--dump-limits flag to inspect what the max file descriptor & stack size is

build.zig

@@ -77,6 +77,8 @@ fn addInternalPackages(step: *std.build.LibExeObjStep, allocator: *std.mem.Alloc
         .path = pkgPath("src/http/network_thread.zig"),
     };
 
+    thread_pool.dependencies = &.{ io, http };
+
     network_thread.dependencies = &.{
         io,
         thread_pool,

src/bundler.zig

@@ -430,6 +430,7 @@ pub const Bundler = struct {
             },
         };
         Output.flush();
+        var writer = Output.writer();
         std.json.stringify(bundler.env.map.*, opts, Output.writer()) catch unreachable;
         Output.flush();
     }

src/cli.zig

@@ -161,6 +161,7 @@ pub const Arguments = struct {
 
     const debug_params = [_]ParamType{
         clap.parseParam("--dump-environment-variables    Dump environment variables from .env and process as JSON and quit. Useful for debugging") catch unreachable,
+        clap.parseParam("--dump-limits                   Dump system limits. Useful for debugging") catch unreachable,
         clap.parseParam("--disable-bun.js                Disable Bun.js from loading in the dev server") catch unreachable,
     };
 
@@ -245,6 +246,7 @@ pub const Arguments = struct {
 
         ctx.debug.dump_environment_variables = args.flag("--dump-environment-variables");
         ctx.debug.fallback_only = args.flag("--disable-bun.js");
+        ctx.debug.dump_limits = args.flag("--dump-limits");
 
         // var output_dir = args.option("--outdir");
         var output_dir: ?string = null;
@@ -565,6 +567,7 @@ pub const PrintBundleCommand = struct {
 pub const Command = struct {
     pub const DebugOptions = struct {
         dump_environment_variables: bool = false,
+        dump_limits: bool = false,
         fallback_only: bool = false,
         silent: bool = false,
     };

src/cli/bun_command.zig

@@ -114,6 +114,12 @@ pub const BunCommand = struct {
             return;
         }
 
+        if (ctx.debug.dump_limits) {
+            fs.FileSystem.printLimits();
+            std.os.exit(0);
+            return;
+        }
+
         var generated_server = false;
         if (this_bundler.options.framework) |*framework| {
             if (framework.toAPI(allocator, this_bundler.fs.top_level_dir) catch null) |_server_conf| {

src/fs.zig

@@ -480,6 +480,24 @@ pub const FileSystem = struct {
         return try allocator.dupe(u8, joined);
     }
 
+    pub fn printLimits() void {
+        const LIMITS = [_]std.os.rlimit_resource{ std.os.rlimit_resource.STACK, std.os.rlimit_resource.NOFILE };
+        Output.print("{{\n", .{});
+
+        inline for (LIMITS) |limit_type, i| {
+            const limit = std.os.getrlimit(limit_type) catch return;
+
+            if (i == 0) {
+                Output.print("  \"stack\": [{d}, {d}],\n", .{ limit.cur, limit.max });
+            } else if (i == 1) {
+                Output.print("  \"files\": [{d}, {d}]\n", .{ limit.cur, limit.max });
+            }
+        }
+
+        Output.print("}}\n", .{});
+        Output.flush();
+    }
+
     pub const RealFS = struct {
         entries_mutex: Mutex = Mutex.init(),
         entries: *EntriesOption.Map,

src/http.zig

@@ -1159,7 +1159,7 @@ pub const RequestContext = struct {
                     handler.handleJSError(.configure_defines, err) catch {};
                     return;
                 };
-                
+
                 var entry_point = boot;
                 if (!std.fs.path.isAbsolute(entry_point)) {
                     const resolved_entry_point = vm.bundler.resolver.resolve(
@@ -3056,6 +3056,12 @@ pub const Server = struct {
             return;
         }
 
+        if (debug.dump_limits) {
+            Fs.FileSystem.printLimits();
+            std.os.exit(0);
+            return;
+        }
+
         if (debug.fallback_only or server.bundler.env.map.get("BUN_DISABLE_BUN_JS") != null) {
             RequestContext.fallback_only = true;
             RequestContext.JavaScriptHandler.javascript_disabled = true;