Add support for piping COPY to/from an external program.

This includes backend "COPY TO/FROM PROGRAM '...'" syntax, and corresponding
psql \copy syntax. Like with reading/writing files, the backend version is
superuser-only, and in the psql version, the program is run in the client.

In the passing, the psql \copy STDIN/STDOUT syntax is subtly changed: if you
the stdin/stdout is quoted, it's now interpreted as a filename. For example,
"\copy foo from 'stdin'" now reads from a file called 'stdin', not from
standard input. Before this, there was no way to specify a filename called
stdin, stdout, pstdin or pstdout.

This creates a new function in pgport, wait_result_to_str(), which can
be used to convert the exit status of a process, as returned by wait(3),
to a human-readable string.

Etsuro Fujita, reviewed by Amit Kapila.

src/port/Makefile

@@ -32,7 +32,8 @@ LIBS += $(PTHREAD_LIBS)
 
 OBJS = $(LIBOBJS) chklocale.o dirmod.o erand48.o exec.o fls.o inet_net_ntop.o \
 	noblock.o path.o pgcheckdir.o pg_crc.o pgmkdirp.o pgsleep.o \
-	pgstrcasecmp.o qsort.o qsort_arg.o quotes.o sprompt.o tar.o thread.o
+	pgstrcasecmp.o qsort.o qsort_arg.o quotes.o sprompt.o tar.o thread.o \
+	wait_error.o
 
 # foo_srv.o and foo.o are both built from foo.c, but only foo.o has -DFRONTEND
 OBJS_SRV = $(OBJS:%.o=%_srv.o)

src/port/exec.c

@@ -505,14 +505,12 @@ pipe_read_line(char *cmd, char *line, int maxsize)
 
 /*
  * pclose() plus useful error reporting
- * Is this necessary?  bjm 2004-05-11
- * Originally this was stated to be here because pipe.c had backend linkage.
- * Perhaps that's no longer so now we have got rid of pipe.c amd 2012-03-28
  */
 int
 pclose_check(FILE *stream)
 {
 	int			exitstatus;
+	char	   *reason;
 
 	exitstatus = pclose(stream);
 
@@ -522,36 +520,21 @@ pclose_check(FILE *stream)
 	if (exitstatus == -1)
 	{
 		/* pclose() itself failed, and hopefully set errno */
-		perror("pclose failed");
+		log_error(_("pclose failed: %s"), strerror(errno));
 	}
-	else if (WIFEXITED(exitstatus))
-		log_error(_("child process exited with exit code %d"),
-				  WEXITSTATUS(exitstatus));
-	else if (WIFSIGNALED(exitstatus))
-#if defined(WIN32)
-		log_error(_("child process was terminated by exception 0x%X"),
-				  WTERMSIG(exitstatus));
-#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
-	{
-		char		str[256];
-
-		snprintf(str, sizeof(str), "%d: %s", WTERMSIG(exitstatus),
-				 WTERMSIG(exitstatus) < NSIG ?
-				 sys_siglist[WTERMSIG(exitstatus)] : "(unknown)");
-		log_error(_("child process was terminated by signal %s"), str);
-	}
-#else
-		log_error(_("child process was terminated by signal %d"),
-				  WTERMSIG(exitstatus));
-#endif
 	else
-		log_error(_("child process exited with unrecognized status %d"),
-				  exitstatus);
-
-	return -1;
+	{
+		reason = wait_result_to_str(exitstatus);
+		log_error("%s", reason);
+#ifdef FRONTEND
+		free(reason);
+#else
+		pfree(reason);
+#endif
+	}
+	return exitstatus;
 }
 
-
 /*
  *	set_pglocale_pgservice
  *

src/port/wait_error.c

@@ -0,0 +1,92 @@
+/*-------------------------------------------------------------------------
+ *
+ * wait_error.c
+ *		Convert a wait/waitpid(2) result code to a human-readable string
+ *
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/port/wait_error.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/wait.h>
+
+/*
+ * Return a human-readable string explaining the reason a child process
+ * terminated. The argument is a return code returned by wait(2) or
+ * waitpid(2). The result is a translated, palloc'd or malloc'd string.
+ */
+char *
+wait_result_to_str(int exitstatus)
+{
+	char		str[512];
+	char	   *result;
+
+	if (WIFEXITED(exitstatus))
+	{
+		/*
+		 * Give more specific error message for some common exit codes that
+		 * have a special meaning in shells.
+		 */
+		switch (WEXITSTATUS(exitstatus))
+		{
+			case 126:
+				snprintf(str, sizeof(str), _("command not executable"));
+				break;
+
+			case 127:
+				snprintf(str, sizeof(str), _("command not found"));
+				break;
+
+			default:
+				snprintf(str, sizeof(str),
+						 _("child process exited with exit code %d"),
+						 WEXITSTATUS(exitstatus));
+		}
+	}
+	else if (WIFSIGNALED(exitstatus))
+#if defined(WIN32)
+		snprintf(str, sizeof(str),
+				 _("child process was terminated by exception 0x%X"),
+				 WTERMSIG(exitstatus));
+#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
+	{
+		char		str2[256];
+
+		snprintf(str2, sizeof(str2), "%d: %s", WTERMSIG(exitstatus),
+				 WTERMSIG(exitstatus) < NSIG ?
+				 sys_siglist[WTERMSIG(exitstatus)] : "(unknown)");
+		snprintf(str, sizeof(str),
+				 _("child process was terminated by signal %s"), str2);
+	}
+#else
+		snprintf(str, sizeof(str),
+				 _("child process was terminated by signal %d"),
+				 WTERMSIG(exitstatus));
+#endif
+	else
+		snprintf(str, sizeof(str),
+				 _("child process exited with unrecognized status %d"),
+				  exitstatus);
+
+#ifndef FRONTEND
+	result = pstrdup(str);
+#else
+	result = strdup(str);
+#endif
+	return result;
+}