将所有图像作为文本中的数据 URI 发送，这样当 javascript 客户端接收到它时，它可以简单地将 img 的 src 设置为 URI。问题（我相信）来自我如何处理消息碎片。发送简单的文本消息工作正常，所以我相信它是导致问题的消息的大小，唯一的主要代码区别是我如何处理消息碎片。从this 文档中，我相信必须做的就是揭开每个分段帧的有效负载并将缓冲区连接在一起。在服务器上读取的 URI 比图像的实际数据 URI 短得多。在客户端，我所做的只是调用 socket.send() 函数。我已经确认我在 javascript FileReader 中读取的数据 URI 是正确的（在客户端）。
int wSock::readData(/*input socket data buffer*/ char ** sockp, /*output payload*/ char ** buffer, /*output payload info*/ WebSocketFrameData * data) {
char * sock = *sockp;
if (!webSocketIsOpened(sock)) return -32; //checks if the socket is open
u_long package_size;
SOCKET socket;
size_t dataRead = 0;
size_t dr = 0;
size_t firstLength = 0;
memcpy_s(&socket, 4, sock, 4);
ioctlsocket(socket, FIONREAD, &package_size);
if (package_size <= 0) return 1;
char * buf = new char[package_size + 1];
while (dataRead < package_size) {
dr = recv(socket, buf + dataRead, package_size - dataRead, NULL);
if (dr == SOCKET_ERROR) {
delete[] buf;
return WSAGetLastError();
}
dataRead += dr;
}
*(buf + package_size) = '\0';
if (package_size > 0) {
decodeFrame(buf, buffer, &firstLength);
if (data != NULL) {
data->payloadLength = firstLength;
data->opcode = *buf & 0b00001111;
}
}
else return 1;
// code handling other opcodes such as a close frame or a ping
char fin = (*buf) >> 7;
if (!fin) { //start handling message fragmentation
printf("Fragmentation! \n");
FD_SET tempRead;
size_t totalLength = firstLength -1; //firstLength includes the null terminator
char * combinedPayloads = new char[totalLength];
memcpy_s(combinedPayloads, totalLength, *buffer, totalLength);
printf("First frage of size: %u \n", totalLength);
while (fin != 1) {
FD_ZERO(&tempRead);
FD_SET(socket, &tempRead);
select(0, &tempRead, NULL, NULL, NULL);
package_size = 0;
ioctlsocket(socket, FIONREAD, &package_size);
printf("Reading next frag of size: %u \n", package_size);
char * contBuf = new char[package_size];
dataRead = 0;
while (dataRead < package_size) {
dr = recv(socket, contBuf + dataRead, package_size - dataRead, NULL);
if (dr == SOCKET_ERROR) {
delete[] contBuf;
return WSAGetLastError();
}
dataRead += dr;
}
char * payload;
size_t payloadLength = 0;
decodeFrame(contBuf, &payload, &payloadLength);
payloadLength--; //the output payloadLength from the decodeFrame function includes a null terminator
char * backBuffer = new char[totalLength];
memcpy_s(backBuffer, totalLength, combinedPayloads, totalLength);
delete[] combinedPayloads;
combinedPayloads = new char[totalLength + payloadLength];
memcpy_s(combinedPayloads, totalLength, backBuffer, totalLength);
memcpy_s(combinedPayloads + totalLength, payloadLength, payload, payloadLength);
fin = contBuf[0] >> 7;
totalLength += payloadLength;
delete[] backBuffer;
delete[] contBuf;
delete[] payload;
if (fin) break;
}
delete[] *buffer;
*buffer = new char[totalLength + 1];
memcpy_s(*buffer, totalLength, combinedPayloads, totalLength);
(*buffer)[totalLength] = '\0';
delete[] combinedPayloads;
data->payloadLength = totalLength;
printf("Finished fragment! Total size: %u \n", totalLength);
}
delete[] buf;
return 0;
}
这是解码每个 websocket 帧的代码。正如我提到的，服务器可以很好地处理较小的聊天消息，所以我认为问题是消息重新组装，但我将包含 decodeFrame 函数，希望它有助于理解。
int wSock::decodeFrame(char * message, char ** output, size_t * payloadLength)
{
char read;
memcpy_s(&read, 1, message + 1, 1);
unsigned long long size = read & 0b01111111;
//takes bits 9 - 15;
int lastByte = 2;
if (size == 126) {
unsigned short rr;
memcpy_s(&rr, 2, message + 2, 2);
size = ntohs(rr);
lastByte = 4;
}
else if (size == 127) {
unsigned long long data;
memcpy_s(&data, 8, message + 2, 8);
size = ntohll(data);
lastByte = 10;
}
if(payloadLength != NULL)
*payloadLength = size + 1;
char mask[4];
memcpy_s(mask, 4, message + lastByte, 4);
*output = new char[(size + 1)];
lastByte += 4;
for (int i = 0; i < size; i++) {
(*output)[i] = message[lastByte + i] ^ mask.mask[i % 4];
}
(*output)[size] = '\0';
return 0;
}
在服务器端进行调试，我将读取的消息写入文本文件。但是，写入的 URI 只有大约 4,000 - 6,000 个字符长，最后 200 - 400 个字符不是有效的 base64 字符，但是这些无效字符之前的字符 do 匹配它们对应的真实字符数据 URI。重新组装过程中的 printf 语句将倾向于读取大约 262,368 个字节（总计），而实际 URI 的长度为 389,906 个字符。在读取 URI 后，服务器将其发送给客户端，这会导致它们断开连接。因此，正如我所提到的，我的猜测是，当我重新组装数据帧时出现了问题。任何帮助将不胜感激。
【问题讨论】：