Do some Db work

src/Db.c

@@ -25,12 +25,13 @@
 
 #include <Memory.h>
 #include <Json.h>
+#include <Util.h>
 
 #include <pthread.h>
 
 struct Db
 {
-    const char *dir;
+    char *dir;
     size_t cacheSize;
     size_t maxCache;
     pthread_mutex_t lock;
@@ -44,7 +45,10 @@ struct DbRef
     pthread_mutex_t lock;
 
     unsigned long ts;
-    char *file;
+    size_t size;
+
+    char *prefix;
+    char *key;
 };
 
 static ssize_t DbComputeSize(HashMap *);
@@ -147,8 +151,32 @@ DbComputeSize(HashMap * json)
     return total;
 }
 
+static char *
+DbHashKey(char *prefix, char *key)
+{
+    return UtilStringConcat(prefix, key);
+}
+
+static char *
+DbFileName(Db * db, char *prefix, char *key)
+{
+    char *tmp = UtilStringConcat(prefix, "/");
+    char *tmp2 = UtilStringConcat(tmp, key);
+    char *tmp3 = UtilStringConcat(tmp2, ".json");
+
+    char *tmp4 = UtilStringConcat(db->dir, "/");
+    char *tmp5 = UtilStringConcat(tmp4, tmp3);
+
+    Free(tmp);
+    Free(tmp2);
+    Free(tmp3);
+    Free(tmp4);
+
+    return tmp5;
+}
+
 Db *
-DbOpen(const char *dir, size_t cache)
+DbOpen(char *dir, size_t cache)
 {
     Db *db;
 
@@ -176,6 +204,10 @@ DbOpen(const char *dir, size_t cache)
             return NULL;
         }
     }
+    else
+    {
+        db->cache = NULL;
+    }
 
     return db;
 }
@@ -183,13 +215,29 @@ DbOpen(const char *dir, size_t cache)
 void
 DbClose(Db * db)
 {
+    char *key;
+    DbRef *val;
+
     if (!db)
     {
         return;
     }
 
     pthread_mutex_destroy(&db->lock);
+
+    if (db->cache)
+    {
+        while (HashMapIterate(db->cache, &key, (void **) &val))
+        {
+            Free(key);
+            JsonFree(val->json);
+            Free(val->prefix);
+            Free(val->key);
+            pthread_mutex_destroy(&val->lock);
+            Free(val);
+        }
         HashMapFree(db->cache);
+    }
 
     Free(db);
 }
@@ -197,31 +245,147 @@ DbClose(Db * db)
 DbRef *
 DbCreate(Db * db, char *prefix, char *key)
 {
+    FILE *fp;
+    char *file;
+
     if (!db || !prefix || !key)
     {
         return NULL;
     }
 
+    file = DbFileName(db, prefix, key);
+
+    if (UtilLastModified(file))
+    {
         return NULL;
+    }
+
+    return DbLock(db, prefix, key);
 }
 
 DbRef *
 DbLock(Db * db, char *prefix, char *key)
 {
+    char *file;
+    char *hash;
+    DbRef *ref;
+
     if (!db || !prefix || !key)
     {
         return NULL;
     }
 
+    ref = NULL;
+    hash = NULL;
+
     pthread_mutex_lock(&db->lock);
 
+    /* Check if the item is in the cache */
+    if (db->cache)
+    {
+        hash = DbHashKey(prefix, key);
+        ref = HashMapGet(db->cache, hash);
+    }
+
+    file = DbFileName(db, prefix, key);
+
+    if (ref)                       /* In cache */
+    {
+        unsigned long diskTs = UtilLastModified(file);
+
+        if (diskTs > ref->ts)
+        {
+            /* File was modified on disk since it was cached */
+            FILE *fp = fopen(file, "r");
+            HashMap *json;
+
+            if (!fp)
+            {
+                ref = NULL;
+                goto finish;
+            }
+
+            json = JsonDecode(fp);
+            fclose(fp);
+
+            if (!json)
+            {
+                ref = NULL;
+                goto finish;
+            }
+
+            JsonFree(ref->json);
+            ref->json = json;
+            ref->ts = diskTs;
+            ref->size = DbComputeSize(ref->json);
+            ref->prefix = UtilStringDuplicate(prefix);
+            ref->key = UtilStringDuplicate(key);
+        }
+    }
+    else
+    {
+        /* Not in cache; load from disk */
+        FILE *fp = fopen(file, "r");
+
+        if (!fp)
+        {
+            ref = NULL;
+            goto finish;
+        }
+
+        ref = Malloc(sizeof(DbRef));
+        if (!ref)
+        {
+            fclose(fp);
+            goto finish;
+        }
+
+        ref->json = JsonDecode(fp);
+
+        fclose(fp);
+
+        if (!ref->json)
+        {
+            Free(ref);
+            ref = NULL;
+            goto finish;
+        }
+
+        pthread_mutex_init(&ref->lock, NULL);
+        ref->ts = UtilServerTs();
+        ref->size = DbComputeSize(ref->json);
+        ref->prefix = prefix;
+        ref->key = key;
+
+        /* If cache is enabled, cache this ref */
+        if (db->cache)
+        {
+            HashMapSet(db->cache, hash, ref);
+            db->cacheSize += ref->size;
+
+            /* Cache is full; evict old items */
+            if (db->cacheSize > db->maxCache)
+            {
+                /* TODO */
+            }
+        }
+    }
+
     pthread_mutex_unlock(&db->lock);
-    return NULL;
+    pthread_mutex_lock(&ref->lock);
+
+finish:
+    Free(file);
+    Free(hash);
+    return ref;
 }
 
 void
 DbUnlock(Db * db, DbRef * ref)
 {
+    FILE *fp;
+    char *file;
+
     if (!db || !ref)
     {
         return;
@@ -229,9 +393,28 @@ DbUnlock(Db * db, DbRef * ref)
 
     pthread_mutex_lock(&db->lock);
 
-    pthread_mutex_unlock(&db->lock);
-
+    file = DbFileName(db, ref->prefix, ref->key);
+    fp = fopen(file, "w");
+    if (!fp)
+    {                              /* TODO: This seems dangerous */
         return;
+    }
+
+    JsonEncode(ref->json, fp);
+    fflush(fp);
+    fclose(fp);
+
+    pthread_mutex_unlock(&ref->lock);
+
+    /* No cache, free it now */
+    if (!db->cache)
+    {
+        JsonFree(ref->json);
+        Free(ref->prefix);
+        Free(ref->key);
+        pthread_mutex_destroy(&ref->lock);
+        Free(ref);
+    }
 }
 
 HashMap *

src/Util.c

@@ -34,6 +34,7 @@
 
 #include <errno.h>
 #include <sys/time.h>
+#include <sys/stat.h>
 #include <limits.h>
 
 unsigned long
@@ -48,6 +49,23 @@ UtilServerTs(void)
     return ts;
 }
 
+unsigned long
+UtilLastModified(char *path)
+{
+    struct stat st;
+    unsigned long ts;
+
+    if (stat(path, &st) == 0)
+    {
+        ts = (st.st_mtim.tv_sec * 1000) + (st.st_mtim.tv_nsec / 1000000);
+        return ts;
+    }
+    else
+    {
+        return 0;
+    }
+}
+
 char *
 UtilUtf8Encode(unsigned long utf8)
 {
@@ -115,6 +133,27 @@ UtilStringDuplicate(char *inStr)
     return outStr;
 }
 
+char *
+UtilStringConcat(char *str1, char *str2)
+{
+    char *ret;
+
+    size_t str1Len = strlen(str1);
+    size_t str2Len = strlen(str2);
+
+    ret = Malloc(str1Len + str2Len + 1);
+
+    if (!ret)
+    {
+        return NULL;
+    }
+
+    strcpy(ret, str1);
+    strcpy(ret + str1Len, str2);
+
+    return ret;
+}
+
 int
 UtilSleepMillis(long ms)
 {

src/include/Db.h

@@ -32,7 +32,7 @@ typedef struct Db Db;
 typedef struct DbRef DbRef;
 
 extern Db *
- DbOpen(const char *, size_t);
+ DbOpen(char *, size_t);
 
 extern void
  DbClose(Db *);

src/include/Json.h

@@ -146,7 +146,7 @@ extern JsonValue *
  JsonValueString(char *string);
 
 extern char *
-JsonValueAsString(JsonValue *);
+ JsonValueAsString(JsonValue *);
 
 extern JsonValue *
  JsonValueInteger(long integer);

src/include/Util.h

@@ -57,6 +57,9 @@
 extern unsigned long
  UtilServerTs(void);
 
+extern unsigned long
+ UtilLastModified(char *);
+
 /*
  * Encode a single UTF-8 codepoint as a string buffer containing
  * between 1 and 4 bytes. The string buffer is allocated on the heap,
@@ -88,6 +91,9 @@ extern char *
 extern char *
  UtilStringDuplicate(char *);
 
+extern char *
+ UtilStringConcat(char *, char *);
+
 /*
  * Sleep for the given number of milliseconds. This is a simple wrapper
  * for nanosleep() that makes its usage much easier.