[chromedriver] Prevent GetLog from returning more than 100,000 at a time.

chrome/test/chromedriver/logging.cc

Index: chrome/test/chromedriver/logging.cc
diff --git a/chrome/test/chromedriver/logging.cc b/chrome/test/chromedriver/logging.cc
index afd73754ca19963be1f6f74e75d15fdb070a88a6..a561275696cdab5107ce99e82ad6cf42bb41d339 100644
--- a/chrome/test/chromedriver/logging.cc
+++ b/chrome/test/chromedriver/logging.cc
@@ -130,6 +130,7 @@ bool HandleLogMessage(int severity,
 const char WebDriverLog::kBrowserType[] = "browser";
 const char WebDriverLog::kDriverType[] = "driver";
 const char WebDriverLog::kPerformanceType[] = "performance";
+const size_t WebDriverLog::kMaxReturnedEntries = 100000;
 
 bool WebDriverLog::NameToLevel(const std::string& name, Log::Level* out_level) {
   for (size_t i = 0; i < arraysize(kNameToLevel); ++i) {
@@ -151,8 +152,25 @@ WebDriverLog::~WebDriverLog() {
 }
 
 std::unique_ptr<base::ListValue> WebDriverLog::GetAndClearEntries() {
-  std::unique_ptr<base::ListValue> ret(entries_.release());
-  entries_.reset(new base::ListValue());
+  std::unique_ptr<base::ListValue> ret(new base::ListValue());
+  if (entries_->GetSize() <= WebDriverLog::kMaxReturnedEntries) {
+    std::swap(entries_, ret);
+  } else {
+    // net::HttpServer has a maximum buffer size of 100MB. If there are too many
+    // log entries, we'll fail to send them all back in one go. So we only
+    // return |kMaxReturnedEntries| entries at a time.
+    // TODO(crbug.com/681892): Add streaming support to net::HttpServer, so that
+    // we don't have to worry about its buffer size.
+    for (size_t i = 0; i < kMaxReturnedEntries; i++) {
+      // base::ListValue doesn't provide a method to split lists in constant
+      // time, so construct a new list for the return value. This should be
+      // revisited if users run into performance problems with large traces.
+      std::unique_ptr<base::Value> entry;
+      if (!entries_->Remove(0, &entry))
+        break;
+      ret->Append(std::move(entry));
+    }
+  }
   return ret;
 }