DRIVERS-2922: Allow valid SRV hostnames with fewer than 3 parts

source/initial-dns-seedlist-discovery/initial-dns-seedlist-discovery.md

@@ -31,7 +31,7 @@ step before it considers the connection string and SDAM specifications. In this
 host names is replaced with a single host name. The format is:
 
 ```
-mongodb+srv://{hostname}.{domainname}/{options}
+mongodb+srv://{subdomain}.{domainname}/{options}
 ```
 
 `{options}` refers to the optional elements from the [Connection String](../connection-string/connection-string-spec.md)
@@ -81,20 +81,26 @@ parse error and MUST NOT do DNS resolution or contact hosts.
 It is an error to specify more than one host name in a connection string with the `mongodb+srv` protocol, and the driver
 MUST raise a parse error and MUST NOT do DNS resolution or contact hosts.
 
-A driver MUST verify that in addition to the `{hostname}`, the `{domainname}` consists of at least two parts: the domain
-name, and a TLD. Drivers MUST raise an error and MUST NOT contact the DNS server to obtain SRV (or TXT records) if the
-full URI does not consist of at least three parts.
+Prior to DNS resolution. `{hostname}` format can follow any of the following formats:
+
+- `{subdomain}`.`{second-level domain}`.`{top-level domain}` (ex: `{blogs.mongodb.com}`)
+- `{second-level domain}`.`{top-level domain}` (ex: `{mongodb.localhost}`)
+- `{top-level domain}` (ex: `{localhost}`)
+
+For the purposes of this document, `{domainname}` refers to all parts of the hostname, excluding the `{subdomain}`.
+
+Node:
 
 If `mongodb+srv` is used, a driver MUST implicitly also enable TLS. Clients can turn this off by passing `tls=false` in
 either the Connection String, or options passed in as parameters in code to the MongoClient constructor (or equivalent
 API for each driver), but not through a TXT record (discussed in a later section).
 
 #### Querying DNS
 
-In this preprocessing step, the driver will query the DNS server for SRV records on `{hostname}.{domainname}`, prefixed
-with the SRV service name and protocol. The SRV service name is provided in the `srvServiceName` URI option and defaults
-to `mongodb`. The protocol is always `tcp`. After prefixing, the URI should look like:
-`_{srvServiceName}._tcp.{hostname}.{domainname}`. This DNS query is expected to respond with one or more SRV records.
+In this preprocessing step, the driver will query the DNS server for SRV records on the hostname, prefixed with the SRV
+service name and protocol. The SRV service name is provided in the `srvServiceName` URI option and defaults to
+`mongodb`. The protocol is always `tcp`. After prefixing, the URI should look like: `_{srvServiceName}._tcp.{hostname}`.
+This DNS query is expected to respond with one or more SRV records.
 
 The priority and weight fields in returned SRV records MUST be ignored.
 
@@ -118,12 +124,12 @@ randomization.
 
 ### Default Connection String Options
 
-As a second preprocessing step, a Client MUST also query the DNS server for TXT records on `{hostname}.{domainname}`. If
-available, a TXT record provides default connection string options. The maximum length of a TXT record string is 255
-characters, but there can be multiple strings per TXT record. A Client MUST support multiple TXT record strings and
-concatenate them as if they were one single string in the order they are defined in each TXT record. The order of
-multiple character strings in each TXT record is guaranteed. A Client MUST NOT allow multiple TXT records for the same
-host name and MUST raise an error when multiple TXT records are encountered.
+As a second preprocessing step, a Client MUST also query the DNS server for TXT records on `{hostname}`. If available, a
+TXT record provides default connection string options. The maximum length of a TXT record string is 255 characters, but
+there can be multiple strings per TXT record. A Client MUST support multiple TXT record strings and concatenate them as
+if they were one single string in the order they are defined in each TXT record. The order of multiple character strings
+in each TXT record is guaranteed. A Client MUST NOT allow multiple TXT records for the same host name and MUST raise an
+error when multiple TXT records are encountered.
 
 Information returned within a TXT record is a simple URI string, just like the `{options}` in a connection string.
 
@@ -148,10 +154,10 @@ the Connection String spec.
 
 ### CNAME not supported
 
-The use of DNS CNAME records is not supported. Clients MUST NOT check for a CNAME record on `{hostname}.{domainname}`. A
-system's DNS resolver could transparently handle CNAME, but because of how clients validate records returned from SRV
-queries, use of CNAME could break validation. Seedlist discovery therefore does not recommend or support the use of
-CNAME records in concert with SRV or TXT records.
+The use of DNS CNAME records is not supported. Clients MUST NOT check for a CNAME record on `{hostname}`. A system's DNS
+resolver could transparently handle CNAME, but because of how clients validate records returned from SRV queries, use of
+CNAME could break validation. Seedlist discovery therefore does not recommend or support the use of CNAME records in
+concert with SRV or TXT records.
 
 ## Example
 
@@ -200,6 +206,12 @@ mongodb://mongodb1.mongodb.com:27317,mongodb2.mongodb.com:27107/?ssl=true&replic
 
 ## Test Plan
 
+### Prose Tests
+
+See README.md in the accompanying [test directory](tests).
+
+### Spec Tests
+
 See README.md in the accompanying [test directory](tests).
 
 Additionally, see the `mongodb+srv` test `invalid-uris.yml` in the
@@ -254,6 +266,9 @@ In the future we could consider using the priority and weight fields of the SRV
 
 ## ChangeLog
 
+- 2024-08-20: Removed requirement for URI to have three '.' separated parts. Replace usage of 'TLD' with 'top-level
+  domain'. `{hostname}` now refers to the entire hostname, not just the `{subdomain}`.
+
 - 2024-03-06: Migrated from reStructuredText to Markdown.
 
 - 2022-10-05: Revise spec front matter and reformat changelog.

source/initial-dns-seedlist-discovery/tests/README.md

@@ -3,6 +3,13 @@
 This directory contains platform-independent tests that drivers can use to prove their conformance to the Initial DNS
 Seedlist Discovery spec.
 
+### Prose Tests
+
+When given a valid SRV with
+
+1. Only one domain level (ex: `{localhost}`)
+2. Only two domain levels (ex: `{mongo.local}`) Parse the connection string without throwing a parse related error.
+
 ## Test Setup
 
 The tests in the `replica-set` directory MUST be executed against a three-node replica set on localhost ports 27017,