From d7db3e433d03b2a171bc70ee9d6e65b3354010c2 Mon Sep 17 00:00:00 2001
From: Donat Zenichev <dzenichev@sipwise.com>
Date: Tue, 4 Apr 2023 11:46:28 +0200
Subject: [PATCH] MT#56321 HeaderFilter: add multi-line headers parsing

We have to add multi-line headers parsing support, to be able
to properly detect and apply filters to such headers.

Since the SEMS prefers to work with single line values,
multi-line values are getting converted into signle line, like that:

  Accept: application/sdp,
    application/isup,
    multipart/mixed

gets converted into:

  Accept: application/sdp,  application/isup,  multipart/mixed

Additionally:
Support of spaces detection in hf names has been added.
We do not consider spaces as part of the hf name, if they are added.

Original ticket number: 56354

Change-Id: I6adda8218ee6b88035fa9297187187d868f4eb60
---
 apps/sbc/HeaderFilter.cpp | 83 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 73 insertions(+), 10 deletions(-)

diff --git a/apps/sbc/HeaderFilter.cpp b/apps/sbc/HeaderFilter.cpp
index 44803352..cef440d3 100644
--- a/apps/sbc/HeaderFilter.cpp
+++ b/apps/sbc/HeaderFilter.cpp
@@ -90,7 +90,7 @@ bool readFilter(AmConfigReader& cfg, const char* cfg_key_filter, const char* cfg
     return true;
 }
 
-int skip_header(const std::string& hdr, size_t start_pos,
+int skip_header(std::string& hdr, size_t start_pos,
         size_t& name_end, size_t& val_begin,
         size_t& val_end, size_t& hdr_end) {
     /* adapted from sip/parse_header.cpp */
@@ -111,8 +111,11 @@ int skip_header(const std::string& hdr, size_t start_pos,
     int st = H_NAME;
     int saved_st = 0;
 
+    /* iterate till actual name, if space(s)/tab(s) in front of hf name */
+    bool iteration_till_name = true;
+
     size_t p = start_pos;
-    for (; p<hdr.length() && st != ST_LF && st != ST_CRLF; p++)
+    for ( ; p < hdr.length() && st != ST_LF && st != ST_CRLF; p++)
     {
         switch (st)
         {
@@ -128,9 +131,20 @@ int skip_header(const std::string& hdr, size_t start_pos,
 
                     case SP:
                     case HTAB:
-                        st = H_HCOLON;
-                        name_end = p;
+                        /* skip spaces/tabs at the beginning of the line (if now expected hf name) */
+                        if (!iteration_till_name) {
+                            st = H_HCOLON;
+                            name_end = p;
+                        } else {
+                            /* remove space from the name */
+                            hdr.erase(p--, 1);
+                        }
                         break;
+
+                    /* other letters apart space, tab and colon */
+                    default:
+                        /* means - no spaces at the beginning of hf name found, start reading the name */
+                        iteration_till_name = false;
                 }
                 break;
 
@@ -156,9 +170,52 @@ int skip_header(const std::string& hdr, size_t start_pos,
                     case_CR_LF;
                 };
 
-                if (st==ST_CR || st==ST_LF)
-                    val_end = p;
+                /* trying to guess, if this is a multi-line header */
+                if (st == ST_CR || st == ST_LF) {
+
+                    /* if next line of SIP message begins with a space, then we should check for a multi-value */
+                    if (hdr[p] == CR && hdr[p+1] == LF && (hdr[p+2] == SP || hdr[p+2] == HTAB))
+                    {
+                        printf("Checking whether the value is multi-line\n");
+
+                        /* next line must not contain colon. No colon - is a clear sign of multi-line value */
+                        size_t tmp = p;
+                        tmp += 2;
+
+                        bool colon_found = false;
+                        for ( ; tmp < hdr.length() && hdr[tmp] != CR && hdr[tmp] != LF; tmp++)
+                        {
+                            if (hdr[tmp] == HCOLON) {
+                                colon_found = true;
+                                break;
+                            }
+                        }
+
+                        if (colon_found) {
+                            /* next line is definitely another header, stop parsing as a value */
+                            val_end = p;
+                        } else {
+                            /* next line is a part of multi-line value */
+                            hdr.erase(p, 2); /* remove CR and LF from the string */
+                            st = H_VALUE;
+                        }
+
+                        break;
 
+                    /* definitely not a multi-value */
+                    } else {
+                        val_end = p;
+                    }
+                }
+
+                /* Beginning of the next part of multi-line value.
+                 * By RFC3261 (section 7.4.1), as well as by RFC2616, multi-line value of hf,
+                 * must begin either with at least one space or tab.
+                 */
+                if (hdr[p] == SP || hdr[p] == HTAB) {
+                    while (hdr[p]  == SP || hdr[p] == HTAB)
+                        p++;
+                }
                 break;
 
             case H_HCOLON:
@@ -188,7 +245,7 @@ int skip_header(const std::string& hdr, size_t start_pos,
     }
     
     hdr_end = p;
-    if (p==hdr.length() && st==H_VALUE) {
+    if (p == hdr.length() && st == H_VALUE) {
         val_end = p;
     }
 
@@ -213,7 +270,7 @@ int inplaceHeaderFilter(string& hdrs, const vector<FilterEntry>& filter_list) {
         /* todo: multi-line header support */
 
         size_t start_pos = 0;
-        while (start_pos<hdrs.length())
+        while (start_pos < hdrs.length())
         {
             size_t name_end, val_begin, val_end, hdr_end;
             int res;
@@ -223,10 +280,15 @@ int inplaceHeaderFilter(string& hdrs, const vector<FilterEntry>& filter_list) {
                 return res;
             }
 
-            string hdr_name = hdrs.substr(start_pos, name_end-start_pos);
+            string hdr_name = hdrs.substr(start_pos, name_end - start_pos);
             std::transform(hdr_name.begin(), hdr_name.end(), hdr_name.begin(), ::tolower);
             bool erase = (f_type == Whitelist);
 
+            string hdr_value = hdrs.substr(val_begin, val_end - val_begin);
+
+            DBG("hdr name parsed: '%s'\n", hdr_name.c_str());
+            DBG("hdr value parsed: '%s'\n", hdr_value.c_str());
+
             for (set<string>::iterator it = headerfilter_list.begin();
                 it != headerfilter_list.end(); ++it)
             {
@@ -237,9 +299,10 @@ int inplaceHeaderFilter(string& hdrs, const vector<FilterEntry>& filter_list) {
             }
 
             if (erase) {
-                DBG("erasing header '%s' by %s\n", hdr_name.c_str(), FilterType2String(f_type));
+                DBG("erasing header '%s' by filter '%s'\n", hdr_name.c_str(), FilterType2String(f_type));
                 hdrs.erase(start_pos, hdr_end-start_pos);
             } else {
+                DBG("header accepted '%s' by filter '%s'\n", hdr_name.c_str(), FilterType2String(f_type));
                 start_pos = hdr_end;
             }
         }