Re: Support json_errdetail in FRONTEND builds

On 2024-Mar-14, Tom Lane wrote:

> Michael Paquier <michael(at)paquier(dot)xyz> writes:
> > Hmm. I am not sure how much protection this would offer, TBH. One
> > thing that I find annoying with common/stringinfo.c as it is currently
> > is that we have two exit() calls in the enlarge path, and it does not
> > seem wise to me to spread that even more.

> I hope nobody is expecting that such code will get accepted. We have
> a policy (and an enforcement mechanism) that libpq.so must not call
> exit(). OAuth code in libpq will need to cope with using pqexpbuffer.

FWIW that's exactly what Jacob's OAUTH patch does -- it teaches the
relevant JSON parser code to use pqexpbuffer when in frontend
environment, and continues to use StringInfo in backend. I find that a
bit cumbersome, but if the idea of changing the StringInfo behavior
(avoiding exit()) is too radical, then perhaps it's better that we go
with Jacob's proposal in the other thread:

+/*
+ * In backend, we will use palloc/pfree along with StringInfo. In frontend, use
+ * malloc and PQExpBuffer, and return JSON_OUT_OF_MEMORY on out-of-memory.
+ */
+#ifdef FRONTEND
+
+#define STRDUP(s) strdup(s)
+#define ALLOC(size) malloc(size)
+
+#define appendStrVal appendPQExpBuffer
+#define appendBinaryStrVal appendBinaryPQExpBuffer
+#define appendStrValChar appendPQExpBufferChar
+#define createStrVal createPQExpBuffer
+#define resetStrVal resetPQExpBuffer
+#define destroyStrVal destroyPQExpBuffer
+
+#else /* !FRONTEND */
+
+#define STRDUP(s) pstrdup(s)
+#define ALLOC(size) palloc(size)
+
+#define appendStrVal appendStringInfo
+#define appendBinaryStrVal appendBinaryStringInfo
+#define appendStrValChar appendStringInfoChar
+#define createStrVal makeStringInfo
+#define resetStrVal resetStringInfo
+#define destroyStrVal destroyStringInfo
+
+#endif

--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/
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