ecpg: Fix zero-termination of string generated by intoasc()

intoasc(), a wrapper for PGTYPESinterval_to_asc that converts an
interval to its textual representation, used a plain memcpy() when
copying its result.  This could miss a zero-termination in the result
string, leading to an incorrect result.

The routines in informix.c do not provide the length of their result
buffer, which would allow a replacement of strcpy() to safer strlcpy()
calls, but this requires an ABI breakage and that cannot happen in
back-branches.

Author: Oleg Tselebrovskiy
Reviewed-by: Ashutosh Bapat
Discussion: https://postgr.es/m/bf47888585149f83b276861a1662f7e4@postgrespro.ru
Backpatch-through: 12

src/interfaces/ecpg/compatlib/informix.c

@@ -674,7 +674,7 @@ intoasc(interval * i, char *str)
 	if (!tmp)
 		return -errno;
 
-	memcpy(str, tmp, strlen(tmp));
+	strcpy(str, tmp);
 	free(tmp);
 	return 0;
 }

src/interfaces/ecpg/test/compat_informix/.gitignore

@@ -4,6 +4,8 @@
 /dec_test.c
 /describe
 /describe.c
+/intoasc
+/intoasc.c
 /rfmtdate
 /rfmtdate.c
 /rfmtlong

src/interfaces/ecpg/test/compat_informix/Makefile

@@ -16,7 +16,8 @@ TESTS = test_informix test_informix.c \
         rnull rnull.c \
         sqlda sqlda.c \
         describe describe.c \
-        charfuncs charfuncs.c
+        charfuncs charfuncs.c \
+        intoasc intoasc.c
 
 all: $(TESTS)
 

src/interfaces/ecpg/test/compat_informix/intoasc.pgc

@@ -0,0 +1,21 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "pgtypes_interval.h"
+
+EXEC SQL BEGIN DECLARE SECTION;
+    char dirty_str[100] = "aaaaaaaaa_bbbbbbbb_ccccccccc_ddddddddd_";
+    interval *interval_ptr;
+EXEC SQL END DECLARE SECTION;
+
+int main()
+{
+    interval_ptr = (interval *) malloc(sizeof(interval));
+    interval_ptr->time = 100000000;
+    interval_ptr->month = 240;
+
+    printf("dirty_str contents before intoasc: %s\n", dirty_str);
+    intoasc(interval_ptr, dirty_str);
+    printf("dirty_str contents after intoasc: %s\n", dirty_str);
+    return 0;
+}

src/interfaces/ecpg/test/ecpg_schedule

@@ -7,6 +7,7 @@ test: compat_informix/sqlda
 test: compat_informix/describe
 test: compat_informix/test_informix
 test: compat_informix/test_informix2
+test: compat_informix/intoasc
 test: compat_oracle/char_array
 test: connect/test2
 test: connect/test3

src/interfaces/ecpg/test/expected/compat_informix-intoasc.c

@@ -0,0 +1,40 @@
+/* Processed by ecpg (regression mode) */
+/* These include files are added by the preprocessor */
+#include <ecpglib.h>
+#include <ecpgerrno.h>
+#include <sqlca.h>
+/* Needed for informix compatibility */
+#include <ecpg_informix.h>
+/* End of automatic include section */
+#define ECPGdebug(X,Y) ECPGdebug((X)+100,(Y))
+
+#line 1 "intoasc.pgc"
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "pgtypes_interval.h"
+
+/* exec sql begin declare section */
+       
+     
+
+#line 7 "intoasc.pgc"
+ char dirty_str [ 100 ] = "aaaaaaaaa_bbbbbbbb_ccccccccc_ddddddddd_" ;
+ 
+#line 8 "intoasc.pgc"
+ interval * interval_ptr ;
+/* exec sql end declare section */
+#line 9 "intoasc.pgc"
+
+
+int main()
+{
+    interval_ptr = (interval *) malloc(sizeof(interval));
+    interval_ptr->time = 100000000;
+    interval_ptr->month = 240;
+
+    printf("dirty_str contents before intoasc: %s\n", dirty_str);
+    intoasc(interval_ptr, dirty_str);
+    printf("dirty_str contents after intoasc: %s\n", dirty_str);
+    return 0;
+}

src/interfaces/ecpg/test/expected/compat_informix-intoasc.stdout

@@ -0,0 +1,2 @@
+dirty_str contents before intoasc: aaaaaaaaa_bbbbbbbb_ccccccccc_ddddddddd_
+dirty_str contents after intoasc: @ 20 years 1 min 40 secs