Add the magic number to the dependency record.

The magic number will be used later to determine if a target has already
been rebuild.

2 files changed, 24 insertions, 2 deletions

diff --git a/src/build.c b/src/build.c
index 73fc757..d217a23 100644
--- a/src/build.c
+++ b/src/build.c
@@ -285,8 +285,8 @@ void add_dep(const char *target, int indent) {
             fp = fopen(dep_path, "w");
             if (!fp)
                 fatal(ERRM_FOPEN, dep_path);
-            /* skip the first n bytes that are reserved for the hash */
-            fseek(fp, 20, SEEK_SET);
+            /* skip the first n bytes that are reserved for the hash + magic number */
+            fseek(fp, 20 + sizeof(unsigned int), SEEK_SET);
         } else {
             fatal(ERRM_FOPEN, dep_path);
         }
@@ -329,7 +329,9 @@ void hash_file(const char *target, unsigned char (*hash)[20]) {
 
 /* Calculate and store the hash of target in the right dependency file */
 void write_dep_hash(const char *target) {
+    assert(getenv("REDO_MAGIC"));
     unsigned char hash[SHA_DIGEST_LENGTH];
+    int magic = atoi(getenv("REDO_MAGIC"));
 
     hash_file(target, &hash);
 
@@ -341,6 +343,9 @@ void write_dep_hash(const char *target) {
     if (write(out, hash, sizeof hash) < (ssize_t) sizeof hash)
         fatal("redo: failed to write hash to '%s'", dep_path);
 
+    if (write(out, &magic, sizeof(unsigned int)) < (ssize_t) sizeof(unsigned int))
+        fatal("redo: failed to write magic number to '%s'", dep_path);
+
     if (close(out))
         fatal("redo: failed to close file descriptor.");
     free(dep_path);
diff --git a/src/redo.c b/src/redo.c
index 69f9ade..0209a4f 100644
--- a/src/redo.c
+++ b/src/redo.c
@@ -3,12 +3,18 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <time.h>
+#include <math.h>
+#include <limits.h>
 #include <unistd.h>
 
 #include "build.h"
 #include "util.h"
 #include "dbg.h"
 
+static inline int digits(unsigned n) {
+  return (int) log10(n) + 1;
+}
 
 int main(int argc, char *argv[]) {
     /* create .redo directory */
@@ -26,6 +32,17 @@ int main(int argc, char *argv[]) {
 
     free(cwd);
 
+    srand(time(NULL)); /* TODO: error checking */
+    unsigned magic = rand();
+
+    char magic_str[digits(UINT_MAX) + 1];
+    sprintf(magic_str, "%u", magic);
+
+    printf("MAGIC: %s\n", magic_str);
+
+    if (setenv("REDO_MAGIC", magic_str, 0))
+        fatal("setenv()");
+
     if (argc < 2) {
         build_target("all");
     } else {