changed the data type for file size. wrote Data_read()

src/cache.c

@@ -1,15 +1,15 @@
 #include "cache.h"
 
-off_t Cache_read(const char *filepath, off_t offset, size_t size)
+long Cache_read(const char *filepath, long offset, long len)
 {
 }
 
-size_t Cache_write(const char *filepath, off_t offset, size_t size,
+long Cache_write(const char *filepath, long offset, long len,
                    const uint8_t *content)
 {
 }
 
-int Cache_create(const char *filepath, size_t size)
+int Cache_create(const char *filepath, long len)
 {
 }
 
@@ -29,16 +29,54 @@ int Meta_read(Cache *cf)
 }
 
 
-size_t Data_read(Cache *cf, off_t offset, size_t size)
+long Data_read(Cache *cf, long offset, long len,
+                const uint8_t *buf);
+{
+    if (len == 0) {
+        fprintf(stderr, "Data_read(): fseek(): requested to read 0 byte!\n");
+        return -1;
+    }
+
+    FILE *fp;
+    fp = fopen(cf->filepath, "r");
+
+    if (!fp) {
+        /* The data file does not exist */
+        return -1;
+    }
+
+    if (fseek(fp, offset, SEEK_SET) == -1) {
+        /* fseek failed */
+        fprintf(stderr, "Data_read(): fseek(): %s\n", strerror(errno));
+        return -1;
+    }
+
+    long byte_read = fread((void*) buf, sizeof(uint8_t), len, fp);
+    if (byte_read != len) {
+        fprintf(stderr,
+                "Data_read(): fread(): requested %ld, returned %llu!\n",
+                len, byte_read);
+        if (feof(fp)) {
+            fprintf(stderr,
+                    "Data_read(): fread(): reached the end of the file!\n");
+        }
+        if (ferror(fp)) {
+            fprintf(stderr,
+                    "Data_read(): fread(): encountered error (from ferror)!\n");
+        }
+    }
+    if (fclose(fp)) {
+        fprintf(stderr, "Data_read(): fclose(): %s\n", strerror(errno));
+        return -1;
+    }
+}
+
+long Data_write(Cache *cf, long offset, long len,
+                 const uint8_t *buf);
 {
 }
 
-size_t Data_write(Cache *cf, off_t offset, size_t size,
-                  const uint8_t *content)
-{
-}
-
-int Data_create(Cache *cf, size_t size)
+int Data_create(Cache *cf, long len)
 {
     int fd;
     int mode;
@@ -49,7 +87,7 @@ int Data_create(Cache *cf, size_t size)
         fprintf(stderr, "Data_create(): %s\n", strerror(errno));
         return 0;
     }
-    if (ftruncate(fd, cf->size) == -1) {
+    if (ftruncate(fd, cf->len) == -1) {
         fprintf(stderr, "Data_create(): %s\n", strerror(errno));
         return 0;
     }

src/cache.h

@@ -7,10 +7,16 @@
  * \file cache.h
  * \brief cache related structures and functions
  * \details think of these as some sort of generic caching layer.
- * \note apologies for whoever is going to be reading this. Sorry for being so
+ * \note
+ *   - apologies for whoever is going to be reading this. Sorry for being so
  * verbose in this header file, this is probably one of the most challenging
  * thing I have ever written so far! Yes I am doing a PhD in computer science,
  * but it doesn't imply that I am good at computer science or programming!
+ *   - We are using 'long' to store file size, because the offset in fseek() is
+ * in long, because the way we use the cache system, you cannot seek past
+ * long. So the biggest file size has to be able to be stored in long. This
+ * makes this program architecturally dependent, but this is due to the
+ * dependency to fseek().
  */
 
 
@@ -18,8 +24,8 @@
  * \brief a cache segment
  */
 typedef struct {
-    off_t *start;
-    off_t *end;
+    long *start;
+    long *end;
 } Seg;
 
 /**
@@ -28,7 +34,7 @@ typedef struct {
  */
 typedef struct {
     const char* filepath;
-    size_t size;
+    long len;
     FILE *data_fd; /**< the file descriptor for the data file */
     FILE *meta_fd; /**< the file descriptor for the meta file */
     int nseg; /**<the number of segments */
@@ -40,12 +46,12 @@ typedef struct {
 /**
  * \brief read from a cache file
  */
-off_t Cache_read(const char *filepath, off_t offset, size_t size);
+long Cache_read(const char *filepath, long offset, long len);
 
 /**
  * \brief write to a cache file
  */
-size_t Cache_write(const char *filepath, off_t offset, size_t size,
+long Cache_write(const char *filepath, long offset, long len,
                    const uint8_t *content);
 
 /**************************** Internal functions ******************************/
@@ -53,7 +59,7 @@ size_t Cache_write(const char *filepath, off_t offset, size_t size,
 /**
  * \brief create a cache file
  */
-int Cache_create(const char *filepath, size_t size);
+int Cache_create(const char *filepath, long len);
 
 /**
  * \brief open a cache file
@@ -72,18 +78,20 @@ int Meta_read(Cache *cf);
 
 /**
  * \brief read a data file
+ * \return -1 when the data file does not exist
  */
-size_t Data_read(Cache *cf, off_t offset, size_t size);
+long Data_read(Cache *cf, long offset, long len,
+                const uint8_t *buf);
 
 /**
  * \brief write to a data file
  */
-size_t Data_write(Cache *cf, off_t offset, size_t size,
-                      const uint8_t *content);
+long Data_write(Cache *cf, long offset, long len,
+                 const uint8_t *buf);
 /**
  * \brief create a data file
  * \details We use sparse creation here
  * \return 1 on success, 0 on failure
  */
-int Data_create(Cache *cf, size_t size);
+int Data_create(Cache *cf, long len);
 #endif