Further enhancements of new API call iso_util_decode_md5_tag().

doc/checksums.txt

@@ -132,12 +132,40 @@ are strings of 32 hex digits:
 
                               Usage at Read Time
 
+                     Checking Before Image Tree Loading
+
+In order to check for a trustworthy loadable image tree, read the first 32
+blocks from to the session start and look in block 16 to 32 for the superblock
+checksum tag by
+  iso_util_decode_md5_tag(block, &tag_type, &pos,
+                          &range_start, &range_size, &next_tag, md5, 2);
+If it appears and has plausible parameters, then check whether its MD5 matches
+the MD5 of the data blocks which were read before.
+(Keep the original MD5 context of the data blocks and clone one for obtaining
+the MD5 bytes.)
+Compute the block into the MD5 checksum after your are done with interpreting
+it.
+
+If those MD5s match, then compute the checksum block into the kept MD5 context
+and go on with reading and computing for the tree checksum tag. This will be
+found at block address next_tag, verified and parsed by:
+  iso_util_decode_md5_tag(block, &tag_type, &pos,
+                          &range_start, &range_size, &next_tag, md5, 3);
+Again, if the parameters match the reading state, the MD5 must match the
+MD5 computed from the data blocks which were before.
+If so, then the tree is ok and safe to be loaded by iso_image_import().
+
+
                            Checking a Whole Session
 
-In order to check the trustworthyness of a whole session, read from its start
+In order to check the trustworthyness of a whole session, continue reading
-up to the session tag. Read the blocks and submit each single one of them to
+and checksumming after the tree was verified. 
 
-  iso_util_decode_md5_tag(block, &pos, &range_start, &range_size, md5, 1);
+Read and checksum the blocks. When reaching block address next_tag (from the
+tree tag) submit this block to
+
+  iso_util_decode_md5_tag(block, &tag_type, &pos,
+                          &range_start, &range_size, &next_tag, md5, 1);
 
 If this returns 1, then check whether the returned parameters pos, range_start,
 and range_size match the state of block reading, and whether the returned
@@ -145,29 +173,10 @@ bytes in parameter md5 match the MD5 computed from the data blocks which were
 read before the tag block.
 
 
-                     Checking before Image Tree Loading
-
-In order to check for a trustworthy loadable image tree, read the first 32
-blocks to the session start and look in block 16 to 32 for the superblock
-checksum tag by
-  iso_util_decode_md5_tag(block, &pos, &range_start, &range_size, md5, 2);
-If one appears and has plausible parameters, then check whether its MD5 matches
-the MD5 of the data blocks read before.
-(Keep the original MD5 context of the data blocks and clone one for obtaining
-the MD5 bytes.)
-
-If those MD5s match, then compute the checksum block into the kept MD5 context
-and go on with searching for the tree checksum tag. This can be found in a
-read-in block by:
-  iso_util_decode_md5_tag(block, &pos, &range_start, &range_size, md5, 3)
-Again, if the parameters match the reading state, the MD5 must match the
-MD5 computed from the data blocks before.
-If so, then the tree is ok and safe to be loaded by iso_image_import().
-
-
                    Checking Single Files in a Loaded Image
 
-The image has to be loaded, so you can obtain IsoNode objects which yield
+Once the image has been loaded, you can obtain MD5 sums from IsoNode objects
+which fulfill
   iso_node_get_type(node) == LIBISO_FILE
 
 The recorded checksum can be obtained by

libisofs/libisofs.h

@@ -5052,6 +5052,11 @@ int iso_file_get_md5(IsoImage *image, IsoFile *file, char md5[16], int flag);
  * start and look out for a session tag on the fly. See doc/checksum.txt .
  * @param data
  *      A complete and aligned data block read from an ISO image session.
+ * @param tag_type
+ *      0= no tag
+ *      1= session tag
+ *      2= superblock tag
+ *      3= tree tag
  * @param pos
  *      Returns the LBA where the tag supposes itself to be stored.
  *      If this does not match the data block LBA then the tag might be
@@ -5078,16 +5083,14 @@ int iso_file_get_md5(IsoImage *image, IsoFile *file, char md5[16], int flag);
  *                 3= tree tag
  * @return
  *      0= not a checksum tag, return parameters are invalid
- *      1= session tag found
+ *      1= checksum tag found, return parameters arevalid
- *      2= superblock tag found
- *      3= tree tag found
  *     <0= error 
  *         return parameters are valid with error ISO_MD5_AREA_CORRUPTED
  *         but not trustworthy because the tag seems corrupted. 
  *
  * @since 0.6.22
  */
-int iso_util_decode_md5_tag(char data[2048], uint32_t *pos,
+int iso_util_decode_md5_tag(char data[2048], int *tag_type, uint32_t *pos,
                             uint32_t *range_start, uint32_t *range_size,
                             uint32_t *next_tag, char md5[16], int flag);
 

libisofs/util.c

@@ -1563,7 +1563,7 @@ int iso_util_hex_to_bin(char *hex, char *bin, int bin_size, int *bin_count,
 }
 
 
-int iso_util_decode_md5_tag(char data[2048], uint32_t *pos,
+int iso_util_decode_md5_tag(char data[2048], int *tag_type, uint32_t *pos,
                             uint32_t *range_start, uint32_t *range_size,
                             uint32_t *next_tag, char md5[16], int flag)
 {
@@ -1587,8 +1587,8 @@ int iso_util_decode_md5_tag(char data[2048], uint32_t *pos,
     break;
     if (i > magic_last )
         return 0;
-    found = i;
+    *tag_type = i;
-    cpt = data + magic_len[found] + 1;
+    cpt = data + magic_len[*tag_type] + 1;
     if (strncmp(cpt, "pos=", 4) != 0)
         return 0;
     cpt+= 4;
@@ -1607,7 +1607,7 @@ int iso_util_decode_md5_tag(char data[2048], uint32_t *pos,
     ret = iso_util_dec_to_uint32(cpt + 11, range_size, 0);
     if (ret <= 0)
         return 0;
-    if (found == 2 || found == 3) {
+    if (*tag_type == 2 || *tag_type == 3) {
         cpt = strstr(cpt, "next=");
         if (cpt == NULL)
             return(0);
@@ -1639,6 +1639,6 @@ int iso_util_decode_md5_tag(char data[2048], uint32_t *pos,
         return ISO_MD5_AREA_CORRUPTED;
     if (*(cpt + 5 + 32) != '\n')
         return 0;
-    return(found);
+    return(1);
 }