Simulate JVM Application Faults

Chaosd simulates JVM application faults through Byteman. The supported fault types are as follows:

• Throw custom exceptions
• Trigger garbage collection
• Increase method latency
• Modify return values of a method
• Trigger faults by setting Byteman configuration files
• Increase JVM pressure

Chaosd also supports injecting the above faults into common services or their Java clients. For example, when a MySQL Java client executes SQL statements of the specified types ("select", "update", "insert", "replace", or "delete"), you can use Chaosd to inject latency or throw exceptions into that client.

This document describes how to use Chaosd to create the above fault types of JVM experiments.

Before creating the experiment, you can run the following command line to see the types of JVM application faults supported by Chaosd:

chaosd attack jvm -h

The result is as follows:

JVM attack related commands

Usage:
  chaosd attack jvm [command]

Available Commands:
  exception   throw specified exception for specified method
  gc          trigger GC for JVM
  latency     inject latency to specified method
  mysql       inject fault into MySQL client
  return      return specified value for specified method
  rule-file   inject fault with configured byteman rule file
  stress      inject stress to JVM

Flags:
  -h, --help       help for jvm
      --pid int    the pid of Java process which needs to attach
      --port int   the port of agent server (default 9288)

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --uid string         the experiment ID

Use "chaosd attack jvm [command] --help" for more information about a command.

To create experiments using the service mode, you need to run Chaosd in the service mode and then send a POST HTTP request to the /api/attack/jvm path of the Chaosd service:

chaosd server --port 31767

curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{fault-configuration}'

For the fault-configuration part in the above command, you need to configure it according to the fault types. For the corresponding parameters and examples, refer to the parameters of each fault type in the following sections.

note

When running an experiment, remember to save the UID information of the experiment. When you want to end the experiment corresponding to the UID, you need to send an HTTP DELETE request to the /api/attack/{uid} path of Chaosd service.

Throw custom exceptions

Parameters for throwing custom exceptions

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "exception".
class	c	class	The name of the Java class	string	required
exception	—	exception	The thrown custom exception	string	required
method	m	method	The name of the method	string	required to be configured
pid	—	pid	The Java process ID where the fault is to be injected	int	required
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Throw custom exceptions using the command-line mode

To see the usage and configuration items of the command that throws custom exceptions, run the following command:

chaosd attack jvm exception --help

The result is as follows:

throw specified exception for specified method

Usage:
  chaosd attack jvm exception [options] [flags]

Flags:
  -c, --class string       Java class name
      --exception string   the exception which needs to throw for action 'exception'
  -h, --help               help for exception
  -m, --method string      the method name in Java class

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which needs to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for throwing custom exceptions

chaosd attack jvm exception -c Main -m sayhello --exception 'java.io.IOException("BOOM")' --pid 30045

The result is as follows:

[2021/08/05 02:39:39.106 +00:00] [INFO] [jvm.go:208] ["byteman rule"] [rule="\nRULE Main-sayhello-exception-q6nd0\nCLASS Main\nMETHOD sayhello\nAT ENTRY\nIF true\nDO \n\tthrow new java.io.IOException(\"BOOM\");\nENDRULE\n"] [file=/tmp/rule.btm296930759]
Attack jvm successfully, uid: 26a45ae2-d395-46f5-a126-2b2c6c85ae9d

Throw custom exceptions using the service mode

Example for throwing custom exceptions using the service mode

curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"exception","class":"Main","method":"sayhello","exception":"java.io.IOException(\"BOOM\")","pid":1828622}'

The result is as follows:

{"status":200,"message":"attack successfully","uid":"c3c519bf-819a-4a7b-97fb-e3d0814481fa"}

Trigger garbage collection

Parameters for triggering garbage collection

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "gc".
pid	—	pid	The Java process ID where the fault is to be injected	int	required
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Trigger garbage collection using the command-line mode

To see the usage and configuration items of the command that triggers garbage collection, run the following command:

chaosd attack jvm gc --help

trigger GC for JVM

Usage:
  chaosd attack jvm gc [flags]

Flags:
  -h, --help   help for gc

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which needs to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for triggering garbage collection

chaosd attack jvm gc --pid 89345

The result is as follows:

[2021/08/05 02:49:47.850 +00:00] [INFO] [jvm.go:208] ["byteman rule"] [rule="\nRULE --gc-u0mlf\nGC\nENDRULE\n"] [file=/tmp/rule.btm012481052]
Attack jvm successfully, uid: f360e70a-5359-49b6-8526-d7e0a3c6f696

Triggering garbage collection is a one-time operation, and the experiment does not require recovery.

Trigger garbage collection using the service mode

Example for triggering garbage collection using the service mode

curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"gc","pid":1828622}'

The result is as follows:

{"status":200,"message":"attack successfully","uid":"c3c519bf-819a-4a7b-97fb-e3d0814481fa"}

Triggering garbage collection is a one-time operation. The experiment does not require recovery.

Increase method latency

Parameters for increasing method latency

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "latency".
class	c	class	The name of the Java class	string	required
latency	—	latency	The duration of increasing method latency	int	required. The unit is millisecond.
method	m	method	The name of the method	string	required
pid	—	pid	The Java process ID where the fault is to be injected	int	required
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Increase method latency using the command-line mode

To see the usage and configuration items of the command that increases method latency, run the following command:

chaosd attack jvm latency --help

The result is as follows:

inject latency to specified method

Usage:
  chaosd attack jvm latency [options] [flags]

Flags:
  -c, --class string    Java class name
  -h, --help            help for latency
      --latency int     the latency duration, unit ms
  -m, --method string   the method name in Java class

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which needs to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for increasing method latency

chaosd attack jvm latency --class Main --method sayhello --latency 5000 --pid 100840

The result is as follows:

[2021/08/05 03:08:50.716 +00:00] [INFO] [jvm.go:208] ["byteman rule"] [rule="\nRULE Main-sayhello-latency-hlib2\nCLASS Main\nMETHOD sayhello\nAT ENTRY\nIF true\nDO \n\tThread.sleep(5000);\nENDRULE\n"] [file=/tmp/rule.btm359997255]
[2021/08/05 03:08:51.155 +00:00] [INFO] [jvm.go:94] ["submit rules"] [output="install rule Main-sayhello-latency-hlib2\n\n"]
Attack jvm successfully, uid: bbe00c57-ac9d-4113-bf0c-2a6f184be261

Increase method latency using the service mode

Example for increasing method latency using the service mode

curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"latency","class":"Main","method":"sayhello","latency":5000,"pid":1828622}'

The result is as follows:

{"status":200,"message":"attack successfully","uid":"a551206c-960d-4ac5-9056-518e512d4d0d"}

Modify return values of a method

Parameters for modifying return values of a method

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "return".
class	c	class	The name of the Java class	string	required to be configured
method	m	method	The name of the method	string	required to be configured
value	—	value	Specifies the return value of the method	string	required to be configured. Currently, the item can be numeric and string types. If the item (return value) is string, double quotes are required, like "chaos".
pid	—	pid	The Java process ID where the fault is needed to be injected	int	required to be configured
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Modify return values of a method using the command-line mode

To see the usage and configuration items of the command that modifies return values of a method, run the following command:

chaosd attack jvm return --help

return specified value for specified method

Usage:
  chaosd attack jvm return [options] [flags]

Flags:
  -c, --class string    Java class name
  -h, --help            help for return
  -m, --method string   the method name in Java class
      --value string    the return value for action 'return'. Only supports number and string types.

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which needs to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for simulating the scenario of modifying return values of a method

chaosd attack jvm return --class Main --method getnum --value 999 --pid 112694

The result is as follows:

[2021/08/05 03:35:10.603 +00:00] [INFO] [jvm.go:208] ["byteman rule"] [rule="\nRULE Main-getnum-return-i6gb7\nCLASS Main\nMETHOD getnum\nAT ENTRY\nIF true\nDO \n\treturn 999;\nENDRULE\n"] [file=/tmp/rule.btm051982059]
[2021/08/05 03:35:10.820 +00:00] [INFO] [jvm.go:94] ["submit rules"] [output="install rule Main-getnum-return-i6gb7\n\n"]
Attack jvm successfully, uid: e2f204f6-4bed-4d92-aade-2b4a47b02e5d

Modify return values of a method using the service mode

Example for modifying return values of a method using the service mode

curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"return","class":"Main","method":"getnum","value":"999","pid":1828622}'

The result is as follows:

{"status":200,"message":"attack successfully","uid":"a551206c-960d-4ac5-9056-518e512d4d0d"}

Trigger faults by setting Byteman configuration files

You can set the fault rules in the Byteman rule configuration file, and then inject the faults by specifying the path of the configuration file using Chaosd. Regarding the Byteman rule configuration, refer to byteman-rule-language.

Parameters for triggering faults by setting Byteman configuration files

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "rule-data".
path	—	—	Specifies the path of the Byteman configuration file	string	required
rule-data	—	rule-data	Specifies the Byteman configuration data	string	required
pid	—	pid	The Java process ID where the fault is to be injected	int	required
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Trigger faults by setting Byteman configuration files using the command-line mode

To see the usage and configuration items of the command that triggers faults by setting Byteman configuration files, run the following command:

chaosd attack jvm rule-file --help

The result is as follows:

inject fault with configured byteman rule file

Usage:
  chaosd attack jvm rule-file [options] [flags]

Flags:
  -h, --help          help for rule-file
  -p, --path string   the path of configured byteman rule file

Global Flags:
      --log-level string   the log level of chaosd, the value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which needs to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for triggering faults by setting Byteman configuration files

First, based on the specific Java program and referring to the Byteman rule language, write a rule configuration file. For example:

RULE modify return value
CLASS Main
METHOD getnum
AT ENTRY
IF true
DO
    return 9999
ENDRULE

Then, save the configuration file to the return.btm file. After that, run the following command to inject faults.

chaosd attack jvm rule-file -p ./return.btm --pid 112694

The result is as follows:

[2021/08/05 03:45:40.757 +00:00] [INFO] [jvm.go:152] ["rule file data:RULE modify return value\nCLASS Main\nMETHOD getnum\nAT ENTRY\nIF true\nDO\n    return 9999\nENDRULE\n"]
[2021/08/05 03:45:41.011 +00:00] [INFO] [jvm.go:94] ["submit rules"] [output="install rule modify return value\n\n"]
Attack jvm successfully, uid: 5ca2e06d-a7c6-421d-bb67-0c9908bac17a

Trigger faults by setting Byteman configuration files using the service mode

You can set the fault rules according to the Byteman rule configuration. For more information about the Byteman rule configuration, refer to byteman-rule-language.

Example for triggering faults by setting Byteman configuration files using the service mode

First, based on the specific Java program and referring to the Byteman rule language, write a rule configuration file. For example:

RULE modify return value
CLASS Main
METHOD getnum
AT ENTRY
IF true
DO
    return 9999
ENDRULE

Then, escape the line breaks in the configuration file to the newline character "\n", and use the escaped text as the value of "rule-data". Run the following command:

curl -X POST 127.0.0.1:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"rule-data","pid":30045,"rule-data":"\nRULE modify return value\nCLASS Main\nMETHOD getnum\nAT ENTRY\nIF true\nDO return 9999\nENDRULE\n"}'

The result is as follows:

{"status":200,"message":"attack successfully","uid":"a551206c-960d-4ac5-9056-518e512d4d0d"}

Increase JVM stress

Parameters for increasing JVM stress

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "stress".
cpu-count	—	cpu-count	The number of CPU cores used for increasing JVM stress	int	You must configure one of cpu-count and mem-type.
mem-type	—	mem-type	The type of OOM	string	Currently, both 'stack' and 'heap' OOM types are supported. You must configure one of cpu-count and mem-type.
pid	—	pid	The Java process ID where the fault is to be injected	int	required
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Increase JVM stress using the command-line mode

To see the usage and configuration items of the command that increases JVM stress, run the following command:

chaosd attack jvm stress --help

The result is as follows:

inject stress to JVM

Usage:
  chaosd attack jvm stress [options] [flags]

Flags:
      --cpu-count int   the CPU core number
  -h, --help            help for stress
      --mem-type int    the memory type to be allocated. The value can be 'stack' or 'heap'.

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which needs to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for increasing JVM stress

chaosd attack jvm stress --cpu-count 2 --pid 123546

The result is as follows:

[2021/08/05 03:59:51.256 +00:00] [INFO] [jvm.go:208] ["byteman rule"] [rule="\nRULE --stress-jfeiu\nSTRESS CPU\nCPUCOUNT 2\nENDRULE\n"] [file=/tmp/rule.btm773062009]
[2021/08/05 03:59:51.613 +00:00] [INFO] [jvm.go:94] ["submit rules"] [output="install rule --stress-jfeiu\n\n"]
Attack jvm successfully, uid: b9b997b5-0a0d-4f1f-9081-d52a32318b84

Increase JVM stress using the service mode

Example for increasing JVM stress using the service mode

curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"stress","cpu-count":1,"pid":1828622}'

The result is as follows:

{"status":200,"message":"attack successfully","uid":"a551206c-960d-4ac5-9056-518e512d4d0d"}

Trigger faults in the MySQL Java client

Parameters for triggering faults

Configuration item	Abbreviation	Service mode field	Description	Type	Value
action	—	action	The action of the experiment.	string	Set to "mysql".
database	d	database	The name of the database to match	string	such as "test". Default value: "" (matches all databases).
exception	—	exception	The custom exception message to throw	string	such as "BOOM". You must set one of exception or latency.
latency	—	latency	The latency of executing the SQL statements	int	in milliseconds, such as 1000. You must set one of exception or latency.
mysql-connector-version	v	mysql-connector-version	The version of the MySQL client (mysql-connector-java)	string	Set to 5 for 5.X.X or 8 for 8.X.X. Default value: 8.
sql-type	—	sql-type	The SQL type to match	string	Optional values: "select", "update", "insert", "replace", "delete". Default value: "" (matches all SQL types).
table	t	table	The name of the table to match	string	such as "t1". Default value: "" (matches all tables).
pid	—	pid	The Java process ID where the fault is to be injected	int	required
port	—	port	The port number attached to the Java process agent. The fault is injected into the Java process through this port number.	int	The default value is 9288.
uid	—	uid	The experiment ID	string	This item is not required to be configured, because Chaosd randomly creates one.

Trigger faults in the MySQL Java client using the command-line mode

Chaosd supports injecting latency or throwing exceptions when the MySQL Java client executes SQL statements of the specified types.

chaosd attack jvm mysql --help

The result is as follows:

inject fault into MySQL client

Usage:
  chaosd attack jvm mysql [options] [flags]

Flags:
  -d, --database string                  the match database
      --exception string                 the exception message needs to throw
  -h, --help                             help for mysql
      --latency int                      the latency duration, unit ms
  -v, --mysql-connector-version string   the version of mysql-connector-java, only support 5.X.X(set to 5) and 8.X.X(set to 8) (default "8")
      --sql-type string                  the match sql type
  -t, --table string                     the match table

Global Flags:
      --log-level string   the log level of chaosd. The value can be 'debug', 'info', 'warn' and 'error'
      --pid int            the pid of Java process which need to attach
      --port int           the port of agent server (default 9288)
      --uid string         the experiment ID

Example for triggering faults

1. Deploy TiDB (or MySQL)

   Run the following command to deploy TiDB in mocktikv mode:

   export tidb_dir="tidb-v5.3.0-linux-amd64"
   curl -fsSL -o ${tidb_dir}.tar.gz https://download.pingcap.org/${tidb_dir}.tar.gz
   tar zxvf ${tidb_dir}.tar.gz
   ${tidb_dir}/bin/tidb-server -store mocktikv -P 4000 > tidb.log 2>&1 &

2. Deploy the demo application

   Deploy a demo application mysqldemo. This application accepts HTTP requests and queries the TiDB (or MySQL) database:

   git clone https://github.com/WangXiangUSTC/byteman-example.git
   cd byteman-example/mysqldemo
   mvn -X package -Dmaven.test.skip=true -Dmaven.wagon.http.ssl.insecure=true -Dmaven.wagon.http.ssl.allowall=true
   export MYSQL_DSN=jdbc:"mysql://127.0.0.1:4000/test"
   export MYSQL_USER=root
   export MYSQL_CONNECTOR_VERSION=8
   mvn exec:java -Dexec.mainClass="com.mysqldemo.App" > mysqldemo.log 2>&1 &

   Run the following command to confirm that the application is serving normally:

   curl -X GET "http://127.0.0.1:8001/query?sql=SELECT%20*%20FROM%20mysql.user"

   You can view the information of the root user in the command output.

3. Inject faults

   Assume the PID of mysqldemo (the Java process ID where the fault is to be injected) is 12345. Run the following command to inject faults into the application:

   chaosd attack jvm mysql --database mysql --table user --port 9288 --exception "BOOM" --pid 12345

   After injecting the fault, when the SQL statements related to the mysql.user table are being executed, the application returns the exception BOOM. After confirming this result, send the query request to mysqldemo again:

   curl -X GET "http://127.0.0.1:8001/query?sql=SELECT%20*%20FROM%20mysql.user"

   The result is as follows:

   java.sql.SQLException: BOOM
   at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
     at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
   at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1206)
     at com.mysqldemo.App.querySQL(App.java:125)
     at com.mysqldemo.App$QueryHandler.handle(App.java:95)
   at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:77)
     at jdk.httpserver/sun.net.httpserver.AuthFilter.doFilter(AuthFilter.java:82)
     at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:80)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Exchange$LinkHandler.handle(ServerImpl.java:692)
   at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:77)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Exchange.run(ServerImpl.java:664)
   at jdk.httpserver/com.sun.net.httpserver.ServerImpl$DefaultExecutor.execute(ServerImpl.java:159)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Dispatcher.handle(ServerImpl.java:442)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Dispatcher.run(ServerImpl.java:408)
     at java.base/java.lang.Thread.run(Thread.java:832)

Trigger faults in the MySQL Java client using the service mode

Chaosd supports injecting latency or throwing exceptions when the MySQL Java client executes SQL statements of the specified types.

Example for triggering faults using the service mode

1. Deploy TiDB (or MySQL) and the demo application

   Before injecting faults, you need to deploy TiDB (or MySQL) and the demo application mysqldemo in advance. For the deployment steps, refer to step 1 and step 2 in the example of triggering faults in the MySQL Java client using the command-line mode.

2. Inject faults

   Assume the PID of mysqldemo (the Java process ID where the fault is to be injected) is 12345. Run the following command to inject faults into the application:

   curl -X POST 172.16.112.130:31767/api/attack/jvm -H "Content-Type:application/json" -d '{"action":"mysql","database":"mysql", "table":"user", "port":9288, "exception":"boom", "pid":12345}'

   The result is as follows:

   java.sql.SQLException: BOOM
   at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
     at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
   at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1206)
     at com.mysqldemo.App.querySQL(App.java:125)
     at com.mysqldemo.App$QueryHandler.handle(App.java:95)
   at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:77)
     at jdk.httpserver/sun.net.httpserver.AuthFilter.doFilter(AuthFilter.java:82)
     at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:80)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Exchange$LinkHandler.handle(ServerImpl.java:692)
   at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:77)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Exchange.run(ServerImpl.java:664)
   at jdk.httpserver/com.sun.net.httpserver.ServerImpl$DefaultExecutor.execute(ServerImpl.java:159)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Dispatcher.handle(ServerImpl.java:442)
     at jdk.httpserver/sun.net.httpserver.ServerImpl$Dispatcher.run(ServerImpl.java:408)
     at java.base/java.lang.Thread.run(Thread.java:832)