feat: hrandfield

src/base_cmd.h

@@ -68,6 +68,7 @@ const std::string kCmdNameHGetAll = "hgetall";
 const std::string kCmdNameHKeys = "hkeys";
 const std::string kCmdNameHLen = "hlen";
 const std::string kCmdNameHStrLen = "hstrlen";
+const std::string kCmdNameHRandField = "hrandfield";
 
 enum CmdFlags {
   kCmdFlagsWrite = (1 << 0),             // May modify the dataset

src/cmd_hash.cc

@@ -7,6 +7,7 @@
 
 #include "cmd_hash.h"
 
+#include "pstd/pstd_string.h"
 #include "store.h"
 
 namespace pikiwidb {
@@ -285,4 +286,112 @@ void HStrLenCmd::DoCmd(PClient* client) {
   client->AppendStringRaw(reply.ReadAddr());
 }
 
+HRandFieldCmd::HRandFieldCmd(const std::string& name, int16_t arity)
+    : BaseCmd(name, arity, kCmdFlagsReadonly, kAclCategoryRead | kAclCategoryHash) {}
+
+bool HRandFieldCmd::DoInitial(PClient* client) {
+  /*
+   * There should not be quantity detection here,
+   * because the quantity detection of redis is after the COUNT integer detection.
+   */
+  // if (client->argv_.size() > 4) {
+  //   client->SetRes(CmdRes::kSyntaxErr);
+  //   return false;
+  // }
+  client->SetKey(client->argv_[1]);
+  return true;
+}
+
+void HRandFieldCmd::DoCmd(PClient* client) {
+  // parse arguments
+  int64_t count{};
+  bool with_values{false};
+  if (client->argv_.size() > 2) {
+    if (pstd::String2int(client->argv_[2], &count) == 0) {
+      client->SetRes(CmdRes::kInvalidInt);
+      return;
+    }
+
+    if (client->argv_.size() > 4) {
+      client->SetRes(CmdRes::kSyntaxErr);
+      return;
+    }
+
+    if (client->argv_.size() > 3) {
+      if (kWithValueString != pstd::StringToLower(client->argv_[3])) {
+        client->SetRes(CmdRes::kSyntaxErr);
+        return;
+      }
+      with_values = true;
+    }
+  }
+
+  // get hash
+  PObject* value = nullptr;
+  PError err = PSTORE.GetValueByType(client->Key(), value, kPTypeHash);
+  if (err != kPErrorOK) {
+    if (err == kPErrorNotExist) {
+      client->AppendString("");
+    } else {
+      client->SetRes(CmdRes::kSyntaxErr, "hrandfield cmd error");
+    }
+    return;
+  }
+  auto hash = value->CastHash();
+  if (hash->empty()) {
+    client->AppendString("");
+    return;
+  }
+
+  // fetch field(s) and reply
+  if (client->argv_.size() > 2) {
+    if (count >= 0) {
+      DoWithPositiveCount(client, hash, count, with_values);
+    } else {
+      DoWithNegativeCount(client, hash, count, with_values);
+    }
+  } else {
+    auto it = std::next(hash->begin(), rand() % hash->size());
+    client->AppendString(it->first);
+  }
+}
+
+void HRandFieldCmd::DoWithPositiveCount(PClient* client, const PHash* hash, int64_t count, bool with_value) {
+  if (hash->size() <= count) {  // reply all fields
+    client->AppendArrayLen(with_value ? hash->size() * 2 : hash->size());
+    for (auto&& kv : *hash) {
+      client->AppendString(kv.first);
+      if (with_value) {
+        client->AppendString(kv.second);
+      }
+    }
+  } else {  // reply [count] fields
+    std::vector<std::pair<PString, PString>> kvs;
+    for (auto&& kv : *hash) {
+      kvs.push_back(kv);
+    }
+    std::shuffle(kvs.begin(), kvs.end(), std::mt19937(rd_()));
+
+    client->AppendArrayLen(with_value ? count * 2 : count);
+    for (size_t i = 0; i < count; i++) {
+      client->AppendString(kvs[i].first);
+      if (with_value) {
+        client->AppendString(kvs[i].second);
+      }
+    }
+  }
+}
+
+void HRandFieldCmd::DoWithNegativeCount(PClient* client, const PHash* hash, int64_t count, bool with_value) {
+  count = -count;
+  client->AppendArrayLen(with_value ? count * 2 : count);
+  while (count--) {
+    auto it = std::next(hash->begin(), rand() % hash->size());
+    client->AppendString(it->first);
+    if (with_value) {
+      client->AppendString(it->second);
+    }
+  }
+}
+
 }  // namespace pikiwidb

src/cmd_hash.h

@@ -7,7 +7,10 @@
 
 #pragma once
 
+#include <random>
+
 #include "base_cmd.h"
+#include "hash.h"
 
 namespace pikiwidb {
 
@@ -99,4 +102,21 @@ class HStrLenCmd : public BaseCmd {
   void DoCmd(PClient *client) override;
 };
 
+class HRandFieldCmd : public BaseCmd {
+ public:
+  HRandFieldCmd(const std::string &name, int16_t arity);
+
+ protected:
+  bool DoInitial(PClient *client) override;
+
+ private:
+  void DoCmd(PClient *client) override;
+  void DoWithPositiveCount(PClient *client, const PHash *hash, int64_t count, bool with_value);
+  void DoWithNegativeCount(PClient *client, const PHash *hash, int64_t count, bool with_value);
+
+  std::random_device rd_;
+
+  static const inline std::string kWithValueString{"withvalues"};
+};
+
 }  // namespace pikiwidb

src/cmd_table_manager.cc

@@ -71,6 +71,7 @@ void CmdTableManager::InitCmdTable() {
   ADD_COMMAND(HKeys, 2);
   ADD_COMMAND(HLen, 2);
   ADD_COMMAND(HStrLen, 3);
+  ADD_COMMAND(HRandField, -2);
 }
 
 std::pair<BaseCmd*, CmdRes::CmdRet> CmdTableManager::GetCommand(const std::string& cmdName, PClient* client) {