libtar: some minor cleanups

 - Use is_memory_zero from libutil
 - Move checksum update function to tar writer code
 - Move checksum verify function to tar reader code
 - Only export the function to compute the checksum

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

3 files changed, 15 insertions, 28 deletions

diff --git a/lib/tar/src/checksum.c b/lib/tar/src/checksum.c
index 6541373..9dc6c0f 100644
--- a/lib/tar/src/checksum.c
+++ b/lib/tar/src/checksum.c
@@ -4,13 +4,9 @@
  *
  * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
  */
-#include "config.h"
-
 #include "tar/format.h"
 
-#include <stdio.h>
-
-static unsigned int get_checksum(const tar_header_t *hdr)
+unsigned int tar_compute_checksum(const tar_header_t *hdr)
 {
 	const unsigned char *header_start = (const unsigned char *)hdr;
 	const unsigned char *chksum_start = (const unsigned char *)hdr->chksum;
@@ -27,22 +23,3 @@ static unsigned int get_checksum(const tar_header_t *hdr)
 		chksum += *p;
 	return chksum;
 }
-
-void update_checksum(tar_header_t *hdr)
-{
-	unsigned int chksum = get_checksum(hdr);
-
-	sprintf(hdr->chksum, "%06o", chksum);
-	hdr->chksum[6] = '\0';
-	hdr->chksum[7] = ' ';
-}
-
-bool is_checksum_valid(const tar_header_t *hdr)
-{
-	unsigned int calculated_chksum = get_checksum(hdr);
-	sqfs_u64 read_chksum;
-
-	if (read_octal(hdr->chksum, sizeof(hdr->chksum), &read_chksum))
-		return 0;
-	return read_chksum == calculated_chksum;
-}
diff --git a/lib/tar/src/read_header.c b/lib/tar/src/read_header.c
index ea4873b..219c9fb 100644
--- a/lib/tar/src/read_header.c
+++ b/lib/tar/src/read_header.c
@@ -10,11 +10,14 @@
 #include <string.h>
 #include <stdlib.h>
 
-static bool is_zero_block(const tar_header_t *hdr)
+static bool is_checksum_valid(const tar_header_t *hdr)
 {
-	const unsigned char *ptr = (const unsigned char *)hdr;
+	sqfs_u64 read_chksum;
 
-	return ptr[0] == '\0' && memcmp(ptr, ptr + 1, sizeof(*hdr) - 1) == 0;
+	if (read_octal(hdr->chksum, sizeof(hdr->chksum), &read_chksum))
+		return false;
+
+	return read_chksum == tar_compute_checksum(hdr);
 }
 
 static int check_version(const tar_header_t *hdr)
@@ -179,7 +182,7 @@ int read_header(istream_t *fp, tar_header_decoded_t *out)
 		if ((size_t)ret < sizeof(hdr))
 			goto out_eof;
 
-		if (is_zero_block(&hdr)) {
+		if (is_memory_zero(&hdr, sizeof(hdr))) {
 			if (prev_was_zero)
 				goto out_eof;
 			prev_was_zero = true;
diff --git a/lib/tar/src/write_header.c b/lib/tar/src/write_header.c
index b0711b3..5d98686 100644
--- a/lib/tar/src/write_header.c
+++ b/lib/tar/src/write_header.c
@@ -9,6 +9,13 @@
 #include "internal.h"
 #include <string.h>
 
+static void update_checksum(tar_header_t *hdr)
+{
+	sprintf(hdr->chksum, "%06o", tar_compute_checksum(hdr));
+	hdr->chksum[6] = '\0';
+	hdr->chksum[7] = ' ';
+}
+
 static void write_binary(char *dst, sqfs_u64 value, int digits)
 {
 	memset(dst, 0, digits);