httpd: refuse a configuration with a line the replay cannot take

The replay takes a line of at most 126 bytes, so a longer one is skipped
on boot. Neither the upload path nor the editor looked at line length,
so the file the user saved was not the configuration the switch would
come up with.

Reject such a body in config_take(), before the sector is erased, which
the upload path already maps to 400. The editor points at the offending
line and its length, and measures it in bytes rather than characters, so
a name written in a non-ASCII script is counted the way the switch
counts it.

httpd/httpd.c

@@ -375,8 +375,8 @@ void gen_random_hex_chars(__xdata uint8_t * b, __xdata uint8_t bytes)
 static uint8_t config_take(void)
 {
 	// #386: needs static, otherwise it still lands in SRAM/DSEG
-	static __xdata uint16_t cfg_pos, cfg_hdr, cfg_body, cfg_end, cfg_last;
-	__xdata uint8_t cfg_bl;
+	static __xdata uint16_t cfg_pos, cfg_hdr, cfg_body, cfg_end, cfg_last, cfg_i;
+	__xdata uint8_t cfg_bl, cfg_run;
 
 	cfg_bl = strlen_x(boundary);
 
@@ -418,6 +418,13 @@ static uint8_t config_take(void)
 				// the payload plus its terminator must fit the sector
 				if (cfg_end - cfg_body + 1 > CONFIG_LEN)
 					return 2;
+				cfg_run = 0;
+				for (cfg_i = cfg_body; cfg_i < cfg_end; cfg_i++) {
+					if (config_buf[cfg_i] == '\n')
+						cfg_run = 0;
+					else if (++cfg_run >= CMD_BUF_SIZE - 1)
+						return 2;
+				}
 				config_buf[cfg_end] = 0;
 				flash_region.addr = CONFIG_START;
 				flash_sector_erase();