Start of PoW mining

mining_pow.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"os"
+	"time"
+)
+
+// mineSqlite3Database mines a SQLite3 database file, by adjusting the user_version field
+// in the database header as a "nonce", and using SHA256 for the actual hashing. The file
+// must exist and must be closed.
+func mineSqlite3Database(fileName string, difficultyBits int) (string, error) {
+	startNonce := uint32(time.Now().Unix())
+	f, err := os.OpenFile(fileName, os.O_RDWR, 0)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	b := make([]byte, 4)
+	for nonce := startNonce + 1; nonce != startNonce; nonce++ {
+		binary.LittleEndian.PutUint32(b, nonce)
+		_, err := f.WriteAt(b, 60) // https://www.sqlite.org/fileformat2.html#database_header
+		if err != nil {
+			return "", err
+		}
+		f.Sync()
+		hash, err := hashFileToBytes(fileName)
+		if err != nil {
+			return "", err
+		}
+		nZeroes := countStartZeroBits(hash)
+		if nZeroes == difficultyBits {
+			return hex.EncodeToString(hash), nil
+		}
+	}
+	return "", nil
+}