database.rules.json

{
  "rules" : {
    "channels" : {
      ".read" : "auth != null",
        "$channelId" : {
          ".write" : "auth != null",
            ".validate" : "newData.hasChildren(['id', 'name', 'createdBy', 'details'])",
              "id" : {
                ".validate" : "newData.val() === $channelId"
              },
              "name" : {
                ".validate" : "newData.val().length > 0"
              },
              "details" : {
                ".validate" : "newData.val().length > 0"
              }
                  
        }
    },
		"messages" : {
      "$channelId" : {
        ".read" : "auth != null",
        ".validate" : "root.child('channels/'+$channelId).exists()",
          "$messageId" : {
            ".write" : "auth != null",
            ".validate" : "newData.hasChildren(['content', 'user', 'timestamp']) && !newData.hasChildren(['image']) || newData.hasChildren(['image', 'user', 'timestamp']) && !newData.hasChildren(['content'])",
        	"content" : {
          	".validate" : "newData.val().length > 0"
        	},
          "image" : {
             ".validate" : "newData.val().length > 0"         
          },
          "user" : {
            ".validate" : "newData.hasChildren(['id', 'name', 'avatar'])"
          }
        }
      }
    },
    "privateMessages" : {
      "$uid1" : {
        "$uid2" : {
          ".read" : "auth != null && ($uid1 === auth.uid || $uid2 === auth.uid)",
          "$messageId" : {
            ".write" : "auth != null",
            ".validate" : "newData.hasChildren(['content', 'user', 'timestamp']) && !newData.hasChildren(['image']) || newData.hasChildren(['image', 'user', 'timestamp']) && !newData.hasChildren(['content'])",
        		"content" : {
          	".validate" : "newData.val().length > 0"
        		},
          	"image" : {
             ".validate" : "newData.val().length > 0"         
          	},
          	"user" : {
            ".validate" : "newData.hasChildren(['id', 'name', 'avatar'])"
          	}
          }
        }
      }
    },
    "presence" : {
      ".read" : "auth != null",
      ".write" : "auth != null"
    },
    "typing" : {
      ".read" : "auth != null",
      ".write" : "auth != null"
    },
    "users" : {
      ".read" : "auth != null",
      "$uid" : {
        ".write" : "auth != null && auth.uid === $uid",
        ".validate" : "newData.hasChildren(['name', 'avatar'])",
      "name" : {
        ".validate" : "newData.val().length > 0"
      	},
      "avatar" : {
        ".validate" : "newData.val().length > 0"
      	},
      }
    }
  }
}