--- /dev/null
+/*-------------------------------------------------------------------------
+ *
+ * tcn.c
+ * triggered change notification support for PostgreSQL
+ *
+ * Portions Copyright (c) 2011-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * contrib/tcn/tcn.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "executor/spi.h"
+#include "commands/async.h"
+#include "commands/trigger.h"
+#include "lib/stringinfo.h"
+#include "utils/rel.h"
+#include "utils/syscache.h"
+
+
+PG_MODULE_MAGIC;
+
+
+/* forward declarations */
+Datum triggered_change_notification(PG_FUNCTION_ARGS);
+
+
+/*
+ * Copy from s (for source) to r (for result), wrapping with q (quote)
+ * characters and doubling any quote characters found.
+ */
+static void
+strcpy_quoted(StringInfo r, const char *s, const char q)
+{
+ appendStringInfoCharMacro(r, q);
+ while (*s)
+ {
+ if (*s == q)
+ appendStringInfoCharMacro(r, q);
+ appendStringInfoCharMacro(r, *s);
+ s++;
+ }
+ appendStringInfoCharMacro(r, q);
+}
+
+/*
+ * triggered_change_notification
+ *
+ * This trigger function will send a notification of data modification with
+ * primary key values. The channel will be "tcn" unless the trigger is
+ * created with a parameter, in which case that parameter will be used.
+ */
+PG_FUNCTION_INFO_V1(triggered_change_notification);
+
+Datum
+triggered_change_notification(PG_FUNCTION_ARGS)
+{
+ TriggerData *trigdata = (TriggerData *) fcinfo->context;
+ Trigger *trigger;
+ int nargs;
+ HeapTuple trigtuple;
+ Relation rel;
+ TupleDesc tupdesc;
+ char *channel;
+ char operation;
+ StringInfo payload = makeStringInfo();
+ bool foundPK;
+
+ List *indexoidlist;
+ ListCell *indexoidscan;
+
+ /* make sure it's called as a trigger */
+ if (!CALLED_AS_TRIGGER(fcinfo))
+ ereport(ERROR,
+ (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
+ errmsg("triggered_change_notification: must be called as trigger")));
+
+ /* and that it's called after the change */
+ if (!TRIGGER_FIRED_AFTER(trigdata->tg_event))
+ ereport(ERROR,
+ (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
+ errmsg("triggered_change_notification: must be called after the change")));
+
+ /* and that it's called for each row */
+ if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
+ ereport(ERROR,
+ (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
+ errmsg("triggered_change_notification: must be called for each row")));
+
+ if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
+ operation = 'I';
+ else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
+ operation = 'U';
+ else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
+ operation = 'D';
+ else
+ {
+ elog(ERROR, "triggered_change_notification: trigger fired by unrecognized operation");
+ operation = 'X'; /* silence compiler warning */
+ }
+
+ trigger = trigdata->tg_trigger;
+ nargs = trigger->tgnargs;
+ if (nargs > 1)
+ ereport(ERROR,
+ (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
+ errmsg("triggered_change_notification: must not be called with more than one parameter")));
+
+ if (nargs == 0)
+ channel = "tcn";
+ else
+ channel = trigger->tgargs[0];
+
+ /* get tuple data */
+ trigtuple = trigdata->tg_trigtuple;
+ rel = trigdata->tg_relation;
+ tupdesc = rel->rd_att;
+
+ foundPK = false;
+
+ /*
+ * Get the list of index OIDs for the table from the relcache, and look up
+ * each one in the pg_index syscache until we find one marked primary key
+ * (hopefully there isn't more than one such).
+ */
+ indexoidlist = RelationGetIndexList(rel);
+
+ foreach(indexoidscan, indexoidlist)
+ {
+ Oid indexoid = lfirst_oid(indexoidscan);
+ HeapTuple indexTuple;
+ Form_pg_index index;
+
+ indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
+ if (!HeapTupleIsValid(indexTuple)) /* should not happen */
+ elog(ERROR, "cache lookup failed for index %u", indexoid);
+ index = (Form_pg_index) GETSTRUCT(indexTuple);
+ /* we're only interested if it is the primary key */
+ if (index->indisprimary)
+ {
+ int numatts = index->indnatts;
+
+ if (numatts > 0)
+ {
+ int i;
+
+ foundPK = true;
+
+ strcpy_quoted(payload, RelationGetRelationName(rel), '"');
+ appendStringInfoCharMacro(payload, ',');
+ appendStringInfoCharMacro(payload, operation);
+
+ for (i = 0; i < numatts; i++)
+ {
+ int colno = index->indkey.values[i];
+
+ appendStringInfoCharMacro(payload, ',');
+ strcpy_quoted(payload, NameStr((tupdesc->attrs[colno - 1])->attname), '"');
+ appendStringInfoCharMacro(payload, '=');
+ strcpy_quoted(payload, SPI_getvalue(trigtuple, tupdesc, colno), '\'');
+ }
+
+ Async_Notify(channel, payload->data);
+ }
+ ReleaseSysCache(indexTuple);
+ break;
+ }
+ ReleaseSysCache(indexTuple);
+ }
+
+ list_free(indexoidlist);
+
+ if (!foundPK)
+ ereport(ERROR,
+ (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
+ errmsg("triggered_change_notification: must be called on a table with a primary key")));
+
+ return PointerGetDatum(NULL); /* after trigger; value doesn't matter */
+}
--- /dev/null
+<!-- doc/src/sgml/tcn.sgml -->
+
+<sect1 id="tcn" xreflabel="tcn">
+ <title>tcn</title>
+
+ <indexterm zone="tcn">
+ <primary>tcn</primary>
+ </indexterm>
+
+ <indexterm zone="tcn">
+ <primary>triggered_change_notification</primary>
+ </indexterm>
+
+ <para>
+ The <filename>tcn</> module provides a trigger function that notifies
+ listeners of changes to any table on which it is attached. It must be
+ used as an <literal>AFTER</> trigger <literal>FOR EACH ROW</>.
+ </para>
+
+ <para>
+ Only one parameter may be suupplied to the function in a
+ <literal>CREATE TRIGGER</> statement, and that is optional. If supplied
+ it will be used for the channel name for the notifications. If omitted
+ <literal>tcn</> will be used for the channel name.
+ </para>
+
+ <para>
+ The payload of the notifications consists of the table name, a letter to
+ indicate which type of operation was performed, and column name/value pairs
+ for primary key columns. Each part is separated from the next by a comma.
+ For ease of parsing using regular expressions, table and column names are
+ always wrapped in double quotes, and data values are always wrapped in
+ single quotes. Embeded quotes are doubled.
+ </para>
+
+ <para>
+ A brief example of using the extension follows.
+
+<programlisting>
+test=# create table tcndata
+test-# (
+test(# a int not null,
+test(# b date not null,
+test(# c text,
+test(# primary key (a, b)
+test(# );
+NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "tcndata_pkey" for table "tcndata"
+CREATE TABLE
+test=# create trigger tcndata_tcn_trigger
+test-# after insert or update or delete on tcndata
+test-# for each row execute procedure triggered_change_notification();
+CREATE TRIGGER
+test=# listen tcn;
+LISTEN
+test=# insert into tcndata values (1, date '2012-12-22', 'one'),
+test-# (1, date '2012-12-23', 'another'),
+test-# (2, date '2012-12-23', 'two');
+INSERT 0 3
+Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
+Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
+Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
+test=# update tcndata set c = 'uno' where a = 1;
+UPDATE 2
+Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
+Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
+test=# delete from tcndata where a = 1 and b = date '2012-12-22';
+DELETE 1
+Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
+</programlisting>
+ </para>
+
+</sect1>
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