Merge pull request #148 from librecaptcha/fix145

Fix for #145: frequent repetition of CAPTCHA challenge

src/main/scala/lc/background/taskThread.scala

@@ -18,22 +18,37 @@ class BackgroundTask(config: Config, captchaManager: CaptchaManager) {
         val challengeGCPstmt = Statements.tlStmts.get.challengeGCPstmt
         challengeGCPstmt.executeUpdate()
 
-        val imageNumResult = Statements.tlStmts.get.getCountChallengeTable.executeQuery()
-        val imageNum = if (imageNumResult.next()) {
-          imageNumResult.getInt("total")
-        } else {
-          0
-        }
+        val allCombinations = allParameterCombinations()
+        val requiredCountPerCombination = Math.max(1, (config.throttle * 1.01) / allCombinations.size).toInt
 
-        val throttle = (config.throttle * 1.1).toInt - imageNum
+        for (param <- allCombinations) {
+          val countExisting = captchaManager.getCount(param).getOrElse(0)
+          val countRequired = requiredCountPerCombination - countExisting
+          if (countRequired > 0) {
+            val countCreate = Math.min(1.0 + requiredCountPerCombination/10.0, countRequired).toInt
+            println(s"Creating $countCreate of $countRequired captchas for $param")
 
-        for (i <- 0 until throttle) {
-          captchaManager.generateChallenge(getRandomParam())
+            for (i <- 0 until countCreate) {
+              captchaManager.generateChallenge(param)
+            }
+          }
         }
       } catch { case exception: Exception => println(exception) }
     }
   }
 
+  private def allParameterCombinations(): List[Parameters] = {
+    (config.captchaConfig).flatMap {captcha =>
+      (captcha.allowedLevels).flatMap {level =>
+        (captcha.allowedMedia).flatMap {media =>
+          (captcha.allowedInputType).map {inputType =>
+            Parameters(level, media, inputType, Some(Size(0, 0)))
+          }
+        }
+      }
+    }
+  }
+
   private def getRandomParam(): Parameters = {
     val captcha = pickRandom(config.captchaConfig)
     val level = pickRandom(captcha.allowedLevels)

src/main/scala/lc/core/captchaManager.scala

@@ -105,19 +105,38 @@ class CaptchaManager(config: Config, captchaProviders: CaptchaProviders) {
     }
   }
 
-  private def getToken(param: Parameters): Option[Int] = {
-    val tokenPstmt = Statements.tlStmts.get.tokenPstmt
-    tokenPstmt.setString(1, param.level)
-    tokenPstmt.setString(2, param.media)
-    tokenPstmt.setString(3, param.input_type)
-    val rs = tokenPstmt.executeQuery()
+  def getCount(param: Parameters): Option[Int] = {
+    val countPstmt = Statements.tlStmts.get.countForParameterPstmt
+    countPstmt.setString(1, param.level)
+    countPstmt.setString(2, param.media)
+    countPstmt.setString(3, param.input_type)
+    val rs = countPstmt.executeQuery()
     if (rs.next()) {
-      Some(rs.getInt("token"))
+      Some(rs.getInt("count"))
     } else {
       None
     }
   }
 
+  private def getToken(param: Parameters): Option[Int] = {
+    val count = getCount(param).getOrElse(0)
+    if (count == 0) {
+      None
+    } else {
+      val tokenPstmt = Statements.tlStmts.get.tokenPstmt
+      tokenPstmt.setString(1, param.level)
+      tokenPstmt.setString(2, param.media)
+      tokenPstmt.setString(3, param.input_type)
+      tokenPstmt.setInt(4, count)
+      val rs = tokenPstmt.executeQuery()
+      if (rs.next()) {
+        Some(rs.getInt("token"))
+      } else {
+        None
+      }
+    }
+  }
+
   private def updateAttempted(token: Int): Unit = {
     val updateAttemptedPstmt = Statements.tlStmts.get.updateAttemptedPstmt
     updateAttemptedPstmt.setInt(1, token)

src/main/scala/lc/database/statements.scala

@@ -70,6 +70,17 @@ class Statements(dbConn: DBConn, maxAttempts: Int) {
       "WHERE token = ?;"
   )
 
+  val countForParameterPstmt: PreparedStatement = dbConn.con.prepareStatement(
+    s"""
+      SELECT count(*) as count
+        FROM challenge
+        WHERE attempted < $maxAttempts AND
+        contentLevel = ? AND
+        contentType = ? AND
+        contentInput = ?
+        """
+  )
+
   val tokenPstmt: PreparedStatement = dbConn.con.prepareStatement(
     s"""
       SELECT token, attempted
@@ -78,7 +89,9 @@ class Statements(dbConn: DBConn, maxAttempts: Int) {
         contentLevel = ? AND
         contentType = ? AND
         contentInput = ?
-        ORDER BY attempted ASC LIMIT 1"""
+        LIMIT 1
+        OFFSET FLOOR(RAND()*?)
+         """
   )
 
   val deleteAnswerPstmt: PreparedStatement = dbConn.con.prepareStatement(