Use zlib for CRC-32

Previously, we had our own CRC that was almost but not quite like
zlib's implementation. However,

* it hasn't been subjected to the same rigor with regard to error-detection
  properties and
* it may not even get used, depending upon whether zlib happens to get
  loaded before or after liberasurecode.

Now, we'll use zlib's CRC-32 when writing new frags, while still
tolerating frags that were created with the old implementation.

Change-Id: Ib5ea2a830c7c23d66bf2ca404a3eb84ad00c5bc5
Closes-Bug: 1666320

4 files changed, 26 insertions, 9 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 8312dd0..693809e 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -34,9 +34,10 @@ liberasurecode_la_SOURCES = \
 
 liberasurecode_la_CPPFLAGS = -Werror @GCOV_FLAGS@
 liberasurecode_la_LIBADD = \
-		builtin/null_code/libnullcode.la -lpthread -lm @GCOV_LDFLAGS@ \
-		builtin/xor_codes/libXorcode.la -lpthread -lm @GCOV_LDFLAGS@ \
-		builtin/rs_vand/liberasurecode_rs_vand.la -lpthread -lm @GCOV_LDFLAGS@
+		builtin/null_code/libnullcode.la \
+		builtin/xor_codes/libXorcode.la \
+		builtin/rs_vand/liberasurecode_rs_vand.la \
+		-lpthread -lm -lz @GCOV_LDFLAGS@
 
 # Version format  (C - A).(A).(R) for C:R:A input
 liberasurecode_la_LDFLAGS = -rpath '$(libdir)' -version-info @LIBERASURECODE_VERSION_INFO@
diff --git a/src/erasurecode.c b/src/erasurecode.c
index d4a06c2..20da457 100644
--- a/src/erasurecode.c
+++ b/src/erasurecode.c
@@ -26,6 +26,7 @@
  * vi: set noai tw=79 ts=4 sw=4:
  */
 
+#include <zlib.h>
 #include "assert.h"
 #include "list.h"
 #include "erasurecode.h"
@@ -1063,9 +1064,17 @@ int liberasurecode_get_fragment_metadata(char *fragment,
             uint32_t stored_chksum = fragment_hdr->meta.chksum[0];
             char *fragment_data = get_data_ptr_from_fragment(fragment);
             uint64_t fragment_size = fragment_hdr->meta.size;
-            computed_chksum = crc32(0, fragment_data, fragment_size);
+            computed_chksum = crc32(0, (unsigned char *) fragment_data, fragment_size);
             if (stored_chksum != computed_chksum) {
-                fragment_metadata->chksum_mismatch = 1;
+                // Try again with our "alternative" crc32; see
+                // https://bugs.launchpad.net/liberasurecode/+bug/1666320
+                computed_chksum = liberasurecode_crc32_alt(
+                    0, fragment_data, fragment_size);
+                if (stored_chksum != computed_chksum) {
+                    fragment_metadata->chksum_mismatch = 1;
+                } else {
+                    fragment_metadata->chksum_mismatch = 0;
+                }
             } else {
                 fragment_metadata->chksum_mismatch = 0;
             }
@@ -1095,7 +1104,13 @@ int is_invalid_fragment_header(fragment_header_t *header)
     stored_csum = get_metadata_chksum((char *) header);
     if (NULL == stored_csum)
         return 1; /* can't verify, possibly crc32 call error */
-    csum = crc32(0, &header->meta, sizeof(fragment_metadata_t));
+    csum = crc32(0, (unsigned char *) &header->meta, sizeof(fragment_metadata_t));
+    if (*stored_csum == csum) {
+        return 0;
+    }
+    // Else, try again with our "alternative" crc32; see
+    // https://bugs.launchpad.net/liberasurecode/+bug/1666320
+    csum = liberasurecode_crc32_alt(0, &header->meta, sizeof(fragment_metadata_t));
     return (*stored_csum != csum);
 }
 
diff --git a/src/erasurecode_helpers.c b/src/erasurecode_helpers.c
index fd14298..4a49786 100644
--- a/src/erasurecode_helpers.c
+++ b/src/erasurecode_helpers.c
@@ -28,6 +28,7 @@
 #include <assert.h>
 #include <stdio.h>
 #include <stdarg.h>
+#include <zlib.h>
 #include "erasurecode_backend.h"
 #include "erasurecode_helpers.h"
 #include "erasurecode_helpers_ext.h"
@@ -474,7 +475,7 @@ inline int set_checksum(ec_checksum_type_t ct, char *buf, int blocksize)
 
     switch(header->meta.chksum_type) {
         case CHKSUM_CRC32:
-            header->meta.chksum[0] = crc32(0, data, blocksize);
+            header->meta.chksum[0] = crc32(0, (unsigned char *) data, blocksize);
             break;
         case CHKSUM_MD5:
             break;
@@ -512,7 +513,7 @@ inline int set_metadata_chksum(char *buf)
         return -1;
     }
 
-    header->metadata_chksum = crc32(0, &header->meta,
+    header->metadata_chksum = crc32(0, (unsigned char *) &header->meta,
                                     sizeof(fragment_metadata_t));
     return 0;
 }
diff --git a/src/utils/chksum/crc32.c b/src/utils/chksum/crc32.c
index 6bc844d..b11dec9 100644
--- a/src/utils/chksum/crc32.c
+++ b/src/utils/chksum/crc32.c
@@ -89,7 +89,7 @@ static int crc32_tab[] = {
 };
 
 int
-crc32(int crc, const void *buf, size_t size)
+liberasurecode_crc32_alt(int crc, const void *buf, size_t size)
 {
   const char *p;