Added custom implementation of a LevelDB wrapper

leveldb_wrapper/LevelDbWrapper.js

@@ -0,0 +1,115 @@
+/**
+ * Extremly basic and stripped-down wrapper class to directly call LevelDB library.
+ * 
+ * This class is able to call an external LevelDB library using the "Foreign Function Interface" module.
+ * It supports synchronously iterating through a database and reading data. Writing isn't implemented yet.
+ * @author clarkx86
+ */
+
+const ffi = require("ffi"),
+      ref = require("ref");
+
+module.exports = class LevelDbWrapper {
+    levelDbLib = null;
+
+    leveldb_db = ref.refType(ref.types.Object);
+    leveldb_options = ref.refType(ref.types.void);
+    leveldb_comparator = ref.refType(ref.types.void);
+    leveldb_snapshot = ref.refType(ref.types.Object);
+    leveldb_options_set_comparator = this.leveldb_comparator;
+    leveldb_options_create_if_missing = ref.types.bool;
+    leveldb_options_paranoid_checks = ref.types.bool;
+
+    leveldb_readoptions = ref.refType(ref.types.Object);
+    leveldb_readoptions_verify_checksums = ref.types.bool;
+    leveldb_readoptions_fill_cache = ref.types.bool;
+
+    leveldb_iterator = ref.refType(ref.types.Object);
+    keyValPointer = ref.refType(ref.types.Object);
+
+    _db = null;
+    _options = null;
+    _readoptions = null;
+    _ite = null;
+
+    keySizePointer = null;
+    valueSizePointer = null;
+
+    constructor(libPath) {
+        this.levelDbLib = ffi.Library(require("path").resolve(libPath), {
+            "leveldb_open": [this.leveldb_db, [this.leveldb_options, "string"]],
+            "leveldb_close": [ref.types.void, [this.leveldb_db]],
+            "leveldb_get": [ref.types.CString, [this.leveldb_db, this.leveldb_readoptions]],
+            "leveldb_create_iterator": [this.leveldb_iterator, [this.leveldb_db, this.leveldb_readoptions]],
+            "leveldb_iter_destroy": [ref.types.void, [this.leveldb_iterator]],
+            "leveldb_iter_valid": [ref.types.byte, [this.leveldb_iterator]],
+            "leveldb_iter_seek_to_first": [ref.types.void, [this.leveldb_iterator]],
+            "leveldb_iter_seek_to_last": [ref.types.void, [this.leveldb_iterator]],
+            "leveldb_iter_next": [ref.types.void, [this.leveldb_iterator]],
+            "leveldb_iter_prev": [ref.types.void, [this.leveldb_iterator]],
+            "leveldb_iter_key": [this.keyValPointer, [this.leveldb_iterator, ref.refType(ref.types.size_t)]],
+            "leveldb_iter_value": [this.keyValPointer, [this.leveldb_iterator, ref.refType(ref.types.size_t)]],
+            "leveldb_options_create": [this.leveldb_options, []],
+            "leveldb_options_set_create_if_missing": ["void", [this.leveldb_options, this.leveldb_options_create_if_missing]],
+            "leveldb_options_set_compression": ["void", [this.leveldb_options, ref.types.int]],
+            "leveldb_options_destroy": ["void", [this.leveldb_options]],
+            "leveldb_readoptions_create": [this.leveldb_readoptions, []],
+            "leveldb_readoptions_destroy": [ref.types.void, [this.leveldb_readoptions]],
+            "leveldb_readoptions_set_verify_checksums": [ref.types.void, [this.leveldb_readoptions, ref.types.bool]],
+            "leveldb_readoptions_set_fill_cache": [ref.types.void, [this.leveldb_readoptions, ref.types.bool]],
+            "leveldb_readoptions_set_snapshot": [ref.types.void, [this.leveldb_readoptions, this.leveldb_snapshot]],
+            "leveldb_readoptions_destroy": ["void", [this.leveldb_readoptions]]
+        });
+    }
+
+    open(path) {
+        this._options = this.levelDbLib.leveldb_options_create();
+        this._readoptions = this.levelDbLib.leveldb_readoptions_create();
+
+        this.levelDbLib.leveldb_options_set_compression(this._options, 4);
+        this._db = this.levelDbLib.leveldb_open(this._options, path);
+
+        // Create iterator
+        this._ite = this.levelDbLib.leveldb_create_iterator(this._db, this._readoptions);
+    }
+
+    close() {
+        this.levelDbLib.leveldb_readoptions_destroy(this._readoptions);
+        this.levelDbLib.leveldb_options_destroy(this._options);
+        this.levelDbLib.leveldb_iter_destroy(this._ite);
+        this.levelDbLib.leveldb_close(this._db);
+    }
+
+    iterate() {
+        let i = 0;
+
+        /*
+         * Investigate behaviour of key/ value size pointer size.
+        */
+
+        // Iterate through every entry
+        for (this.levelDbLib.leveldb_iter_seek_to_first(this._ite); this.levelDbLib.leveldb_iter_valid(this._ite) != 0; this.levelDbLib.leveldb_iter_next(this._ite)) {
+            // Allocate a key- and value size address of size_t to pass onto the LevelDB function
+            this.keySizePointer = ref.alloc(ref.types.size_t, 0),
+            this.valueSizePointer = ref.alloc(ref.types.size_t, 0);
+
+            let key = this.levelDbLib.leveldb_iter_key(this._ite, this.keySizePointer),
+                value = this.levelDbLib.leveldb_iter_value(this._ite, this.valueSizePointer);
+
+            // console.log("valueSizePointer:\t" + ref.readInt64LE(this.valueSizePointer));
+            // console.log("valueLength:\t" + value.byteLength);
+            i++;
+        }
+        return new KeyValuePair()
+    }
+}
+
+class KeyValuePair {
+    key = null;
+    value = null;
+
+    constructor(key, value) {
+        this.key = key;
+        this.value = value;
+    }
+}