Function CopyGetData

src/backend/commands/copyfromparse.c:230–360

* CopyGetData reads data from the source (file or frontend) * * We attempt to read at least minread, and at most maxread, bytes from * the source. The actual number of bytes read is returned; if this is * less than minread, EOF was detected. * * Note: when copying from the frontend, we expect a proper EOF mark per * protocol; if the frontend simply drops the connection, we raise error. *

 * NB: no data conversion is applied here.
 */
int
CopyGetData(CopyFromState cstate, void *databuf, int minread, int maxread)
{
	int			bytesread = 0;

	switch (cstate->copy_src)
	{
		case COPY_FILE:
			bytesread = fread(databuf, 1, maxread, cstate->copy_file);
			if (ferror(cstate->copy_file))
			{
				if (cstate->is_program)
				{
					int olderrno = errno;
					if (cstate->copy_file)
					{
						fclose(cstate->copy_file);
						cstate->copy_file = NULL;
					}
					close_program_pipes(cstate->program_pipes, true);

					/*
					 * If close_program_pipes() didn't throw an error,
					 * the program terminated normally, but closed the
					 * pipe first. Restore errno, and throw an error.
					 */
					errno = olderrno;

					ereport(ERROR,
							(errcode_for_file_access(),
							 errmsg("could not read from COPY program: %m")));
				}
				else
					ereport(ERROR,
						(errcode_for_file_access(),
						 errmsg("could not read from COPY file: %m")));
			}
			if (bytesread == 0)
				cstate->raw_reached_eof = true;
			break;
		case COPY_FRONTEND:
			while (maxread > 0 && bytesread < minread && !cstate->raw_reached_eof)
			{
				int			avail;

				while (cstate->fe_msgbuf->cursor >= cstate->fe_msgbuf->len)
				{
					/* Try to receive another message */
					int			mtype;
					int			maxmsglen;

			readmessage:
					HOLD_CANCEL_INTERRUPTS();
					pq_startmsgread();
					mtype = pq_getbyte();
					if (mtype == EOF)
						ereport(ERROR,
								(errcode(ERRCODE_CONNECTION_FAILURE),