Fix https://github.com/shadowsocks/shadowsocks-libev/issues/1945

Refer: 4af9a1b62b

src/http.c

@@ -32,7 +32,7 @@
 #include <stdlib.h> /* malloc() */
 #include <string.h> /* strncpy() */
 #include <strings.h> /* strncasecmp() */
-#include <ctype.h> /* isblank() */
+#include <ctype.h> /* isblank(), isdigit() */
 
 #include "http.h"
 #include "protocol.h"
@@ -80,6 +80,7 @@ parse_http_header(const char *data, size_t data_len, char **hostname)
     /*
      *  if the user specifies the port in the request, it is included here.
      *  Host: example.com:80
+     *  Host: [2001:db8::1]:8080
      *  so we trim off port portion
      */
     for (i = result - 1; i >= 0; i--)
@@ -87,6 +88,8 @@ parse_http_header(const char *data, size_t data_len, char **hostname)
             (*hostname)[i] = '\0';
             result         = i;
             break;
+        } else if (!isdigit((*hostname)[i])) {
+            break;
         }
 
     return result;