S3 Fuzzer: implemented decision expansion

Decision reached by descending the graph describing the attack surface can
be expanded to fill in all the placeholders

s3tests/functional/test_fuzzer.py

@@ -107,6 +107,33 @@ def test_assemble_decision():
     eq(decision['path'], '/{bucket_readable}')
     assert_raises(KeyError, lambda x: decision[x], 'key3')
 
+def test_expand_key():
+    prng = random.Random(1)
+    test_decision = {
+        'key1': 'value1',
+        'randkey': 'value-{random 10-15 printable}',
+        'indirect': '{key1}',
+        'dbl_indirect': '{indirect}'
+    }
+    decision = SpecialVariables(test_decision, prng)
+
+    randkey = expand_key(decision, 'randkey')
+    indirect = expand_key(decision, 'indirect')
+    dbl_indirect = expand_key(decision, 'dbl_indirect')
+
+    eq(indirect, 'value1')
+    eq(dbl_indirect, 'value1')
+    eq(randkey, 'value-[/pNI$;92@')
+
+def test_expand_loop():
+    prng = random.Random(1)
+    test_decision = {
+        'key1': '{key2}',
+        'key2': '{key1}',
+    }
+    decision = SpecialVariables(test_decision, prng)
+    assert_raises(RuntimeError, expand_key, decision, 'key1')
+
 def test_expand_decision():
     graph = build_graph()
     prng = random.Random(1)
@@ -119,6 +146,6 @@ def test_expand_decision():
     eq(request['key1'], 'value1')
     eq(request['indirect_key1'], 'value1')
     eq(request['path'], '/my-readable-bucket')
-    eq(request['randkey'], 'value-?') #FIXME: again, how to handle the pseudorandom content?
+    eq(request['randkey'], 'value-NI$;92@H/0I') #FIXME: again, how to handle the pseudorandom content?
     assert_raises(KeyError, lambda x: decision[x], 'key3')
 

s3tests/fuzz_headers.py

@@ -4,6 +4,7 @@ from boto import UserAgent
 from . import common
 
 import traceback
+import itertools
 import random
 import string
 import yaml
@@ -44,7 +45,24 @@ def expand_decision(decision, prng):
         decision's values and headers until all values are fully expanded and
         build a request out of the information
     """
-    raise NotImplementedError
+    special_decision = SpecialVariables(decision, prng)
+    for key in special_decision:
+        decision[key] = expand_key(special_decision, key)
+
+    return decision
+
+
+def expand_key(decision, key):
+    c = itertools.count()
+    fmt = string.Formatter()
+    old = decision[key]
+    while True:
+        new = fmt.vformat(old, [], decision)
+        if new == old:
+            return old
+        if next(c) > 5:
+            raise RuntimeError
+        old = new
 
 
 class SpecialVariables(dict):