faset over fra Z3950 til google books

python/gdata/tlslite/utils/ASN1Parser.py

@@ -0,0 +1,34 @@
+"""Class for parsing ASN.1"""
+from compat import *
+from codec import *
+
+#Takes a byte array which has a DER TLV field at its head
+class ASN1Parser:
+    def __init__(self, bytes):
+        p = Parser(bytes)
+        p.get(1) #skip Type
+
+        #Get Length
+        self.length = self._getASN1Length(p)
+
+        #Get Value
+        self.value = p.getFixBytes(self.length)
+
+    #Assuming this is a sequence...
+    def getChild(self, which):
+        p = Parser(self.value)
+        for x in range(which+1):
+            markIndex = p.index
+            p.get(1) #skip Type
+            length = self._getASN1Length(p)
+            p.getFixBytes(length)
+        return ASN1Parser(p.bytes[markIndex : p.index])
+
+    #Decode the ASN.1 DER length field
+    def _getASN1Length(self, p):
+        firstLength = p.get(1)
+        if firstLength<=127:
+            return firstLength
+        else:
+            lengthLength = firstLength & 0x7F
+            return p.get(lengthLength)