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net: dns-sd: use hostname instead of instance name #89341

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net: dns-sd: use hostname instead of instance name #89341

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83a6904
net: dns-sd: use hostname instead of instance name
toonst Apr 29, 2025
619dbaf
tests: net: dns_sd use host name in target field
toonst May 14, 2025
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13 changes: 7 additions & 6 deletions subsys/net/lib/dns/dns_sd.c
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Original file line number Diff line number Diff line change
Expand Up @@ -575,6 +575,7 @@ int add_srv_record(const struct dns_sd_rec *inst, uint32_t ttl,
size_t label_size;
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The commit message talks about domain name, was that suppose to say host name?

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Yea, the terminology in the RFC is a bit confusing. Updated the commit message to be consistent

uint16_t inst_offs;
uint16_t offset = buf_offset;
const char *hostname = net_hostname_get();
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This function is already pretty testable as a unit. Is there any reason not to add hostname as a function parameter?

This change effectively hard-codes the host name, in that it is not easily manipulated by the test harness that tests add_srv_record() as a unit.


if ((DNS_SD_PTR_MASK & instance_offset) != 0) {
NET_DBG("offset %u too big for message compression",
Expand All @@ -593,9 +594,9 @@ int add_srv_record(const struct dns_sd_rec *inst, uint32_t ttl,
/* pointer to .<Instance>.<Service>.<Protocol>.local. */
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Documentation is now wrong in this line if we replace Instance by Hostname

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Acutally it is still correct, the full service name is still in the resource record.

DNS_POINTER_SIZE + sizeof(*rr)
+ sizeof(*rdata)
/* .<Instance> */
/* .<Hostname> */
+ DNS_LABEL_LEN_SIZE
+ strlen(inst->instance)
+ strlen(hostname)
/* pointer to .local. */
+ DNS_POINTER_SIZE;

Expand All @@ -616,9 +617,9 @@ int add_srv_record(const struct dns_sd_rec *inst, uint32_t ttl,
rr->type = htons(DNS_RR_TYPE_SRV);
rr->class_ = htons(DNS_CLASS_IN | DNS_CLASS_FLUSH);
rr->ttl = htonl(ttl);
/* .<Instance>.local. */
/* .<Hostname>.local. */
rr->rdlength = htons(sizeof(*rdata) + DNS_LABEL_LEN_SIZE
+ strlen(inst->instance) +
+ strlen(hostname) +
DNS_POINTER_SIZE);
offset += sizeof(*rr);

Expand All @@ -630,9 +631,9 @@ int add_srv_record(const struct dns_sd_rec *inst, uint32_t ttl,

*host_offset = offset;

label_size = strlen(inst->instance);
label_size = strlen(hostname);
buf[offset++] = label_size;
memcpy(&buf[offset], inst->instance, label_size);
memcpy(&buf[offset], hostname, label_size);
offset += label_size;

domain_offset |= DNS_SD_PTR_MASK;
Expand Down
123 changes: 80 additions & 43 deletions tests/net/lib/dns_sd/src/main.c
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Expand Up @@ -382,56 +382,90 @@ ZTEST(dns_sd, test_add_txt_record)
ZTEST(dns_sd, test_add_srv_record)
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Typo on test commit msg
s/filles/filled/

{
const uint32_t ttl = DNS_SD_SRV_TTL;
const uint32_t offset = 0;
const uint16_t offset = 0;
const uint16_t instance_offset = 0x28;
const uint16_t domain_offset = 0x17;
uint16_t host_offset = UINT16_MAX;

uint16_t host_offset = -1;
static uint8_t actual_buf[BUFSZ];
static const uint8_t expected_buf[] = {
0xc0, 0x28, 0x00, 0x21, 0x80, 0x01, 0x00, 0x00,
0x00, 0x78, 0x00, 0x12, 0x00, 0x00, 0x00, 0x00,
0x1f, 0x90, 0x09, 0x4e, 0x41, 0x53, 0x58, 0x58,
0x58, 0x58, 0x58, 0x58, 0xc0, 0x17
};
const char *hostname = net_hostname_get();
const size_t host_len = strlen(hostname);

int expected_int = sizeof(expected_buf);
int actual_int = add_srv_record(&nasxxxxxx, ttl,
instance_offset, domain_offset,
actual_buf,
offset, sizeof(actual_buf),
&host_offset);
/* -------- happy path -------- */
int len = add_srv_record(&nasxxxxxx, ttl,
instance_offset, domain_offset,
actual_buf, offset, sizeof(actual_buf),
&host_offset);

zassert_equal(actual_int, expected_int, "");
/* size we expect: ptr + rr + rdata + len-byte + host + ptr */
size_t expected_len =
DNS_POINTER_SIZE + /* C0 nn */
sizeof(struct dns_rr) + /* 10-byte RR header */
sizeof(struct dns_srv_rdata) + /* 6-byte rdata */
DNS_LABEL_LEN_SIZE + host_len + /* 1-byte len + hostname */
DNS_POINTER_SIZE; /* C0 nn */

zassert_equal(host_offset, 18, "");
zassert_equal(len, expected_len, "length mismatch");
zassert_equal(host_offset, 18, "host offset mismatch");

zassert_mem_equal(actual_buf, expected_buf,
MIN(actual_int, expected_int), "");
/* first two bytes must be the compression pointer to the instance */
zassert_equal(actual_buf[0], 0xC0, "");
zassert_equal(actual_buf[1], instance_offset, "");

/* offset too big for message compression (instance) */
/* ---- inspect the RR header directly in the buffer ---- */
struct dns_rr *rr = (struct dns_rr *)&actual_buf[2];

zassert_equal(ntohs(rr->type), DNS_RR_TYPE_SRV, "type");
zassert_equal(ntohs(rr->class_), DNS_CLASS_IN | DNS_CLASS_FLUSH, "class");
zassert_equal(ntohl(rr->ttl), ttl, "ttl");
zassert_equal(ntohs(rr->rdlength),
expected_len - DNS_POINTER_SIZE - sizeof(*rr),
"rdlength");

/* ---- inspect the SRV RDATA ---- */
struct dns_srv_rdata *rdata =
(struct dns_srv_rdata *)&actual_buf[2 + sizeof(*rr)];

zassert_equal(rdata->priority, 0, "priority");
zassert_equal(rdata->weight, 0, "weight");
zassert_equal(rdata->port, *nasxxxxxx.port, "port");

/* ---- hostname label ---- */
int actual_hostname_len = actual_buf[host_offset];

zassert_equal(actual_hostname_len, host_len, "act: %d, exp: %d",
actual_hostname_len, host_len);

zassert_mem_equal(&actual_buf[host_offset+1], hostname, host_len, "");

/* last two bytes must be the compression pointer to '.local.' */
uint16_t dom_ptr;

memcpy(&dom_ptr, &actual_buf[host_offset + 1 + host_len], sizeof(dom_ptr));
zassert_equal(ntohs(dom_ptr), DNS_SD_PTR_MASK | domain_offset,
"domain pointer");

/* -------- negative paths (unchanged) -------- */
zassert_equal(-E2BIG,
add_srv_record(&nasxxxxxx, ttl, DNS_SD_PTR_MASK,
domain_offset,
actual_buf, offset,
sizeof(actual_buf),
&host_offset), "");
add_srv_record(&nasxxxxxx, ttl,
DNS_SD_PTR_MASK, domain_offset,
actual_buf, offset, sizeof(actual_buf),
&host_offset),
"instance offset bounds");

/* offset too big for message compression (domain) */
zassert_equal(-E2BIG, add_srv_record(&nasxxxxxx, ttl,
instance_offset,
DNS_SD_PTR_MASK,
actual_buf, offset,
sizeof(actual_buf),
&host_offset), "");
zassert_equal(-E2BIG,
add_srv_record(&nasxxxxxx, ttl,
instance_offset, DNS_SD_PTR_MASK,
actual_buf, offset, sizeof(actual_buf),
&host_offset),
"domain offset bounds");

/* buffer too small */
zassert_equal(-ENOSPC, add_srv_record(&nasxxxxxx, ttl,
instance_offset,
domain_offset,
actual_buf,
offset, 0,
&host_offset), "");
zassert_equal(-ENOSPC,
add_srv_record(&nasxxxxxx, ttl,
instance_offset, domain_offset,
actual_buf, offset, 0,
&host_offset),
"buffer too small");
}

/** Test for @ref add_a_record */
Expand Down Expand Up @@ -522,6 +556,7 @@ ZTEST(dns_sd, test_dns_sd_handle_ptr_query)
.s_addr = htonl(IP_ADDR(177, 5, 240, 13)),
};
static uint8_t actual_rsp[512];

static uint8_t expected_rsp[] = {
0x00, 0x00, 0x84, 0x00, 0x00, 0x00, 0x00, 0x01,
0x00, 0x00, 0x00, 0x03, 0x05, 0x5f, 0x68, 0x74,
Expand All @@ -533,12 +568,14 @@ ZTEST(dns_sd, test_dns_sd_handle_ptr_query)
0x80, 0x01, 0x00, 0x00, 0x11, 0x94, 0x00, 0x07,
0x06, 0x70, 0x61, 0x74, 0x68, 0x3d, 0x2f, 0xc0,
0x28, 0x00, 0x21, 0x80, 0x01, 0x00, 0x00, 0x00,
0x78, 0x00, 0x12, 0x00, 0x00, 0x00, 0x00, 0x1f,
0x90, 0x09, 0x4e, 0x41, 0x53, 0x58, 0x58, 0x58,
0x58, 0x58, 0x58, 0xc0, 0x17, 0xc0, 0x59, 0x00,
0x01, 0x80, 0x01, 0x00, 0x00, 0x00, 0x78, 0x00,
0x04, 0xb1, 0x05, 0xf0, 0x0d,
0x78, 0x00, 0x0f, 0x00, 0x00, 0x00, 0x00, 0x1f,
0x90, 0x06, 0x7a, 0x65, 0x70, 0x68, 0x79, 0x72,
0xc0, 0x17, 0xc0, 0x59, 0x00, 0x01, 0x80, 0x01,
0x00, 0x00, 0x00, 0x78, 0x00, 0x04, 0xb1, 0x05,
0xf0, 0x0d
};


int expected_int = sizeof(expected_rsp);
int actual_int = dns_sd_handle_ptr_query(&nasxxxxxx,
&addr,
Expand Down