qobject: Make QString immutable

The functions to modify a QString's string are all unused now.  Drop
them, and make the string immutable.  Saves 16 bytes per QString on my
system.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201211171152.146877-21-armbru@redhat.com>

include/qapi/qmp/qstring.h

@@ -17,19 +17,13 @@
 
 struct QString {
     struct QObjectBase_ base;
-    char *string;
-    size_t length;
-    size_t capacity;
+    const char *string;
 };
 
 QString *qstring_new(void);
 QString *qstring_from_str(const char *str);
 QString *qstring_from_substr(const char *str, size_t start, size_t end);
 QString *qstring_from_gstring(GString *gstr);
-size_t qstring_get_length(const QString *qstring);
 const char *qstring_get_str(const QString *qstring);
-void qstring_append_int(QString *qstring, int64_t value);
-void qstring_append(QString *qstring, const char *str);
-void qstring_append_chr(QString *qstring, int c);
 
 #endif /* QSTRING_H */

qobject/qstring.c

@@ -24,14 +24,6 @@ QString *qstring_new(void)
     return qstring_from_str("");
 }
 
-/**
- * qstring_get_length(): Get the length of a QString
- */
-size_t qstring_get_length(const QString *qstring)
-{
-    return qstring->length;
-}
-
 /**
  * qstring_from_substr(): Create a new QString from a C string substring
  *
@@ -42,18 +34,9 @@ QString *qstring_from_substr(const char *str, size_t start, size_t end)
     QString *qstring;
 
     assert(start <= end);
-
     qstring = g_malloc(sizeof(*qstring));
     qobject_init(QOBJECT(qstring), QTYPE_QSTRING);
-
-    qstring->length = end - start;
-    qstring->capacity = qstring->length;
-
-    assert(qstring->capacity < SIZE_MAX);
-    qstring->string = g_malloc(qstring->capacity + 1);
-    memcpy(qstring->string, str + start, qstring->length);
-    qstring->string[qstring->length] = 0;
-
+    qstring->string = g_strndup(str + start, end - start);
     return qstring;
 }
 
@@ -79,55 +62,11 @@ QString *qstring_from_gstring(GString *gstr)
 
     qstring = g_malloc(sizeof(*qstring));
     qobject_init(QOBJECT(qstring), QTYPE_QSTRING);
-    qstring->length = gstr->len;
-    qstring->capacity = gstr->allocated_len;
     qstring->string = g_string_free(gstr, false);
     return qstring;
 }
 
 
-static void capacity_increase(QString *qstring, size_t len)
-{
-    if (qstring->capacity < (qstring->length + len)) {
-        assert(len <= SIZE_MAX - qstring->capacity);
-        qstring->capacity += len;
-        assert(qstring->capacity <= SIZE_MAX / 2);
-        qstring->capacity *= 2; /* use exponential growth */
-
-        qstring->string = g_realloc(qstring->string, qstring->capacity + 1);
-    }
-}
-
-/* qstring_append(): Append a C string to a QString
- */
-void qstring_append(QString *qstring, const char *str)
-{
-    size_t len = strlen(str);
-
-    capacity_increase(qstring, len);
-    memcpy(qstring->string + qstring->length, str, len);
-    qstring->length += len;
-    qstring->string[qstring->length] = 0;
-}
-
-void qstring_append_int(QString *qstring, int64_t value)
-{
-    char num[32];
-
-    snprintf(num, sizeof(num), "%" PRId64, value);
-    qstring_append(qstring, num);
-}
-
-/**
- * qstring_append_chr(): Append a C char to a QString
- */
-void qstring_append_chr(QString *qstring, int c)
-{
-    capacity_increase(qstring, 1);
-    qstring->string[qstring->length++] = c;
-    qstring->string[qstring->length] = 0;
-}
-
 /**
  * qstring_get_str(): Return a pointer to the stored string
  *
@@ -158,6 +97,6 @@ void qstring_destroy_obj(QObject *obj)
 
     assert(obj != NULL);
     qs = qobject_to(QString, obj);
-    g_free(qs->string);
+    g_free((char *)qs->string);
     g_free(qs);
 }

tests/check-qobject.c

@@ -155,8 +155,7 @@ static void qobject_is_equal_string_test(void)
     str_case = qstring_from_str("Foo");
 
     /* Should yield "foo" */
-    str_built = qstring_from_substr("form", 0, 2);
-    qstring_append_chr(str_built, 'o');
+    str_built = qstring_from_substr("buffoon", 3, 6);
 
     check_unequal(str_base, str_whitespace_0, str_whitespace_1,
                   str_whitespace_2, str_whitespace_3, str_case);

tests/check-qstring.c

@@ -47,21 +47,6 @@ static void qstring_get_str_test(void)
     qobject_unref(qstring);
 }
 
-static void qstring_append_chr_test(void)
-{
-    int i;
-    QString *qstring;
-    const char *str = "qstring append char unit-test";
-
-    qstring = qstring_new();
-
-    for (i = 0; str[i]; i++)
-        qstring_append_chr(qstring, str[i]);
-
-    g_assert(strcmp(str, qstring_get_str(qstring)) == 0);
-    qobject_unref(qstring);
-}
-
 static void qstring_from_substr_test(void)
 {
     QString *qs;
@@ -90,7 +75,6 @@ int main(int argc, char **argv)
 
     g_test_add_func("/public/from_str", qstring_from_str_test);
     g_test_add_func("/public/get_str", qstring_get_str_test);
-    g_test_add_func("/public/append_chr", qstring_append_chr_test);
     g_test_add_func("/public/from_substr", qstring_from_substr_test);
     g_test_add_func("/public/to_qstring", qobject_to_qstring_test);