PostgreSQL Service Name Enhancement - Wildcard support for LDAP/DNS lookup

<div class="WordSection1"><p class="MsoPlainText">Hi,<p class="MsoPlainText"> <p class="MsoPlainText">I am looking to
patchthe LDAP Service Name feature and would like some feedback prior to doing so. In general, while I personally view
thisas a bug fix, it could also easily be considered to simply be an enhancement to current functionality and therefore
thebelow is written as a proposed enhancement.<p class="MsoPlainText"> <p class="MsoPlainText">Note: This will also
potentiallyserve as my first patch submission, so this will be a "smoke test" of my direct interaction with the mailing
listas a Goldman Sachs Employee for proposal/feedback as well as following up with a potential patch/participation in
commitprocesses, etc. As such my replies and related code submissions may be delayed for processes to happen on my end,
withmy associated apologies in advance. I hope to have this process completed for contribution to the 9.5 release.<p
class="MsoPlainText"> <pclass="MsoPlainText">################## Currently:<br /><br /><p class="MsoPlainText">* Service
namesare provided as an available abstraction mechanism for a host:port (and user, dbname, ssl requirements, etc.)
informationfor connection parameters via libpq.<p class="MsoPlainText">* If service names are used, they must each
individuallyhave an entry in pg_service.conf.<p class="MsoPlainText">* In a service name entry, host:port entries,
hostscan either be directly provided or their values may be referenced via an LDAP location that provides equivalent
name/valuepairs for connection information.<p class="MsoPlainText"> <p class="MsoPlainText">The service name feature
facilitatesthe use of dynamic/managed host entries or allows for active connection configuration management with the
goalin either case of separating such overhead from application or other process configuration.<p
class="MsoPlainText"> <pclass="MsoPlainText">Therefore:<p class="MsoPlainText">* Dynamic DNS entries require a fixed
portor active management of the file (DNS resolution can happen elsewhere)<p class="MsoPlainText">* Non-Dynamic DNS
entriesrequire active management of pg_service.conf, but may still be desirable for configuration management reasons -
versioncontrol?<p class="MsoPlainText">* LDAP entries are largely static, but do require active management of
pg_service.confif new data servers are to be added (or old ones decommissioned)<p class="MsoPlainText"> <p
class="MsoPlainText">Inall cases described above, a newly provisioned data server requires a new service name entry,
whichrequires the file to be actively managed. This mitigates the value of using LDAP or Dynamic DNS entries (with
fixedports in the DNS case) since an active distribution mechanism must still be in place, especially for deployments
ofmany servers and perhaps this useful mechanism is used less often as a result.<p class="MsoPlainText"> <p
class="MsoPlainText">##################Proposal:<p class="MsoPlainText"> <p class="MsoPlainText">* Have a wildcard
entrythat allows string substitution of the service name into either the host field or an LDAP record.<p
class="MsoPlainText"> <pclass="MsoPlainText">I do not want to over complicate the existing configuration file or
parsinglogic as it is pretty lightweight currently. As such, I am looking for feedback related to if it would be
acceptableto have a "wildcard" entry for service names as well as what that wildcard should be. I do *not* propose that
complexstring substitution, including regular expressions, etc. be utilized for service name matching at this time.<p
class="MsoPlainText"> <pclass="MsoPlainText">Per 31.16 in the 9.4 Documentation, a valid service entry is of the
followingformat:<p class="MsoPlainText"> <p class="MsoPlainText">    # comment<p class="MsoPlainText">    [mydb]<p
class="MsoPlainText">   host=somehost.domain.com<p class="MsoPlainText">    port=5433<p class="MsoPlainText">   
user=admin<pclass="MsoPlainText"> <p class="MsoPlainText">Would specifying a special value for the service name,
perhaps[%], be an acceptable implementation of this enhancement/fix to my above concerns?<p class="MsoPlainText"> <p
class="MsoPlainText">Example:<pclass="MsoPlainText"> <p class="MsoPlainText">    # comment<p class="MsoPlainText">   
[%]<pclass="MsoPlainText">    host=%.domain.com<p class="MsoPlainText">    port=5433<p class="MsoPlainText">   
user=admin<pclass="MsoPlainText"> <p class="MsoPlainText">...or more interestingly, per 31.17:<p
class="MsoPlainText"> <pclass="MsoPlainText">    # comment<p class="MsoPlainText">    [%]<p class="MsoPlainText">   
ldap=ldap://ldap.mycompany.com/dc=mycompany,dc=com?uniqueMember?one?(cn=%)<pclass="MsoPlainText"> <p
class="MsoPlainText">Thelocation of [%] and therefore order of the service names would still be honored. I believe this
allowsfor useful functionality:<p class="MsoPlainText">* LDAP wildcard listed first - libpq can always try an LDAP
lookupand proceed with further service names if one is not found in LDAP location<p class="MsoPlainText">* LDAP
wildcardlisted last - only look up LDAP entries if a service name doesn’t match prior service names<p
class="MsoPlainText">*LDAP wildcard in the middle - combination of first 2 behaviors<p class="MsoPlainText">* DNS
wildcardlisted last - try connecting with service name in well-formed dns-based host entry (this likely can't be first
asit would always match)<p class="MsoPlainText">* Combination of the LDAP/keyword = value entries per 31.17: <p
class="MsoPlainText"> <pclass="MsoPlainText">From the existing documentation:  "Processing of pg_service.conf is
terminatedafter a successful LDAP lookup, but is continued if the LDAP server cannot be contacted. This is to provide a
fallbackwith further LDAP URL lines that point to different LDAP servers, classical keyword = value pairs, or default
connectionoptions. If you would rather get an error message in this case, add a syntactically incorrect line after the
LDAPURL."<p class="MsoPlainText"> <p class="MsoPlainText">The "%" in the ldap, host entry would replace with the
servicename in use - also possible to make it less likely to match a future valid "%" by providing it as [%] in the
string,though I don’t know why a % would reasonably show up in an ldap or host record.<p class="MsoPlainText"> <p
class="MsoPlainText">Ihave not made the patch yet, but it looks like this change is isolated to the parseServiceFile
subroutine,currently starting on line 3867 in <a
href="https://github.com/postgres/postgres/blob/master/src/interfaces/libpq/fe-connect.c">https://github.com/postgres/postgres/blob/master/src/interfaces/libpq/fe-connect.c</a>
 (andassociated documentation).<p class="MsoPlainText"> <p class="MsoPlainText">################## Scope:<p
class="MsoPlainText"> <pclass="MsoPlainText">Note that this discussion is scoped only for LDAP directory services and
notfor LDAP authentication/authorization. Again, I do *not* propose that complex string substitution, including regular
expressions,etc. be utilized for service name matching at this time. Just looking for a simple [%] entry, which could
beextended for flexibility in a consistent way, if people find this general case useful.<p class="MsoPlainText"> <p
class="MsoPlainText">Iam looking forward to feedback and our first interaction on the distribution list.<p
class="MsoPlainText"> <pclass="MsoPlainText">Thanks,<p class="MsoPlainText"> <p class="MsoPlainText">Bryan</div>