From 218179642881c41f482f8bd407042b08fa4794dd Mon Sep 17 00:00:00 2001
From: Alan de Freitas <alandefreitas@gmail.com>
Date: Thu, 23 Apr 2026 22:50:15 -0500
Subject: [PATCH] fix: decoded query-size tracking in url_base::edit_params

Latent issue exposed by b54e9e8, not introduced by it.

fix #989
---
 include/boost/url/impl/url_base.hpp | 14 +++----
 test/unit/params_encoded_ref.cpp    |  5 +++
 test/unit/params_ref.cpp            | 61 +++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+), 7 deletions(-)

diff --git a/include/boost/url/impl/url_base.hpp b/include/boost/url/impl/url_base.hpp
index be3c35bef..476127892 100644
--- a/include/boost/url/impl/url_base.hpp
+++ b/include/boost/url/impl/url_base.hpp
@@ -3159,7 +3159,12 @@ edit_params(
     BOOST_ASSERT(pos1 <= impl_.offset(id_frag));
 
     // calc decoded size of old range,
-    // minus one if '?' or '&' prefixed
+    // minus one for the leading '?' which is
+    // not counted in decoded_[id_query].
+    // dn0 may be -1 here when the old range is
+    // empty and the query was non-empty; the
+    // matching subtraction on dn below cancels
+    // that out when the delta is taken.
     auto dn0 =
         static_cast<std::ptrdiff_t>(
             detail::decode_bytes_unsafe(
@@ -3168,8 +3173,6 @@ edit_params(
                     pos1 - pos0)));
     if(impl_.len(id_query) > 0)
         dn0 -= 1;
-    if(dn0 < 0)
-        dn0 = 0;
 
 //------------------------------------------------
 //
@@ -3267,16 +3270,13 @@ edit_params(
         }
     }
 
-    // calc decoded size of new range,
-    // minus one if '?' or '&' prefixed
+    // calc decoded size of new range; see dn0.
     auto dn =
         static_cast<std::ptrdiff_t>(
             detail::decode_bytes_unsafe(
                 core::string_view(dest0, dest - dest0)));
     if(impl_.len(id_query) > 0)
         dn -= 1;
-    if(dn < 0)
-        dn = 0;
 
     if(dn >= dn0)
         impl_.decoded_[id_query] +=
diff --git a/test/unit/params_encoded_ref.cpp b/test/unit/params_encoded_ref.cpp
index 10811b234..8004958cc 100644
--- a/test/unit/params_encoded_ref.cpp
+++ b/test/unit/params_encoded_ref.cpp
@@ -121,6 +121,11 @@ struct params_encoded_ref_test
         params_encoded_ref ps(u.encoded_params());
         f(ps);
         BOOST_TEST_EQ(u.encoded_query(), s1);
+        BOOST_TEST_EQ(
+            u.encoded_query().decoded_size(),
+            pct_string_view(s1).decoded_size());
+        BOOST_TEST_NO_THROW(u.encoded_target());
+        BOOST_TEST_NO_THROW(u.encoded_resource());
         if(! BOOST_TEST_EQ(
                 ps.size(), init.size()))
             return;
diff --git a/test/unit/params_ref.cpp b/test/unit/params_ref.cpp
index cf68456ba..9c08bfc12 100644
--- a/test/unit/params_ref.cpp
+++ b/test/unit/params_ref.cpp
@@ -142,6 +142,11 @@ struct params_ref_test
         params_ref ps(u.params());
         f(ps);
         BOOST_TEST_EQ(u.encoded_query(), s1);
+        BOOST_TEST_EQ(
+            u.encoded_query().decoded_size(),
+            pct_string_view(s1).decoded_size());
+        BOOST_TEST_NO_THROW(u.encoded_target());
+        BOOST_TEST_NO_THROW(u.encoded_resource());
         if(! BOOST_TEST_EQ(
                 ps.size(), init.size()))
             return;
@@ -814,6 +819,62 @@ struct params_ref_test
             check(f, "?k0&k1=&k2=key", "k0&k1=" BIGSTR "&k2=key",
                 { {"k0",no_value}, {"k1",BIGSTR}, {"k2","key"} });
         }
+
+        // issue #989: encoded_target() asserts after
+        // successive params().set() on a fresh url.
+        // Regression for broken decoded_[id_query]
+        // bookkeeping in url_base::edit_params.
+        {
+            url u;
+            u.params().set("a", "b");
+            BOOST_TEST_EQ(u.encoded_query(), "a=b");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 3u);
+            BOOST_TEST_EQ(u.encoded_target(), "?a=b");
+
+            u.params().set("c", "d");
+            BOOST_TEST_EQ(u.encoded_query(), "a=b&c=d");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 7u);
+            BOOST_TEST_EQ(u.encoded_target(), "?a=b&c=d");
+        }
+
+        // Related: erase first param must leave a
+        // consistent decoded_[id_query].
+        {
+            url u("?a=b&c=d");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 7u);
+            u.params().erase(u.params().begin());
+            BOOST_TEST_EQ(u.encoded_query(), "c=d");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 3u);
+            BOOST_TEST_EQ(u.encoded_target(), "?c=d");
+        }
+
+        // Related: erase last param must leave a
+        // consistent decoded_[id_query].
+        {
+            url u("?a=b&c=d");
+            u.params().erase(std::next(u.params().begin()));
+            BOOST_TEST_EQ(u.encoded_query(), "a=b");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 3u);
+            BOOST_TEST_EQ(u.encoded_target(), "?a=b");
+        }
+
+        // Related: insert at front of non-empty query.
+        {
+            url u("?x=y");
+            u.params().insert(u.params().begin(), {"a", "b"});
+            BOOST_TEST_EQ(u.encoded_query(), "a=b&x=y");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 7u);
+            BOOST_TEST_EQ(u.encoded_target(), "?a=b&x=y");
+        }
+
+        // Related: append to non-empty query.
+        {
+            url u("?x=y");
+            u.params().append({"a", "b"});
+            BOOST_TEST_EQ(u.encoded_query(), "x=y&a=b");
+            BOOST_TEST_EQ(u.encoded_query().decoded_size(), 7u);
+            BOOST_TEST_EQ(u.encoded_target(), "?x=y&a=b");
+        }
     }
 
     static