Work in progress on writable encoding

Would help using adapt(unicode) to quote strings without a connection,
see ticket #331.

Currently in heisenbug state: if test_connection_wins_anyway and
test_encoding_default run (in this order), the latter fail because the
returned value is "'\xe8 '", with an extra space. Skipping the first
test, the second succeed.

The bad value is returned by the libpq:

    ql = PQescapeString(to+eq+1, from, len);

just returns len = 2 and an extra space in the string... meh.

psycopg/adapter_qstring.c

@@ -36,29 +36,44 @@ static const char *default_encoding = "latin1";
 
 /* qstring_quote - do the quote process on plain and unicode strings */
 
+const char *
+_qstring_get_encoding(qstringObject *self)
+{
+    /* if the wrapped object is an unicode object we can encode it to match
+       conn->encoding but if the encoding is not specified we don't know what
+       to do and we raise an exception */
+    if (self->conn) {
+        return self->conn->codec;
+    }
+    else {
+        return self->encoding ? self->encoding : default_encoding;
+    }
+}
+
 static PyObject *
 qstring_quote(qstringObject *self)
 {
     PyObject *str = NULL;
     char *s, *buffer = NULL;
     Py_ssize_t len, qlen;
-    const char *encoding = default_encoding;
+    const char *encoding;
     PyObject *rv = NULL;
 
-    /* if the wrapped object is an unicode object we can encode it to match
-       conn->encoding but if the encoding is not specified we don't know what
-       to do and we raise an exception */
-    if (self->conn) {
-        encoding = self->conn->codec;
-    }
-
+    encoding = _qstring_get_encoding(self);
     Dprintf("qstring_quote: encoding to %s", encoding);
 
-    if (PyUnicode_Check(self->wrapped) && encoding) {
+    if (PyUnicode_Check(self->wrapped)) {
+        if (encoding) {
             str = PyUnicode_AsEncodedString(self->wrapped, encoding, NULL);
             Dprintf("qstring_quote: got encoded object at %p", str);
             if (str == NULL) goto exit;
         }
+        else {
+            PyErr_SetString(PyExc_TypeError,
+                "missing encoding to encode unicode object");
+            goto exit;
+        }
+    }
 
 #if PY_MAJOR_VERSION < 3
     /* if the wrapped object is a simple string, we don't know how to
@@ -150,15 +165,34 @@ qstring_conform(qstringObject *self, PyObject *args)
 static PyObject *
 qstring_get_encoding(qstringObject *self)
 {
-    const char *encoding = default_encoding;
-
-    if (self->conn) {
-        encoding = self->conn->codec;
-    }
-
+    const char *encoding;
+    encoding = _qstring_get_encoding(self);
     return Text_FromUTF8(encoding);
 }
 
+static int
+qstring_set_encoding(qstringObject *self, PyObject *pyenc)
+{
+    int rv = -1;
+    const char *tmp;
+    char *cenc;
+
+    /* get a C copy of the encoding (which may come from unicode) */
+    Py_INCREF(pyenc);
+    if (!(pyenc = psycopg_ensure_bytes(pyenc))) { goto exit; }
+    if (!(tmp = Bytes_AsString(pyenc))) { goto exit; }
+    if (0 > psycopg_strdup(&cenc, tmp, 0)) { goto exit; }
+
+    Dprintf("qstring_set_encoding: encoding set to %s", cenc);
+    PyMem_Free((void *)self->encoding);
+    self->encoding = cenc;
+    rv = 0;
+
+exit:
+    Py_XDECREF(pyenc);
+    return rv;
+}
+
 /** the QuotedString object **/
 
 /* object member list */
@@ -183,7 +217,7 @@ static PyMethodDef qstringObject_methods[] = {
 static PyGetSetDef qstringObject_getsets[] = {
     { "encoding",
         (getter)qstring_get_encoding,
-        (setter)NULL,
+        (setter)qstring_set_encoding,
         "current encoding of the adapter" },
     {NULL}
 };
@@ -216,6 +250,7 @@ qstring_dealloc(PyObject* obj)
     Py_CLEAR(self->wrapped);
     Py_CLEAR(self->buffer);
     Py_CLEAR(self->conn);
+    PyMem_Free((void *)self->encoding);
 
     Dprintf("qstring_dealloc: deleted qstring object at %p, refcnt = "
         FORMAT_CODE_PY_SSIZE_T,

psycopg/adapter_qstring.h

@@ -39,6 +39,9 @@ typedef struct {
     PyObject *buffer;
 
     connectionObject *conn;
+
+    const char *encoding;
+
 } qstringObject;
 
 #ifdef __cplusplus

tests/test_types_basic.py

@@ -344,6 +344,43 @@ class TypesBasicTests(ConnectingTestCase):
         self.assertEqual(a, [2,4,'nada'])
 
 
+class TestStringAdapter(ConnectingTestCase):
+    def test_encoding_default(self):
+        from psycopg2.extensions import adapt
+        a = adapt("hello")
+        self.assertEqual(a.encoding, 'latin1')
+        self.assertEqual(a.getquoted(), "'hello'")
+
+        egrave = u'\xe8'
+        self.assertEqual(adapt(egrave).getquoted(), "'\xe8'")
+
+    def test_encoding_error(self):
+        from psycopg2.extensions import adapt
+        snowman = u"\u2603"
+        a = adapt(snowman)
+        self.assertRaises(UnicodeEncodeError, a.getquoted)
+
+    def test_set_encoding(self):
+        from psycopg2.extensions import adapt
+        snowman = u"\u2603"
+        a = adapt(snowman)
+        a.encoding = 'utf8'
+        self.assertEqual(a.encoding, 'utf8')
+        self.assertEqual(a.getquoted(), "'\xe2\x98\x83'")
+
+    def test_connection_wins_anyway(self):
+        from psycopg2.extensions import adapt
+        snowman = u"\u2603"
+        a = adapt(snowman)
+        a.encoding = 'latin9'
+
+        self.conn.set_client_encoding('utf8')
+        a.prepare(self.conn)
+
+        self.assertEqual(a.encoding, 'utf_8')
+        self.assertEqual(a.getquoted(), "'\xe2\x98\x83'")
+
+
 class AdaptSubclassTest(unittest.TestCase):
     def test_adapt_subtype(self):
         from psycopg2.extensions import adapt
@@ -380,7 +417,6 @@ class AdaptSubclassTest(unittest.TestCase):
         finally:
             del psycopg2.extensions.adapters[A, psycopg2.extensions.ISQLQuote]
 
-
     @testutils.skip_before_python(3)
     def test_adapt_subtype_3(self):
         from psycopg2.extensions import adapt, register_adapter, AsIs
@@ -480,6 +516,7 @@ class ByteaParserTest(unittest.TestCase):
 
         self.assertEqual(rv, tgt)
 
+
 def skip_if_cant_cast(f):
     @wraps(f)
     def skip_if_cant_cast_(self, *args, **kwargs):
@@ -499,4 +536,3 @@ def test_suite():
 
 if __name__ == "__main__":
     unittest.main()
-