Better ASSERT output from union_string.h (#39518)

Commit Message: Better ASSERT output from union_string.h
Additional Description: The existing ASSERT just tells us "a validation
went wrong somewhere". Sometimes the stack trace helps, but sometimes it
doesn't. This change makes the ASSERT error give us a [somewhat mangled]
description of what kind of validator was running, and the horrible
string it was running on, e.g.
```
[./envoy/common/union_string.h:180] assert failure: valid(). Details: N5Envoy4Http21HeaderStringValidatorE failed to validate string "�2}���i���IS9䄒�i���X�?���i��������X�?�!ꨤI�W����"
```
vs. the old output
```
[./envoy/common/union_string.h:172] assert failure: valid().
```

Risk Level: None, it only changes anything if an ASSERT fails.
Testing: Used while debugging another issue.
Docs Changes: n/a
Release Notes: n/a
Platform Specific Features: n/a

---------

Signed-off-by: Raven Black <[email protected]>

Author: ravenblackx

envoy/common/union_string.h

@@ -6,6 +6,7 @@
 #include "source/common/common/utility.h"
 
 #include "absl/container/inlined_vector.h"
+#include "absl/strings/str_cat.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/variant.h"
 
@@ -60,15 +61,20 @@ template <class Validator> class UnionStringBase {
    */
   UnionStringBase() : buffer_(std::in_place_type<InlinedStringVector>) {
     ASSERT((getInVec(buffer_).capacity()) >= MaxIntegerLength);
-    ASSERT(valid());
+    assertValid();
+  }
+
+  inline void assertValid() const {
+    ASSERT(valid(), absl::StrCat(typeid(Validator).name(), " failed to validate string \"",
+                                 getStringView(), "\""));
   }
 
   /**
    * Constructor for a string reference.
    * @param ref_value MUST point to data that will live beyond the lifetime of any request/response
    *        using the string (since a codec may optimize for zero copy).
    */
-  explicit UnionStringBase(absl::string_view ref_value) : buffer_(ref_value) { ASSERT(valid()); }
+  explicit UnionStringBase(absl::string_view ref_value) : buffer_(ref_value) { assertValid(); }
 
   UnionStringBase(UnionStringBase&& move_value) noexcept : buffer_(std::move(move_value.buffer_)) {
     move_value.clear();
@@ -84,7 +90,9 @@ template <class Validator> class UnionStringBase {
     // Make sure the requested memory allocation is below uint32_t::max
     const uint64_t new_capacity = static_cast<uint64_t>(data_size) + size();
     validateCapacity(new_capacity);
-    ASSERT(valid(absl::string_view(data, data_size)));
+    ASSERT(valid(absl::string_view(data, data_size)),
+           absl::StrCat(typeid(Validator).name(), " failed to validate string \"",
+                        absl::string_view(data, data_size), "\""));
 
     switch (type()) {
     case Type::Reference: {
@@ -171,7 +179,7 @@ template <class Validator> class UnionStringBase {
 
     getInVec(buffer_).reserve(size);
     getInVec(buffer_).assign(data, data + size);
-    ASSERT(valid());
+    assertValid();
   }
 
   /**
@@ -207,7 +215,7 @@ template <class Validator> class UnionStringBase {
    */
   void setReference(absl::string_view ref_value) {
     buffer_ = ref_value;
-    ASSERT(valid());
+    assertValid();
   }
 
   /**