add error handling (with caveat)

src/lambda.zig

@@ -13,7 +13,7 @@ pub fn run(event_handler: fn (*std.mem.Allocator, []const u8) anyerror![]const u
     const url = try std.fmt.allocPrint(allocator, "{s}{s}{s}/next", .{ prefix, lambda_runtime_uri, postfix });
     defer allocator.free(url);
 
-    std.log.info("Event Url: {s}", .{url});
+    std.log.notice("Bootstrap initializing with event url: {s}", .{url});
 
     while (true) {
         var req_alloc = std.heap.ArenaAllocator.init(allocator);
@@ -21,9 +21,14 @@ pub fn run(event_handler: fn (*std.mem.Allocator, []const u8) anyerror![]const u
         const req_allocator = &req_alloc.allocator;
         var client = try requestz.Client.init(req_allocator);
         // defer client.deinit();
+        // Lambda freezes the process at this line of code. During warm start,
+        // the process will unfreeze and data will be sent in response to client.get
         var response = client.get(url, .{}) catch |err| {
-            // TODO: report error
             std.log.err("Get fail: {}", .{err});
+            // Documentation says something about "exit immediately". The
+            // Lambda infrastrucutre restarts, so it's unclear if that's necessary.
+            // It seems as though a continue should be fine, and slightly faster
+            // std.os.exit(1);
             continue;
         };
         defer response.deinit();
@@ -32,17 +37,51 @@ pub fn run(event_handler: fn (*std.mem.Allocator, []const u8) anyerror![]const u
         for (response.headers.items()) |h| {
             if (std.mem.indexOf(u8, h.name.value, "Lambda-Runtime-Aws-Request-Id")) |_|
                 request_id = h.value;
+            // TODO: XRay uses an environment variable to do its magic. It's our
+            //       responsibility to set this, but no zig-native setenv(3)/putenv(3)
+            //       exists. I would kind of rather not link in libc for this,
+            //       so we'll hold for now and think on this
+            //        if (std.mem.indexOf(u8, h.name.value, "Lambda-Runtime-Trace-Id")) |_|
+            //            std.process.
+            // std.os.setenv("AWS_LAMBDA_RUNTIME_API");
         }
         if (request_id == null) {
-            // TODO: report error
+            // We can't report back an issue because the runtime error reporting endpoint
+            // uses request id in its path. So the best we can do is log the error and move
+            // on here.
             std.log.err("Could not find request id: skipping request", .{});
             continue;
         }
         const req_id = request_id.?;
 
         const event_response = event_handler(req_allocator, response.body) catch |err| {
-            // TODO: report error
-            std.log.err("Error posting response for request id {s}: {}", .{ req_id, err });
+            // Stack trace will return null if stripped
+            const return_trace = @errorReturnTrace();
+            std.log.err("Caught error: {}. Return Trace: {}", .{ err, return_trace });
+            const err_url = try std.fmt.allocPrint(req_allocator, "{s}{s}/runtime/invocation/{s}/error", .{ prefix, lambda_runtime_uri, req_id });
+            defer req_allocator.free(err_url);
+            const content =
+                \\  {s}
+                \\    "errorMessage": "{s}",
+                \\    "errorType": "HandlerReturnedError",
+                \\    "stackTrace": [ "{}" ]
+                \\  {s}
+            ;
+            const content_fmt = try std.fmt.allocPrint(req_allocator, content, .{ "{", @errorName(err), return_trace, "}" });
+            defer req_allocator.free(content_fmt);
+            std.log.err("Posting to {s}: Data {s}", .{ err_url, content_fmt });
+            var headers = .{.{ "Lambda-Runtime-Function-Error-Type", "HandlerReturned" }};
+            // TODO: Determine why this post is not returning
+            var err_resp = client.post(err_url, .{
+                .content = content_fmt,
+                .headers = headers,
+            }) catch |post_err| { // Well, at this point all we can do is shout at the void
+                std.log.err("Error posting response for request id {s}: {}", .{ req_id, post_err });
+                std.os.exit(0);
+                continue;
+            };
+            std.log.err("Post complete", .{});
+            defer err_resp.deinit();
             continue;
         };
         const response_url = try std.fmt.allocPrint(req_allocator, "{s}{s}{s}/{s}/response", .{ prefix, lambda_runtime_uri, postfix, req_id });