dns-domain: add calls to join/split SRV/DNS-SD service domains
This adds dns_service_join() and dns_service_split() which may be used to concatenate a DNS-SD service name, am SRV service type string, and a domain name into a full resolvable DNS domain name string. If the service name is specified as NULL, only the type and domain are appended, to implement classic, non-DNS-SD SRV lookups. The reverse is dns_service_split() which takes the full name, and split it into the three components again.
This commit is contained in:
Lennart Poettering
+176
-17
@@ -751,6 +751,34 @@ int dns_name_to_wire_format(const char *domain, uint8_t *buffer, size_t len) {
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return out - buffer;
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}
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static bool srv_type_label_is_valid(const char *label, size_t n) {
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size_t k;
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assert(label);
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if (n < 2) /* Label needs to be at least 2 chars long */
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return false;
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if (label[0] != '_') /* First label char needs to be underscore */
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return false;
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/* Second char must be a letter */
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if (!(label[1] >= 'A' && label[1] <= 'Z') &&
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!(label[1] >= 'a' && label[1] <= 'z'))
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return false;
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/* Third and further chars must be alphanumeric or a hyphen */
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for (k = 2; k < n; k++) {
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if (!(label[k] >= 'A' && label[k] <= 'Z') &&
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!(label[k] >= 'a' && label[k] <= 'z') &&
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!(label[k] >= '0' && label[k] <= '9') &&
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label[k] != '-')
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return false;
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}
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return true;
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}
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int dns_srv_type_verify(const char *name) {
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unsigned c = 0;
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int r;
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@@ -760,7 +788,6 @@ int dns_srv_type_verify(const char *name) {
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for (;;) {
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char label[DNS_LABEL_MAX];
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int k;
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/* This more or less implements RFC 6335, Section 5.1 */
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@@ -770,28 +797,18 @@ int dns_srv_type_verify(const char *name) {
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if (r < 0)
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return r;
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if (r == 0)
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return c >= 2; /* At least two labels */
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if (r < 2) /* Label needs to be at least 2 chars long */
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return 0;
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if (label[0] != '_') /* First label char needs to be underscore */
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break;
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if (c >= 2)
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return 0;
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/* Second char must be a letter */
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if (!(label[1] >= 'A' && label[1] <= 'Z') &&
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!(label[1] >= 'a' && label[1] <= 'z'))
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if (!srv_type_label_is_valid(label, r))
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return 0;
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/* Third and further chars must be alphanumeric or a hyphen */
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for (k = 2; k < r; k++) {
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if (!(label[k] >= 'A' && label[k] <= 'Z') &&
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!(label[k] >= 'a' && label[k] <= 'z') &&
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!(label[k] >= '0' && label[k] <= '9') &&
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label[k] != '-')
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return 0;
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}
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c++;
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}
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return c == 2; /* exactly two labels */
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}
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bool dns_service_name_is_valid(const char *name) {
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@@ -816,3 +833,145 @@ bool dns_service_name_is_valid(const char *name) {
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return true;
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}
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int dns_service_join(const char *name, const char *type, const char *domain, char **ret) {
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_cleanup_free_ char *escaped = NULL, *n = NULL;
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int r;
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assert(type);
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assert(domain);
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assert(ret);
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if (!dns_srv_type_verify(type))
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return -EINVAL;
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if (!name)
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return dns_name_concat(type, domain, ret);
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if (!dns_service_name_is_valid(name))
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return -EINVAL;
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r = dns_label_escape(name, strlen(name), &escaped);
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if (r < 0)
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return r;
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r = dns_name_concat(type, domain, &n);
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if (r < 0)
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return r;
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return dns_name_concat(escaped, n, ret);
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}
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static bool dns_service_name_label_is_valid(const char *label, size_t n) {
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char *s;
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assert(label);
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if (memchr(label, 0, n))
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return false;
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s = strndupa(label, n);
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return dns_service_name_is_valid(s);
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}
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int dns_service_split(const char *joined, char **_name, char **_type, char **_domain) {
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_cleanup_free_ char *name = NULL, *type = NULL, *domain = NULL;
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const char *p = joined, *q = NULL, *d = NULL;
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char a[DNS_LABEL_MAX], b[DNS_LABEL_MAX], c[DNS_LABEL_MAX];
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int an, bn, cn, r;
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unsigned x = 0;
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assert(joined);
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/* Get first label from the full name */
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an = dns_label_unescape(&p, a, sizeof(a));
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if (an < 0)
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return an;
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if (an > 0) {
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x++;
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/* If there was a first label, try to get the second one */
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bn = dns_label_unescape(&p, b, sizeof(b));
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if (bn < 0)
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return bn;
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if (bn > 0) {
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x++;
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/* If there was a second label, try to get the third one */
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q = p;
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cn = dns_label_unescape(&p, c, sizeof(c));
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if (cn < 0)
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return cn;
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if (cn > 0)
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x++;
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} else
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cn = 0;
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} else
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an = 0;
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if (x >= 2 && srv_type_label_is_valid(b, bn)) {
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if (x >= 3 && srv_type_label_is_valid(c, cn)) {
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if (dns_service_name_label_is_valid(a, an)) {
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/* OK, got <name> . <type> . <type2> . <domain> */
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name = strndup(a, an);
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if (!name)
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return -ENOMEM;
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type = new(char, bn+1+cn+1);
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if (!type)
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return -ENOMEM;
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strcpy(stpcpy(stpcpy(type, b), "."), c);
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d = p;
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goto finish;
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}
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} else if (srv_type_label_is_valid(a, an)) {
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/* OK, got <type> . <type2> . <domain> */
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name = NULL;
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type = new(char, an+1+bn+1);
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if (!type)
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return -ENOMEM;
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strcpy(stpcpy(stpcpy(type, a), "."), b);
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d = q;
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goto finish;
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}
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}
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name = NULL;
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type = NULL;
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d = joined;
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finish:
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r = dns_name_normalize(d, &domain);
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if (r < 0)
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return r;
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if (_domain) {
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*_domain = domain;
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domain = NULL;
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}
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if (_type) {
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*_type = type;
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type = NULL;
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}
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if (_name) {
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*_name = name;
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name = NULL;
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}
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return 0;
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}
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@@ -73,3 +73,6 @@ int dns_name_to_wire_format(const char *domain, uint8_t *buffer, size_t len);
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int dns_srv_type_verify(const char *name);
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bool dns_service_name_is_valid(const char *name);
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int dns_service_join(const char *name, const char *type, const char *domain, char **ret);
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int dns_service_split(const char *joined, char **name, char **type, char **domain);
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