Overview

java-rawsocket project is a helper aims for creating TCP Half Open Connection or Embryonic Connection wrote in Java.

There are two implementations available. The first one is based on the JNI (Java Native Interface) and the second one is based on the Foreign Function.

ℹ️ The used C code wasn't written by me, but it's plan I shall rewrite it from scratch.

ℹ️ You find out the full article aboute this code on dev.to/ulrich

The Foreign Function implementation

Build

Requirement : you have to install the Java 22 SDK at minimum to build and execute the socket-tester with the Foreign Function feature.

Afterward, go to the foreign-function folder and execute the following command in your terminal:

❯ mvn clean package

Run

Start a Web server to simulate the endpoint. As example:

❯ python3 -m http.server

Display the options:

❯ sudo ~/.sdkman/candidates/java/22.0.1-oracle/bin/java \
        --enable-preview \
        --enable-native-access=ALL-UNNAMED \
        -jar ./target/foreign-function-jar-with-dependencies.jar --help

Start the test:

❯ sudo ~/.sdkman/candidates/java/22.0.1-oracle/bin/java \                                                                                                            
        --enable-preview \                                                                                           
        --enable-native-access=ALL-UNNAMED \                                                               
        ./target/java-rawsocket-ff-jar-with-dependencies.jar

Out example:

❯ sudo ~/.sdkman/candidates/java/22.0.1-oracle/bin/java \
        --enable-preview \
        --enable-native-access=ALL-UNNAMED \
        -jar ./target/foreign-function-jar-with-dependencies.jar       
19:20:47.774 [main] INFO com.reservoircode.net.SocketTester -- Running SocketTester for destination address 127.0.0.1:8080
[INFO (native)] Selected source port number: 35940
[INFO (native)] TCP header sequence number: 272214228
[INFO (native)] Successfully sent 60 bytes SYN!
[INFO (native)] Received bytes: 40
[INFO (native)] Destination port: 35940
[INFO (native)] Successfully received 40 bytes
[INFO (native)] Received syn: 0, ack: 1, rst: 1
[INFO (native)] TCP header sequence number response: 0
[INFO (native)] TCP header ack sequence number response: 272214229
[INFO (native)] tcph->syn: 0
[INFO (native)] tcph->ack: 16777216
[INFO (native)] SYN ACK received -> Success

The JNI implementation

Build

Go to the jni folder and execute the following command in your terminal:

❯ mvn clean compile jar:jar

The jar file contains the class and the compiled library.

During the Maven build, the POM handles several plugins for executing the following actions:

• Compile the SocketTester class
• Generate the header file based necessary for JNI (com_reservoircode_net_SocketTester.h)
• Run the GCC compiler to create the native library (libSocketTester.so)
• Package the class and library in JAR file

Run

Start a Web server to simulate the endpoint. As example:

❯ python3 -m http.server

Start the test:

❯ sudo java -jar ./target/java-rawsocket-jni.jar

The default values used in the SocketTester are:

• Source IP: 127.0.0.1
• Destination IP: 127.0.0.1
• Destination PORT: 8000
• Read timeout (ms): 100
• Write timeout (ms): 100

Out example:

❯ sudo java -jar ./target/java-rawsocket.jar
[INFO (J)] Testing 127.0.0.1:8000...
[INFO (C)] Starting connection with following parameters. Source IP: 127.0.0.1, destination IP: 127.0.0.1, destination port: 8000, read timeout: 100, write timeout: 100
[INFO (C)] Selected source port number: 57916
[INFO (C)] Successfully sent 60 bytes SYN!
[INFO (C)] Received bytes: 48
[INFO (C)] Destination port: 57916
[INFO (C)] Successfully received 48 bytes
[INFO (C)] Received: syn= 1, ack= 1, rst= 0
[INFO (C)] SYN ACK received -> Success
[INFO (J)] Connection successful

On the output console you can see Java ([INFO (J)]) and C logs ([INFO (C)]).

Troubleshooting

If you encounter some trouble during the test related to privilege issues, we have to execute the following command:

❯ cd target
❯ unzip java-rawsocket.jar
❯ sudo setcap cap_net_raw+ep libSocketTester.so