text: /*
   * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   *   * Redistributions of source code must retain the above copyright notice,
   *     this list of conditions and the following disclaimer.
   *   * Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   *   * Neither the name of Redis nor the names of its contributors may be used
   *     to endorse or promote products derived from this software without
   *     specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
   * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   */
  
  #include "server.h"
  #include <math.h> /* isnan(), isinf() */
  
  /* Forward declarations */
  int getGenericCommand(client *c);
  
  /*-----------------------------------------------------------------------------
   * String Commands
   *----------------------------------------------------------------------------*/
  
  static int checkStringLength(client *c, long long size) {
      if (!(c->flags & CLIENT_MASTER) && size > server.proto_max_bulk_len) {
          addReplyError(c,"string exceeds maximum allowed size (proto-max-bulk-len)");
          return C_ERR;
      }
      return C_OK;
  }
  
  /* The setGenericCommand() function implements the SET operation with different
   * options and variants. This function is called in order to implement the
   * following commands: SET, SETEX, PSETEX, SETNX, GETSET.
   *实现了 SET 、 SETEX 、 PSETEX 和 SETNX 命令
   * 'flags' changes the behavior of the command (NX, XX or GET, see below).
   *
   * 'expire' represents an expire to set in form of a Redis object as passed
   * by the user. It is interpreted according to the specified 'unit'.
   *
   * 'ok_reply' and 'abort_reply' is what the function will reply to the client
   * if the operation is performed, or when it is not because of NX or
   * XX flags.
   *
   * If ok_reply is NULL "+OK" is used.
   * If abort_reply is NULL, "$-1" is used. */
  
  #define OBJ_NO_FLAGS 0
  #define OBJ_SET_NX (1<<0)          /* Set if key not exists. */
  #define OBJ_SET_XX (1<<1)          /* Set if key exists. */
  #define OBJ_EX (1<<2)              /* Set if time in seconds is given */
  #define OBJ_PX (1<<3)              /* Set if time in ms in given */
  #define OBJ_KEEPTTL (1<<4)         /* Set and keep the ttl */
  #define OBJ_SET_GET (1<<5)         /* Set if want to get key before set */
  #define OBJ_EXAT (1<<6)            /* Set if timestamp in second is given */
  #define OBJ_PXAT (1<<7)            /* Set if timestamp in ms is given */
  #define OBJ_PERSIST (1<<8)         /* Set if we need to remove the ttl */
  
  /* Forward declaration */
  static int getExpireMillisecondsOrReply(client *c, robj *expire, int flags, int unit, long long *milliseconds);
  
  void setGenericCommand(client *c, int flags, robj *key, robj *val, robj *expire, int unit, robj *ok_reply, robj *abort_reply) {
      long long milliseconds = 0; /* initialized to avoid any harmness warning */
      if (expire && getExpireMillisecondsOrReply(c, expire, flags, unit, &milliseconds) != C_OK) {
          return;
      }
  
      if (flags & OBJ_SET_GET) {
          if (getGenericCommand(c) == C_ERR) return;
      }
      // 如果设置了 NX 或者 XX 参数，那么检查条件是否不符合这两个设置
      // 在条件不符合时报错，报错的内容由 abort_reply 参数决定
      if ((flags & OBJ_SET_NX && lookupKeyWrite(c->db,key) != NULL) ||
          (flags & OBJ_SET_XX && lookupKeyWrite(c->db,key) == NULL))
      {
          if (!(flags & OBJ_SET_GET)) {
              addReply(c, abort_reply ? abort_reply : shared.null[c->resp]);
          }
          return;
      }
  
      genericSetKey(c,c->db,key, val,flags & OBJ_KEEPTTL,1);
      //数据库设置为脏,避免公用冲突
      server.dirty++;
      notifyKeyspaceEvent(NOTIFY_STRING,"set",key,c->db->id);
  
      if (expire) {
          setExpire(c,c->db,key,milliseconds);
          /* Propagate as SET Key Value PXAT millisecond-timestamp if there is
           * EX/PX/EXAT/PXAT flag. */
          robj *milliseconds_obj = createStringObjectFromLongLong(milliseconds);
          rewriteClientCommandVector(c, 5, shared.set, key, val, shared.pxat, milliseconds_obj);
          decrRefCount(milliseconds_obj);
          notifyKeyspaceEvent(NOTIFY_GENERIC,"expire",key,c->db->id);
      }
  
      if (!(flags & OBJ_SET_GET)) {
          addReply(c, ok_reply ? ok_reply : shared.ok);
      }
  
      /* Propagate without the GET argument (Isn't needed if we had expire since in that case we completely re-written the command argv) */
      if ((flags & OBJ_SET_GET) && !expire) {
          int argc = 0;
          int j;
          robj **argv = zmalloc((c->argc-1)*sizeof(robj*));
          for (j=0; j < c->argc; j++) {
              char *a = c->argv[j]->ptr;
              /* Skip GET which may be repeated multiple times. */
              if (j >= 3 &&
                  (a[0] == 'g' || a[0] == 'G') &&
                  (a[1] == 'e' || a[1] == 'E') &&
                  (a[2] == 't' || a[2] == 'T') && a[3] == '\0')
                  continue;
              argv[argc++] = c->argv[j];
              incrRefCount(c->argv[j]);
          }
          replaceClientCommandVector(c, argc, argv);
      }
  }
  
  /*
   * Extract the `expire` argument of a given GET/SET command as an absolute timestamp in milliseconds.
   *
   * "client" is the client that sent the `expire` argument.
   * "expire" is the `expire` argument to be extracted.
   * "flags" represents the behavior of the command (e.g. PX or EX).
   * "unit" is the original unit of the given `expire` argument (e.g. UNIT_SECONDS).
   * "milliseconds" is output argument.
   *
   * If return C_OK, "milliseconds" output argument will be set to the resulting absolute timestamp.
   * If return C_ERR, an error reply has been added to the given client.
   */
  static int getExpireMillisecondsOrReply(client *c, robj *expire, int flags, int unit, long long *milliseconds) {
      int ret = getLongLongFromObjectOrReply(c, expire, milliseconds, NULL);
      if (ret != C_OK) {
          return ret;
      }
  
      if (*milliseconds <= 0 || (unit == UNIT_SECONDS && *milliseconds > LLONG_MAX / 1000)) {
          /* Negative value provided or multiplication is gonna overflow. */
          addReplyErrorFormat(c, "invalid expire time in %s", c->cmd->name);
          return C_ERR;
      }
  
      if (unit == UNIT_SECONDS) *milliseconds *= 1000;
  
      if ((flags & OBJ_PX) || (flags & OBJ_EX)) {
          *milliseconds += mstime();
      }
  
      if (*milliseconds <= 0) {
          /* Overflow detected. */
          addReplyErrorFormat(c,"invalid expire time in %s",c->cmd->name);
          return C_ERR;
      }
  
      return C_OK;
  }
  
  #define COMMAND_GET 0
  #define COMMAND_SET 1
  /*
   * The parseExtendedStringArgumentsOrReply() function performs the common validation for extended
   * string arguments used in SET and GET command.
   *
   * Get specific commands - PERSIST/DEL
   * Set specific commands - XX/NX/GET
   * Common commands - EX/EXAT/PX/PXAT/KEEPTTL
   *
   * Function takes pointers to client, flags, unit, pointer to pointer of expire obj if needed
   * to be determined and command_type which can be COMMAND_GET or COMMAND_SET.
   *
   * If there are any syntax violations C_ERR is returned else C_OK is returned.
   *
   * Input flags are updated upon parsing the arguments. Unit and expire are updated if there are any
   * EX/EXAT/PX/PXAT arguments. Unit is updated to millisecond if PX/PXAT is set.
   */
  int parseExtendedStringArgumentsOrReply(client *c, int *flags, int *unit, robj **expire, int command_type) {
  
      int j = command_type == COMMAND_GET ? 2 : 3;
      for (; j < c->argc; j++) {
          char *opt = c->argv[j]->ptr;
          robj *next = (j == c->argc-1) ? NULL : c->argv[j+1];
  
          if ((opt[0] == 'n' || opt[0] == 'N') &&
              (opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&
              !(*flags & OBJ_SET_XX) && (command_type == COMMAND_SET))
          {
              *flags |= OBJ_SET_NX;
          } else if ((opt[0] == 'x' || opt[0] == 'X') &&
                     (opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&
                     !(*flags & OBJ_SET_NX) && (command_type == COMMAND_SET))
          {
              *flags |= OBJ_SET_XX;
          } else if ((opt[0] == 'g' || opt[0] == 'G') &&
                     (opt[1] == 'e' || opt[1] == 'E') &&
                     (opt[2] == 't' || opt[2] == 'T') && opt[3] == '\0' &&
                     (command_type == COMMAND_SET))
          {
              *flags |= OBJ_SET_GET;
          } else if (!strcasecmp(opt, "KEEPTTL") && !(*flags & OBJ_PERSIST) &&
              !(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&
              !(*flags & OBJ_PX) && !(*flags & OBJ_PXAT) && (command_type == COMMAND_SET))
          {
              *flags |= OBJ_KEEPTTL;
          } else if (!strcasecmp(opt,"PERSIST") && (command_type == COMMAND_GET) &&
                 !(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&
                 !(*flags & OBJ_PX) && !(*flags & OBJ_PXAT) &&
                 !(*flags & OBJ_KEEPTTL))
          {
              *flags |= OBJ_PERSIST;
          } else if ((opt[0] == 'e' || opt[0] == 'E') &&
                     (opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&
                     !(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&
                     !(*flags & OBJ_EXAT) && !(*flags & OBJ_PX) &&
                     !(*flags & OBJ_PXAT) && next)
          {
              *flags |= OBJ_EX;
              *expire = next;
              j++;
          } else if ((opt[0] == 'p' || opt[0] == 'P') &&
                     (opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&
                     !(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&
                     !(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&
                     !(*flags & OBJ_PXAT) && next)
          {
              *flags |= OBJ_PX;
              *unit = UNIT_MILLISECONDS;
              *expire = next;
              j++;
          } else if ((opt[0] == 'e' || opt[0] == 'E') &&
                     (opt[1] == 'x' || opt[1] == 'X') &&
                     (opt[2] == 'a' || opt[2] == 'A') &&
                     (opt[3] == 't' || opt[3] == 'T') && opt[4] == '\0' &&
                     !(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&
                     !(*flags & OBJ_EX) && !(*flags & OBJ_PX) &&
                     !(*flags & OBJ_PXAT) && next)
          {
              *flags |= OBJ_EXAT;
              *expire = next;
              j++;
          } else if ((opt[0] == 'p' || opt[0] == 'P') &&
                     (opt[1] == 'x' || opt[1] == 'X') &&
                     (opt[2] == 'a' || opt[2] == 'A') &&
                     (opt[3] == 't' || opt[3] == 'T') && opt[4] == '\0' &&
                     !(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&
                     !(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&
                     !(*flags & OBJ_PX) && next)
          {
              *flags |= OBJ_PXAT;
              *unit = UNIT_MILLISECONDS;
              *expire = next;
              j++;
          } else {
              addReplyErrorObject(c,shared.syntaxerr);
              return C_ERR;
          }
      }
      return C_OK;
  }
  
  /* SET key value [NX] [XX] [KEEPTTL] [GET] [EX <seconds>] [PX <milliseconds>]
   *     [EXAT <seconds-timestamp>][PXAT <milliseconds-timestamp>] */
  void setCommand(client *c) {
      robj *expire = NULL;
      int unit = UNIT_SECONDS;
      int flags = OBJ_NO_FLAGS;
  
      if (parseExtendedStringArgumentsOrReply(c,&flags,&unit,&expire,COMMAND_SET) != C_OK) {
          return;
      }
  
      c->argv[2] = tryObjectEncoding(c->argv[2]);
      setGenericCommand(c,flags,c->argv[1],c->argv[2],expire,unit,NULL,NULL);
  }
  
  void setnxCommand(client *c) {
      c->argv[2] = tryObjectEncoding(c->argv[2]);
      setGenericCommand(c,OBJ_SET_NX,c->argv[1],c->argv[2],NULL,0,shared.cone,shared.czero);
  }
  
  void setexCommand(client *c) {
      c->argv[3] = tryObjectEncoding(c->argv[3]);
      setGenericCommand(c,OBJ_EX,c->argv[1],c->argv[3],c->argv[2],UNIT_SECONDS,NULL,NULL);
  }
  
  void psetexCommand(client *c) {
      c->argv[3] = tryObjectEncoding(c->argv[3]);
      setGenericCommand(c,OBJ_PX,c->argv[1],c->argv[3],c->argv[2],UNIT_MILLISECONDS,NULL,NULL);
  }
  
  int getGenericCommand(client *c) {
      robj *o;
      // 尝试从数据库中取出键 c->argv[1] 对应的值对象
      // 如果键不存在时，向客户端发送回复信息，并返回 NULL
      if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.null[c->resp])) == NULL)
          return C_OK;
      // 值对象存在，检查它的类型
      if (checkType(c,o,OBJ_STRING)) {
          return C_ERR;
      }
      // 类型正确，向客户端返回对象的值
      addReplyBulk(c,o);
      return C_OK;
  }
  
  void getCommand(client *c) {
      getGenericCommand(c);
  }
  
  /*
   * GETEX <key> [PERSIST][EX seconds][PX milliseconds][EXAT seconds-timestamp][PXAT milliseconds-timestamp]
   *
   * The getexCommand() function implements extended options and variants of the GET command. Unlike GET
   * command this command is not read-only.
   * 
   * The default behavior when no options are specified is same as GET and does not alter any TTL.
   *
   * Only one of the below options can be used at a given time.
   *
   * 1. PERSIST removes any TTL associated with the key.
   * 2. EX Set expiry TTL in seconds.
   * 3. PX Set expiry TTL in milliseconds.
   * 4. EXAT Same like EX instead of specifying the number of seconds representing the TTL
   *      (time to live), it takes an absolute Unix timestamp
   * 5. PXAT Same like PX instead of specifying the number of milliseconds representing the TTL
   *      (time to live), it takes an absolute Unix timestamp
   *
   * Command would either return the bulk string, error or nil.
   */
  void getexCommand(client *c) {
      robj *expire = NULL;
      int unit = UNIT_SECONDS;
      int flags = OBJ_NO_FLAGS;
  
      if (parseExtendedStringArgumentsOrReply(c,&flags,&unit,&expire,COMMAND_GET) != C_OK) {
          return;
      }
  
      robj *o;
  
      if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.null[c->resp])) == NULL)
          return;
  
      if (checkType(c,o,OBJ_STRING)) {
          return;
      }
  
      /* Validate the expiration time value first */
      long long milliseconds = 0;
      if (expire && getExpireMillisecondsOrReply(c, expire, flags, unit, &milliseconds) != C_OK) {
          return;
      }
  
      /* We need to do this before we expire the key or delete it */
      addReplyBulk(c,o);
  
      /* This command is never propagated as is. It is either propagated as PEXPIRE[AT],DEL,UNLINK or PERSIST.
       * This why it doesn't need special handling in feedAppendOnlyFile to convert relative expire time to absolute one. */
      if (((flags & OBJ_PXAT) || (flags & OBJ_EXAT)) && checkAlreadyExpired(milliseconds)) {
          /* When PXAT/EXAT absolute timestamp is specified, there can be a chance that timestamp
           * has already elapsed so delete the key in that case. */
          int deleted = server.lazyfree_lazy_expire ? dbAsyncDelete(c->db, c->argv[1]) :
                        dbSyncDelete(c->db, c->argv[1]);
          serverAssert(deleted);
          robj *aux = server.lazyfree_lazy_expire ? shared.unlink : shared.del;
          rewriteClientCommandVector(c,2,aux,c->argv[1]);
          signalModifiedKey(c, c->db, c->argv[1]);
          notifyKeyspaceEvent(NOTIFY_GENERIC, "del", c->argv[1], c->db->id);
          server.dirty++;
      } else if (expire) {
          setExpire(c,c->db,c->argv[1],milliseconds);
          /* Propagate as PXEXPIREAT millisecond-timestamp if there is
           * EX/PX/EXAT/PXAT flag and the key has not expired. */
          robj *milliseconds_obj = createStringObjectFromLongLong(milliseconds);
          rewriteClientCommandVector(c,3,shared.pexpireat,c->argv[1],milliseconds_obj);
          decrRefCount(milliseconds_obj);
          signalModifiedKey(c, c->db, c->argv[1]);
          notifyKeyspaceEvent(NOTIFY_GENERIC,"expire",c->argv[1],c->db->id);
          server.dirty++;
      } else if (flags & OBJ_PERSIST) {
          if (removeExpire(c->db, c->argv[1])) {
              signalModifiedKey(c, c->db, c->argv[1]);
              rewriteClientCommandVector(c, 2, shared.persist, c->argv[1]);
              notifyKeyspaceEvent(NOTIFY_GENERIC,"persist",c->argv[1],c->db->id);
              server.dirty++;
          }
      }
  }
  
  void getdelCommand(client *c) {
      if (getGenericCommand(c) == C_ERR) return;
      int deleted = server.lazyfree_lazy_user_del ? dbAsyncDelete(c->db, c->argv[1]) :
                    dbSyncDelete(c->db, c->argv[1]);
      if (deleted) {
          /* Propagate as DEL/UNLINK command */
          robj *aux = server.lazyfree_lazy_user_del ? shared.unlink : shared.del;
          rewriteClientCommandVector(c,2,aux,c->argv[1]);
          signalModifiedKey(c, c->db, c->argv[1]);
          notifyKeyspaceEvent(NOTIFY_GENERIC, "del", c->argv[1], c->db->id);
          server.dirty++;
      }
  }
  
  void getsetCommand(client *c) {
      if (getGenericCommand(c) == C_ERR) return;
      c->argv[2] = tryObjectEncoding(c->argv[2]);
      setKey(c,c->db,c->argv[1],c->argv[2]);
      notifyKeyspaceEvent(NOTIFY_STRING,"set",c->argv[1],c->db->id);
      server.dirty++;
  
      /* Propagate as SET command */
      rewriteClientCommandArgument(c,0,shared.set);
  }
  
  void setrangeCommand(client *c) {
      robj *o;
      long offset;
      sds value = c->argv[3]->ptr;
  
      if (getLongFromObjectOrReply(c,c->argv[2],&offset,NULL) != C_OK)
          return;
  
      if (offset < 0) {
          addReplyError(c,"offset is out of range");
          return;
      }
  
      o = lookupKeyWrite(c->db,c->argv[1]);
      if (o == NULL) {
          /* Return 0 when setting nothing on a non-existing string */
          if (sdslen(value) == 0) {
              addReply(c,shared.czero);
              return;
          }
  
          /* Return when the resulting string exceeds allowed size */
          if (checkStringLength(c,offset+sdslen(value)) != C_OK)
              return;
  
          o = createObject(OBJ_STRING,sdsnewlen(NULL, offset+sdslen(value)));
          dbAdd(c->db,c->argv[1],o);
      } else {
          size_t olen;
  
          /* Key exists, check type */
          if (checkType(c,o,OBJ_STRING))
              return;
  
          /* Return existing string length when setting nothing */
          olen = stringObjectLen(o);
          if (sdslen(value) == 0) {
              addReplyLongLong(c,olen);
              return;
          }
  
          /* Return when the resulting string exceeds allowed size */
          if (checkStringLength(c,offset+sdslen(value)) != C_OK)
              return;
  
          /* Create a copy when the object is shared or encoded. */
          o = dbUnshareStringValue(c->db,c->argv[1],o);
      }
  
      if (sdslen(value) > 0) {//感觉这里不需要加上>0的判断条件了
          o->ptr = sdsgrowzero(o->ptr,offset+sdslen(value));
          memcpy((char*)o->ptr+offset,value,sdslen(value));
          signalModifiedKey(c,c->db,c->argv[1]);
          notifyKeyspaceEvent(NOTIFY_STRING,
              "setrange",c->argv[1],c->db->id);
          server.dirty++;
      }
      addReplyLongLong(c,sdslen(o->ptr));
  }
  
  void getrangeCommand(client *c) {
      robj *o;
      long long start, end;
      char *str, llbuf[32];
      size_t strlen;
  
      if (getLongLongFromObjectOrReply(c,c->argv[2],&start,NULL) != C_OK)
          return;
      if (getLongLongFromObjectOrReply(c,c->argv[3],&end,NULL) != C_OK)
          return;
      if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptybulk)) == NULL ||
          checkType(c,o,OBJ_STRING)) return;
  
      if (o->encoding == OBJ_ENCODING_INT) {
          str = llbuf;
          strlen = ll2string(llbuf,sizeof(llbuf),(long)o->ptr);
      } else {
          str = o->ptr;
          strlen = sdslen(str);
      }
  
      /* Convert negative indexes */
      if (start < 0 && end < 0 && start > end) {
          addReply(c,shared.emptybulk);
          return;
      }
      if (start < 0) start = strlen+start;
      if (end < 0) end = strlen+end;
      if (start < 0) start = 0;
      if (end < 0) end = 0;
      if ((unsigned long long)end >= strlen) end = strlen-1;
  
      /* Precondition: end >= 0 && end < strlen, so the only condition where
       * nothing can be returned is: start > end. */
      if (start > end || strlen == 0) {
          addReply(c,shared.emptybulk);
      } else {
          addReplyBulkCBuffer(c,(char*)str+start,end-start+1);
      }
  }
  
  void mgetCommand(client *c) {
      int j;
  
      addReplyArrayLen(c,c->argc-1);
      for (j = 1; j < c->argc; j++) {
          robj *o = lookupKeyRead(c->db,c->argv[j]);
          if (o == NULL) {
              addReplyNull(c);
          } else {
              if (o->type != OBJ_STRING) {
                  addReplyNull(c);
              } else {
                  addReplyBulk(c,o);
              }
          }
      }
  }
  
  void msetGenericCommand(client *c, int nx) {
      int j;
  
      if ((c->argc % 2) == 0) {
          addReplyErrorFormat(c,"wrong number of arguments for '%s' command",
                              c->cmd->name);
          return;
      }
  
      /* Handle the NX flag. The MSETNX semantic is to return zero and don't
       * set anything if at least one key already exists. */
      if (nx) {
          for (j = 1; j < c->argc; j += 2) {
              if (lookupKeyWrite(c->db,c->argv[j]) != NULL) {
                  addReply(c, shared.czero);
                  return;
              }
          }
      }
  
      for (j = 1; j < c->argc; j += 2) {
          c->argv[j+1] = tryObjectEncoding(c->argv[j+1]);
          setKey(c,c->db,c->argv[j],c->argv[j+1]);
          notifyKeyspaceEvent(NOTIFY_STRING,"set",c->argv[j],c->db->id);
      }
      server.dirty += (c->argc-1)/2;
      addReply(c, nx ? shared.cone : shared.ok);
  }
  
  void msetCommand(client *c) {
      msetGenericCommand(c,0);
  }
  
  void msetnxCommand(client *c) {
      msetGenericCommand(c,1);
  }
  
  void incrDecrCommand(client *c, long long incr) {
      long long value, oldvalue;
      robj *o, *new;
  
      o = lookupKeyWrite(c->db,c->argv[1]);
      if (checkType(c,o,OBJ_STRING)) return;
      if (getLongLongFromObjectOrReply(c,o,&value,NULL) != C_OK) return;
  
      oldvalue = value;
      if ((incr < 0 && oldvalue < 0 && incr < (LLONG_MIN-oldvalue)) ||
          (incr > 0 && oldvalue > 0 && incr > (LLONG_MAX-oldvalue))) {
          addReplyError(c,"increment or decrement would overflow");
          return;
      }
      value += incr;
  
      if (o && o->refcount == 1 && o->encoding == OBJ_ENCODING_INT &&
          (value < 0 || value >= OBJ_SHARED_INTEGERS) &&
          value >= LONG_MIN && value <= LONG_MAX)
      {
          new = o;
          o->ptr = (void*)((long)value);
      } else {
          new = createStringObjectFromLongLongForValue(value);
          if (o) {
              dbOverwrite(c->db,c->argv[1],new);
          } else {
              dbAdd(c->db,c->argv[1],new);
          }
      }
      signalModifiedKey(c,c->db,c->argv[1]);
      notifyKeyspaceEvent(NOTIFY_STRING,"incrby",c->argv[1],c->db->id);
      server.dirty++;
      addReplyLongLong(c, value);
  }
  
  void incrCommand(client *c) {
      incrDecrCommand(c,1);
  }
  
  void decrCommand(client *c) {
      incrDecrCommand(c,-1);
  }
  
  void incrbyCommand(client *c) {
      long long incr;
  
      if (getLongLongFromObjectOrReply(c, c->argv[2], &incr, NULL) != C_OK) return;
      incrDecrCommand(c,incr);
  }
  
  void decrbyCommand(client *c) {
      long long incr;
  
      if (getLongLongFromObjectOrReply(c, c->argv[2], &incr, NULL) != C_OK) return;
      incrDecrCommand(c,-incr);
  }
  
  void incrbyfloatCommand(client *c) {
      long double incr, value;
      robj *o, *new;
  
      o = lookupKeyWrite(c->db,c->argv[1]);
      if (checkType(c,o,OBJ_STRING)) return;
      if (getLongDoubleFromObjectOrReply(c,o,&value,NULL) != C_OK ||
          getLongDoubleFromObjectOrReply(c,c->argv[2],&incr,NULL) != C_OK)
          return;
  
      value += incr;
      if (isnan(value) || isinf(value)) {
          addReplyError(c,"increment would produce NaN or Infinity");
          return;
      }
      new = createStringObjectFromLongDouble(value,1);
      if (o)
          dbOverwrite(c->db,c->argv[1],new);
      else
          dbAdd(c->db,c->argv[1],new);
      signalModifiedKey(c,c->db,c->argv[1]);
      notifyKeyspaceEvent(NOTIFY_STRING,"incrbyfloat",c->argv[1],c->db->id);
      server.dirty++;
      addReplyBulk(c,new);
  
      /* Always replicate INCRBYFLOAT as a SET command with the final value
       * in order to make sure that differences in float precision or formatting
       * will not create differences in replicas or after an AOF restart. */
      rewriteClientCommandArgument(c,0,shared.set);
      rewriteClientCommandArgument(c,2,new);
      rewriteClientCommandArgument(c,3,shared.keepttl);
  }
  
  void appendCommand(client *c) {
      size_t totlen;
      robj *o, *append;
  
      o = lookupKeyWrite(c->db,c->argv[1]);
      if (o == NULL) {
          /* Create the key */
          c->argv[2] = tryObjectEncoding(c->argv[2]);
          dbAdd(c->db,c->argv[1],c->argv[2]);
          incrRefCount(c->argv[2]);
          totlen = stringObjectLen(c->argv[2]);
      } else {
          /* Key exists, check type */
          if (checkType(c,o,OBJ_STRING))
              return;
  
          /* "append" is an argument, so always an sds */
          append = c->argv[2];
          totlen = stringObjectLen(o)+sdslen(append->ptr);
          if (checkStringLength(c,totlen) != C_OK)
              return;
  
          /* Append the value */
          o = dbUnshareStringValue(c->db,c->argv[1],o);
          o->ptr = sdscatlen(o->ptr,append->ptr,sdslen(append->ptr));
          totlen = sdslen(o->ptr);
      }
      signalModifiedKey(c,c->db,c->argv[1]);
      notifyKeyspaceEvent(NOTIFY_STRING,"append",c->argv[1],c->db->id);
      server.dirty++;
      addReplyLongLong(c,totlen);
  }
  
  void strlenCommand(client *c) {
      robj *o;
      if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
          checkType(c,o,OBJ_STRING)) return;
      addReplyLongLong(c,stringObjectLen(o));
  }
  
  
  /* STRALGO -- Implement complex algorithms on strings.
   *
   * STRALGO <algorithm> ... arguments ... */
  void stralgoLCS(client *c);     /* This implements the LCS algorithm. */
  void stralgoCommand(client *c) {
      /* Select the algorithm. */
      if (!strcasecmp(c->argv[1]->ptr,"lcs")) {
          stralgoLCS(c);
      } else {
          addReplyErrorObject(c,shared.syntaxerr);
      }
  }
  
  /* STRALGO <algo> [IDX] [LEN] [MINMATCHLEN <len>] [WITHMATCHLEN]
   *     STRINGS <string> <string> | KEYS <keya> <keyb>
   */
  void stralgoLCS(client *c) {
      uint32_t i, j;
      long long minmatchlen = 0;
      sds a = NULL, b = NULL;
      int getlen = 0, getidx = 0, withmatchlen = 0;
      robj *obja = NULL, *objb = NULL;
  
      for (j = 2; j < (uint32_t)c->argc; j++) {
          char *opt = c->argv[j]->ptr;
          int moreargs = (c->argc-1) - j;
  
          if (!strcasecmp(opt,"IDX")) {
              getidx = 1;
          } else if (!strcasecmp(opt,"LEN")) {
              getlen = 1;
          } else if (!strcasecmp(opt,"WITHMATCHLEN")) {
              withmatchlen = 1;
          } else if (!strcasecmp(opt,"MINMATCHLEN") && moreargs) {
              if (getLongLongFromObjectOrReply(c,c->argv[j+1],&minmatchlen,NULL)
                  != C_OK) goto cleanup;
              if (minmatchlen < 0) minmatchlen = 0;
              j++;
          } else if (!strcasecmp(opt,"STRINGS") && moreargs > 1) {
              if (a != NULL) {
                  addReplyError(c,"Either use STRINGS or KEYS");
                  goto cleanup;
              }
              a = c->argv[j+1]->ptr;
              b = c->argv[j+2]->ptr;
              j += 2;
          } else if (!strcasecmp(opt,"KEYS") && moreargs > 1) {
              if (a != NULL) {
                  addReplyError(c,"Either use STRINGS or KEYS");
                  goto cleanup;
              }
              obja = lookupKeyRead(c->db,c->argv[j+1]);
              objb = lookupKeyRead(c->db,c->argv[j+2]);
              if ((obja && obja->type != OBJ_STRING) ||
                  (objb && objb->type != OBJ_STRING))
              {
                  addReplyError(c,
                      "The specified keys must contain string values");
                  /* Don't cleanup the objects, we need to do that
                   * only after calling getDecodedObject(). */
                  obja = NULL;
                  objb = NULL;
                  goto cleanup;
              }
              obja = obja ? getDecodedObject(obja) : createStringObject("",0);
              objb = objb ? getDecodedObject(objb) : createStringObject("",0);
              a = obja->ptr;
              b = objb->ptr;
              j += 2;
          } else {
              addReplyErrorObject(c,shared.syntaxerr);
              goto cleanup;
          }
      }
  
      /* Complain if the user passed ambiguous parameters. */
      if (a == NULL) {
          addReplyError(c,"Please specify two strings: "
                          "STRINGS or KEYS options are mandatory");
          goto cleanup;
      } else if (getlen && getidx) {
          addReplyError(c,
              "If you want both the length and indexes, please "
              "just use IDX.");
          goto cleanup;
      }
  
      /* Detect string truncation or later overflows. */
      if (sdslen(a) >= UINT32_MAX-1 || sdslen(b) >= UINT32_MAX-1) {
          addReplyError(c, "String too long for LCS");
          goto cleanup;
      }
  
      /* Compute the LCS using the vanilla dynamic programming technique of
       * building a table of LCS(x,y) substrings. */
      uint32_t alen = sdslen(a);
      uint32_t blen = sdslen(b);
  
      /* Setup an uint32_t array to store at LCS[i,j] the length of the
       * LCS A0..i-1, B0..j-1. Note that we have a linear array here, so
       * we index it as LCS[j+(blen+1)*j] */
      #define LCS(A,B) lcs[(B)+((A)*(blen+1))]
  
      /* Try to allocate the LCS table, and abort on overflow or insufficient memory. */
      unsigned long long lcssize = (unsigned long long)(alen+1)*(blen+1); /* Can't overflow due to the size limits above. */
      unsigned long long lcsalloc = lcssize * sizeof(uint32_t);
      uint32_t *lcs = NULL;
      if (lcsalloc < SIZE_MAX && lcsalloc / lcssize == sizeof(uint32_t))
          lcs = ztrymalloc(lcsalloc);
      if (!lcs) {
          addReplyError(c, "Insufficient memory");
          goto cleanup;
      }
  
      /* Start building the LCS table. */
      for (uint32_t i = 0; i <= alen; i++) {
          for (uint32_t j = 0; j <= blen; j++) {
              if (i == 0 || j == 0) {
                  /* If one substring has length of zero, the
                   * LCS length is zero. */
                  LCS(i,j) = 0;
              } else if (a[i-1] == b[j-1]) {
                  /* The len LCS (and the LCS itself) of two
                   * sequences with the same final character, is the
                   * LCS of the two sequences without the last char
                   * plus that last char. */
                  LCS(i,j) = LCS(i-1,j-1)+1;
              } else {
                  /* If the last character is different, take the longest
                   * between the LCS of the first string and the second
                   * minus the last char, and the reverse. */
                  uint32_t lcs1 = LCS(i-1,j);
                  uint32_t lcs2 = LCS(i,j-1);
                  LCS(i,j) = lcs1 > lcs2 ? lcs1 : lcs2;
              }
          }
      }
  
      /* Store the actual LCS string in "result" if needed. We create
       * it backward, but the length is already known, we store it into idx. */
      uint32_t idx = LCS(alen,blen);
      sds result = NULL;        /* Resulting LCS string. */
      void *arraylenptr = NULL; /* Deferred length of the array for IDX. */
      uint32_t arange_start = alen, /* alen signals that values are not set. */
               arange_end = 0,
               brange_start = 0,
               brange_end = 0;
  
      /* Do we need to compute the actual LCS string? Allocate it in that case. */
      int computelcs = getidx || !getlen;
      if (computelcs) result = sdsnewlen(SDS_NOINIT,idx);
  
      /* Start with a deferred array if we have to emit the ranges. */
      uint32_t arraylen = 0;  /* Number of ranges emitted in the array. */
      if (getidx) {
          addReplyMapLen(c,2);
          addReplyBulkCString(c,"matches");
          arraylenptr = addReplyDeferredLen(c);
      }
  
      i = alen, j = blen;
      while (computelcs && i > 0 && j > 0) {
          int emit_range = 0;
          if (a[i-1] == b[j-1]) {
              /* If there is a match, store the character and reduce
               * the indexes to look for a new match. */
              result[idx-1] = a[i-1];
  
              /* Track the current range. */
              if (arange_start == alen) {
                  arange_start = i-1;
                  arange_end = i-1;
                  brange_start = j-1;
                  brange_end = j-1;
              } else {
                  /* Let's see if we can extend the range backward since
                   * it is contiguous. */
                  if (arange_start == i && brange_start == j) {
                      arange_start--;
                      brange_start--;
                  } else {
                      emit_range = 1;
                  }
              }
              /* Emit the range if we matched with the first byte of
               * one of the two strings. We'll exit the loop ASAP. */
              if (arange_start == 0 || brange_start == 0) emit_range = 1;
              idx--; i--; j--;
          } else {
              /* Otherwise reduce i and j depending on the largest
               * LCS between, to understand what direction we need to go. */
              uint32_t lcs1 = LCS(i-1,j);
              uint32_t lcs2 = LCS(i,j-1);
              if (lcs1 > lcs2)
                  i--;
              else
                  j--;
              if (arange_start != alen) emit_range = 1;
          }
  
          /* Emit the current range if needed. */
          uint32_t match_len = arange_end - arange_start + 1;
          if (emit_range) {
              if (minmatchlen == 0 || match_len >= minmatchlen) {
                  if (arraylenptr) {
                      addReplyArrayLen(c,2+withmatchlen);
                      addReplyArrayLen(c,2);
                      addReplyLongLong(c,arange_start);
                      addReplyLongLong(c,arange_end);
                      addReplyArrayLen(c,2);
                      addReplyLongLong(c,brange_start);
                      addReplyLongLong(c,brange_end);
                      if (withmatchlen) addReplyLongLong(c,match_len);
                      arraylen++;
                  }
              }
              arange_start = alen; /* Restart at the next match. */
          }
      }
  
      /* Signal modified key, increment dirty, ... */
  
      /* Reply depending on the given options. */
      if (arraylenptr) {
          addReplyBulkCString(c,"len");
          addReplyLongLong(c,LCS(alen,blen));
          setDeferredArrayLen(c,arraylenptr,arraylen);
      } else if (getlen) {
          addReplyLongLong(c,LCS(alen,blen));
      } else {
          addReplyBulkSds(c,result);
          result = NULL;
      }
  
      /* Cleanup. */
      sdsfree(result);
      zfree(lcs);
  
  cleanup:
      if (obja) decrRefCount(obja);
      if (objb) decrRefCount(objb);
      return;
  }
  
  