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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-COPY"
>31.9. Functions Associated with the <TT
CLASS="COMMAND"
>COPY</TT
> Command</A
></H1
><P
> The <TT
CLASS="COMMAND"
>COPY</TT
> command in
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> has options to read from or write
to the network connection used by <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>.
The functions described in this section allow applications to take
advantage of this capability by supplying or consuming copied data.
</P
><P
> The overall process is that the application first issues the SQL
<TT
CLASS="COMMAND"
>COPY</TT
> command via <CODE
CLASS="FUNCTION"
>PQexec</CODE
> or one
of the equivalent functions. The response to this (if there is no
error in the command) will be a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object bearing
a status code of <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
> or
<TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
> (depending on the specified copy
direction). The application should then use the functions of this
section to receive or transmit data rows. When the data transfer is
complete, another <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object is returned to indicate
success or failure of the transfer. Its status will be
<TT
CLASS="LITERAL"
>PGRES_COMMAND_OK</TT
> for success or
<TT
CLASS="LITERAL"
>PGRES_FATAL_ERROR</TT
> if some problem was encountered.
At this point further SQL commands can be issued via
<CODE
CLASS="FUNCTION"
>PQexec</CODE
>. (It is not possible to execute other SQL
commands using the same connection while the <TT
CLASS="COMMAND"
>COPY</TT
>
operation is in progress.)
</P
><P
> If a <TT
CLASS="COMMAND"
>COPY</TT
> command is issued via
<CODE
CLASS="FUNCTION"
>PQexec</CODE
> in a string that could contain additional
commands, the application must continue fetching results via
<CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> after completing the <TT
CLASS="COMMAND"
>COPY</TT
>
sequence. Only when <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> returns
<TT
CLASS="SYMBOL"
>NULL</TT
> is it certain that the <CODE
CLASS="FUNCTION"
>PQexec</CODE
>
command string is done and it is safe to issue more commands.
</P
><P
> The functions of this section should be executed only after obtaining
a result status of <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
> or
<TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
> from <CODE
CLASS="FUNCTION"
>PQexec</CODE
> or
<CODE
CLASS="FUNCTION"
>PQgetResult</CODE
>.
</P
><P
> A <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object bearing one of these status values
carries some additional data about the <TT
CLASS="COMMAND"
>COPY</TT
> operation
that is starting. This additional data is available using functions
that are also used in connection with query results:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQNFIELDS-1"
></A
><CODE
CLASS="FUNCTION"
>PQnfields</CODE
>
</DT
><DD
><P
> Returns the number of columns (fields) to be copied.
</P
></DD
><DT
><A
NAME="LIBPQ-PQBINARYTUPLES-1"
></A
><CODE
CLASS="FUNCTION"
>PQbinaryTuples</CODE
>
</DT
><DD
><P
> 0 indicates the overall copy format is textual (rows separated by
newlines, columns separated by separator characters, etc). 1
indicates the overall copy format is binary. See <A
HREF="sql-copy.html"
>COPY</A
> for more information.
</P
></DD
><DT
><A
NAME="LIBPQ-PQFFORMAT-1"
></A
><CODE
CLASS="FUNCTION"
>PQfformat</CODE
>
</DT
><DD
><P
> Returns the format code (0 for text, 1 for binary) associated with
each column of the copy operation. The per-column format codes
will always be zero when the overall copy format is textual, but
the binary format can support both text and binary columns.
(However, as of the current implementation of <TT
CLASS="COMMAND"
>COPY</TT
>,
only binary columns appear in a binary copy; so the per-column
formats always match the overall format at present.)
</P
></DD
></DL
></DIV
><P>
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> These additional data values are only available when using protocol
3.0. When using protocol 2.0, all these functions will return 0.
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-COPY-SEND"
>31.9.1. Functions for Sending <TT
CLASS="COMMAND"
>COPY</TT
> Data</A
></H2
><P
> These functions are used to send data during <TT
CLASS="LITERAL"
>COPY FROM
STDIN</TT
>. They will fail if called when the connection is not in
<TT
CLASS="LITERAL"
>COPY_IN</TT
> state.
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQPUTCOPYDATA"
></A
><CODE
CLASS="FUNCTION"
>PQputCopyData</CODE
>
</DT
><DD
><P
> Sends data to the server during <TT
CLASS="LITERAL"
>COPY_IN</TT
> state.
</P><PRE
CLASS="SYNOPSIS"
>int PQputCopyData(PGconn *conn,
const char *buffer,
int nbytes);</PRE
><P>
</P
><P
> Transmits the <TT
CLASS="COMMAND"
>COPY</TT
> data in the specified
<TT
CLASS="PARAMETER"
>buffer</TT
>, of length <TT
CLASS="PARAMETER"
>nbytes</TT
>, to the server.
The result is 1 if the data was sent, zero if it was not sent
because the attempt would block (this case is only possible if the
connection is in nonblocking mode), or -1 if an error occurred.
(Use <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to retrieve details if
the return value is -1. If the value is zero, wait for write-ready
and try again.)
</P
><P
> The application can divide the <TT
CLASS="COMMAND"
>COPY</TT
> data stream
into buffer loads of any convenient size. Buffer-load boundaries
have no semantic significance when sending. The contents of the
data stream must match the data format expected by the
<TT
CLASS="COMMAND"
>COPY</TT
> command; see <A
HREF="sql-copy.html"
>COPY</A
> for details.
</P
></DD
><DT
><A
NAME="LIBPQ-PQPUTCOPYEND"
></A
><CODE
CLASS="FUNCTION"
>PQputCopyEnd</CODE
>
</DT
><DD
><P
> Sends end-of-data indication to the server during <TT
CLASS="LITERAL"
>COPY_IN</TT
> state.
</P><PRE
CLASS="SYNOPSIS"
>int PQputCopyEnd(PGconn *conn,
const char *errormsg);</PRE
><P>
</P
><P
> Ends the <TT
CLASS="LITERAL"
>COPY_IN</TT
> operation successfully if
<TT
CLASS="PARAMETER"
>errormsg</TT
> is <TT
CLASS="SYMBOL"
>NULL</TT
>. If
<TT
CLASS="PARAMETER"
>errormsg</TT
> is not <TT
CLASS="SYMBOL"
>NULL</TT
> then the
<TT
CLASS="COMMAND"
>COPY</TT
> is forced to fail, with the string pointed to by
<TT
CLASS="PARAMETER"
>errormsg</TT
> used as the error message. (One should not
assume that this exact error message will come back from the server,
however, as the server might have already failed the
<TT
CLASS="COMMAND"
>COPY</TT
> for its own reasons. Also note that the option
to force failure does not work when using pre-3.0-protocol
connections.)
</P
><P
> The result is 1 if the termination data was sent, zero if it was
not sent because the attempt would block (this case is only possible
if the connection is in nonblocking mode), or -1 if an error
occurred. (Use <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to retrieve
details if the return value is -1. If the value is zero, wait for
write-ready and try again.)
</P
><P
> After successfully calling <CODE
CLASS="FUNCTION"
>PQputCopyEnd</CODE
>, call
<CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> to obtain the final result status of the
<TT
CLASS="COMMAND"
>COPY</TT
> command. One can wait for this result to be
available in the usual way. Then return to normal operation.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-COPY-RECEIVE"
>31.9.2. Functions for Receiving <TT
CLASS="COMMAND"
>COPY</TT
> Data</A
></H2
><P
> These functions are used to receive data during <TT
CLASS="LITERAL"
>COPY TO
STDOUT</TT
>. They will fail if called when the connection is not in
<TT
CLASS="LITERAL"
>COPY_OUT</TT
> state.
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQGETCOPYDATA"
></A
><CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
>
</DT
><DD
><P
> Receives data from the server during <TT
CLASS="LITERAL"
>COPY_OUT</TT
> state.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetCopyData(PGconn *conn,
char **buffer,
int async);</PRE
><P>
</P
><P
> Attempts to obtain another row of data from the server during a
<TT
CLASS="COMMAND"
>COPY</TT
>. Data is always returned one data row at
a time; if only a partial row is available, it is not returned.
Successful return of a data row involves allocating a chunk of
memory to hold the data. The <TT
CLASS="PARAMETER"
>buffer</TT
> parameter must
be non-<TT
CLASS="SYMBOL"
>NULL</TT
>. <TT
CLASS="PARAMETER"
>*buffer</TT
> is set to
point to the allocated memory, or to <TT
CLASS="SYMBOL"
>NULL</TT
> in cases
where no buffer is returned. A non-<TT
CLASS="SYMBOL"
>NULL</TT
> result
buffer should be freed using <CODE
CLASS="FUNCTION"
>PQfreemem</CODE
> when no longer
needed.
</P
><P
> When a row is successfully returned, the return value is the number
of data bytes in the row (this will always be greater than zero).
The returned string is always null-terminated, though this is
probably only useful for textual <TT
CLASS="COMMAND"
>COPY</TT
>. A result
of zero indicates that the <TT
CLASS="COMMAND"
>COPY</TT
> is still in
progress, but no row is yet available (this is only possible when
<TT
CLASS="PARAMETER"
>async</TT
> is true). A result of -1 indicates that the
<TT
CLASS="COMMAND"
>COPY</TT
> is done. A result of -2 indicates that an
error occurred (consult <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> for the reason).
</P
><P
> When <TT
CLASS="PARAMETER"
>async</TT
> is true (not zero),
<CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> will not block waiting for input; it
will return zero if the <TT
CLASS="COMMAND"
>COPY</TT
> is still in progress
but no complete row is available. (In this case wait for read-ready
and then call <CODE
CLASS="FUNCTION"
>PQconsumeInput</CODE
> before calling
<CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> again.) When <TT
CLASS="PARAMETER"
>async</TT
> is
false (zero), <CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> will block until data is
available or the operation completes.
</P
><P
> After <CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> returns -1, call
<CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> to obtain the final result status of the
<TT
CLASS="COMMAND"
>COPY</TT
> command. One can wait for this result to be
available in the usual way. Then return to normal operation.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-COPY-DEPRECATED"
>31.9.3. Obsolete Functions for <TT
CLASS="COMMAND"
>COPY</TT
></A
></H2
><P
> These functions represent older methods of handling <TT
CLASS="COMMAND"
>COPY</TT
>.
Although they still work, they are deprecated due to poor error handling,
inconvenient methods of detecting end-of-data, and lack of support for binary
or nonblocking transfers.
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQGETLINE"
></A
><CODE
CLASS="FUNCTION"
>PQgetline</CODE
>
</DT
><DD
><P
> Reads a newline-terminated line of characters (transmitted
by the server) into a buffer string of size <TT
CLASS="PARAMETER"
>length</TT
>.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetline(PGconn *conn,
char *buffer,
int length);</PRE
><P>
</P
><P
> This function copies up to <TT
CLASS="PARAMETER"
>length</TT
>-1 characters into
the buffer and converts the terminating newline into a zero byte.
<CODE
CLASS="FUNCTION"
>PQgetline</CODE
> returns <TT
CLASS="SYMBOL"
>EOF</TT
> at the
end of input, 0 if the entire line has been read, and 1 if the
buffer is full but the terminating newline has not yet been read.
</P
><P
> Note that the application must check to see if a new line consists
of the two characters <TT
CLASS="LITERAL"
>\.</TT
>, which indicates
that the server has finished sending the results of the
<TT
CLASS="COMMAND"
>COPY</TT
> command. If the application might receive
lines that are more than <TT
CLASS="PARAMETER"
>length</TT
>-1 characters long,
care is needed to be sure it recognizes the <TT
CLASS="LITERAL"
>\.</TT
>
line correctly (and does not, for example, mistake the end of a
long data line for a terminator line).
</P
></DD
><DT
><A
NAME="LIBPQ-PQGETLINEASYNC"
></A
><CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
>
</DT
><DD
><P
> Reads a row of <TT
CLASS="COMMAND"
>COPY</TT
> data (transmitted by the
server) into a buffer without blocking.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetlineAsync(PGconn *conn,
char *buffer,
int bufsize);</PRE
><P>
</P
><P
> This function is similar to <CODE
CLASS="FUNCTION"
>PQgetline</CODE
>, but it can be used
by applications
that must read <TT
CLASS="COMMAND"
>COPY</TT
> data asynchronously, that is, without blocking.
Having issued the <TT
CLASS="COMMAND"
>COPY</TT
> command and gotten a <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
>
response, the
application should call <CODE
CLASS="FUNCTION"
>PQconsumeInput</CODE
> and
<CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
> until the
end-of-data signal is detected.
</P
><P
> Unlike <CODE
CLASS="FUNCTION"
>PQgetline</CODE
>, this function takes
responsibility for detecting end-of-data.
</P
><P
> On each call, <CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
> will return data if a
complete data row is available in <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>'s input buffer.
Otherwise, no data is returned until the rest of the row arrives.
The function returns -1 if the end-of-copy-data marker has been recognized,
or 0 if no data is available, or a positive number giving the number of
bytes of data returned. If -1 is returned, the caller must next call
<CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>, and then return to normal processing.
</P
><P
> The data returned will not extend beyond a data-row boundary. If possible
a whole row will be returned at one time. But if the buffer offered by
the caller is too small to hold a row sent by the server, then a partial
data row will be returned. With textual data this can be detected by testing
whether the last returned byte is <TT
CLASS="LITERAL"
>\n</TT
> or not. (In a binary
<TT
CLASS="COMMAND"
>COPY</TT
>, actual parsing of the <TT
CLASS="COMMAND"
>COPY</TT
> data format will be needed to make the
equivalent determination.)
The returned string is not null-terminated. (If you want to add a
terminating null, be sure to pass a <TT
CLASS="PARAMETER"
>bufsize</TT
> one smaller
than the room actually available.)
</P
></DD
><DT
><A
NAME="LIBPQ-PQPUTLINE"
></A
><CODE
CLASS="FUNCTION"
>PQputline</CODE
>
</DT
><DD
><P
> Sends a null-terminated string to the server. Returns 0 if
OK and <TT
CLASS="SYMBOL"
>EOF</TT
> if unable to send the string.
</P><PRE
CLASS="SYNOPSIS"
>int PQputline(PGconn *conn,
const char *string);</PRE
><P>
</P
><P
> The <TT
CLASS="COMMAND"
>COPY</TT
> data stream sent by a series of calls
to <CODE
CLASS="FUNCTION"
>PQputline</CODE
> has the same format as that
returned by <CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
>, except that
applications are not obliged to send exactly one data row per
<CODE
CLASS="FUNCTION"
>PQputline</CODE
> call; it is okay to send a partial
line or multiple lines per call.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Before <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> protocol 3.0, it was necessary
for the application to explicitly send the two characters
<TT
CLASS="LITERAL"
>\.</TT
> as a final line to indicate to the server that it had
finished sending <TT
CLASS="COMMAND"
>COPY</TT
> data. While this still works, it is deprecated and the
special meaning of <TT
CLASS="LITERAL"
>\.</TT
> can be expected to be removed in a
future release. It is sufficient to call <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
> after
having sent the actual data.
</P
></BLOCKQUOTE
></DIV
></DD
><DT
><A
NAME="LIBPQ-PQPUTNBYTES"
></A
><CODE
CLASS="FUNCTION"
>PQputnbytes</CODE
>
</DT
><DD
><P
> Sends a non-null-terminated string to the server. Returns
0 if OK and <TT
CLASS="SYMBOL"
>EOF</TT
> if unable to send the string.
</P><PRE
CLASS="SYNOPSIS"
>int PQputnbytes(PGconn *conn,
const char *buffer,
int nbytes);</PRE
><P>
</P
><P
> This is exactly like <CODE
CLASS="FUNCTION"
>PQputline</CODE
>, except that the data
buffer need not be null-terminated since the number of bytes to send is
specified directly. Use this procedure when sending binary data.
</P
></DD
><DT
><A
NAME="LIBPQ-PQENDCOPY"
></A
><CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>
</DT
><DD
><P
> Synchronizes with the server.
</P><PRE
CLASS="SYNOPSIS"
>int PQendcopy(PGconn *conn);</PRE
><P>
This function waits until the server has finished the copying.
It should either be issued when the last string has been sent
to the server using <CODE
CLASS="FUNCTION"
>PQputline</CODE
> or when the
last string has been received from the server using
<CODE
CLASS="FUNCTION"
>PGgetline</CODE
>. It must be issued or the server
will get <SPAN
CLASS="QUOTE"
>"out of sync"</SPAN
> with the client. Upon return
from this function, the server is ready to receive the next SQL
command. The return value is 0 on successful completion,
nonzero otherwise. (Use <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to
retrieve details if the return value is nonzero.)
</P
><P
> When using <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
>, the application should
respond to a <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
> result by executing
<CODE
CLASS="FUNCTION"
>PQgetline</CODE
> repeatedly, followed by
<CODE
CLASS="FUNCTION"
>PQendcopy</CODE
> after the terminator line is seen.
It should then return to the <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> loop
until <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> returns a null pointer.
Similarly a <TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
> result is processed
by a series of <CODE
CLASS="FUNCTION"
>PQputline</CODE
> calls followed by
<CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>, then return to the
<CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> loop. This arrangement will
ensure that a <TT
CLASS="COMMAND"
>COPY</TT
> command embedded in a series
of <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> commands will be executed correctly.
</P
><P
> Older applications are likely to submit a <TT
CLASS="COMMAND"
>COPY</TT
>
via <CODE
CLASS="FUNCTION"
>PQexec</CODE
> and assume that the transaction
is done after <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>. This will work
correctly only if the <TT
CLASS="COMMAND"
>COPY</TT
> is the only
<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> command in the command string.
</P
></DD
></DL
></DIV
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></HTML
>
Mini Shell