tar: store negative mtime as 0; pack very large files using base-256 encoding

function                                             old     new   delta
writeTarHeader                                       841     979    +138

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 33 insertions, 5 deletions

diff --git a/archival/tar.c b/archival/tar.c
index 01b83d5e2..ebaa183b4 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -264,7 +264,8 @@ static int writeTarHeader(struct TarBallInfo *tbInfo,
         PUT_OCTAL(header.uid, statbuf->st_uid);
         PUT_OCTAL(header.gid, statbuf->st_gid);
         memset(header.size, '0', sizeof(header.size)-1); /* Regular file size is handled later */
-        PUT_OCTAL(header.mtime, statbuf->st_mtime);
+        /* users report that files with negative st_mtime cause trouble, so: */
+        PUT_OCTAL(header.mtime, statbuf->st_mtime >= 0 ? statbuf->st_mtime : 0);
 
         /* Enter the user and group names */
         safe_strncpy(header.uname, get_cached_username(statbuf->st_uid), sizeof(header.uname));
@@ -316,15 +317,42 @@ static int writeTarHeader(struct TarBallInfo *tbInfo,
         } else if (S_ISFIFO(statbuf->st_mode)) {
                 header.typeflag = FIFOTYPE;
         } else if (S_ISREG(statbuf->st_mode)) {
-                if (sizeof(statbuf->st_size) > 4
-                 && statbuf->st_size > (off_t)0777777777777LL
+                /* header.size field is 12 bytes long */
+                /* Does octal-encoded size fit? */
+                uoff_t filesize = statbuf->st_size;
+                if (sizeof(filesize) <= 4
+                 || filesize <= (uoff_t)0777777777777LL
                 ) {
+                        PUT_OCTAL(header.size, filesize);
+                }
+                /* Does base256-encoded size fit?
+                 * It always does unless off_t is wider than 64 bits.
+                 */
+                else if (ENABLE_FEATURE_TAR_GNU_EXTENSIONS
+#if ULLONG_MAX > 0xffffffffffffffffLL /* 2^64-1 */
+                 && (filesize <= 0x3fffffffffffffffffffffffLL)
+#endif
+                ) {
+                        /* GNU tar uses "base-256 encoding" for very large numbers.
+                         * Encoding is binary, with highest bit always set as a marker
+                         * and sign in next-highest bit:
+                         * 80 00 .. 00 - zero
+                         * bf ff .. ff - largest positive number
+                         * ff ff .. ff - minus 1
+                         * c0 00 .. 00 - smallest negative number
+                         */
+                        char *p8 = header.size + sizeof(header.size);
+                        do {
+                                *--p8 = (uint8_t)filesize;
+                                filesize >>= 8;
+                        } while (p8 != header.size);
+                        *p8 |= 0x80;
+                } else {
                         bb_error_msg_and_die("can't store file '%s' "
                                 "of size %"OFF_FMT"u, aborting",
                                 fileName, statbuf->st_size);
                 }
                 header.typeflag = REGTYPE;
-                PUT_OCTAL(header.size, statbuf->st_size);
         } else {
                 bb_error_msg("%s: unknown file type", fileName);
                 return FALSE;
diff --git a/include/archive.h b/include/archive.h
index b139dc5be..9e176d335 100644
--- a/include/archive.h
+++ b/include/archive.h
@@ -125,7 +125,7 @@ typedef struct archive_handle_t {
 #define TAR_BLOCK_SIZE 512
 #define NAME_SIZE      100
 #define NAME_SIZE_STR "100"
-typedef struct tar_header_t {       /* byte offset */
+typedef struct tar_header_t {     /* byte offset */
         char name[NAME_SIZE];     /*   0-99 */
         char mode[8];             /* 100-107 */
         char uid[8];              /* 108-115 */