bitcoin-util: Add netmagic command

diff --git a/doc/release-notes-35610.md b/doc/release-notes-35610.md
new file mode 100644
index 00000000..8e0dd208
--- /dev/null
+++ b/doc/release-notes-35610.md
@@ -0,0 +1,6 @@
+Tools and Utilities
+-------------------
+
+- A new `bitcoin-util netmagic` command returns the network magic of the
+  selected chain.
+
diff --git a/src/bitcoin-util.cpp b/src/bitcoin-util.cpp
index aa3fd306..f17c7a0d 100644
--- a/src/bitcoin-util.cpp
+++ b/src/bitcoin-util.cpp
@@ -36,6 +36,7 @@ static void SetupBitcoinUtilArgs(ArgsManager &argsman)
     argsman.AddArg("-version", "Print version and exit", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
 
     argsman.AddCommand("grind", "Perform proof of work on hex header string");
+    argsman.AddCommand("netmagic", "Get the network magic bytes of the selected chain");
 
     SetupChainParamsBaseOptions(argsman);
 }
@@ -150,6 +151,17 @@ static int Grind(const std::vector<std::string>& args, std::string& strPrint)
     return EXIT_SUCCESS;
 }
 
+static int NetMagic(const std::vector<std::string>& args, std::string& strPrint)
+{
+    if (!args.empty()) {
+        strPrint = "netmagic does not take arguments";
+        return EXIT_FAILURE;
+    }
+
+    strPrint = HexStr(Params().MessageStart());
+    return EXIT_SUCCESS;
+}
+
 MAIN_FUNCTION
 {
     ArgsManager& args = gArgs;
@@ -179,6 +191,8 @@ MAIN_FUNCTION
     try {
         if (cmd->command == "grind") {
             ret = Grind(cmd->args, strPrint);
+        } else if (cmd->command == "netmagic") {
+            ret = NetMagic(cmd->args, strPrint);
         } else {
             assert(false); // unknown command should be caught earlier
         }
diff --git a/test/functional/data/util/bitcoin-util-test.json b/test/functional/data/util/bitcoin-util-test.json
index 896decc4..9c37a4e5 100644
--- a/test/functional/data/util/bitcoin-util-test.json
+++ b/test/functional/data/util/bitcoin-util-test.json
@@ -29,6 +29,55 @@
     "error_txt": "Could not decode block header",
     "description": ""
   },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["netmagic"],
+    "return_code": 0,
+    "output_cmp": "netmagic-mainnet.hex",
+    "description": "netmagic returns mainnet magic bytes"
+  },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["-regtest", "netmagic"],
+    "return_code": 0,
+    "output_cmp": "netmagic-regtest.hex",
+    "description": "netmagic returns regtest magic bytes"
+  },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["-testnet", "netmagic"],
+    "return_code": 0,
+    "output_cmp": "netmagic-testnet.hex",
+    "description": "netmagic returns testnet magic bytes"
+  },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["-testnet4", "netmagic"],
+    "return_code": 0,
+    "output_cmp": "netmagic-testnet4.hex",
+    "description": "netmagic returns testnet4 magic bytes"
+  },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["-signet", "netmagic"],
+    "return_code": 0,
+    "output_cmp": "netmagic-signet.hex",
+    "description": "netmagic returns signet magic bytes"
+  },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["-signet", "-signetchallenge=512102f7561d208dd9ae99bf497273e16f389bdbd6c4742ddb8e6b216e64fa2928ad8f51ae", "netmagic"],
+    "return_code": 0,
+    "output_cmp": "netmagic-signet-custom.hex",
+    "description": "netmagic returns custom signet magic bytes"
+  },
+  {
+    "exec": "./bitcoin-util",
+    "args": ["netmagic", "extra_arg"],
+    "return_code": 1,
+    "error_txt": "netmagic does not take arguments",
+    "description": "netmagic rejects extra arguments"
+  },
   { "exec": "./bitcoin-tx",
     "args": ["-create", "nversion=1"],
     "output_cmp": "blanktxv1.hex",
diff --git a/test/functional/data/util/netmagic-mainnet.hex b/test/functional/data/util/netmagic-mainnet.hex
new file mode 100644
index 00000000..94b2c335
--- /dev/null
+++ b/test/functional/data/util/netmagic-mainnet.hex
@@ -0,0 +1 @@
+f9beb4d9
diff --git a/test/functional/data/util/netmagic-regtest.hex b/test/functional/data/util/netmagic-regtest.hex
new file mode 100644
index 00000000..e2a9cb27
--- /dev/null
+++ b/test/functional/data/util/netmagic-regtest.hex
@@ -0,0 +1 @@
+fabfb5da
diff --git a/test/functional/data/util/netmagic-signet-custom.hex b/test/functional/data/util/netmagic-signet-custom.hex
new file mode 100644
index 00000000..b24f8cb4
--- /dev/null
+++ b/test/functional/data/util/netmagic-signet-custom.hex
@@ -0,0 +1 @@
+a5df2dcb
diff --git a/test/functional/data/util/netmagic-signet.hex b/test/functional/data/util/netmagic-signet.hex
new file mode 100644
index 00000000..69a8b588
--- /dev/null
+++ b/test/functional/data/util/netmagic-signet.hex
@@ -0,0 +1 @@
+0a03cf40
diff --git a/test/functional/data/util/netmagic-testnet.hex b/test/functional/data/util/netmagic-testnet.hex
new file mode 100644
index 00000000..90b026d4
--- /dev/null
+++ b/test/functional/data/util/netmagic-testnet.hex
@@ -0,0 +1 @@
+0b110907
diff --git a/test/functional/data/util/netmagic-testnet4.hex b/test/functional/data/util/netmagic-testnet4.hex
new file mode 100644
index 00000000..8967d142
--- /dev/null
+++ b/test/functional/data/util/netmagic-testnet4.hex
@@ -0,0 +1 @@
+1c163f28