feat(serve): support `--port 0` to use an open port (#23846)

Closes https://github.com/denoland/deno/issues/23845

9 files changed, 96 insertions, 16 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 14ee88169..39b0c00e6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -705,6 +705,7 @@ dependencies = [
  "once_cell",
  "os_pipe",
  "pretty_assertions",
+ "regex",
  "serde",
  "test_server",
  "tokio",
diff --git a/cli/args/flags.rs b/cli/args/flags.rs
index dca9cfa49..9de1c6057 100644
--- a/cli/args/flags.rs
+++ b/cli/args/flags.rs
@@ -26,7 +26,6 @@ use serde::Serialize;
 use std::env;
 use std::ffi::OsString;
 use std::net::SocketAddr;
-use std::num::NonZeroU16;
 use std::num::NonZeroU32;
 use std::num::NonZeroU8;
 use std::num::NonZeroUsize;
@@ -283,7 +282,7 @@ impl RunFlags {
 pub struct ServeFlags {
   pub script: String,
   pub watch: Option<WatchFlagsWithPaths>,
-  pub port: NonZeroU16,
+  pub port: u16,
   pub host: String,
 }
 
@@ -293,7 +292,7 @@ impl ServeFlags {
     Self {
       script,
       watch: None,
-      port: NonZeroU16::new(port).unwrap(),
+      port,
       host: host.to_owned(),
     }
   }
@@ -2464,8 +2463,8 @@ fn serve_subcommand() -> Command {
     .arg(
       Arg::new("port")
         .long("port")
-        .help("The TCP port to serve on, defaulting to 8000.")
-        .value_parser(value_parser!(NonZeroU16)),
+        .help("The TCP port to serve on, defaulting to 8000. Pass 0 to pick a random free port.")
+        .value_parser(value_parser!(u16)),
     )
     .arg(
       Arg::new("host")
@@ -4127,9 +4126,7 @@ fn serve_parse(
   app: Command,
 ) -> clap::error::Result<()> {
   // deno serve implies --allow-net=host:port
-  let port = matches
-    .remove_one::<NonZeroU16>("port")
-    .unwrap_or(NonZeroU16::new(8000).unwrap());
+  let port = matches.remove_one::<u16>("port").unwrap_or(8000);
   let host = matches
     .remove_one::<String>("host")
     .unwrap_or_else(|| "0.0.0.0".to_owned());
@@ -5322,6 +5319,32 @@ mod tests {
         ..Flags::default()
       }
     );
+
+    let r = flags_from_vec(svec![
+      "deno",
+      "serve",
+      "--port",
+      "0",
+      "--host",
+      "example.com",
+      "main.ts"
+    ]);
+    assert_eq!(
+      r.unwrap(),
+      Flags {
+        subcommand: DenoSubcommand::Serve(ServeFlags::new_default(
+          "main.ts".to_string(),
+          0,
+          "example.com"
+        )),
+        permissions: PermissionFlags {
+          allow_net: Some(vec!["example.com:0".to_owned()]),
+          ..Default::default()
+        },
+        code_cache_enabled: true,
+        ..Flags::default()
+      }
+    );
   }
 
   #[test]
diff --git a/cli/args/mod.rs b/cli/args/mod.rs
index 0a0f7d704..b3d508e18 100644
--- a/cli/args/mod.rs
+++ b/cli/args/mod.rs
@@ -62,7 +62,6 @@ use std::env;
 use std::io::BufReader;
 use std::io::Cursor;
 use std::net::SocketAddr;
-use std::num::NonZeroU16;
 use std::num::NonZeroUsize;
 use std::path::Path;
 use std::path::PathBuf;
@@ -1036,7 +1035,7 @@ impl CliOptions {
     }
   }
 
-  pub fn serve_port(&self) -> Option<NonZeroU16> {
+  pub fn serve_port(&self) -> Option<u16> {
     if let DenoSubcommand::Serve(flags) = self.sub_command() {
       Some(flags.port)
     } else {
diff --git a/cli/worker.rs b/cli/worker.rs
index 151a4ec4f..bfdeb3568 100644
--- a/cli/worker.rs
+++ b/cli/worker.rs
@@ -1,6 +1,5 @@
 // Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
 
-use std::num::NonZeroU16;
 use std::path::Path;
 use std::path::PathBuf;
 use std::rc::Rc;
@@ -148,7 +147,7 @@ struct SharedWorkerState {
   disable_deprecated_api_warning: bool,
   verbose_deprecated_api_warning: bool,
   code_cache: Option<Arc<dyn code_cache::CodeCache>>,
-  serve_port: Option<NonZeroU16>,
+  serve_port: Option<u16>,
   serve_host: Option<String>,
 }
 
@@ -418,7 +417,7 @@ impl CliMainWorkerFactory {
     feature_checker: Arc<FeatureChecker>,
     options: CliMainWorkerOptions,
     node_ipc: Option<i64>,
-    serve_port: Option<NonZeroU16>,
+    serve_port: Option<u16>,
     serve_host: Option<String>,
     enable_future_features: bool,
     disable_deprecated_api_warning: bool,
diff --git a/runtime/worker_bootstrap.rs b/runtime/worker_bootstrap.rs
index e1abf87fc..0838da2d1 100644
--- a/runtime/worker_bootstrap.rs
+++ b/runtime/worker_bootstrap.rs
@@ -4,7 +4,6 @@ use deno_core::v8;
 use deno_core::ModuleSpecifier;
 use serde::Serialize;
 use std::cell::RefCell;
-use std::num::NonZeroU16;
 use std::thread;
 
 use deno_terminal::colors;
@@ -93,7 +92,7 @@ pub struct BootstrapOptions {
   pub future: bool,
   pub mode: WorkerExecutionMode,
   // Used by `deno serve`
-  pub serve_port: Option<NonZeroU16>,
+  pub serve_port: Option<u16>,
   pub serve_host: Option<String>,
 }
 
@@ -198,7 +197,7 @@ impl BootstrapOptions {
       self.verbose_deprecated_api_warning,
       self.future,
       self.mode as u8 as _,
-      self.serve_port.map(|x| x.into()).unwrap_or_default(),
+      self.serve_port.unwrap_or_default(),
       self.serve_host.as_deref(),
     );
 
diff --git a/tests/Cargo.toml b/tests/Cargo.toml
index fa633f607..af220aae7 100644
--- a/tests/Cargo.toml
+++ b/tests/Cargo.toml
@@ -52,6 +52,7 @@ hyper-util.workspace = true
 once_cell.workspace = true
 os_pipe.workspace = true
 pretty_assertions.workspace = true
+regex.workspace = true
 serde.workspace = true
 test_util.workspace = true
 tokio.workspace = true
diff --git a/tests/integration/mod.rs b/tests/integration/mod.rs
index 59bf0db37..d35fabc02 100644
--- a/tests/integration/mod.rs
+++ b/tests/integration/mod.rs
@@ -60,6 +60,8 @@ mod publish;
 mod repl;
 #[path = "run_tests.rs"]
 mod run;
+#[path = "serve_tests.rs"]
+mod serve;
 #[path = "shared_library_tests.rs"]
 mod shared_library_tests;
 #[path = "task_tests.rs"]
diff --git a/tests/integration/serve_tests.rs b/tests/integration/serve_tests.rs
new file mode 100644
index 000000000..92b0576ed
--- /dev/null
+++ b/tests/integration/serve_tests.rs
@@ -0,0 +1,51 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+use std::io::Read;
+
+use deno_fetch::reqwest;
+use pretty_assertions::assert_eq;
+use regex::Regex;
+use test_util as util;
+
+#[tokio::test]
+async fn deno_serve_port_0() {
+  let mut child = util::deno_cmd()
+    .current_dir(util::testdata_path())
+    .arg("serve")
+    .arg("--port")
+    .arg("0")
+    .arg("./serve.ts")
+    .stdout_piped()
+    .spawn()
+    .unwrap();
+  let stdout = child.stdout.as_mut().unwrap();
+  let mut buffer = [0; 50];
+  let _read = stdout.read(&mut buffer).unwrap();
+  let msg = std::str::from_utf8(&buffer).unwrap();
+  let port_regex = Regex::new(r"(\d+)").unwrap();
+  let port = port_regex.find(msg).unwrap().as_str();
+
+  let cert = reqwest::Certificate::from_pem(include_bytes!(
+    "../testdata/tls/RootCA.crt"
+  ))
+  .unwrap();
+
+  let client = reqwest::Client::builder()
+    .add_root_certificate(cert)
+    .http2_prior_knowledge()
+    .build()
+    .unwrap();
+
+  let res = client
+    .get(&format!("http://127.0.0.1:{port}"))
+    .send()
+    .await
+    .unwrap();
+  assert_eq!(200, res.status());
+
+  let body = res.text().await.unwrap();
+  assert_eq!(body, "deno serve --port 0 works!");
+
+  child.kill().unwrap();
+  child.wait().unwrap();
+}
diff --git a/tests/testdata/serve.ts b/tests/testdata/serve.ts
new file mode 100644
index 000000000..cdd8476eb
--- /dev/null
+++ b/tests/testdata/serve.ts
@@ -0,0 +1,5 @@
+export default {
+  fetch(_req: Request) {
+    return new Response("deno serve --port 0 works!");
+  },
+};