From 748379f0b07df948cf9074d2d500b5bc5484e1da Mon Sep 17 00:00:00 2001
From: c65722 <53181351+c65722@users.noreply.github.com>
Date: Sun, 15 Sep 2024 14:29:35 +0100
Subject: [PATCH] Add Strip TCP header operation

---
 src/core/config/Categories.json           |   1 +
 src/core/operations/StripTCPHeader.mjs    |  60 +++++++++++
 tests/operations/index.mjs                |   1 +
 tests/operations/tests/StripTCPHeader.mjs | 126 ++++++++++++++++++++++
 4 files changed, 188 insertions(+)
 create mode 100644 src/core/operations/StripTCPHeader.mjs
 create mode 100644 tests/operations/tests/StripTCPHeader.mjs

diff --git a/src/core/config/Categories.json b/src/core/config/Categories.json
index bebdd6a5e2..f19f0a7d0a 100644
--- a/src/core/config/Categories.json
+++ b/src/core/config/Categories.json
@@ -235,6 +235,7 @@
             "Parse IPv6 address",
             "Parse IPv4 header",
             "Parse TCP",
+            "Strip TCP header",
             "Parse UDP",
             "Parse SSH Host Key",
             "Parse URI",
diff --git a/src/core/operations/StripTCPHeader.mjs b/src/core/operations/StripTCPHeader.mjs
new file mode 100644
index 0000000000..747744b213
--- /dev/null
+++ b/src/core/operations/StripTCPHeader.mjs
@@ -0,0 +1,60 @@
+/**
+ * @author c65722 []
+ * @copyright Crown Copyright 2024
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+import Stream from "../lib/Stream.mjs";
+
+/**
+ * Strip TCP header operation
+ */
+class StripTCPHeader extends Operation {
+
+    /**
+     * StripTCPHeader constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Strip TCP header";
+        this.module = "Default";
+        this.description = "Strips the TCP header from a TCP segment, outputting the payload.";
+        this.infoURL = "https://wikipedia.org/wiki/Transmission_Control_Protocol";
+        this.inputType = "ArrayBuffer";
+        this.outputType = "ArrayBuffer";
+        this.args = [];
+    }
+
+    /**
+     * @param {ArrayBuffer} input
+     * @param {Object[]} args
+     * @returns {ArrayBuffer}
+     */
+    run(input, args) {
+        const MIN_HEADER_LEN = 20;
+        const DATA_OFFSET_OFFSET = 12;
+        const DATA_OFFSET_LEN_BITS = 4;
+
+        const s = new Stream(new Uint8Array(input));
+        if (s.length < MIN_HEADER_LEN) {
+            throw new OperationError("Need at least 20 bytes for a TCP Header");
+        }
+
+        s.moveTo(DATA_OFFSET_OFFSET);
+        const dataOffsetWords = s.readBits(DATA_OFFSET_LEN_BITS);
+        const dataOffsetBytes = dataOffsetWords * 4;
+        if (s.length < dataOffsetBytes) {
+            throw new OperationError("Input length is less than data offset");
+        }
+
+        s.moveTo(dataOffsetBytes);
+
+        return s.getBytes().buffer;
+    }
+
+}
+
+export default StripTCPHeader;
diff --git a/tests/operations/index.mjs b/tests/operations/index.mjs
index 40ce7a2ee6..7b7622058a 100644
--- a/tests/operations/index.mjs
+++ b/tests/operations/index.mjs
@@ -142,6 +142,7 @@ import "./tests/SIGABA.mjs";
 import "./tests/SM4.mjs";
 // import "./tests/SplitColourChannels.mjs"; // Cannot test operations that use the File type yet
 import "./tests/StrUtils.mjs";
+import "./tests/StripTCPHeader.mjs";
 import "./tests/Subsection.mjs";
 import "./tests/SwapCase.mjs";
 import "./tests/SymmetricDifference.mjs";
diff --git a/tests/operations/tests/StripTCPHeader.mjs b/tests/operations/tests/StripTCPHeader.mjs
new file mode 100644
index 0000000000..1d98d41163
--- /dev/null
+++ b/tests/operations/tests/StripTCPHeader.mjs
@@ -0,0 +1,126 @@
+/**
+ * Strip TCP header tests.
+ *
+ * @author c65722 []
+ * @copyright Crown Copyright 2024
+ * @license Apache-2.0
+ */
+
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Strip TCP header: No options, No payload",
+        input: "7f900050000fa4b2000cb2a45010bff100000000",
+        expectedOutput: "",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Strip TCP header",
+                args: [],
+            },
+            {
+                op: "To Hex",
+                args: ["None", 0]
+            }
+        ]
+    },
+    {
+        name: "Strip TCP header: No options, Payload",
+        input: "7f900050000fa4b2000cb2a45010bff100000000ffffffffffffffff",
+        expectedOutput: "ffffffffffffffff",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Strip TCP header",
+                args: [],
+            },
+            {
+                op: "To Hex",
+                args: ["None", 0]
+            }
+        ]
+    },
+    {
+        name: "Strip TCP header: Options, No payload",
+        input: "7f900050000fa4b2000cb2a47010bff100000000020405b404020000",
+        expectedOutput: "",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Strip TCP header",
+                args: [],
+            },
+            {
+                op: "To Hex",
+                args: ["None", 0]
+            }
+        ]
+    },
+    {
+        name: "Strip TCP header: Options, Payload",
+        input: "7f900050000fa4b2000cb2a47010bff100000000020405b404020000ffffffffffffffff",
+        expectedOutput: "ffffffffffffffff",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Strip TCP header",
+                args: [],
+            },
+            {
+                op: "To Hex",
+                args: ["None", 0]
+            }
+        ]
+    },
+    {
+        name: "Strip TCP header: Input length less than minimum header length",
+        input: "7f900050000fa4b2000cb2a45010bff1000000",
+        expectedOutput: "Need at least 20 bytes for a TCP Header",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Strip TCP header",
+                args: [],
+            },
+            {
+                op: "To Hex",
+                args: ["None", 0]
+            }
+        ]
+    },
+    {
+        name: "Strip TCP header: Input length less than data offset",
+        input: "7f900050000fa4b2000cb2a47010bff100000000",
+        expectedOutput: "Input length is less than data offset",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Strip TCP header",
+                args: [],
+            },
+            {
+                op: "To Hex",
+                args: ["None", 0]
+            }
+        ]
+    }
+]);