commit 0292e292d21498d1bec00cd7341b0cab802725b5
Author: juancwu <git@juancwu.dev>
Date:   Sat Jan 17 03:11:05 2026 +0000

    basic ip echo server

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..89d117e
--- /dev/null
+++ b/.gitignore
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diff --git a/Cargo.lock b/Cargo.lock
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index 0000000..70235c0
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+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a9d8416fa8b42f5c947f8482c43e7d89e73a173cead56d044f6a56104a6d1b53"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b9d782e804c2f632e395708e99a94275910eb9100b2114651e04744e9b125006"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "960e6da069d81e09becb0ca57a65220ddff016ff2d6af6a223cf372a506593a3"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa7359d10048f68ab8b09fa71c3daccfb0e9b559aed648a8f95469c27057180c"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e7ac75179f18232fe9c285163565a57ef8d3c89254a30685b57d83a38d326c2"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c3842cdd74a865a8066ab39c8a7a473c0778a3f29370b5fd6b4b9aa7df4a499"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ffa179e2d07eee8ad8f57493436566c7cc30ac536a3379fdf008f47f6bb7ae1"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6bbff5f0aada427a1e5a6da5f1f98158182f26556f345ac9e04d36d0ebed650"
+
+[[package]]
+name = "zmij"
+version = "1.0.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bd8f3f50b848df28f887acb68e41201b5aea6bc8a8dacc00fb40635ff9a72fea"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..a328db6
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "ip-echo"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+axum = "0.8.8"
+tokio = { version = "1.49.0", features = ["full"] }
diff --git a/conf/set-env.sh b/conf/set-env.sh
new file mode 100644
index 0000000..283c365
--- /dev/null
+++ b/conf/set-env.sh
@@ -0,0 +1,6 @@
+echo "project dir is ${PROJECT_DIR}"
+
+rustupHomeDir="${PROJECT_DIR}/.rustup"
+mkdir -p "${rustupHomeDir}"
+export RUSTUP_HOME="${rustupHomeDir}"
+export LIBRARY_PATH="${LIBRARY_PATH}:${PROJECT_DIR}/nix/profile/default/lib"
diff --git a/devbox.json b/devbox.json
new file mode 100644
index 0000000..765316a
--- /dev/null
+++ b/devbox.json
@@ -0,0 +1,16 @@
+{
+  "$schema": "https://raw.githubusercontent.com/jetify-com/devbox/0.16.0/.schema/devbox.schema.json",
+  "packages": [
+    "rustup@latest",
+    "posting@latest"
+  ],
+  "env": {
+    "PROJECT_DIR": "$PWD"
+  },
+  "shell": {
+    "init_hook": [". conf/set-env.sh", "rustup default stable", "cargo fetch"],
+    "scripts": {
+      "test": ["echo \"Error: no test specified\" && exit 1"]
+    }
+  }
+}
diff --git a/devbox.lock b/devbox.lock
new file mode 100644
index 0000000..01d4813
--- /dev/null
+++ b/devbox.lock
@@ -0,0 +1,122 @@
+{
+  "lockfile_version": "1",
+  "packages": {
+    "github:NixOS/nixpkgs/nixpkgs-unstable": {
+      "last_modified": "2026-01-10T08:02:33Z",
+      "resolved": "github:NixOS/nixpkgs/3146c6aa9995e7351a398e17470e15305e6e18ff?lastModified=1768032153&narHash=sha256-6kD1MdY9fsE6FgSwdnx29hdH2UcBKs3%2F%2BJJleMShuJg%3D"
+    },
+    "posting@latest": {
+      "last_modified": "2025-12-31T19:51:29Z",
+      "resolved": "github:NixOS/nixpkgs/fe575ad78fa6df638340aa673ea84709c5bd5da0#posting",
+      "source": "devbox-search",
+      "version": "2.9.2",
+      "systems": {
+        "aarch64-darwin": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/hjbxzh8786f382g9jkp6v7i4iqdw7xjk-posting-2.9.2",
+              "default": true
+            },
+            {
+              "name": "dist",
+              "path": "/nix/store/ansfrnlwbf1g8dh0lfa51s55s8vk8dvw-posting-2.9.2-dist"
+            }
+          ],
+          "store_path": "/nix/store/hjbxzh8786f382g9jkp6v7i4iqdw7xjk-posting-2.9.2"
+        },
+        "aarch64-linux": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/vxa5nibxp4cda64fh51vx8wlg3907jn6-posting-2.9.2",
+              "default": true
+            },
+            {
+              "name": "dist",
+              "path": "/nix/store/b2hr0drzxylwra8hci0lwix0hxy513bv-posting-2.9.2-dist"
+            }
+          ],
+          "store_path": "/nix/store/vxa5nibxp4cda64fh51vx8wlg3907jn6-posting-2.9.2"
+        },
+        "x86_64-darwin": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/zby80gkdmkzbq9s6yq3i8bbx2imx0kni-posting-2.9.2",
+              "default": true
+            },
+            {
+              "name": "dist",
+              "path": "/nix/store/z31zvam1yir8x9zgy9ahm2flk7qizzs8-posting-2.9.2-dist"
+            }
+          ],
+          "store_path": "/nix/store/zby80gkdmkzbq9s6yq3i8bbx2imx0kni-posting-2.9.2"
+        },
+        "x86_64-linux": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/pk41ahg5jp7sbriif8myym9wz9d94hp7-posting-2.9.2",
+              "default": true
+            },
+            {
+              "name": "dist",
+              "path": "/nix/store/mhii5pmhz9j40bd78n5x36gaz98w472b-posting-2.9.2-dist"
+            }
+          ],
+          "store_path": "/nix/store/pk41ahg5jp7sbriif8myym9wz9d94hp7-posting-2.9.2"
+        }
+      }
+    },
+    "rustup@latest": {
+      "last_modified": "2025-12-31T03:27:36Z",
+      "plugin_version": "0.0.1",
+      "resolved": "github:NixOS/nixpkgs/f665af0cdb70ed27e1bd8f9fdfecaf451260fc55#rustup",
+      "source": "devbox-search",
+      "version": "1.28.2",
+      "systems": {
+        "aarch64-darwin": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/v0cfpbl35r8y950rx1l17xs8i09pjq1b-rustup-1.28.2",
+              "default": true
+            }
+          ],
+          "store_path": "/nix/store/v0cfpbl35r8y950rx1l17xs8i09pjq1b-rustup-1.28.2"
+        },
+        "aarch64-linux": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/rfi35nzh27wx48v3chbxl7kwp0cyfaab-rustup-1.28.2",
+              "default": true
+            }
+          ],
+          "store_path": "/nix/store/rfi35nzh27wx48v3chbxl7kwp0cyfaab-rustup-1.28.2"
+        },
+        "x86_64-darwin": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/60xn8pb5myf7kddr1wg7q0fpr0g2fl2y-rustup-1.28.2",
+              "default": true
+            }
+          ],
+          "store_path": "/nix/store/60xn8pb5myf7kddr1wg7q0fpr0g2fl2y-rustup-1.28.2"
+        },
+        "x86_64-linux": {
+          "outputs": [
+            {
+              "name": "out",
+              "path": "/nix/store/w3hyqp287l6j790wn81x8chj5bcb69wb-rustup-1.28.2",
+              "default": true
+            }
+          ],
+          "store_path": "/nix/store/w3hyqp287l6j790wn81x8chj5bcb69wb-rustup-1.28.2"
+        }
+      }
+    }
+  }
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..1a037e5
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,34 @@
+use axum::{Router, extract::ConnectInfo, http::HeaderMap, routing::get};
+use std::net::SocketAddr;
+
+#[tokio::main]
+async fn main() {
+    let app = Router::new().route("/", get(get_ip));
+
+    // Run on localhost:3000
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:55667")
+        .await
+        .unwrap();
+    println!("Listening on: {}", listener.local_addr().unwrap());
+
+    axum::serve(
+        listener,
+        app.into_make_service_with_connect_info::<SocketAddr>(),
+    )
+    .await
+    .unwrap();
+}
+
+async fn get_ip(headers: HeaderMap, ConnectInfo(addr): ConnectInfo<SocketAddr>) -> String {
+    // 1. Check X-Forwarded-For (standard for reverse proxies)
+    let ip = headers
+        .get("x-forwarded-for")
+        .and_then(|value| value.to_str().ok())
+        .and_then(|s| s.split(',').next()) // Get the first IP in the list
+        .map(|s| s.trim().to_string())
+        // 2. Fallback to direct connection if header is missing
+        .unwrap_or_else(|| addr.ip().to_string());
+
+    // This will return either an IPv4 or IPv6 string depending on how the client connected
+    format!("{}\n", ip)
+}