1 files changed, 65 insertions, 0 deletions
diff --git a/src/port/unsetenv.c b/src/port/unsetenv.c
new file mode 100644
index 0000000..62b806d
--- /dev/null
+++ b/src/port/unsetenv.c
@@ -0,0 +1,65 @@
+/*-------------------------------------------------------------------------
+ *
+ * unsetenv.c
+ *	  unsetenv() emulation for machines without it
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/port/unsetenv.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+
+int
+unsetenv(const char *name)
+{
+	char	   *envstr;
+
+	/* Error conditions, per POSIX */
+	if (name == NULL || name[0] == '\0' || strchr(name, '=') != NULL)
+	{
+		errno = EINVAL;
+		return -1;
+	}
+
+	if (getenv(name) == NULL)
+		return 0;				/* no work */
+
+	/*
+	 * The technique embodied here works if libc follows the Single Unix Spec
+	 * and actually uses the storage passed to putenv() to hold the environ
+	 * entry.  When we clobber the entry in the second step we are ensuring
+	 * that we zap the actual environ member.  However, there are some libc
+	 * implementations (notably recent BSDs) that do not obey SUS but copy the
+	 * presented string.  This method fails on such platforms.  Hopefully all
+	 * such platforms have unsetenv() and thus won't be using this hack. See:
+	 * http://www.greenend.org.uk/rjk/2008/putenv.html
+	 *
+	 * Note that repeatedly setting and unsetting a var using this code will
+	 * leak memory.
+	 */
+
+	envstr = (char *) malloc(strlen(name) + 2);
+	if (!envstr)				/* not much we can do if no memory */
+		return -1;
+
+	/* Override the existing setting by forcibly defining the var */
+	sprintf(envstr, "%s=", name);
+	if (putenv(envstr))
+		return -1;
+
+	/* Now we can clobber the variable definition this way: */
+	strcpy(envstr, "=");
+
+	/*
+	 * This last putenv cleans up if we have multiple zero-length names as a
+	 * result of unsetting multiple things.
+	 */
+	return putenv(envstr);
+}