Add specific exceptions for String issues (#155)

This change helps telling unicode-related exceptions from other PyAsn1Error exceptions.

3 files changed, 52 insertions, 24 deletions

diff --git a/pyasn1/error.py b/pyasn1/error.py
index 7f606bb..fb23f1d 100644
--- a/pyasn1/error.py
+++ b/pyasn1/error.py
@@ -13,6 +13,34 @@ class PyAsn1Error(Exception):
     """
 
 
+class PyAsn1StringError(PyAsn1Error, UnicodeError):
+    """Create pyasn1 exception object
+
+    The `PyAsn1StringError` exception is a base class for errors relating to
+    string encoding/decoding and other related problems
+    """
+    def __init__(self, message, unicode_error=None):
+        if isinstance(unicode_error, UnicodeError):
+            UnicodeError.__init__(self, *unicode_error.args)
+        PyAsn1Error.__init__(self, message)
+
+
+class PyAsn1StringDecodeError(PyAsn1StringError, UnicodeDecodeError):
+    """Create pyasn1 exception object
+
+    The `PyAsn1StringDecodeError` exception represents a failure to decode
+    underlying bytes values to a string
+    """
+
+
+class PyAsn1StringEncodeError(PyAsn1StringError, UnicodeEncodeError):
+    """Create pyasn1 exception object
+
+    The `PyAsn1StringEncodeError` exception represents a failure to encode
+    underlying string value as bytes
+    """
+
+
 class ValueConstraintError(PyAsn1Error):
     """Create pyasn1 exception object
 
diff --git a/pyasn1/type/char.py b/pyasn1/type/char.py
index 617b98d..03121a0 100644
--- a/pyasn1/type/char.py
+++ b/pyasn1/type/char.py
@@ -54,9 +54,9 @@ class AbstractCharacterString(univ.OctetString):
                 # `str` is Py2 text representation
                 return self._value.encode(self.encoding)
 
-            except UnicodeEncodeError:
-                raise error.PyAsn1Error(
-                    "Can't encode string '%s' with codec %s" % (self._value, self.encoding)
+            except UnicodeEncodeError as e:
+                raise error.PyAsn1StringEncodeError(
+                    "Can't encode string '%s' with codec %s" % (self._value, self.encoding), e
                 )
 
         def __unicode__(self):
@@ -75,9 +75,9 @@ class AbstractCharacterString(univ.OctetString):
                 else:
                     return unicode(value)
 
-            except (UnicodeDecodeError, LookupError):
-                raise error.PyAsn1Error(
-                    "Can't decode string '%s' with codec %s" % (value, self.encoding)
+            except (UnicodeDecodeError, LookupError) as e:
+                raise error.PyAsn1StringDecodeError(
+                    "Can't decode string '%s' with codec %s" % (value, self.encoding), e
                 )
 
         def asOctets(self, padding=True):
@@ -94,9 +94,9 @@ class AbstractCharacterString(univ.OctetString):
         def __bytes__(self):
             try:
                 return self._value.encode(self.encoding)
-            except UnicodeEncodeError:
-                raise error.PyAsn1Error(
-                    "Can't encode string '%s' with codec %s" % (self._value, self.encoding)
+            except UnicodeEncodeError as e:
+                raise error.PyAsn1StringEncodeError(
+                    "Can't encode string '%s' with codec %s" % (self._value, self.encoding), e
                 )
 
         def prettyIn(self, value):
@@ -112,9 +112,9 @@ class AbstractCharacterString(univ.OctetString):
                 else:
                     return str(value)
 
-            except (UnicodeDecodeError, LookupError):
-                raise error.PyAsn1Error(
-                    "Can't decode string '%s' with codec %s" % (value, self.encoding)
+            except (UnicodeDecodeError, LookupError) as e:
+                raise error.PyAsn1StringDecodeError(
+                    "Can't decode string '%s' with codec %s" % (value, self.encoding), e
                 )
 
         def asOctets(self, padding=True):
diff --git a/pyasn1/type/univ.py b/pyasn1/type/univ.py
index 4c8c8e4..7d88957 100644
--- a/pyasn1/type/univ.py
+++ b/pyasn1/type/univ.py
@@ -825,9 +825,9 @@ class OctetString(base.AbstractSimpleAsn1Item):
             elif isinstance(value, unicode):
                 try:
                     return value.encode(self.encoding)
-                except (LookupError, UnicodeEncodeError):
-                    raise error.PyAsn1Error(
-                        "Can't encode string '%s' with codec %s" % (value, self.encoding)
+                except (LookupError, UnicodeEncodeError) as e:
+                    raise error.PyAsn1StringEncodeError(
+                        "Can't encode string '%s' with codec %s" % (value, self.encoding), e
                     )
             elif isinstance(value, (tuple, list)):
                 try:
@@ -846,9 +846,9 @@ class OctetString(base.AbstractSimpleAsn1Item):
             try:
                 return self._value.decode(self.encoding)
 
-            except UnicodeDecodeError:
-                raise error.PyAsn1Error(
-                    "Can't decode string '%s' with codec %s" % (self._value, self.encoding)
+            except UnicodeDecodeError as e:
+                raise error.PyAsn1StringDecodeError(
+                    "Can't decode string '%s' with codec %s" % (self._value, self.encoding), e
                 )
 
         def asOctets(self):
@@ -864,9 +864,9 @@ class OctetString(base.AbstractSimpleAsn1Item):
             elif isinstance(value, str):
                 try:
                     return value.encode(self.encoding)
-                except UnicodeEncodeError:
-                    raise error.PyAsn1Error(
-                        "Can't encode string '%s' with '%s' codec" % (value, self.encoding)
+                except UnicodeEncodeError as e:
+                    raise error.PyAsn1StringEncodeError(
+                        "Can't encode string '%s' with '%s' codec" % (value, self.encoding), e
                     )
             elif isinstance(value, OctetString):  # a shortcut, bytes() would work the same way
                 return value.asOctets()
@@ -881,9 +881,9 @@ class OctetString(base.AbstractSimpleAsn1Item):
             try:
                 return self._value.decode(self.encoding)
 
-            except UnicodeDecodeError:
-                raise error.PyAsn1Error(
-                    "Can't decode string '%s' with '%s' codec at '%s'" % (self._value, self.encoding, self.__class__.__name__)
+            except UnicodeDecodeError as e:
+                raise error.PyAsn1StringDecodeError(
+                    "Can't decode string '%s' with '%s' codec at '%s'" % (self._value, self.encoding, self.__class__.__name__), e
                 )
 
         def __bytes__(self):