[go] net: document LookupSRV cname return value

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net: document LookupSRV cname return value

Document that the first return value of LookupSRV is the canonical
name of the DNS target that was looked up, which may differ from
the input name due to CNAME records.

Fixes #49982
Change-Id: I574e0f5cdc381d3d9b11b5bd7a5acbea2c9e185d
GitHub-Last-Rev: a8dd7287f807513f6d03e4f5c0b5ac1ccb1b6053
GitHub-Pull-Request: golang/go#77475

Change diff

diff --git a/src/net/lookup.go b/src/net/lookup.go
index d4be8ea..5ab4153 100644
--- a/src/net/lookup.go
+++ b/src/net/lookup.go
@@ -487,6 +487,9 @@
 // publishing SRV records under non-standard names, if both service
 // and proto are empty strings, LookupSRV looks up name directly.
 //
+// The returned cname is the canonical name of the DNS target that was
+// looked up, which may differ from the input name due to CNAME records.
+//
 // The returned service names are validated to be properly
 // formatted presentation-format domain names. If the response contains
 // invalid names, those records are filtered out and an error
@@ -505,6 +508,9 @@
 // publishing SRV records under non-standard names, if both service
 // and proto are empty strings, LookupSRV looks up name directly.
 //
+// The returned cname is the canonical name of the DNS target that was
+// looked up, which may differ from the input name due to CNAME records.
+//
 // The returned service names are validated to be properly
 // formatted presentation-format domain names. If the response contains
 // invalid names, those records are filtered out and an error

Change information

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  • M src/net/lookup.go
Change size: XS
Delta: 1 file changed, 6 insertions(+), 0 deletions(-)
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File src/net/lookup.go
Line 491, Patchset 1 (Latest):// looked up, which may differ from the input name due to CNAME records.
Damien Neil . unresolved

I don't understand "...which may differ from the input name due to CNAME records". CNAME records don't seem to have anything to do with this name; so far as I can tell the first return parameter is entirely determined from the service, proto, and name parameters.

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    Yongqi Jia (Gerrit)

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    Commit message

    net: document LookupSRV cname return value

    Document that the first return value (cname) of LookupSRV and
    Resolver.LookupSRV is the owner name from the first SRV answer
    record, which is typically the constructed DNS name
    (_service._proto.name) but may differ if CNAME records redirect
    the query to another name.

    Fixes #49982
    Change-Id: Ibfa2a5f07bf5991eac77f882a751447f5dd6bc4e
    Change diff
    diff --git a/src/net/lookup.go b/src/net/lookup.go
    index d4be8ea..06e14df 100644
    --- a/src/net/lookup.go
    +++ b/src/net/lookup.go
    @@ -487,6 +487,11 @@

     // publishing SRV records under non-standard names, if both service
     // and proto are empty strings, LookupSRV looks up name directly.
     //
    +// The returned cname is the owner name from the first SRV answer
    +// record, which is typically the constructed DNS name
    +// (_service._proto.name) but may differ if CNAME records redirect
    +// the query to another name.

    +//
     // The returned service names are validated to be properly
     // formatted presentation-format domain names. If the response contains
     // invalid names, those records are filtered out and an error
    @@ -505,6 +510,11 @@

     // publishing SRV records under non-standard names, if both service
     // and proto are empty strings, LookupSRV looks up name directly.
     //
    +// The returned cname is the owner name from the first SRV answer
    +// record, which is typically the constructed DNS name
    +// (_service._proto.name) but may differ if CNAME records redirect
    +// the query to another name.

    +//
     // The returned service names are validated to be properly
     // formatted presentation-format domain names. If the response contains
     // invalid names, those records are filtered out and an error
    Change information
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    • M src/net/lookup.go
    Change size: S
    Delta: 1 file changed, 10 insertions(+), 0 deletions(-)
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      Yongqi Jia (Gerrit)
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      Yongqi Jia (Gerrit)
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      File src/net/lookup.go
      Line 491, Patchset 1 (Latest):// looked up, which may differ from the input name due to CNAME records.
      Damien Neil . resolved
      I don't understand "...which may differ from the input name due to CNAME records". CNAME records don't seem to have anything to do with this name; so far as I can tell the first return parameter is entirely determined from the service, proto, and name parameters.
      Yongqi Jia
      Done.
      You're right — the original wording was misleading. The cname return value isn't a CNAME record; it's the owner name from the first SRV answer record in the DNS response (see goLookupSRV in lookup.go around line 749, where cname = h.Name).
      I've updated the documentation in PS2 to:
      ```

      // The returned cname is the owner name from the first SRV answer
      // record, which is typically the constructed DNS name
      // (_service._proto.name) but may differ if CNAME records redirect
      // the query to another name.
      ```
      This makes clear that: (1) it comes from the DNS response header, not from CNAME records themselves; (2) it's typically identical to the constructed query name; (3) CNAME redirection is mentioned only as one possible reason for divergence, not as the definition.
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            Commit message:
            net: document LookupSRV cname return value

            Document that the first return value of LookupSRV is the canonical
            name of the DNS target that was looked up, which may differ from

            the input name due to CNAME records.

            Fixes #49982
            Change-Id: I574e0f5cdc381d3d9b11b5bd7a5acbea2c9e185d
            GitHub-Last-Rev: 9c756d48d55587f373c7cf273aa64c960a7a94a8
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