</para>
<para>
- This is a template for a procedural-language handler written in C:
-<programlisting>
-#include "postgres.h"
-#include "executor/spi.h"
-#include "commands/trigger.h"
-#include "fmgr.h"
-#include "access/heapam.h"
-#include "utils/syscache.h"
-#include "catalog/pg_proc.h"
-#include "catalog/pg_type.h"
-
-PG_MODULE_MAGIC;
-
-PG_FUNCTION_INFO_V1(plsample_call_handler);
-
-Datum
-plsample_call_handler(PG_FUNCTION_ARGS)
-{
- Datum retval;
-
- if (CALLED_AS_TRIGGER(fcinfo))
- {
- /*
- * Called as a trigger function
- */
- TriggerData *trigdata = (TriggerData *) fcinfo->context;
-
- retval = ...
- }
- else
- {
- /*
- * Called as a function
- */
-
- retval = ...
- }
-
- return retval;
-}
-</programlisting>
- Only a few thousand lines of code have to be added instead of the
- dots to complete the call handler.
- </para>
-
- <para>
- After having compiled the handler function into a loadable module
- (see <xref linkend="dfunc"/>), the following commands then
- register the sample procedural language:
-<programlisting>
-CREATE FUNCTION plsample_call_handler() RETURNS language_handler
- AS '<replaceable>filename</replaceable>'
- LANGUAGE C;
-CREATE LANGUAGE plsample
- HANDLER plsample_call_handler;
-</programlisting>
+ A template for a procedural-language handler written as a C extension is
+ provided in <literal>src/test/modules/plsample</literal>. This is a
+ working sample demonstrating one way to create a procedural-language
+ handler, process parameters, and return a value.
</para>
<para>
--- /dev/null
+CREATE EXTENSION plsample;
+-- Create and test some dummy functions
+CREATE FUNCTION plsample_result_text(a1 numeric, a2 text, a3 integer[])
+RETURNS TEXT
+AS $$
+ Example of source with text result.
+$$ LANGUAGE plsample;
+SELECT plsample_result_text(1.23, 'abc', '{4, 5, 6}');
+NOTICE: source text of function "plsample_result_text":
+ Example of source with text result.
+
+NOTICE: argument: 0; name: a1; value: 1.23
+NOTICE: argument: 1; name: a2; value: abc
+NOTICE: argument: 2; name: a3; value: {4,5,6}
+ plsample_result_text
+---------------------------------------
+ +
+ Example of source with text result.+
+
+(1 row)
+
+CREATE FUNCTION plsample_result_void(a1 text[])
+RETURNS VOID
+AS $$
+ Example of source with void result.
+$$ LANGUAGE plsample;
+SELECT plsample_result_void('{foo, bar, hoge}');
+NOTICE: source text of function "plsample_result_void":
+ Example of source with void result.
+
+NOTICE: argument: 0; name: a1; value: {foo,bar,hoge}
+ plsample_result_void
+----------------------
+
+(1 row)
+
--- /dev/null
+/*-------------------------------------------------------------------------
+ *
+ * plsample.c
+ * Handler for the PL/Sample procedural language
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * src/test/modules/plsample/plsample.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "catalog/pg_proc.h"
+#include "catalog/pg_type.h"
+#include "commands/event_trigger.h"
+#include "commands/trigger.h"
+#include "funcapi.h"
+#include "utils/builtins.h"
+#include "utils/lsyscache.h"
+#include "utils/syscache.h"
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(plsample_call_handler);
+
+static Datum plsample_func_handler(PG_FUNCTION_ARGS);
+
+/*
+ * Handle function, procedure, and trigger calls.
+ */
+Datum
+plsample_call_handler(PG_FUNCTION_ARGS)
+{
+ Datum retval = (Datum) 0;
+
+ PG_TRY();
+ {
+ /*
+ * Determine if called as function or trigger and call appropriate
+ * subhandler.
+ */
+ if (CALLED_AS_TRIGGER(fcinfo))
+ {
+ /*
+ * This function has been called as a trigger function, where
+ * (TriggerData *) fcinfo->context includes the information of the
+ * context.
+ */
+ }
+ else if (CALLED_AS_EVENT_TRIGGER(fcinfo))
+ {
+ /*
+ * This function is called as an event trigger function, where
+ * (EventTriggerData *) fcinfo->context includes the information
+ * of the context.
+ */
+ }
+ else
+ {
+ /* Regular function handler */
+ retval = plsample_func_handler(fcinfo);
+ }
+ }
+ PG_FINALLY();
+ {
+ }
+ PG_END_TRY();
+
+ return retval;
+}
+
+/*
+ * plsample_func_handler
+ *
+ * Function called by the call handler for function execution.
+ */
+static Datum
+plsample_func_handler(PG_FUNCTION_ARGS)
+{
+ HeapTuple pl_tuple;
+ Datum ret;
+ char *source;
+ bool isnull;
+ FmgrInfo *arg_out_func;
+ Form_pg_type type_struct;
+ HeapTuple type_tuple;
+ Form_pg_proc pl_struct;
+ volatile MemoryContext proc_cxt = NULL;
+ Oid *argtypes;
+ char **argnames;
+ char *argmodes;
+ char *proname;
+ Form_pg_type pg_type_entry;
+ Oid result_typioparam;
+ FmgrInfo result_in_func;
+ int numargs;
+
+ /* Fetch the source text of the function. */
+ pl_tuple = SearchSysCache(PROCOID,
+ ObjectIdGetDatum(fcinfo->flinfo->fn_oid), 0, 0, 0);
+ if (!HeapTupleIsValid(pl_tuple))
+ elog(ERROR, "cache lookup failed for function %u",
+ fcinfo->flinfo->fn_oid);
+
+ /*
+ * Extract and print the source text of the function. This can be used as
+ * a base for the function validation and execution.
+ */
+ pl_struct = (Form_pg_proc) GETSTRUCT(pl_tuple);
+ proname = pstrdup(NameStr(pl_struct->proname));
+ ret = SysCacheGetAttr(PROCOID, pl_tuple, Anum_pg_proc_prosrc, &isnull);
+ if (isnull)
+ elog(ERROR, "could not find source text of function \"%s\"",
+ proname);
+ ReleaseSysCache(pl_tuple);
+ source = DatumGetCString(DirectFunctionCall1(textout, ret));
+ ereport(NOTICE,
+ (errmsg("source text of function \"%s\": %s",
+ proname, source)));
+
+ /*
+ * Allocate a context that will hold all the Postgres data for the
+ * procedure.
+ */
+ proc_cxt = AllocSetContextCreate(TopMemoryContext,
+ "PL/Sample function",
+ ALLOCSET_SMALL_SIZES);
+
+ arg_out_func = (FmgrInfo *) palloc0(fcinfo->nargs * sizeof(FmgrInfo));
+ numargs = get_func_arg_info(pl_tuple, &argtypes, &argnames, &argmodes);
+
+ /*
+ * Iterate through all of the function arguments, printing each input
+ * value.
+ */
+ for (int i = 0; i < numargs; i++)
+ {
+ Oid argtype = pl_struct->proargtypes.values[i];
+ char *value;
+
+ type_tuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(argtype));
+ if (!HeapTupleIsValid(type_tuple))
+ elog(ERROR, "cache lookup failed for type %u", argtype);
+
+ type_struct = (Form_pg_type) GETSTRUCT(type_tuple);
+ fmgr_info_cxt(type_struct->typoutput, &(arg_out_func[i]), proc_cxt);
+ ReleaseSysCache(type_tuple);
+
+ value = OutputFunctionCall(&arg_out_func[i], fcinfo->args[i].value);
+ ereport(NOTICE,
+ (errmsg("argument: %d; name: %s; value: %s",
+ i, argnames[i], value)));
+ }
+
+ /*
+ * Get the required information for input conversion of the return value.
+ *
+ * If the function uses VOID as result, it is better to return NULL.
+ * Anyway, let's be honest. This is just a template, so there is not much
+ * we can do here. This returns NULL except if the result type is text,
+ * where the result is the source text of the function.
+ */
+ if (pl_struct->prorettype != TEXTOID)
+ PG_RETURN_NULL();
+
+ type_tuple = SearchSysCache1(TYPEOID,
+ ObjectIdGetDatum(pl_struct->prorettype));
+ if (!HeapTupleIsValid(type_tuple))
+ elog(ERROR, "cache lookup failed for type %u", pl_struct->prorettype);
+ pg_type_entry = (Form_pg_type) GETSTRUCT(type_tuple);
+ result_typioparam = getTypeIOParam(type_tuple);
+
+ fmgr_info_cxt(pg_type_entry->typinput, &result_in_func, proc_cxt);
+ ReleaseSysCache(type_tuple);
+
+ ret = InputFunctionCall(&result_in_func, source, result_typioparam, -1);
+ PG_RETURN_DATUM(ret);
+}
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