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Changed error detection check when sending data via socket #404

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Dec 16, 2024
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Changed error detection check when sending data via socket #404

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5 changes: 3 additions & 2 deletions clickhouse/base/socket.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -457,11 +457,12 @@ size_t SocketOutput::DoWrite(const void* data, size_t len) {
static const int flags = 0;
#endif

if (::send(s_, (const char*)data, (int)len, flags) != (int)len) {
const ssize_t ret = ::send(s_, (const char*)data, (int)len, flags);
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@Enmk Enmk Dec 13, 2024 •
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So is it possible that less data would be sent than requested? If yes, what will happen?

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@dngrudin dngrudin Dec 13, 2024

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I've had this happen (it happens very rarely, so I can't give an example of the sequence of actions that would lead to it). I don't know the exact reasons, since this is not typical for blocking sockets. Perhaps this happens when the server is slow in reading data from the socket compared to writing to the data on the client. I also found an increase in the frequency of such situations when using the 'strace' utility (but perhaps this was due to something else).
If, after the size has returned smaller, resend what was not sent, then all the data will be written to the table.

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@Enmk Enmk Dec 16, 2024

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ok, but it seems like resent is not implemented

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@dngrudin dngrudin Dec 16, 2024

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This is implemented in this place:

void WireFormat::WriteAll(OutputStream& output, const void* buf, size_t len) {
    const size_t original_len = len;
    const uint8_t* p = static_cast<const uint8_t*>(buf);

    size_t written_previously = 1; // 1 to execute loop at least once
    while (len > 0 && written_previously) {
        written_previously = output.Write(p, len);

        p += written_previously;
        len -= written_previously;
    }

    if (len) {
        throw ProtocolError("Failed to write " + std::to_string(original_len)
                + " bytes, only written " + std::to_string(original_len - len));
    }
}

As I understand it, all data is sent through this call.

if (ret < 0) {
throw std::system_error(getSocketErrorCode(), getErrorCategory(), "fail to send " + std::to_string(len) + " bytes of data");
}

return len;
return (size_t)ret;
}


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