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Batch file list responses to reduce TCP segments

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Buffer JSON file list entries into ~1.4KB batches before sending to avoid one TCP segment per file. This eliminates client delayed ACK delays that were causing large directory listings to take tens of seconds. Falls back to per-entry sends if buffer allocation fails.
This commit is contained in:
Justin Mitchell
2026-07-14 05:15:00 -04:00
parent c1a396c1ba
commit 302c0771dd
1 changed files with 40 additions and 7 deletions
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src/network/CrossPointWebServer.cpp
+39 -6
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@@ -26,6 +26,7 @@
#include "html/SettingsPageHtml.generated.h"
#include "html/js/jszip_minJs.generated.h"
#include "util/BookCacheUtils.h"
#include <Memory.h>
namespace {
// Folders/files to hide from the web interface file browser
@@ -484,13 +485,33 @@ void CrossPointWebServer::handleFileListData() const {
server->setContentLength(CONTENT_LENGTH_UNKNOWN);
server->send(200, "application/json", "");
server->sendContent("[");
// Batch entries into ~one-TCP-segment flushes. One sendContent per entry
// means one chunked frame in its own TCP segment per file; the client's
// delayed ACK (~40-200 ms each) turns a large directory into tens of
// seconds. ~1.4 KB batches collapse that to a handful of segments.
constexpr size_t BATCH_CAPACITY = 1400;
auto batch = makeUniqueNoThrow<char[]>(BATCH_CAPACITY);
size_t batchLen = 0;
const auto flushBatch = [&]() {
if (batchLen == 0) return;
server->sendContent(batch.get(), batchLen);
batchLen = 0;
};
char output[512];
constexpr size_t outputSize = sizeof(output);
bool seenFirst = false;
JsonDocument doc;
scanFiles(currentPath.c_str(), [this, &output, &doc, seenFirst](const FileInfo& info) mutable {
if (batch) {
batch[batchLen++] = '[';
} else {
LOG_ERR("WEB", "OOM: file list batch buffer; falling back to per-entry sends");
server->sendContent("[");
}
scanFiles(currentPath.c_str(), [&](const FileInfo& info) {
doc.clear();
doc["name"] = info.name;
doc["size"] = info.size;
@@ -504,14 +525,26 @@ void CrossPointWebServer::handleFileListData() const {
return;
}
if (seenFirst) {
server->sendContent(",");
const size_t need = written + (seenFirst ? 1 : 0);
if (batch) {
if (batchLen + need > BATCH_CAPACITY) flushBatch();
if (seenFirst) batch[batchLen++] = ',';
memcpy(batch.get() + batchLen, output, written);
batchLen += written;
} else {
seenFirst = true;
}
if (seenFirst) server->sendContent(",");
server->sendContent(output);
}
seenFirst = true;
});
if (batch) {
if (batchLen + 1 > BATCH_CAPACITY) flushBatch();
batch[batchLen++] = ']';
flushBatch();
} else {
server->sendContent("]");
}
// End of streamed response, empty chunk to signal client
server->sendContent("");
LOG_DBG("WEB", "Served file listing page for path: %s", currentPath.c_str());