Sensible default maximum difficulty

Fixes #144

src/class_sqlThread.py

@@ -326,7 +326,13 @@ class sqlThread(threading.Thread):
             shared.config.set('bitmessagesettings', 'maxdownloadrate', '0')
             shared.config.set('bitmessagesettings', 'maxuploadrate', '0')
             shared.config.set('bitmessagesettings', 'settingsversion', '10')
-            shared.writeKeysFile()                
+            shared.writeKeysFile()
+            
+        # sanity check
+        if shared.config.getint('bitmessagesettings', 'maxacceptablenoncetrialsperbyte') == 0:
+            shared.config.set('bitmessagesettings','maxacceptablenoncetrialsperbyte', str(shared.ridiculousDifficulty * shared.networkDefaultProofOfWorkNonceTrialsPerByte))
+        if shared.config.getint('bitmessagesettings', 'maxacceptablepayloadlengthextrabytes') == 0:
+            shared.config.set('bitmessagesettings','maxacceptablepayloadlengthextrabytes', str(shared.ridiculousDifficulty * shared.networkDefaultPayloadLengthExtraBytes))
 
         # The format of data stored in the pubkeys table has changed. Let's
         # clear it, and the pubkeys from inventory, so that they'll be re-downloaded.

src/proofofwork.py

@@ -133,6 +133,31 @@ def _doGPUPoW(target, initialHash):
         raise Exception("GPU did not calculate correctly.")
     logger.debug("GPU PoW done")
     return [trialValue, nonce]
+    
+def estimate(difficulty, format = False):
+    ret = difficulty / 10
+    if ret < 1:
+        ret = 1
+    if format:
+        out = str(int(ret)) + " seconds"
+        if ret > 60:
+            ret /= 60
+            out = str(int(ret)) + " minutes"
+        if ret > 60:
+            ret /= 60
+            out = str(int(ret)) + " hours"
+        if ret > 24:
+            ret /= 24
+            out = str(int(ret)) + " days"
+        if ret > 7:
+            out = str(int(ret)) + " weeks"
+        if ret > 31:
+            out = str(int(ret)) + " months"
+        if ret > 366:
+            ret /= 366
+            out = str(int(ret)) + " years"
+    else:
+        return ret
 
 def run(target, initialHash):
     target = int(target)

src/shared.py

@@ -91,6 +91,10 @@ objectProcessorQueue = Queue.Queue(
     )  # receiveDataThreads dump objects they hear on the network into this queue to be processed.
 streamsInWhichIAmParticipating = {}
 
+# sanity check, prevent doing ridiculous PoW
+# 20 million PoWs equals approximately 2 days on dev's dual R9 290
+ridiculousDifficulty = 20000000
+
 #If changed, these values will cause particularly unexpected behavior: You won't be able to either send or receive messages because the proof of work you do (or demand) won't match that done or demanded by others. Don't change them!
 networkDefaultProofOfWorkNonceTrialsPerByte = 1000 #The amount of work that should be performed (and demanded) per byte of the payload.
 networkDefaultPayloadLengthExtraBytes = 1000 #To make sending short messages a little more difficult, this value is added to the payload length for use in calculating the proof of work target.