}
}
-// Converts a string to a length-prefixed set of DNS labels.
-// @buf must be strlen(name)+2 or longer. name and buf must
-// not overlap. name_len should be the length of name
+/* This is an inefficient representation; only use it via the dnslabel_table_*
+ * functions, so that is can be safely replaced with something smarter later. */
+#define MAX_LABELS 128
+// Structures used to implement name compression
+struct dnslabel_entry { char *v; int pos; };
+struct dnslabel_table {
+ int n_labels; // number of current entries
+ // map from name to position in message
+ struct dnslabel_entry labels[MAX_LABELS];
+};
+
+// Initialize dnslabel_table.
+static void
+dnslabel_table_init(struct dnslabel_table *table)
+{
+ table->n_labels = 0;
+}
+
+// Free all storage held by table, but not the table itself.
+static void
+dnslabel_clear(struct dnslabel_table *table)
+{
+ int i;
+ for (i = 0; i < table->n_labels; ++i)
+ free(table->labels[i].v);
+ table->n_labels = 0;
+}
+
+// return the position of the label in the current message, or -1 if the label
+// hasn't been used yet.
+static int
+dnslabel_table_get_pos(const struct dnslabel_table *table, const char *label)
+{
+ int i;
+ for (i = 0; i < table->n_labels; ++i) {
+ if (!strcmp(label, table->labels[i].v))
+ return table->labels[i].pos;
+ }
+ return -1;
+}
+
+// remember that we've used the label at position pos
+static int
+dnslabel_table_add(struct dnslabel_table *table, const char *label, int pos)
+{
+ char *v;
+ int p;
+ if (table->n_labels == MAX_LABELS)
+ return (-1);
+ v = strdup(label);
+ if (v == NULL)
+ return (-1);
+ p = table->n_labels++;
+ table->labels[p].v = v;
+ table->labels[p].pos = pos;
+
+ return (0);
+}
+
+// Converts a string to a length-prefixed set of DNS labels, starting
+// at buf[j]. name and buf must not overlap. name_len should be the length
+// of name. table is optional, and is used for compression.
//
// Input: abc.def
// Output: <3>abc<3>def<0>
//
-// Returns the length of the data. negative on error
-// -1 label was > 63 bytes
-// -2 name was > 255 bytes
-static int
-dnsname_to_labels(u8 *const buf, const char *name, const int name_len) {
+// Returns the first index after the encoded name, or negative on error.
+// -1 label was > 63 bytes
+// -2 name too long to fit in buffer.
+//
+static off_t
+dnsname_to_labels(u8 *const buf, size_t buf_len, off_t j,
+ const char *name, const int name_len,
+ struct dnslabel_table *table) {
const char *end = name + name_len;
- int j = 0; // current offset into buf
+ int ref = 0;
+ u16 _t;
+
+#define APPEND16(x) do { \
+ if (j + 2 > (off_t)buf_len) \
+ goto overflow; \
+ _t = htons(x); \
+ memcpy(buf + j, &_t, 2); \
+ j += 2; \
+ } while (0)
+#define APPEND32(x) do { \
+ if (j + 4 > (off_t)buf_len) \
+ goto overflow; \
+ _t32 = htonl(x); \
+ memcpy(buf + j, &_t32, 4); \
+ j += 4; \
+ } while (0)
if (name_len > 255) return -2;
for (;;) {
const char *const start = name;
+ if (table && (ref = dnslabel_table_get_pos(table, name)) >= 0) {
+ APPEND16(ref | 0xc000);
+ return j;
+ }
name = strchr(name, '.');
if (!name) {
const unsigned int label_len = end - start;
if (label_len > 63) return -1;
+ if ((size_t)(j+label_len+1) > buf_len) return -2;
+ if (table) dnslabel_table_add(table, start, j);
buf[j++] = label_len;
memcpy(buf + j, start, end - start);
// append length of the label.
const unsigned int label_len = name - start;
if (label_len > 63) return -1;
+ if ((size_t)(j+label_len+1) > buf_len) return -2;
+ if (table) dnslabel_table_add(table, start, j);
buf[j++] = label_len;
memcpy(buf + j, start, name - start);
// in which case the zero is already there
if (!j || buf[j-1]) buf[j++] = 0;
return j;
+ overflow:
+ return (-2);
}
// Finds the length of a dns request for a DNS name of the given
evdns_request_data_build(const char *const name, const int name_len,
const u16 trans_id, const u16 type, const u16 class,
u8 *const buf, size_t buf_len) {
- int j = 0; // current offset into buf
+ off_t j = 0; // current offset into buf
u16 _t; // used by the macros
- u8 *labels;
- int labels_len;
-
-#define APPEND16(x) do { \
- if (j + 2 > buf_len) \
- return (-1); \
- _t = htons(x); \
- memcpy(buf + j, &_t, 2); j += 2; \
-} while(0)
-
+
APPEND16(trans_id);
APPEND16(0x0100); // standard query, recusion needed
APPEND16(1); // one question
APPEND16(0); // no authority
APPEND16(0); // no additional
- labels = (u8 *) malloc(name_len + 2);
- if (labels == NULL)
- return (-1);
- labels_len = dnsname_to_labels(labels, name, name_len);
- if (labels_len < 0) {
- free(labels);
- return (labels_len);
+ j = dnsname_to_labels(buf, buf_len, j, name, name_len, NULL);
+ if (j < 0) {
+ return (int)j;
}
- if ((size_t)(j + labels_len) > buf_len) {
- free(labels);
- return (-1);
- }
- memcpy(buf + j, labels, labels_len);
- j += labels_len;
- free(labels);
APPEND16(type);
APPEND16(class);
-#undef APPEND16
- return (j);
+ return (int)j;
+ overflow:
+ return (-1);
}
+#undef APPEND16
+#undef APPEND32
+
// this is a libevent callback function which is called when a request
// has timed out.
static void
projects / libevent / commitdiff