Use setenv() in preference to putenv().

Since at least 2001 we've used putenv() and avoided setenv(), on the
grounds that the latter was unportable and not in POSIX.  However,
POSIX added it that same year, and by now the situation has reversed:
setenv() is probably more portable than putenv(), since POSIX now
treats the latter as not being a core function.  And setenv() has
cleaner semantics too.  So, let's reverse that old policy.

This commit adds a simple src/port/ implementation of setenv() for
any stragglers (we have one in the buildfarm, but I'd not be surprised
if that code is never used in the field).  More importantly, extend
win32env.c to also support setenv().  Then, replace usages of putenv()
with setenv(), and get rid of some ad-hoc implementations of setenv()
wannabees.

Also, adjust our src/port/ implementation of unsetenv() to follow the
POSIX spec that it returns an error indicator, rather than returning
void as per the ancient BSD convention.  I don't feel a need to make
all the call sites check for errors, but the portability stub ought
to match real-world practice.

Discussion: https://postgr.es/m/2065122.1609212051@sss.pgh.pa.us

1 files changed, 44 insertions, 6 deletions

diff --git a/src/port/win32env.c b/src/port/win32env.c
index 177488cc67e..f5bed672974 100644
--- a/src/port/win32env.c
+++ b/src/port/win32env.c
@@ -1,8 +1,10 @@
 /*-------------------------------------------------------------------------
  *
  * win32env.c
- *	  putenv() and unsetenv() for win32, which update both process environment
- *	  and caches in (potentially multiple) C run-time library (CRT) versions.
+ *	  putenv(), setenv(), and unsetenv() for win32.
+ *
+ * These functions update both the process environment and caches in
+ * (potentially multiple) C run-time library (CRT) versions.
  *
  * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -16,6 +18,11 @@
 
 #include "c.h"
 
+
+/*
+ * Note that unlike POSIX putenv(), this doesn't use the passed-in string
+ * as permanent storage.
+ */
 int
 pgwin32_putenv(const char *envval)
 {
@@ -64,7 +71,7 @@ pgwin32_putenv(const char *envval)
 	}
 	*cp = '\0';
 	cp++;
-	if (strlen(cp))
+	if (*cp)
 	{
 		/*
 		 * Only call SetEnvironmentVariable() when we are adding a variable,
@@ -110,16 +117,47 @@ pgwin32_putenv(const char *envval)
 	return _putenv(envval);
 }
 
-void
+int
+pgwin32_setenv(const char *name, const char *value, int overwrite)
+{
+	int			res;
+	char	   *envstr;
+
+	/* Error conditions, per POSIX */
+	if (name == NULL || name[0] == '\0' || strchr(name, '=') != NULL ||
+		value == NULL)
+	{
+		errno = EINVAL;
+		return -1;
+	}
+
+	/* No work if variable exists and we're not to replace it */
+	if (overwrite == 0 && getenv(name) != NULL)
+		return 0;
+
+	envstr = (char *) malloc(strlen(name) + strlen(value) + 2);
+	if (!envstr)				/* not much we can do if no memory */
+		return -1;
+
+	sprintf(envstr, "%s=%s", name, value);
+
+	res = pgwin32_putenv(envstr);
+	free(envstr);
+	return res;
+}
+
+int
 pgwin32_unsetenv(const char *name)
 {
+	int			res;
 	char	   *envbuf;
 
 	envbuf = (char *) malloc(strlen(name) + 2);
 	if (!envbuf)
-		return;
+		return -1;
 
 	sprintf(envbuf, "%s=", name);
-	pgwin32_putenv(envbuf);
+	res = pgwin32_putenv(envbuf);
 	free(envbuf);
+	return res;
 }