feat: implement FT.TAGVALS (#3493)

* feat: implement FT.TAGVALS

Fixes #3491

---------

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/core/search/indices.cc

@@ -149,6 +149,15 @@ void BaseStringIndex<C>::Remove(DocId id, DocumentAccessor* doc, string_view fie
   }
 }
 
+template <typename C> vector<string> BaseStringIndex<C>::GetTerms() const {
+  vector<string> res;
+  res.reserve(entries_.size());
+  for (const auto& [term, _] : entries_) {
+    res.push_back(string{term});
+  }
+  return res;
+}
+
 template struct BaseStringIndex<CompressedSortedSet>;
 template struct BaseStringIndex<SortedVector>;
 

src/core/search/indices.h

@@ -51,6 +51,9 @@ template <typename C> struct BaseStringIndex : public BaseIndex {
   // Pointer is valid as long as index is not mutated. Nullptr if not found
   const Container* Matching(std::string_view str) const;
 
+  // Returns all the terms that appear as keys in the reverse index.
+  std::vector<std::string> GetTerms() const;
+
  protected:
   Container* GetOrCreate(std::string_view word);
 

src/facade/error.h

@@ -39,5 +39,6 @@ extern const char kInvalidDumpValueErr[];
 extern const char kSyntaxErrType[];
 extern const char kScriptErrType[];
 extern const char kConfigErrType[];
+extern const char kSearchErrType[];
 
 }  // namespace facade

src/facade/facade.cc

@@ -101,6 +101,7 @@ const char kInvalidDumpValueErr[] = "DUMP payload version or checksum are wrong"
 const char kSyntaxErrType[] = "syntax_error";
 const char kScriptErrType[] = "script_error";
 const char kConfigErrType[] = "config_error";
+const char kSearchErrType[] = "search_error";
 
 const char* RespExpr::TypeName(Type t) {
   switch (t) {

src/server/search/doc_index.cc

@@ -10,6 +10,7 @@
 
 #include "base/logging.h"
 #include "core/overloaded.h"
+#include "core/search/indices.h"
 #include "server/engine_shard_set.h"
 #include "server/search/doc_accessors.h"
 #include "server/server_state.h"
@@ -17,6 +18,8 @@
 namespace dfly {
 
 using namespace std;
+using facade::ErrorReply;
+using nonstd::make_unexpected;
 
 namespace {
 
@@ -269,6 +272,20 @@ DocIndexInfo ShardDocIndex::GetInfo() const {
   return {*base_, key_index_.Size()};
 }
 
+io::Result<StringVec, ErrorReply> ShardDocIndex::GetTagVals(string_view field) const {
+  search::BaseIndex* base_index = indices_.GetIndex(field);
+  if (base_index == nullptr) {
+    return make_unexpected(ErrorReply{"-No such field"});
+  }
+
+  search::TagIndex* tag_index = dynamic_cast<search::TagIndex*>(base_index);
+  if (tag_index == nullptr) {
+    return make_unexpected(ErrorReply{"-Not a tag field"});
+  }
+
+  return tag_index->GetTerms();
+}
+
 ShardDocIndices::ShardDocIndices() : local_mr_{ServerState::tlocal()->data_heap()} {
 }
 

src/server/search/doc_index.h

@@ -138,6 +138,8 @@ class ShardDocIndex {
 
   DocIndexInfo GetInfo() const;
 
+  io::Result<StringVec, facade::ErrorReply> GetTagVals(std::string_view field) const;
+
  private:
   // Clears internal data. Traverses all matching documents and assigns ids.
   void Rebuild(const OpArgs& op_args, PMR_NS::memory_resource* mr);

src/server/search/search_family.cc

@@ -798,6 +798,41 @@ void SearchFamily::FtProfile(CmdArgList args, ConnectionContext* cntx) {
   }
 }
 
+void SearchFamily::FtTagVals(CmdArgList args, ConnectionContext* cntx) {
+  string_view index_name = ArgS(args, 0);
+  string_view field_name = ArgS(args, 1);
+  VLOG(1) << "FtTagVals: " << index_name << " " << field_name;
+
+  vector<io::Result<StringVec, ErrorReply>> shard_results(shard_set->size(), StringVec{});
+
+  cntx->transaction->ScheduleSingleHop([&](Transaction* t, EngineShard* es) {
+    if (auto* index = es->search_indices()->GetIndex(index_name); index)
+      shard_results[es->shard_id()] = index->GetTagVals(field_name);
+    else
+      shard_results[es->shard_id()] = nonstd::make_unexpected(ErrorReply("-Unknown Index name"));
+
+    return OpStatus::OK;
+  });
+
+  absl::flat_hash_set<string> result_set;
+
+  // Check first if either shard had errors. Also merge the results into a single set.
+  for (auto& res : shard_results) {
+    if (res) {
+      result_set.insert(make_move_iterator(res->begin()), make_move_iterator(res->end()));
+    } else {
+      res.error().kind = facade::kSearchErrType;
+      return cntx->SendError(res.error());
+    }
+  }
+
+  shard_results.clear();
+  vector<string> vec(result_set.begin(), result_set.end());
+
+  auto* rb = static_cast<RedisReplyBuilder*>(cntx->reply_builder());
+  rb->SendStringArr(vec, RedisReplyBuilder::SET);
+}
+
 void SearchFamily::FtAggregate(CmdArgList args, ConnectionContext* cntx) {
   const auto params = ParseAggregatorParamsOrReply(args, cntx);
   if (!params)
@@ -871,7 +906,8 @@ void SearchFamily::Register(CommandRegistry* registry) {
             << CI{"FT._LIST", kReadOnlyMask, 1, 0, 0, acl::FT_SEARCH}.HFUNC(FtList)
             << CI{"FT.SEARCH", kReadOnlyMask, -3, 0, 0, acl::FT_SEARCH}.HFUNC(FtSearch)
             << CI{"FT.AGGREGATE", kReadOnlyMask, -3, 0, 0, acl::FT_SEARCH}.HFUNC(FtAggregate)
-            << CI{"FT.PROFILE", kReadOnlyMask, -4, 0, 0, acl::FT_SEARCH}.HFUNC(FtProfile);
+            << CI{"FT.PROFILE", kReadOnlyMask, -4, 0, 0, acl::FT_SEARCH}.HFUNC(FtProfile)
+            << CI{"FT.TAGVALS", kReadOnlyMask, 3, 0, 0, acl::FT_SEARCH}.HFUNC(FtTagVals);
 }
 
 }  // namespace dfly

src/server/search/search_family.h

@@ -22,6 +22,7 @@ class SearchFamily {
   static void FtSearch(CmdArgList args, ConnectionContext* cntx);
   static void FtProfile(CmdArgList args, ConnectionContext* cntx);
   static void FtAggregate(CmdArgList args, ConnectionContext* cntx);
+  static void FtTagVals(CmdArgList args, ConnectionContext* cntx);
 
  public:
   static void Register(CommandRegistry* registry);

src/server/search/search_family_test.cc

@@ -310,7 +310,13 @@ TEST_F(SearchFamilyTest, Tags) {
   Run({"hset", "d:5", "color", "green"});
   Run({"hset", "d:6", "color", "blue"});
 
-  EXPECT_EQ(Run({"ft.create", "i1", "on", "hash", "schema", "color", "tag"}), "OK");
+  EXPECT_EQ(Run({"ft.create", "i1", "on", "hash", "schema", "color", "tag", "dummy", "numeric"}),
+            "OK");
+  EXPECT_THAT(Run({"ft.tagvals", "i2", "color"}), ErrArg("Unknown Index name"));
+  EXPECT_THAT(Run({"ft.tagvals", "i1", "foo"}), ErrArg("No such field"));
+  EXPECT_THAT(Run({"ft.tagvals", "i1", "dummy"}), ErrArg("Not a tag field"));
+  auto resp = Run({"ft.tagvals", "i1", "color"});
+  ASSERT_THAT(resp, IsUnordArray("red", "blue", "green"));
 
   // Tags don't participate in full text search
   EXPECT_THAT(Run({"ft.search", "i1", "red"}), kNoResults);
@@ -323,6 +329,14 @@ TEST_F(SearchFamilyTest, Tags) {
               AreDocIds("d:1", "d:2", "d:3", "d:4", "d:5"));
   EXPECT_THAT(Run({"ft.search", "i1", "@color:{blue | green}"}),
               AreDocIds("d:1", "d:2", "d:3", "d:5", "d:6"));
+
+  EXPECT_EQ(Run({"ft.create", "i2", "on", "hash", "schema", "c1", "as", "c2", "tag"}), "OK");
+
+  // TODO: there is a discrepancy here between redis stack and Dragonfly,
+  // we accept the original field when it has alias, while redis stack does not.
+  //
+  // EXPECT_THAT(Run({"ft.tagvals", "i2", "c1"}), ErrArg("No such field"));
+  EXPECT_THAT(Run({"ft.tagvals", "i2", "c2"}), ArrLen(0));
 }
 
 TEST_F(SearchFamilyTest, TagOptions) {