1 files changed, 206 insertions, 0 deletions
diff --git a/src/port/tar.c b/src/port/tar.c
new file mode 100644
index 0000000..4afe9f2
--- /dev/null
+++ b/src/port/tar.c
@@ -0,0 +1,206 @@
+#include "c.h"
+
+#include <sys/stat.h>
+
+#include "pgtar.h"
+
+/*
+ * Print a numeric field in a tar header.  The field starts at *s and is of
+ * length len; val is the value to be written.
+ *
+ * Per POSIX, the way to write a number is in octal with leading zeroes and
+ * one trailing space (or NUL, but we use space) at the end of the specified
+ * field width.
+ *
+ * However, the given value may not fit in the available space in octal form.
+ * If that's true, we use the GNU extension of writing \200 followed by the
+ * number in base-256 form (ie, stored in binary MSB-first).  (Note: here we
+ * support only non-negative numbers, so we don't worry about the GNU rules
+ * for handling negative numbers.)
+ */
+void
+print_tar_number(char *s, int len, uint64 val)
+{
+	if (val < (((uint64) 1) << ((len - 1) * 3)))
+	{
+		/* Use octal with trailing space */
+		s[--len] = ' ';
+		while (len)
+		{
+			s[--len] = (val & 7) + '0';
+			val >>= 3;
+		}
+	}
+	else
+	{
+		/* Use base-256 with leading \200 */
+		s[0] = '\200';
+		while (len > 1)
+		{
+			s[--len] = (val & 255);
+			val >>= 8;
+		}
+	}
+}
+
+
+/*
+ * Read a numeric field in a tar header.  The field starts at *s and is of
+ * length len.
+ *
+ * The POSIX-approved format for a number is octal, ending with a space or
+ * NUL.  However, for values that don't fit, we recognize the GNU extension
+ * of \200 followed by the number in base-256 form (ie, stored in binary
+ * MSB-first).  (Note: here we support only non-negative numbers, so we don't
+ * worry about the GNU rules for handling negative numbers.)
+ */
+uint64
+read_tar_number(const char *s, int len)
+{
+	uint64		result = 0;
+
+	if (*s == '\200')
+	{
+		/* base-256 */
+		while (--len)
+		{
+			result <<= 8;
+			result |= (unsigned char) (*++s);
+		}
+	}
+	else
+	{
+		/* octal */
+		while (len-- && *s >= '0' && *s <= '7')
+		{
+			result <<= 3;
+			result |= (*s - '0');
+			s++;
+		}
+	}
+	return result;
+}
+
+
+/*
+ * 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 of
+ * the tar format.
+ */
+enum tarError
+tarCreateHeader(char *h, const char *filename, const char *linktarget,
+				pgoff_t size, mode_t mode, uid_t uid, gid_t gid, time_t mtime)
+{
+	if (strlen(filename) > 99)
+		return TAR_NAME_TOO_LONG;
+
+	if (linktarget && strlen(linktarget) > 99)
+		return TAR_SYMLINK_TOO_LONG;
+
+	memset(h, 0, 512);			/* assume tar header size */
+
+	/* Name 100 */
+	strlcpy(&h[0], filename, 100);
+	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 - this doesn't include the file type bits (S_IFMT)  */
+	print_tar_number(&h[100], 8, (mode & 07777));
+
+	/* User ID 8 */
+	print_tar_number(&h[108], 8, uid);
+
+	/* Group 8 */
+	print_tar_number(&h[116], 8, gid);
+
+	/* File size 12 */
+	if (linktarget != NULL || S_ISDIR(mode))
+		/* Symbolic link or directory has size zero */
+		print_tar_number(&h[124], 12, 0);
+	else
+		print_tar_number(&h[124], 12, size);
+
+	/* Mod Time 12 */
+	print_tar_number(&h[136], 12, mtime);
+
+	/* Checksum 8 cannot be calculated until we've filled all other fields */
+
+	if (linktarget != NULL)
+	{
+		/* Type - Symbolic link */
+		h[156] = '2';
+		/* Link Name 100 */
+		strlcpy(&h[157], linktarget, 100);
+	}
+	else if (S_ISDIR(mode))
+	{
+		/* Type - directory */
+		h[156] = '5';
+	}
+	else
+	{
+		/* Type - regular file */
+		h[156] = '0';
+	}
+
+	/* Magic 6 */
+	strcpy(&h[257], "ustar");
+
+	/* Version 2 */
+	memcpy(&h[263], "00", 2);
+
+	/* User 32 */
+	/* XXX: Do we need to care about setting correct username? */
+	strlcpy(&h[265], "postgres", 32);
+
+	/* Group 32 */
+	/* XXX: Do we need to care about setting correct group name? */
+	strlcpy(&h[297], "postgres", 32);
+
+	/* Major Dev 8 */
+	print_tar_number(&h[329], 8, 0);
+
+	/* Minor Dev 8 */
+	print_tar_number(&h[337], 8, 0);
+
+	/* Prefix 155 - not used, leave as nulls */
+
+	/* Finally, compute and insert the checksum */
+	print_tar_number(&h[148], 8, tarChecksum(h));
+
+	return TAR_OK;
+}