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r9254@Kushana: nickm | 2006-10-17 17:23:36 -0400

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Implement dns label compression.  Clients do not need this much; dns servers definitely do.


svn:r9073
This commit is contained in:
Nick Mathewson 2006-12-12 02:50:17 +00:00
parent 0efcd826b2
commit e190acf780
1 changed files with 87 additions and 47 deletions
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134
src/or/eventdns.c
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@ -395,7 +395,7 @@ struct server_port {
struct server_request_section {
int n_items;
int j;
char buf[512];
u8 buf[512];
};
struct server_request {
@ -1261,6 +1261,59 @@ nameserver_ready_callback(int fd, short events, void *arg) {
}
}
/* This is an inefficient representation; only use it via the dnslabel_table_*
* functions. */
#define MAX_LABELS 128
struct dnslabel_entry { char *v; int pos; };
struct dnslabel_table {
int n_labels;
struct dnslabel_entry labels[MAX_LABELS];
};
static void
dnslabel_table_init(struct dnslabel_table *table)
{
table->n_labels = 0;
}
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;
}
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;
}
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.
// @buf must be strlen(name)+2 or longer. name and buf must
// not overlap. name_len should be the length of name
@ -1270,20 +1323,39 @@ nameserver_ready_callback(int fd, short events, void *arg) {
//
// 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) {
// -2 name too long to fit in buffer.
//
// XXXX Changed interface.
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) \
return (-2); \
_t = htons(x); \
memcpy(buf + j, &_t, 2); \
j += 2; \
} 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 (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);
@ -1293,6 +1365,8 @@ dnsname_to_labels(u8 *const buf, const char *name, const int name_len) {
// append length of the label.
const unsigned int label_len = name - start;
if (label_len > 63) return -1;
if (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);
@ -1329,18 +1403,9 @@ evdns_request_data_build(const char *const name, const int name_len, const u16 t
u8 *const buf, size_t buf_len) {
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 > (off_t)buf_len) \
return (-1); \
_t = htons(x); \
memcpy(buf + j, &_t, 2); \
j += 2; \
} while (0)
#define APPEND32(x) do { \
if (j + 4 > buf_len) \
if (j + 4 > (off_t)buf_len) \
return (-1); \
_t32 = htonl(x); \
memcpy(buf + j, &_t32, 4); \
@ -1355,21 +1420,10 @@ evdns_request_data_build(const char *const name, const int name_len, const u16 t
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 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);
@ -1384,12 +1438,10 @@ evdns_request_add_reply(struct evdns_request *_req, int section, const char *nam
struct server_request *req = TO_SERVER_REQUEST(_req);
struct server_request_section **secp;
int j;
char *buf;
u8 *buf;
int buf_len;
u16 _t; // used by the macros
u32 _t32; // used by the macros
u8 *labels;
int labels_len, name_len;
switch (section) {
case EVDNS_ANSWER_SECTION:
@ -1414,23 +1466,11 @@ evdns_request_add_reply(struct evdns_request *_req, int section, const char *nam
j = (*secp)->j;
// format is <label:name><u16:type><u16:class><u32:ttl><u16:len><data...>
name_len = strlen(name);
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, strlen(name), NULL);
if (j < 0) {
return 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);