MINOR: h2: expose tune.h2.initial-window-size to configure the window size

This will be advertised in the settings frame.

doc/configuration.txt

@@ -600,6 +600,7 @@ The following keywords are supported in the "global" section :
    - tune.chksize
    - tune.comp.maxlevel
    - tune.h2.header-table-size
+   - tune.h2.initial-window-size
    - tune.http.cookielen
    - tune.http.logurilen
    - tune.http.maxhdr
@@ -1375,6 +1376,16 @@ tune.h2.header-table-size <number>
   memory is consumed for each HTTP/2 connection. It is recommended not to
   change it.
 
+tune.h2.initial-window-size <number>
+  Sets the HTTP/2 initial window size, which is the number of bytes the client
+  can upload before waiting for an acknowledgement from haproxy. This setting
+  only affects payload contents (ie: the body of POST requests), not headers.
+  The default value is 65535, which roughly allows up to 5 Mbps of upload
+  bandwidth per client over a network showing a 100 ms ping time, or 500 Mbps
+  over a 1-ms local network. It can make sense to increase this value to allow
+  faster uploads, or to reduce it to increase fairness when dealing with many
+  clients. It doesn't affect resource usage.
+
 tune.http.cookielen <number>
   Sets the maximum length of captured cookies. This is the maximum value that
   the "capture cookie xxx len yyy" will be allowed to take, and any upper value

src/mux_h2.c

@@ -18,6 +18,7 @@
 
 /* a few settings from the global section */
 static int h2_settings_header_table_size      =  4096; /* initial value */
+static int h2_settings_initial_window_size    = 65535; /* initial value */
 
 
 /*****************************************************************/
@@ -146,6 +147,22 @@ static int h2_parse_header_table_size(char **args, int section_type, struct prox
 	return 0;
 }
 
+/* config parser for global "tune.h2.initial-window-size" */
+static int h2_parse_initial_window_size(char **args, int section_type, struct proxy *curpx,
+                                        struct proxy *defpx, const char *file, int line,
+                                        char **err)
+{
+	if (too_many_args(1, args, err, NULL))
+		return -1;
+
+	h2_settings_initial_window_size = atoi(args[1]);
+	if (h2_settings_initial_window_size < 0) {
+		memprintf(err, "'%s' expects a positive numeric value.", args[0]);
+		return -1;
+	}
+	return 0;
+}
+
 
 /****************************************/
 /* MUX initialization and instanciation */
@@ -175,6 +192,7 @@ static struct alpn_mux_list alpn_mux_h2 =
 /* config keyword parsers */
 static struct cfg_kw_list cfg_kws = {ILH, {
 	{ CFG_GLOBAL, "tune.h2.header-table-size",      h2_parse_header_table_size      },
+	{ CFG_GLOBAL, "tune.h2.initial-window-size",    h2_parse_initial_window_size    },
 	{ 0, NULL, NULL }
 }};