XA transaction ids can be decoded from PostgreSQL transaction ids.

psycopg/xid_type.c

@@ -278,16 +278,21 @@ PyTypeObject XidType = {
  */
 XidObject *xid_ensure(PyObject *oxid)
 {
-    /* TODO: string roundtrip. */
+    XidObject *rv = NULL;
+
     if (PyObject_TypeCheck(oxid, &XidType)) {
         Py_INCREF(oxid);
-        return (XidObject *)oxid;
+        rv = (XidObject *)oxid;
+    }
+    else if (PyString_Check(oxid)) {
+        rv = xid_from_string(oxid);
     }
     else {
         PyErr_SetString(PyExc_TypeError,
             "not a valid transaction id");
-        return NULL;
     }
+
+    return rv;
 }
 
 
@@ -323,6 +328,26 @@ exit:
     return rv;
 }
 
+/* decode a base64-encoded string */
+
+static PyObject *
+_xid_decode64(PyObject *s)
+{
+    PyObject *base64 = NULL;
+    PyObject *decode = NULL;
+    PyObject *rv = NULL;
+
+    if (!(base64 = PyImport_ImportModule("base64"))) { goto exit; }
+    if (!(decode = PyObject_GetAttrString(base64, "b64decode"))) { goto exit; }
+    if (!(rv = PyObject_CallFunctionObjArgs(decode, s, NULL))) { goto exit; }
+
+exit:
+    Py_XDECREF(decode);
+    Py_XDECREF(base64);
+
+    return rv;
+}
+
 /* Return the PostgreSQL transaction_id for this XA xid.
  *
  * PostgreSQL wants just a string, while the DBAPI supports the XA standard
@@ -381,14 +406,103 @@ exit:
     return buf;
 }
 
-/* Build a Xid from a string representation.
+
+/* Return the regex object to parse a Xid string.
  *
- * If the xid is in the format generated by Psycopg, unpack the tuple into
- * the struct members. Otherwise generate an "unparsed" xid.
- */
-XidObject *
-xid_from_string(PyObject *str) {
-    /* TODO: currently always generates an unparsed xid. */
+ * Return a borrowed reference. */
+
+static PyObject *
+_xid_get_parse_regex(void) {
+    static PyObject *rv;
+
+    if (!rv) {
+        PyObject *re_mod = NULL;
+        PyObject *comp = NULL;
+        PyObject *regex = NULL;
+
+        Dprintf("compiling regexp to parse transaction id");
+
+        if (!(re_mod = PyImport_ImportModule("re"))) { goto exit; }
+        if (!(comp = PyObject_GetAttrString(re_mod, "compile"))) { goto exit; }
+        if (!(regex = PyObject_CallFunction(comp, "s",
+                "^(\\d+)_([^_]*)_([^_]*)$"))) {
+            goto exit;
+        }
+
+        /* Good, compiled. */
+        rv = regex;
+        regex = NULL;
+
+exit:
+        Py_XDECREF(regex);
+        Py_XDECREF(comp);
+        Py_XDECREF(re_mod);
+    }
+
+    return rv;
+}
+
+/* Try to parse a Xid string representation in a Xid object.
+ *
+ *
+ * Return NULL + exception if parsing failed. Else a new Xid object. */
+
+static XidObject *
+_xid_parse_string(PyObject *str) {
+    PyObject *regex;
+    PyObject *m = NULL;
+    PyObject *group = NULL;
+    PyObject *item = NULL;
+    PyObject *format_id = NULL;
+    PyObject *egtrid = NULL;
+    PyObject *ebqual = NULL;
+    PyObject *gtrid = NULL;
+    PyObject *bqual = NULL;
+    XidObject *rv = NULL;
+
+    /* check if the string is a possible XA triple with a regexp */
+    if (!(regex = _xid_get_parse_regex())) { goto exit; }
+    if (!(m = PyObject_CallMethod(regex, "match", "O", str))) { goto exit; }
+    if (m == Py_None) {
+        PyErr_SetString(PyExc_ValueError, "bad xid format");
+        goto exit;
+    }
+
+    /* Extract the components from the regexp */
+    if (!(group = PyObject_GetAttrString(m, "group"))) { goto exit; }
+    if (!(item = PyObject_CallFunction(group, "i", 1))) { goto exit; }
+    if (!(format_id = PyObject_CallFunctionObjArgs(
+            (PyObject *)&PyInt_Type, item, NULL))) {
+        goto exit;
+    }
+    if (!(egtrid = PyObject_CallFunction(group, "i", 2))) { goto exit; }
+    if (!(gtrid = _xid_decode64(egtrid))) { goto exit; }
+
+    if (!(ebqual = PyObject_CallFunction(group, "i", 3))) { goto exit; }
+    if (!(bqual = _xid_decode64(ebqual))) { goto exit; }
+
+    /* Try to build the xid with the parsed material */
+    rv = (XidObject *)PyObject_CallFunctionObjArgs((PyObject *)&XidType,
+        format_id, gtrid, bqual, NULL);
+
+exit:
+    Py_XDECREF(bqual);
+    Py_XDECREF(ebqual);
+    Py_XDECREF(gtrid);
+    Py_XDECREF(egtrid);
+    Py_XDECREF(format_id);
+    Py_XDECREF(item);
+    Py_XDECREF(group);
+    Py_XDECREF(m);
+
+    return rv;
+}
+
+/* Return a new Xid object representing a transaction ID not conform to
+ * the XA specifications. */
+
+static XidObject *
+_xid_unparsed_from_string(PyObject *str) {
     XidObject *xid = NULL;
     XidObject *rv = NULL;
     PyObject *format_id = NULL;
@@ -430,6 +544,28 @@ exit:
     return rv;
 }
 
+/* Build a Xid from a string representation.
+ *
+ * If the xid is in the format generated by Psycopg, unpack the tuple into
+ * the struct members. Otherwise generate an "unparsed" xid.
+ */
+XidObject *
+xid_from_string(PyObject *str) {
+    XidObject *rv;
+
+    /* Try to parse an XA triple from the string. This may fail for several
+     * reasons, such as the rules stated in Xid.__init__. */
+    rv = _xid_parse_string(str);
+    if (!rv) {
+        /* If parsing failed, treat the string as an unparsed id */
+        PyErr_Clear();
+        rv = _xid_unparsed_from_string(str);
+    }
+
+    return rv;
+}
+
+
 /* conn_tpc_recover -- return a list of pending TPC Xid */
 
 PyObject *

tests/test_connection.py

@@ -308,6 +308,51 @@ class ConnectionTwoPhaseTests(unittest.TestCase):
             (tests.dbname,))
         self.assertEqual('42_Z3RyaWQ=_YnF1YWw=', cur.fetchone()[0])
 
+    def test_xid_roundtrip(self):
+        for fid, gtrid, bqual in [
+            (0, "", ""),
+            (42, "gtrid", "bqual"),
+            (0x7fffffff, "x" * 64, "y" * 64),
+        ]:
+            cnn = self.connect()
+            xid = cnn.xid(fid, gtrid, bqual)
+            cnn.tpc_begin(xid)
+            cnn.tpc_prepare()
+            cnn.close()
+
+            cnn = self.connect()
+            xids = [ xid for xid in cnn.tpc_recover()
+                if xid.database == tests.dbname ]
+            self.assertEqual(1, len(xids))
+            xid = xids[0]
+            self.assertEqual(xid.format_id, fid)
+            self.assertEqual(xid.gtrid, gtrid)
+            self.assertEqual(xid.bqual, bqual)
+
+            cnn.tpc_rollback(xid)
+
+    def test_unparsed_roundtrip(self):
+        for tid in [
+            '',
+            'hello, world!',
+            'x' * 199,  # PostgreSQL's limit in transaction id length
+        ]:
+            cnn = self.connect()
+            cnn.tpc_begin(tid)
+            cnn.tpc_prepare()
+            cnn.close()
+
+            cnn = self.connect()
+            xids = [ xid for xid in cnn.tpc_recover()
+                if xid.database == tests.dbname ]
+            self.assertEqual(1, len(xids))
+            xid = xids[0]
+            self.assertEqual(xid.format_id, -2)
+            self.assertEqual(xid.gtrid, tid)
+            self.assertEqual(xid.bqual, None)
+
+            cnn.tpc_rollback(xid)
+
 
 def test_suite():
     return unittest.TestLoader().loadTestsFromName(__name__)