[python][patch] Add options length parameter to value.string(...)

[Phil Muldoon <pmuldoon@redhat.com>]

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This patch adds an optional length parameter to the value.string() 
method.  This allows partial string fetches, and string fetches that 
ignore embedded null characters in the C/C++ string case.  If the length 
parameter is omitted, the method will maintain the existing behaviour of 
fetching a string until a terminating null in the C/C++ case.

Regards

Phil


ChangeLog

2009-04-06  Phil Muldoon  <pmuldoon@redhat.com>

    * python/python-value.c (valpy_string): Parse length keyword. Use
    length keyword in LA_GET_STRING.
    * c-lang.c (c_get_string): If the length parameter is specified,
    use that.

testsuite/ChangeLog

2009-04-06  Phil Muldoon  <pmuldoon@redhat.com>

    * gdb.python/python-value.exp (test_value_in_inferior): Add
    variable length string fetch tests.
    * gdb.python/python-value.c (main): Add strings for string fetch tests.




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diff --git a/gdb/c-lang.c b/gdb/c-lang.c
index 8b5410f..344c836 100644
--- a/gdb/c-lang.c
+++ b/gdb/c-lang.c
@@ -249,12 +249,17 @@ c_get_string (struct value *value, gdb_byte **buffer, int *length,
       int i;
       const gdb_byte *contents = value_contents (value);
 
-      /* Look for a null character.  */
-      for (i = 0; i < fetchlimit; i++)
-	if (extract_unsigned_integer (contents + i * width, width) == 0)
-	  break;
-
-      /* I is now either the number of non-null characters, or FETCHLIMIT.  */
+      /* If a length is specified, use that.  */
+      if ( *length >= 0 )
+	i = *length;
+      else
+	/* Otherwise, look for a null character.  */
+	for (i = 0; i < fetchlimit; i++)
+	  if (extract_unsigned_integer (contents + i * width, width) == 0)
+	    break;
+      
+      /* I is now either a user-defined length, the number of non-null
+	 characters, or FETCHLIMIT.  */      
       *length = i * width;
       *buffer = xmalloc (*length);
       memcpy (*buffer, contents, *length);
@@ -262,7 +267,10 @@ c_get_string (struct value *value, gdb_byte **buffer, int *length,
     }
   else
     {
-      err = read_string (value_as_address (value), -1, width, fetchlimit,
+      /* Copy length to orig_len, as read_string will write the number
+	 of characters 'read' to length.  */
+      int orig_len = *length;
+      err = read_string (value_as_address (value), orig_len, width, fetchlimit,
 			 buffer, length);
       if (err)
 	{
diff --git a/gdb/python/python-value.c b/gdb/python/python-value.c
index b55463c..a308a7a 100644
--- a/gdb/python/python-value.c
+++ b/gdb/python/python-value.c
@@ -179,7 +179,7 @@ valpy_type (PyObject *self, PyObject *args)
 static PyObject *
 valpy_string (PyObject *self, PyObject *args, PyObject *kw)
 {
-  int length, ret = 0;
+  int length = -1, ret = 0;
   gdb_byte *buffer;
   struct value *value = ((value_object *) self)->value;
   volatile struct gdb_exception except;
@@ -188,10 +188,10 @@ valpy_string (PyObject *self, PyObject *args, PyObject *kw)
   const char *errors = NULL;
   const char *user_encoding = NULL;
   const char *la_encoding = NULL;
-  static char *keywords[] = { "encoding", "errors" };
+  static char *keywords[] = { "encoding", "errors", "length" };
 
-  if (!PyArg_ParseTupleAndKeywords (args, kw, "|ss", keywords,
-				    &user_encoding, &errors))
+  if (!PyArg_ParseTupleAndKeywords (args, kw, "|ssi", keywords,
+				    &user_encoding, &errors, &length))
     return NULL;
 
   TRY_CATCH (except, RETURN_MASK_ALL)
@@ -957,7 +957,7 @@ static PyMethodDef value_object_methods[] = {
   { "dereference", valpy_dereference, METH_NOARGS, "Dereferences the value." },
   { "type", valpy_type, METH_NOARGS, "Return type of the value." },
   { "string", (PyCFunction) valpy_string, METH_VARARGS | METH_KEYWORDS,
-    "string ([encoding] [, errors]) -> string\n\
+    "string ([encoding] [, errors] [, length]) -> string\n\
 Return Unicode string representation of the value." },
   {NULL}  /* Sentinel */
 };
diff --git a/gdb/testsuite/gdb.python/python-value.c b/gdb/testsuite/gdb.python/python-value.c
index 092c520..f3d6284 100644
--- a/gdb/testsuite/gdb.python/python-value.c
+++ b/gdb/testsuite/gdb.python/python-value.c
@@ -44,6 +44,8 @@ main (int argc, char *argv[])
   struct s s;
   union u u;
   PTR x = &s;
+  char st[17] = "divide et impera";
+  char nullst[17] = "divide\0et\0impera";
 
   s.a = 3;
   s.b = 5;
diff --git a/gdb/testsuite/gdb.python/python-value.exp b/gdb/testsuite/gdb.python/python-value.exp
index cbcf91f..9169fc7 100644
--- a/gdb/testsuite/gdb.python/python-value.exp
+++ b/gdb/testsuite/gdb.python/python-value.exp
@@ -234,6 +234,23 @@ proc test_value_in_inferior {} {
 
   # Test address attribute
   gdb_test "python print 'result =', arg0.address" "= 0x\[\[:xdigit:\]\]+" "Test address attribute"
+
+  # Test string fetches,  both partial and whole.
+  gdb_test "print st" "\"divide et impera\""
+  gdb_py_test_silent_cmd "python st = gdb.history (0)" "get value from history" 1
+  gdb_test "python print st.string ()"  "divide et impera"  "Test string with no length"
+  gdb_test "python print st.string (length = -1)" "divide et impera" "Test string (length = -1) is all of the string"
+  gdb_test "python print st.string (length = 6)" "divide"
+  gdb_test "python print st.string (length = 0)" "" "Test string (length = 0) is empty"
+
+  # Fetch a string that has embedded nulls.
+  gdb_test "print nullst" "\"divide\\\\000et\\\\000impera\".*"
+  gdb_py_test_silent_cmd "python nullst = gdb.history (0)" "get value from history" 1
+  gdb_test "python print nullst.string ()" "divide" "Test string to first null"
+  # Python cannot print strings that contain the null (\0) character.
+  # For the purposes of this test, use repr()
+  gdb_py_test_silent_cmd "python nullst = nullst.string (length = 9)" "get string beyond null" 1
+  gdb_test "python print repr(nullst)" "u'divide\\\\x00et'"
 }
 
 proc test_value_after_death {} {