From b313be24768a08812bdc27059ce17808cb7c4107 Mon Sep 17 00:00:00 2001
From: Emil Lerch <emil@lerch.org>
Date: Sat, 16 Sep 2023 10:33:29 -0700
Subject: [PATCH] add standalone web server support

---
 src/standalone_server_build.zig |  17 ++++++
 src/universal_lambda.zig        | 102 +++++++++++++++++++++++++++++---
 src/universal_lambda_build.zig  |   3 +-
 3 files changed, 112 insertions(+), 10 deletions(-)
 create mode 100644 src/standalone_server_build.zig

diff --git a/src/standalone_server_build.zig b/src/standalone_server_build.zig
new file mode 100644
index 0000000..881e27b
--- /dev/null
+++ b/src/standalone_server_build.zig
@@ -0,0 +1,17 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+/// adds a build step to the build
+///
+/// * standalone_server: This will run the handler as a standalone web server
+///
+pub fn configureBuild(b: *std.build.Builder, exe: *std.Build.Step.Compile) !void {
+    _ = exe;
+    // We don't actually need to do much here. Basically we need a dummy step,
+    // but one which the user will select, which will allow our options mechanism
+    // to kick in
+
+    // Package step
+    const standalone_step = b.step("standalone_server", "Run the function in its own web server");
+    standalone_step.dependOn(b.getInstallStep());
+}
diff --git a/src/universal_lambda.zig b/src/universal_lambda.zig
index 7296dc2..2e964e6 100644
--- a/src/universal_lambda.zig
+++ b/src/universal_lambda.zig
@@ -8,6 +8,14 @@ const log = std.log.scoped(.universal_lambda);
 // TODO: Should this be union?
 pub const Context = struct {};
 
+const runFn = blk: {
+    switch (build_options.build_type) {
+        .standalone_server => break :blk runStandaloneServer,
+        .exe_run => break :blk runExe,
+        else => @compileError("Provider interface for " ++ @tagName(build_options.build_type) ++ " has not yet been implemented"),
+    }
+};
+
 fn deinit() void {
     // if (client) |*c| c.deinit();
     // client = null;
@@ -19,19 +27,95 @@ fn deinit() void {
 /// This function is intended to loop infinitely. If not used in this manner,
 /// make sure to call the deinit() function
 pub fn run(allocator: ?std.mem.Allocator, event_handler: HandlerFn) !void { // TODO: remove inferred error set?
-    switch (build_options.build_type) {
-        .exe_run => try runExe(allocator, event_handler),
-        else => return error.NotImplemented,
-    }
+    try runFn(allocator, event_handler);
 }
 
 fn runExe(allocator: ?std.mem.Allocator, event_handler: HandlerFn) !void {
-    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
-    defer _ = gpa.deinit();
-    const gpa_alloc = allocator orelse gpa.allocator();
+    var arena = std.heap.ArenaAllocator.init(allocator orelse std.heap.page_allocator);
+    defer arena.deinit();
 
-    // TODO: set up an arena for this? Are we doing an arena for every type?
+    const aa = arena.allocator();
+
+    // We're setting up an arena allocator. While we could use a gpa and get
+    // some additional safety, this is now "production" runtime, and those
+    // things are better handled by unit tests
     const writer = std.io.getStdOut().writer();
-    try writer.writeAll(try event_handler(gpa_alloc, "", .{}));
+    try writer.writeAll(try event_handler(aa, "", .{}));
     try writer.writeAll("\n");
 }
+
+/// Will create a web server and marshall all requests back to our event handler
+/// To keep things simple, we'll have this on a single thread, at least for now
+fn runStandaloneServer(allocator: ?std.mem.Allocator, event_handler: HandlerFn) !void {
+    const alloc = allocator orelse std.heap.page_allocator;
+
+    var arena = std.heap.ArenaAllocator.init(alloc);
+    defer arena.deinit();
+
+    var aa = arena.allocator();
+    var server = std.http.Server.init(aa, .{ .reuse_address = true });
+    defer server.deinit();
+    const address = try std.net.Address.parseIp("127.0.0.1", 8080); // TODO: allow config
+    try server.listen(address);
+    const server_port = server.socket.listen_address.in.getPort();
+    var uri: ["http://127.0.0.1:99999".len]u8 = undefined;
+    _ = try std.fmt.bufPrint(&uri, "http://127.0.0.1:{d}", .{server_port});
+    log.info("server listening at {s}", .{uri});
+
+    // No threads, maybe later
+    //log.info("starting server thread, tid {d}", .{std.Thread.getCurrentId()});
+    while (true) {
+        defer {
+            if (!arena.reset(.{ .retain_with_limit = 1024 * 1024 })) {
+                // reallocation failed, arena is degraded
+                log.warn("Arena reset failed and is degraded. Resetting arena", .{});
+                arena.deinit();
+                arena = std.heap.ArenaAllocator.init(alloc);
+                aa = arena.allocator();
+            }
+        }
+        processRequest(aa, &server, event_handler) catch |e| {
+            log.err("Unexpected error processing request: {any}", .{e});
+            if (@errorReturnTrace()) |trace| {
+                std.debug.dumpStackTrace(trace.*);
+            }
+        };
+    }
+}
+
+fn processRequest(aa: std.mem.Allocator, server: *std.http.Server, event_handler: HandlerFn) !void {
+    var res = try server.accept(.{ .allocator = aa });
+    defer {
+        _ = res.reset();
+        if (res.headers.owned and res.headers.list.items.len > 0) res.headers.deinit();
+        res.deinit();
+    }
+    try res.wait(); // wait for client to send a complete request head
+
+    const errstr = "Internal Server Error\n";
+    var errbuf: [errstr.len]u8 = undefined;
+    @memcpy(&errbuf, errstr);
+    var response_bytes: []const u8 = errbuf[0..];
+
+    var body =
+        if (res.request.content_length) |l|
+        try res.reader().readAllAlloc(aa, @as(usize, l))
+    else
+        try aa.dupe(u8, "");
+    // no need to free - will be handled by arena
+
+    response_bytes = event_handler(aa, body, .{}) catch |e| brk: {
+        res.status = .internal_server_error;
+        // TODO: more about this particular request
+        log.err("Unexpected error from executor processing request: {any}", .{e});
+        if (@errorReturnTrace()) |trace| {
+            std.debug.dumpStackTrace(trace.*);
+        }
+        break :brk "Unexpected error generating request to lambda";
+    };
+    res.transfer_encoding = .{ .content_length = response_bytes.len };
+
+    try res.do();
+    _ = try res.writer().writeAll(response_bytes);
+    try res.finish();
+}
diff --git a/src/universal_lambda_build.zig b/src/universal_lambda_build.zig
index b1d3482..498cbd2 100644
--- a/src/universal_lambda_build.zig
+++ b/src/universal_lambda_build.zig
@@ -7,7 +7,7 @@ const std = @import("std");
 pub const BuildType = enum {
     awslambda,
     exe_run,
-    standalone_run,
+    standalone_server,
     cloudflare,
     flexilib,
 };
@@ -15,6 +15,7 @@ pub const BuildType = enum {
 pub fn configureBuild(b: *std.Build, exe: *std.Build.Step.Compile) !void {
     // Add steps
     try @import("lambdabuild.zig").configureBuild(b, exe);
+    try @import("standalone_server_build.zig").configureBuild(b, exe);
     // Add options module so we can let our universal_lambda know what
     // type of interface is necessary