core: Generate output source file

This commit reduces the amount of passes required to 2 as well as
generating the actual output file.

Signed-off-by: Ian Moffett <ian@mirocom.org>

src/main.c

@@ -1,4 +1,5 @@
 #define _DEFAULT_SOURCE
+#include <sys/mman.h>
 #include <sys/queue.h>
 #include <sys/stat.h>
 #include <stdio.h>
@@ -12,7 +13,7 @@
 #include <string.h>
 
 #define MAGIC_SIZE 5
-#define CAV_PASSES 3
+#define CAV_PASSES 2
 #define CAV_VERSION "0.0.1"
 
 #define CAV_OFF_INDEX(INDEX) \
@@ -57,7 +58,7 @@ struct cav_offset {
     char magic[MAGIC_SIZE];
     uint32_t off;
     size_t size;
-};
+} __attribute__((packed));
 
 /*
  * Represents an offset descriptor used before holding
@@ -163,7 +164,7 @@ state_init(struct cav_state *state)
         return -1;
     }
 
-    state->out_fd = open(output_name, O_WRONLY | O_CREAT, 0600);
+    state->out_fd = open(output_name, O_WRONLY | O_CREAT | O_TRUNC, 0600);
     if (state->out_fd < 0) {
         close(state->dir_fd);
         return -1;
@@ -264,6 +265,79 @@ consume_scan(const char *dir_path, struct cav_state *state, DIR *subdir)
     }
 }
 
+/*
+ * File a file segment within the archive
+ *
+ * @state: Cav state
+ * @desc:  Offset descriptor
+ */
+static void
+fill_segment(struct cav_state *state, struct cav_offdesc *desc)
+{
+    struct cav_offset *off;
+    void *mem;
+    int fd;
+
+    if (state == NULL || desc == NULL) {
+        return;
+    }
+
+    off = &desc->off;
+    fd = open(desc->path, O_RDONLY);
+    if (fd < 0) {
+        perror("open");
+        return;
+    }
+
+    /* Map the file */
+    mem = mmap(
+        NULL,
+        off->size,
+        PROT_READ,
+        MAP_SHARED,
+        fd,
+        0
+    );
+
+    /* File name goes before file contents */
+    write(state->out_fd, desc->path, strlen(desc->path) + 1);
+    write(state->out_fd, mem, off->size);
+
+    /* Clean up */
+    munmap(mem, off->size);
+    close(fd);
+}
+
+/*
+ * Construct the on-disk offset table
+ *
+ * @state: Cav state
+ */
+static void
+build_offtab(struct cav_state *state)
+{
+    struct cav_offdesc *off_desc;
+    struct cav_offset *off;
+
+    if (state == NULL) {
+        return;
+    }
+
+    /* First, write out the offset table */
+    TAILQ_FOREACH(off_desc, &state->offq, link) {
+        off = &off_desc->off;
+        off->off = state->cur_off;
+
+        state->cur_off += off->size;
+        write(state->out_fd, off, sizeof(*off));
+    }
+
+    /* Next, write out the segments */
+    TAILQ_FOREACH(off_desc, &state->offq, link) {
+        fill_segment(state, off_desc);
+    }
+}
+
 /*
  * Consume a single pass in our yummy yummy consumption
  * process only to be thrown up again along with stomach
@@ -272,8 +346,6 @@ consume_scan(const char *dir_path, struct cav_state *state, DIR *subdir)
 static void
 consume_pass(struct cav_state *state)
 {
-    struct cav_offdesc *off;
-
     if (state == NULL) {
         return;
     }
@@ -287,11 +359,11 @@ consume_pass(struct cav_state *state)
             state->file_count,
             state->cur_off
         );
-
-        TAILQ_FOREACH(off, &state->offq, link) {
-            printf("[*] %s\n", off->path);
-        }
-
+        break;
+    case 1:
+        printf("[pass 1] building offset table + segments...\n");
+        state->cur_off = CAV_OFF_INDEX(state->file_count);
+        build_offtab(state);
         break;
     }
 }
@@ -333,9 +405,9 @@ main(int argc, char **argv)
     /*
      * There are three passes required in the consumption operation
      *
-     * pass 0): Obtain number of files for offset table creation
-     * pass 1): Construct an offset table using what we know
-     * pass 2): Construct the archive segments
+     * pass 0): Obtain number of files for offset table creation.
+     * pass 1): Construct an offset table using what we know and
+     *          populate file entries.
      */
     for (int i = 0; i < CAV_PASSES; ++i) {
         consume_pass(&state);