Reading and writing the cache

logsend/whatsnew.c

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <unistd.h>
+#include <openssl/sha.h>
 
 const char *read_line() {
 	size_t buf_size = 10;
@@ -31,8 +38,47 @@ void dump_lines(const char *const *lines) {
 		fputs(*lines ++, stdout);
 }
 
+uint8_t last[SHA_DIGEST_LENGTH] = {0};
+
 int main(int argc, const char *argv[]) {
+	if (!argv[1]) {
+		fprintf(stderr, "Need to know the cache file\n");
+		return 1;
+	}
+	int cache = open(argv[1], O_RDONLY);
+	if (cache == -1) {
+		if (errno != ENOENT) {
+			perror("Can't open the cache:");
+			return 1;
+		}
+	} else {
+		ssize_t result = read(cache, last, SHA_DIGEST_LENGTH);
+		if (result == -1) {
+			perror("Can't read the cache:");
+			return 1;
+		}
+		if (result != SHA_DIGEST_LENGTH) {
+			fputs("Corrupt cache\n", stderr);
+			return 1;
+		}
+		close(cache);
+	}
 	const char *const *lines = read_lines();
 	dump_lines(lines);
+	cache = open(argv[1], O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
+	if (cache == -1) {
+		perror("Can't open cache for write:");
+		return 1;
+	}
+	ssize_t result = write(cache, last, SHA_DIGEST_LENGTH);
+	if (result == -1) {
+		perror("Can't write the cache:");
+		return 1;
+	}
+	if (result != SHA_DIGEST_LENGTH) {
+		fputs("Short write to cache\n", stderr);
+		return 1;
+	}
+	close(cache);
 	return 0;
 }