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danlapiddanlapid
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Add user exception metadata to internal exception
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‎src/workerd/jsg/BUILD.bazel‎

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@@ -118,6 +118,7 @@ wd_cc_library(
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tags = ["no-clang-tidy"],
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deps = [
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":exception",
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":exception_metadata_capnp",
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":macro-meta",
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":memory-tracker",
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":meta",
@@ -222,6 +223,12 @@ wd_cc_capnp_library(
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visibility = ["//visibility:public"],
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)
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wd_cc_capnp_library(
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name = "exception_metadata_capnp",
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srcs = ["exception-metadata.capnp"],
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visibility = ["//visibility:public"],
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)
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js_capnp_library(
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name = "rtti_capnp_js",
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srcs = ["rtti.capnp"],

‎src/workerd/jsg/exception-metadata.capnp‎

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@@ -0,0 +1,15 @@
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@0xa9ae63464030fcef;
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# Schema for JavaScript exception metadata passed through KJ exception details
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using Cxx = import "/capnp/c++.capnp";
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$Cxx.namespace("workerd::jsg");
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$Cxx.allowCancellation;
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struct JsExceptionMetadata {
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# JavaScript error type (e.g., "Error", "TypeError", "RangeError")
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errorType @0 :Text;
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# Full stack trace string as produced by V8
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# Example: "Error: User-thrown exception\n at Object.fetch (foo:4:11)"
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stackTrace @1 :Text;
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}

‎src/workerd/jsg/util.c++‎

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@@ -7,8 +7,12 @@
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#include "ser.h"
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#include "setup.h"
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#include <workerd/jsg/exception-metadata.capnp.h>
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#include <openssl/rand.h>
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#include <capnp/message.h>
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#include <capnp/serialize.h>
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#include <kj/debug.h>
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#include <cstdlib>
@@ -454,6 +458,50 @@ void addExceptionDetail(Lock& js, kj::Exception& exception, v8::Local<v8::Value>
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}
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}
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void addJsExceptionMetadata(Lock& js, kj::Exception& exception, v8::Local<v8::Value> handle) {
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// Extract JavaScript error type and stack trace
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if (!handle->IsObject()) {
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return; // Not an error object, nothing to extract
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}
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auto isolate = js.v8Isolate;
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auto context = isolate->GetCurrentContext();
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auto errorObj = handle.As<v8::Object>();
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// Build Cap'n Proto message
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capnp::MallocMessageBuilder message;
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auto metadata = message.initRoot<JsExceptionMetadata>();
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// Limit for user-controlled fields (4KB)
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constexpr size_t MAX_FIELD_SIZE = 4096;
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// Extract error name (e.g., "Error", "TypeError", "RangeError")
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auto nameProp = errorObj->Get(context, v8StrIntern(isolate, "name"_kj));
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if (!nameProp.IsEmpty() && nameProp.ToLocalChecked()->IsString()) {
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auto errorType = kj::str(nameProp.ToLocalChecked().As<v8::String>());
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// Truncate to 4KB if needed
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if (errorType.size() > MAX_FIELD_SIZE) {
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errorType = kj::str(errorType.slice(0, MAX_FIELD_SIZE));
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}
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metadata.setErrorType(errorType);
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}
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// Extract stack trace string
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auto stackProp = errorObj->Get(context, v8StrIntern(isolate, "stack"_kj));
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if (!stackProp.IsEmpty() && stackProp.ToLocalChecked()->IsString()) {
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auto stackTrace = kj::str(stackProp.ToLocalChecked().As<v8::String>());
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// Truncate to 4KB if needed
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if (stackTrace.size() > MAX_FIELD_SIZE) {
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stackTrace = kj::str(stackTrace.slice(0, MAX_FIELD_SIZE));
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}
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metadata.setStackTrace(stackTrace);
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}
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// Serialize to bytes using Cap'n Proto
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auto words = capnp::messageToFlatArray(message);
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exception.setDetail(JS_EXCEPTION_METADATA_DETAIL_ID, kj::heapArray(words.asBytes()));
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}
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static kj::String typeErrorMessage(TypeErrorContext c, const char* expectedType) {
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kj::String type;
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‎src/workerd/jsg/util.h‎

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@@ -89,9 +89,16 @@ void throwInternalError(
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constexpr kj::Exception::DetailTypeId TUNNELED_EXCEPTION_DETAIL_ID = 0xe8027292171b1646ull;
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// Detail type for JavaScript exception metadata (error type and stack trace)
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constexpr kj::Exception::DetailTypeId JS_EXCEPTION_METADATA_DETAIL_ID = 0xa9ae63464030fcefull;
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// Add a serialized copy of the exception value to the KJ exception, as a "detail".
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void addExceptionDetail(Lock& js, kj::Exception& exception, v8::Local<v8::Value> handle);
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// Extract and add JavaScript exception metadata (error type and stack trace) to the KJ exception.
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// Serializes using Cap'n Proto schema defined in exception-metadata.capnp.
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void addJsExceptionMetadata(Lock& js, kj::Exception& exception, v8::Local<v8::Value> handle);
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struct TypeErrorContext {
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enum Kind : uint8_t {
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METHOD_ARGUMENT, // has type name, member (method) name, and argument index

‎src/workerd/jsg/value.h‎

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@@ -1503,6 +1503,7 @@ class ExceptionWrapper {
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}();
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addExceptionDetail(js, result, handle);
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addJsExceptionMetadata(js, result, handle);
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return result;
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}
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};

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