ipp_converter: Cleanup vector construction

- Use constructor where possible
- Reserve space where known

Bug: None
Test: manual
Change-Id: I5f7c00d1cd67300a54f25ea48e238571017e1b13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283890
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Auto-Submit: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786008}

chrome/services/ipp_parser/public/cpp/ipp_converter.cc

@@ -58,7 +58,7 @@ ssize_t IppWrite(base::span<uint8_t>* dst, ipp_uchar_t* source, size_t bytes) {
 
 // Returns a parsed HttpHeader on success, empty Optional on failure.
 base::Optional<HttpHeader> ParseHeader(base::StringPiece header) {
-  if (header.find(kCarriage) != std::string::npos) {
+  if (base::Contains(header, kCarriage)) {
     return base::nullopt;
   }
 
@@ -116,8 +116,11 @@ base::Optional<ValueType> ValueTagToType(const int value_tag) {
 }
 
 std::vector<bool> IppGetBools(ipp_attribute_t* attr) {
+  const size_t count = ippGetCount(attr);
+
   std::vector<bool> ret;
-  for (int i = 0; i < ippGetCount(attr); ++i) {
+  ret.reserve(count);
+  for (size_t i = 0; i < count; ++i) {
     // No decipherable failure condition for this libCUPS method.
     ret.push_back(ippGetBoolean(attr, i));
   }
@@ -125,8 +128,11 @@ std::vector<bool> IppGetBools(ipp_attribute_t* attr) {
 }
 
 base::Optional<std::vector<int>> IppGetInts(ipp_attribute_t* attr) {
+  const size_t count = ippGetCount(attr);
+
   std::vector<int> ret;
-  for (int i = 0; i < ippGetCount(attr); ++i) {
+  ret.reserve(count);
+  for (size_t i = 0; i < count; ++i) {
     int v = ippGetInteger(attr, i);
     if (!v) {
       return base::nullopt;
@@ -137,8 +143,11 @@ base::Optional<std::vector<int>> IppGetInts(ipp_attribute_t* attr) {
 }
 
 base::Optional<std::vector<std::string>> IppGetStrings(ipp_attribute_t* attr) {
+  const size_t count = ippGetCount(attr);
+
   std::vector<std::string> ret;
-  for (int i = 0; i < ippGetCount(attr); ++i) {
+  ret.reserve(count);
+  for (size_t i = 0; i < count; ++i) {
     const char* v = ippGetString(
         attr, i, nullptr /* TODO(crbug.com/945409): figure out language */);
     if (!v) {
@@ -169,13 +178,11 @@ base::Optional<std::vector<uint8_t>> BuildRequestLine(
     base::StringPiece method,
     base::StringPiece endpoint,
     base::StringPiece http_version) {
-  std::vector<uint8_t> ret;
   std::string status_line =
       base::StrCat({method, kStatusDelimiter, endpoint, kStatusDelimiter,
                     http_version, kCarriage});
 
-  std::copy(status_line.begin(), status_line.end(), std::back_inserter(ret));
-  return ret;
+  return std::vector<uint8_t>(status_line.begin(), status_line.end());
 }
 
 base::Optional<std::vector<HttpHeader>> ParseHeaders(
@@ -184,6 +191,7 @@ base::Optional<std::vector<HttpHeader>> ParseHeaders(
       headers_slice, kCarriage, base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
 
   std::vector<HttpHeader> ret;
+  ret.reserve(raw_headers.size());
   for (auto raw_header : raw_headers) {
     auto header = ParseHeader(raw_header);
     if (!header) {
@@ -207,9 +215,7 @@ base::Optional<std::vector<uint8_t>> BuildHeaders(
   // End-of-headers sentinel is a double carriage return; add the second one.
   headers += kCarriage;
 
-  std::vector<uint8_t> ret;
-  std::copy(headers.begin(), headers.end(), std::back_inserter(ret));
-  return ret;
+  return std::vector<uint8_t>(headers.begin(), headers.end());
 }
 
 // Synchronously reads/parses |ipp_slice| and returns the resulting ipp_t
@@ -226,7 +232,7 @@ printing::ScopedIppPtr ParseIppMessage(base::span<const uint8_t> ipp_slice) {
 
   if (ret == IPP_STATE_ERROR) {
     // Read failed, clear and return nullptr
-    ipp.reset(nullptr);
+    ipp.reset();
   }
 
   return ipp;
@@ -280,6 +286,10 @@ base::Optional<std::vector<uint8_t>> BuildIppRequest(
 
   // Marshall request
   std::vector<uint8_t> ret;
+  const size_t request_size = request_line_buffer->size() +
+                              headers_buffer->size() +
+                              ipp_message_buffer->size() + ipp_data.size();
+  ret.reserve(request_size);
 
   ret.insert(ret.end(), request_line_buffer->begin(),
              request_line_buffer->end());