From 498b0f6be30d108dd78dc427beaad11767589a84 Mon Sep 17 00:00:00 2001
From: bneradt <bneradt@yahooinc.com>
Date: Mon, 18 May 2026 13:22:35 -0500
Subject: [PATCH] Quiet ESI streaming gunzip zero-output logs

ESI streaming gunzip can receive valid gzip chunks that consume input
without producing output, such as an initial header-only chunk. Those
chunks currently emit a `buf below zero` error even though the stream
continues successfully, which creates noisy Traffic Server logs.

This treats zero-output progress as normal streaming inflate behavior
and reserves error logging for actual zlib failures. It also extends the
ESI gzip unit test support to capture error logs and covers the
header-only chunk case.
---
 plugins/esi/lib/EsiGunzip.cc    | 27 +++++++++++++++------------
 plugins/esi/test/gzip_test.cc   | 26 ++++++++++++++++++++++++++
 plugins/esi/test/print_funcs.cc | 14 +++++++++++++-
 3 files changed, 54 insertions(+), 13 deletions(-)

diff --git a/plugins/esi/lib/EsiGunzip.cc b/plugins/esi/lib/EsiGunzip.cc
index ec1341d8182..19bfc6c2057 100644
--- a/plugins/esi/lib/EsiGunzip.cc
+++ b/plugins/esi/lib/EsiGunzip.cc
@@ -72,29 +72,32 @@ EsiGunzip::stream_decode(const char *data, int data_len, std::string &udata)
     int32_t curr_buf_size;
 
     do {
-      _zstrm.next_out  = reinterpret_cast<Bytef *>(raw_buf);
-      _zstrm.avail_out = BUF_SIZE;
-      inflate_result   = inflate(&_zstrm, Z_SYNC_FLUSH);
-      curr_buf_size    = -1;
-      if ((inflate_result == Z_OK) || (inflate_result == Z_BUF_ERROR)) {
-        curr_buf_size = BUF_SIZE - _zstrm.avail_out;
-      } else if (inflate_result == Z_STREAM_END) {
+      _zstrm.next_out            = reinterpret_cast<Bytef *>(raw_buf);
+      _zstrm.avail_out           = BUF_SIZE;
+      auto const avail_in_before = _zstrm.avail_in;
+      inflate_result             = inflate(&_zstrm, Z_SYNC_FLUSH);
+      if ((inflate_result == Z_OK) || (inflate_result == Z_BUF_ERROR) || (inflate_result == Z_STREAM_END)) {
         curr_buf_size = BUF_SIZE - _zstrm.avail_out;
+      } else {
+        TSError("[%s] Failure while inflating; error code %d", __FUNCTION__, inflate_result);
+        _success = false;
+        return false;
       }
       if (curr_buf_size > BUF_SIZE) {
         TSError("[%s] buf too large", __FUNCTION__);
         break;
       }
-      if (curr_buf_size < 1) {
-        TSError("[%s] buf below zero", __FUNCTION__);
+      if (curr_buf_size < 1 && avail_in_before == _zstrm.avail_in) {
         break;
       }
 
       // push empty object onto list and add data to in-list object to
       // avoid data copy for temporary
-      buf_list.push_back(string());
-      string &curr_buf = buf_list.back();
-      curr_buf.assign(raw_buf, curr_buf_size);
+      if (curr_buf_size > 0) {
+        buf_list.push_back(string());
+        string &curr_buf = buf_list.back();
+        curr_buf.assign(raw_buf, curr_buf_size);
+      }
 
       if (inflate_result == Z_STREAM_END) {
         break;
diff --git a/plugins/esi/test/gzip_test.cc b/plugins/esi/test/gzip_test.cc
index a6bd50fa593..5d19366a7ca 100644
--- a/plugins/esi/test/gzip_test.cc
+++ b/plugins/esi/test/gzip_test.cc
@@ -26,12 +26,16 @@
 
 #include <catch2/catch_test_macros.hpp>
 
+#include "EsiGunzip.h"
 #include "Utils.h"
 #include "gzip.h"
 
 using std::string;
 using namespace EsiLib;
 
+extern void   enableFakeErrorLog();
+extern string gFakeErrorLog;
+
 TEST_CASE("test esi plugin - gzip")
 {
   SECTION("===================== Test 1")
@@ -102,4 +106,26 @@ TEST_CASE("test esi plugin - gzip")
     // check output of gunzip
     CHECK(gunzip(expected_cdata, 32, buf_list) == false);
   }
+
+  SECTION("streaming gunzip does not log an error for chunks with no output")
+  {
+    const char expected_data[] = "Hello World!";
+
+    string cdata;
+    REQUIRE(gzip(expected_data, 12, cdata));
+
+    EsiGunzip gunzip;
+    string    data;
+
+    enableFakeErrorLog();
+    REQUIRE(gunzip.stream_decode(cdata.data(), GZIP_HEADER_SIZE, data));
+    CHECK(data.empty());
+    CHECK(gFakeErrorLog.empty());
+
+    REQUIRE(gunzip.stream_decode(cdata.data() + GZIP_HEADER_SIZE, cdata.size() - GZIP_HEADER_SIZE, data));
+    REQUIRE(gunzip.stream_finish());
+
+    CHECK(data == expected_data);
+    CHECK(gFakeErrorLog.empty());
+  }
 }
diff --git a/plugins/esi/test/print_funcs.cc b/plugins/esi/test/print_funcs.cc
index 2596a462054..d73b973d654 100644
--- a/plugins/esi/test/print_funcs.cc
+++ b/plugins/esi/test/print_funcs.cc
@@ -34,9 +34,11 @@ static const int LINE_SIZE = 1024 * 1024;
 namespace
 {
 bool fakeDebugLogEnabled;
-}
+bool fakeErrorLogEnabled;
+} // namespace
 
 std::string gFakeDebugLog;
+std::string gFakeErrorLog;
 
 void
 enableFakeDebugLog()
@@ -45,6 +47,13 @@ enableFakeDebugLog()
   gFakeDebugLog.assign("");
 }
 
+void
+enableFakeErrorLog()
+{
+  fakeErrorLogEnabled = true;
+  gFakeErrorLog.assign("");
+}
+
 void
 DbgCtl::print(const char *tag, const char * /* file */, const char * /* function */, int /* line */, const char *fmt, ...)
 {
@@ -101,4 +110,7 @@ TSError(const char *fmt, ...)
   vsnprintf(buf, LINE_SIZE, fmt, ap);
   printf("Error: %s\n", buf);
   va_end(ap);
+  if (fakeErrorLogEnabled) {
+    gFakeErrorLog.append(buf);
+  }
 }