* error return codes

* add a lot of #define's
  * add imdb_error() for converting error code to detailed description

src/database.c

@@ -24,7 +24,7 @@
   bytes = pread((db)->fd, (buf), (len), (off)); \
   if (errno) { \
     strncpy((db)->error, strerror(errno), sizeof(db->error)); \
-    return -1; \
+    return IMDB_ERR_SYSTEM; \
   }
 
 #define DB_WRITE(db, buf, len, off) \
@@ -32,7 +32,7 @@
   bytes = pwrite((db)->fd, (buf), (len), (off)); \
   if (errno) { \
     strncpy((db)->error, strerror(errno), sizeof(db->error)); \
-    return -1; \
+    return IMDB_ERR_SYSTEM; \
   }
 
 const char *imdb_hdr_fmt = "IMDB v%02u, CAPS: %s;";
@@ -74,31 +74,31 @@ imdb_open(const char *path, int mode, int *error) {
   assert(error != NULL);
 
   if (stat(path, &st) < 0) {
-    *error = -1;
+    *error = IMDB_ERR_SYSTEM;
     return NULL;
   }
 
   if ((fd = open(path, (mode & IMDB_FLAG_WRITE) ? O_RDWR : O_RDONLY)) < 0) {
-    *error = -1;
+    *error = IMDB_ERR_SYSTEM;
     return NULL;
   }
 
   errno = 0;
   bytes = pread(fd, buf, IMDB_REC_LEN, 0);
   if (bytes < IMDB_REC_LEN) {
-    *error = errno ? -1 : -3; /* empty file, damaged database or IO error */
+    *error = errno ? IMDB_ERR_SYSTEM : IMDB_ERR_CORRUPTDB;
     return NULL;
   }
 
   p = buf + 0;
   if (memcmp("IMDB", p, 4) != 0) {
-    *error = -3; /* Not a database file */
+    *error = IMDB_ERR_CORRUPTDB;
     return NULL;
   }
 
   p = buf + 6;
   if (atoi(p) != IMDB_VERSION) {
-    *error = -4; /* Database version mismatch */
+    *error = IMDB_ERR_WRONGVERS;
     return NULL;
   }
 
@@ -114,7 +114,7 @@ imdb_open(const char *path, int mode, int *error) {
   /* all seems to be ok */
 
   if ((db = calloc(1, sizeof(imdb_db_t))) == NULL) {
-    *error = -2; /* out of memory */
+    *error = IMDB_ERR_OOM;
     return NULL;
   }
 
@@ -146,6 +146,22 @@ imdb_close(imdb_db_t *db)
     close(db->fd);
 }
 
+const char *
+imdb_error(int error) {
+   if (error == IMDB_SUCCESS) {
+     return "success";
+   } else if (error == IMDB_ERR_SYSTEM) {
+     return strerror(errno);
+   } else if (error == IMDB_ERR_OOM) {
+     return "can't allocate memory";
+   } else if (error == IMDB_ERR_CORRUPTDB) {
+     return "database corrupted";
+   } else if (error == IMDB_ERR_WRONGVERS) {
+     return "database version differs from library version";
+   }
+   return "unknown error";
+}
+
 int imdb_read_rec(imdb_db_t *db, imdb_rec_t *rec)
 {
   ssize_t bytes = 0;
@@ -157,7 +173,7 @@ int imdb_read_rec(imdb_db_t *db, imdb_rec_t *rec)
   DB_READ(db, rec->data, IMDB_REC_LEN, rec->num * IMDB_REC_LEN);
 
   if (bytes != IMDB_REC_LEN)
-    return -1;
+    return errno ? IMDB_ERR_SYSTEM : 0;
 
   if (rec->data[0] != 0xFF)
     return 0;
@@ -176,7 +192,7 @@ int imdb_write_rec(imdb_db_t *db, imdb_rec_t *rec)
   DB_WRITE(db, rec->data, IMDB_REC_LEN, rec->num * IMDB_REC_LEN);
 
   if (bytes != IMDB_REC_LEN)
-    return -1;
+    return IMDB_ERR_SYSTEM;
 
   return 1;
 }
@@ -235,6 +251,7 @@ imdb_search(imdb_db_t     * const db,
   unsigned char *p = NULL;
   float ratio_s = 0.0; /* source */
   float ratio_t = 0.0; /* tested */
+  int ret = 0;
 
   assert(db      != NULL);
   assert(sample  != NULL);
@@ -248,9 +265,9 @@ imdb_search(imdb_db_t     * const db,
   blk.start = 1;
   blk.records = blk_size;
 
-  if (imdb_read_rec(db, sample) < 1) {
+  if ((ret = imdb_read_rec(db, sample)) < 1) {
     strncpy(db->error, "Can't read source sample", sizeof(db->error));
-    return -1;
+    return ret;
   }
 
   if (search->limit == 0)

src/database.h

@@ -13,6 +13,13 @@
 #define IMDB_CAP_RATIO     1 << (8 + 2)
 /* 3 used, 5 reserved */
 
+#define IMDB_SUCCESS          0
+/* database errors */
+#define IMDB_ERR_SYSTEM      -1 /* see errno for details */
+#define IMDB_ERR_OOM         -2 /* can't allocate memory */
+#define IMDB_ERR_CORRUPTDB   -3 /* empty or currupted database */
+#define IMDB_ERR_WRONGVERS   -4 /* database version mismatch */
+
 typedef struct {
   int fd;
   int flags;
@@ -92,8 +99,7 @@ typedef struct {
 } imdb_match_t;
 
 /**
- * @return 1 on success, 0 if record not used
- *          and -1 if record number not exists,
+ * @returns 1 on success, 0 if record missing and <0 on error
  */
 int imdb_read_rec (imdb_db_t *db, imdb_rec_t *rec);
 int imdb_write_rec(imdb_db_t *db, imdb_rec_t *rec);
@@ -116,10 +122,7 @@ bool imdb_create(const char *path);
  * @param mode Database open modes. See IMDB_FLAG_* defines above
  * @param error Pointer to error code storage
  * @returns Pointer to database handle on success, NULL on error
- *  -1 -- system error, see @a errno for details
- *  -2 -- malloc() failed
- *  -3 -- damaged database
- *  -4 -- database version mismatch
+ * @note use @a imdb_error() to get error description
  */
 imdb_db_t * imdb_open(const char *path, int mode, int *error);
 
@@ -129,14 +132,17 @@ imdb_db_t * imdb_open(const char *path, int mode, int *error);
  */
 void imdb_close(imdb_db_t *db);
 
+/**
+ * @brief Get error desctiption by error code
+ * @param error Error code, see IMDB_ERR_* defines above
+ */
+const char * imdb_error(int code);
+
 float
 ratio_from_rec_data(unsigned char * const data);
 
 /**
- @returns:
-  -1 on error
-   0 if nothing found
-  >0 if found some matches
+ @returns: >0 if found some matches, 0 if nothing found, <0 on error
  */
 int
 imdb_search(imdb_db_t     * const db,

tests/database.c

@@ -24,7 +24,7 @@ int main()
 
   rec[0].num = 1;
   err = imdb_read_rec(db, rec);
-  assert(err < 0); /* no such record */
+  assert(err == 0); /* no such record */
 
   memset(rec[0].data, 0xAA, IMDB_REC_LEN);
   memset(rec[0].data, 0xFF, 1); /* record is used */