[PATCH 1/6] Add support for longer filenames in tar headers (up to 254 bytes).

New functions tarHeaderRename() and tarHeaderGetName() are exposed to
store and retrieve the longer filenames.

tarCreateHeader() continues to limit filenames to 99 bytes to preserve
compatability with existing consumers.
---
src/include/pgtar.h | 2 +
src/port/tar.c | 134 ++++++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 121 insertions(+), 15 deletions(-)

diff --git a/src/include/pgtar.h b/src/include/pgtar.h
index 906db7c..b1c68fc 100644
--- a/src/include/pgtar.h
+++ b/src/include/pgtar.h
@@ -20,4 +20,6 @@ enum tarError
};

extern enum tarError tarCreateHeader(char *h, const char *filename, const char *linktarget, size_t size, mode_t mode, uid_t uid, gid_t gid, time_t mtime);
+extern enum tarError tarHeaderRename(char *h, const char *filename);
extern int tarChecksum(char *header);
+extern size_t tarHeaderGetName(const char *h, char *buf, size_t buflen);
diff --git a/src/port/tar.c b/src/port/tar.c
index 72fd4e1..23f0201 100644
--- a/src/port/tar.c
+++ b/src/port/tar.c
@@ -45,6 +45,122 @@ tarChecksum(char *header)


/*
+ * Split a file path for use in a tar header. The return value is the second
+ * half of the path if a split is required and possible, NULL otherwise.
+ */
+static const char *
+tarSplitName(const char *filename, size_t len)
+{
+ const char *sep;
+
+ if (len <= 99)
+ sep = NULL;
+ else if ((sep = strchr(&filename[len-99], '/')) != NULL)
+ sep++;
+
+ return NULL;
+}
+
+
+/*
+ * Fill in the name and prefix fields of the tar format header pointed to by
+ * h. This should only be used when initially filling out the header.
+ */
+static enum tarError
+tarHeaderSetName(char *h, const char *filename, bool isdir, bool longname)
+{
+ const char *prefix, *base;
+ size_t len, baselen, prelen;
+
+ len = strlen(filename);
+ if (longname)
+ base = tarSplitName(filename, len);
+ else
+ base = NULL;
+ if (base == NULL)
+ {
+ prefix = "";
+ prelen = 0;
+ base = filename;
+ baselen = len;
+ }
+ else
+ {
+ prefix = filename;
+ prelen = (base - filename) - 1;
+ baselen = len - (base - filename);
+ }
+
+ /*
+ * Save room for a trailing slash if this is a directory or symlink to a
+ * directory
+ */
+ if (isdir && base[baselen-1] != '/')
+ baselen++;
+
+ if (baselen > 99 || prelen > 154)
+ return TAR_NAME_TOO_LONG;
+
+ memcpy(&h[345], prefix, prelen);
+ memset(&h[345+prelen], 0, 155 - prelen);
+ memcpy(&h[0], base, baselen);
+ memset(&h[0+baselen], 0, 100 - baselen);
+
+ /*
+ * 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.
+ */
+ if (isdir && base[baselen-1] != '/')
+ h[0+baselen-1] = '/';
+
+ return TAR_OK;
+}
+
+
+/*
+ * Wrapper around tarHeaderSetName() to be used when changing the name in an
+ * existing header.
+ */
+enum tarError
+tarHeaderRename(char *h, const char *filename)
+{
+ size_t len;
+ bool isdir;
+ enum tarError err;
+
+ /* If the existing name ends with a slash then this must be preserved */
+ len = strnlen(h, 100);
+ isdir = (len > 0 && h[len-1] == '/');
+
+ err = tarHeaderSetName(h, filename, isdir, true);
+
+ if (err == TAR_OK)
+ /* Recalculate checksum as per tarCreateHeader() */
+ sprintf(&h[148], "%06o ", tarChecksum(h));
+
+ return err;
+}
+
+
+/*
+ * Copy the full pathname from the tar header pointed to by h into
+ * buf. Returns the total length of the path, if this is >= len then the path
+ * has been truncated.
+ */
+size_t
+tarHeaderGetName(const char *h, char *buf, size_t buflen)
+{
+ strlcpy(buf, &h[345], buflen);
+ if (buflen && buf[0] != '\0')
+ strlcat(buf, "/", buflen);
+ strlcat(buf, &h[0], buflen);
+
+ return (strlen(&h[345]) + 1 + strlen(&h[0]));
+}
+
+
+/*
* 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.
@@ -68,20 +184,8 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
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';
- }
+ tarHeaderSetName(h, filename,
+ (linktarget != NULL || S_ISDIR(mode)), false);

/* Mode 8 - this doesn't include the file type bits (S_IFMT) */
sprintf(&h[100], "%07o ", (int) (mode & 07777));
@@ -139,7 +243,7 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
/* Minor Dev 8 */
sprintf(&h[337], "%07o ", 0);

- /* Prefix 155 - not used, leave as nulls */
+ /* Prefix 155 - not currently used, leave as nulls */

/*
* We mustn't overwrite the next field while inserting the checksum.
--
2.3.0