Better handle invalid content-type (#28377)

src/core/ext/transport/chttp2/transport/hpack_encoder.cc

@@ -611,7 +611,10 @@ void HPackCompressor::Framer::Encode(TeMetadata, TeMetadata::ValueType value) {
 
 void HPackCompressor::Framer::Encode(ContentTypeMetadata,
                                      ContentTypeMetadata::ValueType value) {
-  GPR_ASSERT(value == ContentTypeMetadata::ValueType::kApplicationGrpc);
+  if (value != ContentTypeMetadata::ValueType::kApplicationGrpc) {
+    gpr_log(GPR_ERROR, "Not encoding bad content-type header");
+    return;
+  }
   EncodeAlwaysIndexed(
       &compressor_->content_type_index_, GRPC_MDSTR_CONTENT_TYPE,
       StaticSlice::FromStaticString("application/grpc").c_slice(),

src/core/lib/transport/metadata_batch.h

@@ -888,12 +888,23 @@ class MetadataMap {
 
     template <typename Which>
     void Encode(Which, const typename Which::ValueType& value) {
-      size_ += Which::key().length() + Which::Encode(value).length() + 32;
+      Add(Which(), value);
+    }
+
+    void Encode(ContentTypeMetadata,
+                const typename ContentTypeMetadata::ValueType& value) {
+      if (value == ContentTypeMetadata::kInvalid) return;
+      Add(ContentTypeMetadata(), value);
     }
 
     size_t size() const { return size_; }
 
    private:
+    template <typename Which>
+    void Add(Which, const typename Which::ValueType& value) {
+      size_ += Which::key().length() + Which::Encode(value).length() + 32;
+    }
+
     uint32_t size_ = 0;
   };
 

test/core/end2end/fuzzers/api_fuzzer_corpus/testcase-4902018028535808

@@ -0,0 +1,35 @@
+actions {
+  create_channel {
+    target: "unix:"
+    channel_actions {
+      add_n_bytes_writable: 42932895744
+      add_n_bytes_readable: 34359738368
+    }
+  }
+}
+actions {
+  create_call {
+    propagation_mask: 9869440
+    method {
+      value: "v"
+      intern: true
+    }
+    timeout: 1000000000
+  }
+}
+actions {
+  queue_batch {
+    operations {
+      send_initial_metadata {
+        metadata {
+          key {
+            value: "content-type"
+          }
+          value {
+            value: "u-bin"
+          }
+        }
+      }
+    }
+  }
+}