1 files changed, 151 insertions, 0 deletions
diff --git a/src/common/psprintf.c b/src/common/psprintf.c
new file mode 100644
index 0000000..52223c3
--- /dev/null
+++ b/src/common/psprintf.c
@@ -0,0 +1,151 @@
+/*-------------------------------------------------------------------------
+ *
+ * psprintf.c
+ *		sprintf into an allocated-on-demand buffer
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/common/psprintf.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+
+#include "postgres.h"
+
+#include "utils/memutils.h"
+
+#else
+
+#include "postgres_fe.h"
+
+/* It's possible we could use a different value for this in frontend code */
+#define MaxAllocSize	((Size) 0x3fffffff) /* 1 gigabyte - 1 */
+
+#endif
+
+
+/*
+ * psprintf
+ *
+ * Format text data under the control of fmt (an sprintf-style format string)
+ * and return it in an allocated-on-demand buffer.  The buffer is allocated
+ * with palloc in the backend, or malloc in frontend builds.  Caller is
+ * responsible to free the buffer when no longer needed, if appropriate.
+ *
+ * Errors are not returned to the caller, but are reported via elog(ERROR)
+ * in the backend, or printf-to-stderr-and-exit() in frontend builds.
+ * One should therefore think twice about using this in libpq.
+ */
+char *
+psprintf(const char *fmt,...)
+{
+	int			save_errno = errno;
+	size_t		len = 128;		/* initial assumption about buffer size */
+
+	for (;;)
+	{
+		char	   *result;
+		va_list		args;
+		size_t		newlen;
+
+		/*
+		 * Allocate result buffer.  Note that in frontend this maps to malloc
+		 * with exit-on-error.
+		 */
+		result = (char *) palloc(len);
+
+		/* Try to format the data. */
+		errno = save_errno;
+		va_start(args, fmt);
+		newlen = pvsnprintf(result, len, fmt, args);
+		va_end(args);
+
+		if (newlen < len)
+			return result;		/* success */
+
+		/* Release buffer and loop around to try again with larger len. */
+		pfree(result);
+		len = newlen;
+	}
+}
+
+/*
+ * pvsnprintf
+ *
+ * Attempt to format text data under the control of fmt (an sprintf-style
+ * format string) and insert it into buf (which has length len).
+ *
+ * If successful, return the number of bytes emitted, not counting the
+ * trailing zero byte.  This will always be strictly less than len.
+ *
+ * If there's not enough space in buf, return an estimate of the buffer size
+ * needed to succeed (this *must* be more than the given len, else callers
+ * might loop infinitely).
+ *
+ * Other error cases do not return, but exit via elog(ERROR) or exit().
+ * Hence, this shouldn't be used inside libpq.
+ *
+ * Caution: callers must be sure to preserve their entry-time errno
+ * when looping, in case the fmt contains "%m".
+ *
+ * Note that the semantics of the return value are not exactly C99's.
+ * First, we don't promise that the estimated buffer size is exactly right;
+ * callers must be prepared to loop multiple times to get the right size.
+ * (Given a C99-compliant vsnprintf, that won't happen, but it is rumored
+ * that some implementations don't always return the same value ...)
+ * Second, we return the recommended buffer size, not one less than that;
+ * this lets overflow concerns be handled here rather than in the callers.
+ */
+size_t
+pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
+{
+	int			nprinted;
+
+	nprinted = vsnprintf(buf, len, fmt, args);
+
+	/* We assume failure means the fmt is bogus, hence hard failure is OK */
+	if (unlikely(nprinted < 0))
+	{
+#ifndef FRONTEND
+		elog(ERROR, "vsnprintf failed: %m with format string \"%s\"", fmt);
+#else
+		fprintf(stderr, "vsnprintf failed: %s with format string \"%s\"\n",
+				strerror(errno), fmt);
+		exit(EXIT_FAILURE);
+#endif
+	}
+
+	if ((size_t) nprinted < len)
+	{
+		/* Success.  Note nprinted does not include trailing null. */
+		return (size_t) nprinted;
+	}
+
+	/*
+	 * We assume a C99-compliant vsnprintf, so believe its estimate of the
+	 * required space, and add one for the trailing null.  (If it's wrong, the
+	 * logic will still work, but we may loop multiple times.)
+	 *
+	 * Choke if the required space would exceed MaxAllocSize.  Note we use
+	 * this palloc-oriented overflow limit even when in frontend.
+	 */
+	if (unlikely((size_t) nprinted > MaxAllocSize - 1))
+	{
+#ifndef FRONTEND
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("out of memory")));
+#else
+		fprintf(stderr, _("out of memory\n"));
+		exit(EXIT_FAILURE);
+#endif
+	}
+
+	return nprinted + 1;
+}