Unify some tar functionality across different parts

Move some of the tar functionality that existed mostly duplicated
in both pg_dump and the walsender basebackup functionality into
port/tar.c instead, so it can be used from both. It will also be
used by pg_basebackup in the future, which would've caused a third
copy of it around.

Zoltan Boszormenyi and Magnus Hagander

src/port/Makefile

@@ -32,7 +32,7 @@ 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 sprompt.o thread.o
+	pgstrcasecmp.o qsort.o qsort_arg.o sprompt.o tar.o thread.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/tar.c

@@ -0,0 +1,143 @@
+#include "c.h"
+#include <sys/stat.h>
+
+/*
+ * Utility routine to print possibly larger than 32 bit integers in a
+ * portable fashion.  Filled with zeros.
+ */
+static void
+print_val(char *s, uint64 val, unsigned int base, size_t len)
+{
+	int			i;
+
+	for (i = len; i > 0; i--)
+	{
+		int			digit = val % base;
+
+		s[i - 1] = '0' + digit;
+		val = val / base;
+	}
+}
+
+
+/*
+ * Calculate the tar checksum for a header. The header is assumed to always
+ * be 512 bytes, per the tar standard.
+ */
+int
+tarChecksum(char *header)
+{
+	int			i,
+				sum;
+
+	/*
+	 * Per POSIX, the checksum is the simple sum of all bytes in the header,
+	 * treating the bytes as unsigned, and treating the checksum field (at
+	 * offset 148) as though it contained 8 spaces.
+	 */
+	sum = 8 * ' ';				/* presumed value for checksum field */
+	for (i = 0; i < 512; i++)
+		if (i < 148 || i >= 156)
+			sum += 0xFF & header[i];
+	return sum;
+}
+
+
+/*
+ * Fill in the buffer pointed to by h with a tar format header. This buffer
+ * must always have space for 512 characters, which is a requirement by
+ * the tar format.
+ */
+void
+tarCreateHeader(char *h, const char *filename, const char *linktarget,
+				size_t size, mode_t mode, uid_t uid, gid_t gid, time_t mtime)
+{
+	/*
+	 * Note: most of the fields in a tar header are not supposed to be
+	 * null-terminated.  We use sprintf, which will write a null after the
+	 * required bytes; that null goes into the first byte of the next field.
+	 * This is okay as long as we fill the fields in order.
+	 */
+	memset(h, 0, 512);			/* assume tar header size */
+
+	/* Name 100 */
+	sprintf(&h[0], "%.99s", filename);
+	if (linktarget != NULL || S_ISDIR(mode))
+	{
+		/*
+		 * We only support symbolic links to directories, and this is
+		 * indicated in the tar format by adding a slash at the end of the
+		 * name, the same as for regular directories.
+		 */
+		int			flen = strlen(filename);
+
+		flen = Min(flen, 99);
+		h[flen] = '/';
+		h[flen + 1] = '\0';
+	}
+
+	/* Mode 8 */
+	sprintf(&h[100], "%07o ", (int) mode);
+
+	/* User ID 8 */
+	sprintf(&h[108], "%07o ", uid);
+
+	/* Group 8 */
+	sprintf(&h[116], "%07o ", gid);
+
+	/* File size 12 - 11 digits, 1 space; use print_val for 64 bit support */
+	if (linktarget != NULL || S_ISDIR(mode))
+		/* Symbolic link or directory has size zero */
+		print_val(&h[124], 0, 8, 11);
+	else
+		print_val(&h[124], size, 8, 11);
+	sprintf(&h[135], " ");
+
+	/* Mod Time 12 */
+	sprintf(&h[136], "%011o ", (int) mtime);
+
+	/* Checksum 8 cannot be calculated until we've filled all other fields */
+
+	if (linktarget != NULL)
+	{
+		/* Type - Symbolic link */
+		sprintf(&h[156], "2");
+		/* Link Name 100 */
+		sprintf(&h[157], "%.99s", linktarget);
+	}
+	else if (S_ISDIR(mode))
+		/* Type - directory */
+		sprintf(&h[156], "5");
+	else
+		/* Type - regular file */
+		sprintf(&h[156], "0");
+
+	/* Magic 6 */
+	sprintf(&h[257], "ustar");
+
+	/* Version 2 */
+	sprintf(&h[263], "00");
+
+	/* User 32 */
+	/* XXX: Do we need to care about setting correct username? */
+	sprintf(&h[265], "%.31s", "postgres");
+
+	/* Group 32 */
+	/* XXX: Do we need to care about setting correct group name? */
+	sprintf(&h[297], "%.31s", "postgres");
+
+	/* Major Dev 8 */
+	sprintf(&h[329], "%07o ", 0);
+
+	/* Minor Dev 8 */
+	sprintf(&h[337], "%07o ", 0);
+
+	/* Prefix 155 - not used, leave as nulls */
+
+	/*
+	 * We mustn't overwrite the next field while inserting the checksum.
+	 * Fortunately, the checksum can't exceed 6 octal digits, so we just write
+	 * 6 digits, a space, and a null, which is legal per POSIX.
+	 */
+	sprintf(&h[148], "%06o ", tarChecksum(h));
+}