MINOR: http-ana: Add option to keep query-string on a localtion-based redirect

On prefix-based redirect, there is an option to drop the query-string of the
location. Here it is the opposite. an option is added to preserve the
query-string of the original URI for a localtion-based redirect.

By setting "keep-query" option, for a location-based redirect only, the
query-string of the original URI is appended to the location. If there is no
query-string, nothing is added (no empty '?'). If there is already a
non-empty query-string on the localtion, the original one is appended with
'&' separator.

This patch should fix issue #2728.

doc/configuration.txt

@@ -11461,6 +11461,14 @@ redirect scheme   <sch> [code <code>] <option> [{if | unless} <condition>]
         cookie set with "NAME=value". You have to clear the cookie "NAME=" for
         that, because the browser makes the difference.
 
+      - "keep-query"
+        When this keyword is used in a location-based redirection, then the
+        query-string of the original URI, if any, will be appended to the
+        location. If no query-string is found, nothing is added. If the
+        location already contains a query-string, the original one will be
+        appended with the '&' delimiter.
+
+
   Example: move the login URL only to HTTPS.
         acl clear      dst_port  80
         acl secure     dst_port  8080

include/haproxy/http_ana-t.h

@@ -167,6 +167,7 @@ enum {
 	REDIRECT_FLAG_APPEND_SLASH = 2,	/* append a slash if missing at the end */
 	REDIRECT_FLAG_FROM_REQ = 4,     /* redirect rule on the request path */
 	REDIRECT_FLAG_IGNORE_EMPTY = 8, /* silently ignore empty location expressions */
+	REDIRECT_FLAG_KEEP_QS = 16,	/* append the query string to location, if any */
 };
 
 /* Redirect types (location, prefix, extended ) */

src/http_ana.c

@@ -2420,6 +2420,7 @@ int http_apply_redirect_rule(struct redirect_rule *rule, struct stream *s, struc
 		}
 		case REDIRECT_TYPE_LOCATION:
 		default:
+			memset(chunk->area, 0x50, chunk->size);
 			if (rule->rdr_str) { /* this is an old "redirect" rule */
 				/* add location */
 				if (!chunk_memcat(chunk, rule->rdr_str, rule->rdr_len))
@@ -2437,6 +2438,36 @@ int http_apply_redirect_rule(struct redirect_rule *rule, struct stream *s, struc
 
 				chunk->data += len;
 			}
+
+			if (rule->flags & REDIRECT_FLAG_KEEP_QS) {
+				struct ist path;
+				struct http_uri_parser parser;
+				char *ptr, *end;
+				char sep = '?';
+
+				ptr = memchr(chunk->area, '?', chunk->data);
+				if (ptr != NULL)
+					sep = ((ptr+1 != b_tail(chunk)) ? '&' : '\0');
+
+				sl = http_get_stline(htx);
+				parser = http_uri_parser_init(htx_sl_req_uri(sl));
+				path = http_parse_path(&parser);
+				ptr = istptr(path);
+				end = istend(path);
+
+				/* look up the '?' */
+				do {
+					if (ptr == end)
+						return 0;
+				} while (*ptr++ != '?');
+
+				if (ptr == end)
+					break;
+				if (sep != '\0' && !chunk_memcat(chunk, &sep, 1))
+					goto fail;
+				if (!chunk_memcat(chunk, ptr, end-ptr))
+					goto fail;
+			}
 			break;
 	}
 	location = ist2(chunk->area, chunk->data);

src/http_rules.c

@@ -402,6 +402,9 @@ struct redirect_rule *http_parse_redirect_rule(const char *file, int linenum, st
 		else if (strcmp(args[cur_arg], "drop-query") == 0) {
 			flags |= REDIRECT_FLAG_DROP_QS;
 		}
+		else if (strcmp(args[cur_arg], "keep-query") == 0) {
+			flags |= REDIRECT_FLAG_KEEP_QS;
+		}
 		else if (strcmp(args[cur_arg], "append-slash") == 0) {
 			flags |= REDIRECT_FLAG_APPEND_SLASH;
 		}
@@ -419,7 +422,7 @@ struct redirect_rule *http_parse_redirect_rule(const char *file, int linenum, st
 		}
 		else {
 			memprintf(errmsg,
-			          "expects 'code', 'prefix', 'location', 'scheme', 'set-cookie', 'clear-cookie', 'drop-query', 'ignore-empty' or 'append-slash' (was '%s')",
+			          "expects 'code', 'prefix', 'location', 'scheme', 'set-cookie', 'clear-cookie', 'drop-query', 'keep-query', 'ignore-empty' or 'append-slash' (was '%s')",
 			          args[cur_arg]);
 			goto err;
 		}