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Make GetConfigOption/GetConfigOptionResetString return "" for NULL.

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As per the preceding commit, GUC APIs generally expose NULL-valued
string variables as empty strings.  Extend that policy to
GetConfigOption() and GetConfigOptionResetString(), eliminating
a crash hazard for unwary callers, as well as a fundamental
ambiguity in GetConfigOption()'s API.

No back-patch, since this is an API change and conceivably somebody
somewhere is depending on this corner case.

Xing Guo, Aleksander Alekseev, Tom Lane

Discussion: https://postgr.es/m/CACpMh+AyDx5YUpPaAgzVwC1d8zfOL4JoD-uyFDnNSa1z0EsDQQ@mail.gmail.com
This commit is contained in:
Tom Lane
2023-11-02 11:53:36 -04:00
parent 7704a1a72e
commit 0bc726d95a
1 changed files with 5 additions and 4 deletions
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9
src/backend/utils/misc/guc.c
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@ -4215,8 +4215,7 @@ SetConfigOption(const char *name, const char *value,
/* /*
* Fetch the current value of the option `name', as a string. * Fetch the current value of the option `name', as a string.
* *
* If the option doesn't exist, return NULL if missing_ok is true (NOTE that * If the option doesn't exist, return NULL if missing_ok is true,
* this cannot be distinguished from a string variable with a NULL value!),
* otherwise throw an ereport and don't return. * otherwise throw an ereport and don't return.
* *
* If restrict_privileged is true, we also enforce that only superusers and * If restrict_privileged is true, we also enforce that only superusers and
@ -4259,7 +4258,8 @@ GetConfigOption(const char *name, bool missing_ok, bool restrict_privileged)
return buffer; return buffer;
case PGC_STRING: case PGC_STRING:
return *((struct config_string *) record)->variable; return *((struct config_string *) record)->variable ?
*((struct config_string *) record)->variable : "";
case PGC_ENUM: case PGC_ENUM:
return config_enum_lookup_by_value((struct config_enum *) record, return config_enum_lookup_by_value((struct config_enum *) record,
@ -4306,7 +4306,8 @@ GetConfigOptionResetString(const char *name)
return buffer; return buffer;
case PGC_STRING: case PGC_STRING:
return ((struct config_string *) record)->reset_val; return ((struct config_string *) record)->reset_val ?
((struct config_string *) record)->reset_val : "";
case PGC_ENUM: case PGC_ENUM:
return config_enum_lookup_by_value((struct config_enum *) record, return config_enum_lookup_by_value((struct config_enum *) record,