Address review comments

src/workerd/api/kv.c++

@@ -95,8 +95,10 @@ kj::Own<kj::HttpClient> KvNamespace::getHttpClient(IoContext& context,
     KJ_UNREACHABLE;
   }();
 
-  auto client = context.getHttpClientWithSpans<std::initializer_list>(
-      subrequestChannel, true, kj::none, operationName, {{"db.system"_kjc, "cloudflare-kv"_kjc}});
+  kj::Vector<SpanTagParams> tags;
+  tags.add("db.system"_kjc, kj::str("cloudflare-kv"_kjc));
+  auto client = context.getHttpClientWithSpans(
+      subrequestChannel, true, kj::none, operationName, kj::mv(tags));
   headers.add(FLPROD_405_HEADER, urlStr);
   for (const auto& header: additionalHeaders) {
     headers.add(header.name.asPtr(), header.value.asPtr());

src/workerd/api/r2-bucket.c++

@@ -30,14 +30,14 @@ kj::Own<kj::HttpClient> r2GetClient(IoContext& context,
     kj::LiteralStringConst method,
     kj::Maybe<kj::StringPtr> bucket,
     kj::Maybe<StringTagParams> extraTag) {
-  kj::Vector<IoContext::SpanTagParams> tags;
-  tags.add(IoContext::SpanTagParams{"rpc.service"_kjc, "r2"_kjc});
-  tags.add(IoContext::SpanTagParams{"rpc.method"_kjc, kj::str(method)});
+  kj::Vector<SpanTagParams> tags;
+  tags.add("rpc.service"_kjc, kj::str("r2"_kjc));
+  tags.add("rpc.method"_kjc, kj::str(method));
   KJ_IF_SOME(b, bucket) {
-    tags.add(IoContext::SpanTagParams{"cloudflare.r2.bucket"_kjc, kj::str(b)});
+    tags.add("cloudflare.r2.bucket"_kjc, kj::str(b));
   }
   KJ_IF_SOME(tag, extraTag) {
-    tags.add(IoContext::SpanTagParams{tag.key, kj::str(tag.value)});
+    tags.add(tag.key, kj::str(tag.value));
   }
 
   return context.getHttpClientWithSpans(subrequestChannel, true, kj::none, op, kj::mv(tags));
@@ -397,9 +397,8 @@ R2Bucket::get(jsg::Lock& js,
   return js.evalNow([&] {
     auto& context = IoContext::current();
 
-    auto client =
-        r2GetClient(context, clientIndex, "r2_get"_kjc, "GetObject"_kjc, this->adminBucketName(),
-            kj::Maybe<StringTagParams>({"cloudflare.r2.key"_kjc, name.asPtr()}));
+    auto client = r2GetClient(context, clientIndex, "r2_get"_kjc, "GetObject"_kjc,
+        this->adminBucketName(), StringTagParams{"cloudflare.r2.key"_kjc, name.asPtr()});
 
     capnp::JsonCodec json;
     json.handleByAnnotation<R2BindingRequest>();
@@ -461,9 +460,8 @@ jsg::Promise<kj::Maybe<jsg::Ref<R2Bucket::HeadResult>>> R2Bucket::put(jsg::Lock&
     });
 
     auto& context = IoContext::current();
-    auto client =
-        r2GetClient(context, clientIndex, "r2_put"_kjc, "PutObject"_kjc, this->adminBucketName(),
-            kj::Maybe<StringTagParams>({"cloudflare.r2.key"_kjc, name.asPtr()}));
+    auto client = r2GetClient(context, clientIndex, "r2_put"_kjc, "PutObject"_kjc,
+        this->adminBucketName(), StringTagParams{"cloudflare.r2.key"_kjc, name.asPtr()});
 
     capnp::JsonCodec json;
     json.handleByAnnotation<R2BindingRequest>();
@@ -765,8 +763,7 @@ jsg::Promise<void> R2Bucket::delete_(jsg::Lock& js,
       KJ_UNREACHABLE;
     };
     auto client = r2GetClient(context, clientIndex, "r2_delete"_kjc, "DeleteObject"_kjc,
-        this->adminBucketName(),
-        kj::Maybe<StringTagParams>({"cloudflare.r2.delete"_kjc, deleteKey().asPtr()}));
+        this->adminBucketName(), StringTagParams{"cloudflare.r2.delete"_kjc, deleteKey().asPtr()});
 
     capnp::JsonCodec json;
     json.handleByAnnotation<R2BindingRequest>();

src/workerd/api/r2-multipart.c++

@@ -32,7 +32,7 @@ jsg::Promise<R2MultipartUpload::UploadedPart> R2MultipartUpload::uploadPart(jsg:
     auto& context = IoContext::current();
     auto client = r2GetClient(context, this->bucket->clientIndex, "r2_uploadPart"_kjc,
         "UploadPart"_kjc, this->bucket->adminBucketName(),
-        kj::Maybe<StringTagParams>({"cloudflare.r2.upload_id"_kjc, uploadId.asPtr()}));
+        StringTagParams{"cloudflare.r2.upload_id"_kjc, uploadId.asPtr()});
 
     capnp::JsonCodec json;
     json.handleByAnnotation<R2BindingRequest>();
@@ -98,7 +98,7 @@ jsg::Promise<jsg::Ref<R2Bucket::HeadResult>> R2MultipartUpload::complete(jsg::Lo
     auto& context = IoContext::current();
     auto client = r2GetClient(context, this->bucket->clientIndex, "r2_completeMultipartUpload"_kjc,
         "CompleteMultipartUpload"_kjc, this->bucket->adminBucketName(),
-        kj::Maybe<StringTagParams>({"cloudflare.r2.upload_id"_kjc, uploadId.asPtr()}));
+        StringTagParams{"cloudflare.r2.upload_id"_kjc, uploadId.asPtr()});
 
     capnp::JsonCodec json;
     json.handleByAnnotation<R2BindingRequest>();
@@ -149,7 +149,7 @@ jsg::Promise<void> R2MultipartUpload::abort(
     auto& context = IoContext::current();
     auto client = r2GetClient(context, this->bucket->clientIndex, "r2_abortMultipartUpload"_kjc,
         "AbortMultipartUpload"_kjc, this->bucket->adminBucketName(),
-        kj::Maybe<StringTagParams>({"cloudflare.r2.upload_id"_kjc, uploadId.asPtr()}));
+        StringTagParams{"cloudflare.r2.upload_id"_kjc, uploadId.asPtr()});
 
     capnp::JsonCodec json;
     json.handleByAnnotation<R2BindingRequest>();

src/workerd/io/io-context.c++

@@ -835,23 +835,15 @@ kj::Own<WorkerInterface> IoContext::getSubrequestChannel(
       });
 }
 
-template <template <class> class T>
 kj::Own<WorkerInterface> IoContext::getSubrequestChannelWithSpans(uint channel,
     bool isInHouse,
     kj::Maybe<kj::String> cfBlobJson,
     kj::ConstString operationName,
-    T<SpanTagParams> tags) {
+    kj::Vector<SpanTagParams> tags) {
   return getSubrequest(
       [&](TraceContext& tracing, IoChannelFactory& channelFactory) {
-    for (const SpanTagParams& tag: tags) {
-      KJ_SWITCH_ONEOF(tag.value) {
-        KJ_CASE_ONEOF(c, kj::LiteralStringConst) {
-          tracing.userSpan.setTag(kj::mv(tag.key), kj::str(c));
-        }
-        KJ_CASE_ONEOF(str, kj::String) {
-          tracing.userSpan.setTag(kj::mv(tag.key), kj::str(str));
-        }
-      }
+    for (SpanTagParams& tag: tags) {
+      tracing.userSpan.setTag(kj::mv(tag.key), kj::mv(tag.value));
     }
     return getSubrequestChannelImpl(
         channel, isInHouse, kj::mv(cfBlobJson), tracing, channelFactory);
@@ -901,29 +893,15 @@ kj::Own<kj::HttpClient> IoContext::getHttpClient(
       getSubrequestChannel(channel, isInHouse, kj::mv(cfBlobJson), kj::mv(operationName)));
 }
 
-template <template <class> class T>
 kj::Own<kj::HttpClient> IoContext::getHttpClientWithSpans(uint channel,
     bool isInHouse,
     kj::Maybe<kj::String> cfBlobJson,
     kj::ConstString operationName,
-    T<SpanTagParams> tags) {
+    kj::Vector<SpanTagParams> tags) {
   return asHttpClient(getSubrequestChannelWithSpans(
       channel, isInHouse, kj::mv(cfBlobJson), kj::mv(operationName), kj::mv(tags)));
 }
 
-// We don't want to declare the templated methods in the header – just generate code for the two
-// supported container types explicitly.
-template kj::Own<kj::HttpClient> IoContext::getHttpClientWithSpans(uint channel,
-    bool isInHouse,
-    kj::Maybe<kj::String> cfBlobJson,
-    kj::ConstString operationName,
-    kj::Vector<SpanTagParams> tags);
-template kj::Own<kj::HttpClient> IoContext::getHttpClientWithSpans(uint channel,
-    bool isInHouse,
-    kj::Maybe<kj::String> cfBlobJson,
-    kj::ConstString operationName,
-    std::initializer_list<SpanTagParams> tags);
-
 kj::Own<kj::HttpClient> IoContext::getHttpClientNoChecks(uint channel,
     bool isInHouse,
     kj::Maybe<kj::String> cfBlobJson,

src/workerd/io/io-context.h

@@ -91,6 +91,12 @@ class WarningAggregator final: public kj::AtomicRefcounted {
   kj::MutexGuarded<kj::Vector<kj::Own<WarningContext>>> warnings;
 };
 
+// Used to add span tags within user tracing.
+struct SpanTagParams {
+  kj::LiteralStringConst key;
+  kj::String value;
+};
+
 // Represents one incoming request being handled by a IoContext. In non-actor scenarios,
 // there is only ever one IncomingRequest per IoContext, but with actors there could be many.
 //
@@ -710,21 +716,11 @@ class IoContext final: public kj::Refcounted, private kj::TaskSet::ErrorHandler
       kj::Maybe<kj::String> cfBlobJson,
       kj::ConstString operationName);
 
-  // As above, but with list of span tags to add.
-  // TODO(o11y): For now this only supports literal values based on initializer_list constraints.
-  // Add syntactic sugar to kj::vector so that we can pass in a vector more ergonomically and use
-  // that instead to support other value types.
-  struct SpanTagParams {
-    kj::LiteralStringConst key;
-    kj::OneOf<kj::LiteralStringConst, kj::String> value;
-  };
-
-  template <template <class> class T>
   kj::Own<WorkerInterface> getSubrequestChannelWithSpans(uint channel,
       bool isInHouse,
       kj::Maybe<kj::String> cfBlobJson,
       kj::ConstString operationName,
-      T<SpanTagParams> tags);
+      kj::Vector<SpanTagParams> tags);
 
   // Like getSubrequestChannel() but doesn't enforce limits. Use for trusted paths only.
   kj::Own<WorkerInterface> getSubrequestChannelNoChecks(uint channel,
@@ -740,12 +736,11 @@ class IoContext final: public kj::Refcounted, private kj::TaskSet::ErrorHandler
       kj::ConstString operationName);
 
   // As above, but with list of span tags to add, analogous to getSubrequestChannelWithSpans().
-  template <template <class> class T>
   kj::Own<kj::HttpClient> getHttpClientWithSpans(uint channel,
       bool isInHouse,
       kj::Maybe<kj::String> cfBlobJson,
       kj::ConstString operationName,
-      T<SpanTagParams> tags);
+      kj::Vector<SpanTagParams> tags);
 
   // Convenience methods that call getSubrequest*() and adapt the returned WorkerInterface objects
   // to HttpClient.