MINOR: config: add new setting "http-reuse"

For now it only supports "never", meaning that we never want to reuse a
shared connection, and "always", meaning that we can use any connection
that was not marked private. When "never" is set, this also implies that
no idle connection may become a shared one.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 0ce3ea9..37c2cb5 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -76,7 +76,15 @@
 /* bits for proxy->options */
 #define PR_O_REDISP     0x00000001      /* allow reconnection to dispatch in case of errors */
 #define PR_O_TRANSP     0x00000002      /* transparent mode : use original DEST as dispatch */
-/* unused: 0x04, 0x08, 0x10 */
+
+/* HTTP server-side reuse */
+#define PR_O_REUSE_NEVR 0x00000000      /* never reuse a shared connection */
+#define PR_O_REUSE_SAFE 0x00000004      /* only reuse a shared connection when it's safe to do so */
+#define PR_O_REUSE_AGGR 0x00000008      /* aggressively reuse a shared connection */
+#define PR_O_REUSE_ALWS 0x0000000C      /* always reuse a shared connection */
+#define PR_O_REUSE_MASK 0x0000000C      /* mask to retrieve shared connection preferences */
+
+/* unused: 0x10 */
 #define PR_O_PREF_LAST  0x00000020      /* prefer last server */
 #define PR_O_DISPATCH   0x00000040      /* use dispatch mode */
 #define PR_O_FORCED_ID  0x00000080      /* proxy's ID was forced in the configuration */
diff --git a/src/cfgparse.c b/src/cfgparse.c
index fb9d45b..9a2316f 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -5024,6 +5024,30 @@
 		if (alertif_too_many_args_idx(1, 0, file, linenum, args, &err_code))
 			goto out;
 	}
+	else if (!strcmp(args[0], "http-reuse")) {
+		if (warnifnotcap(curproxy, PR_CAP_BE, file, linenum, args[0], NULL))
+			err_code |= ERR_WARN;
+
+		if (strcmp(args[1], "never") == 0) {
+			/* enable a graceful server shutdown on an HTTP 404 response */
+			curproxy->options &= ~PR_O_REUSE_MASK;
+			curproxy->options |= PR_O_REUSE_NEVR;
+			if (alertif_too_many_args_idx(0, 1, file, linenum, args, &err_code))
+				goto out;
+		}
+		else if (strcmp(args[1], "always") == 0) {
+			/* enable a graceful server shutdown on an HTTP 404 response */
+			curproxy->options &= ~PR_O_REUSE_MASK;
+			curproxy->options |= PR_O_REUSE_ALWS;
+			if (alertif_too_many_args_idx(0, 1, file, linenum, args, &err_code))
+				goto out;
+		}
+		else {
+			Alert("parsing [%s:%d] : '%s' only supports 'never', 'always'.\n", file, linenum, args[0]);
+			err_code |= ERR_ALERT | ERR_FATAL;
+			goto out;
+		}
+	}
 	else if (!strcmp(args[0], "http-check")) {
 		if (warnifnotcap(curproxy, PR_CAP_BE, file, linenum, args[0], NULL))
 			err_code |= ERR_WARN;