Move MHTML file writing out of the renderer main thread.

third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp

Index: third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
diff --git a/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp b/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
index 65b80bb57f24fd2b79b42d806b99db30182bea19..3d4bd00f6b3d11f7ed7d126ebf38c6f33678cb60 100644
--- a/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
+++ b/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
@@ -45,12 +45,23 @@
 #include "wtf/text/Base64.h"
 #include "wtf/text/StringBuilder.h"
 
-namespace blink {
+
+namespace {
 
 const char* const quotedPrintable = "quoted-printable";
 const char* const base64 = "base64";
 const char* const binary = "binary";
 
+enum class Encoding {
+    QuotedPrintable,
+    Base64,
+    Binary,
+};
+
+}
+
+namespace blink {
+
 static String replaceNonPrintableCharacters(const String& text)
 {
     StringBuilder stringBuilder;
@@ -108,7 +119,7 @@ bool MHTMLArchive::canLoadArchive(const KURL& url)
 
 void MHTMLArchive::generateMHTMLHeader(
     const String& boundary, const String& title, const String& mimeType,
-    SharedBuffer& outputBuffer)
+    std::vector<char>& outputBuffer)
 {
     ASSERT(!boundary.isEmpty());
     ASSERT(!mimeType.isEmpty());
@@ -141,7 +152,8 @@ void MHTMLArchive::generateMHTMLHeader(
     ASSERT(stringBuilder.toString().containsOnlyASCII());
     CString asciiString = stringBuilder.toString().utf8();
 
-    outputBuffer.append(asciiString.data(), asciiString.length());
+    outputBuffer.reserve(outputBuffer.size() + asciiString.length());
+    outputBuffer.insert(outputBuffer.end(), asciiString.data(), asciiString.data() + asciiString.length());
 }
 
 void MHTMLArchive::generateMHTMLPart(
@@ -149,7 +161,7 @@ void MHTMLArchive::generateMHTMLPart(
     const String& contentID,
     EncodingPolicy encodingPolicy,
     const SerializedResource& resource,
-    SharedBuffer& outputBuffer)
+    std::vector<char>& outputBuffer)
 {
     ASSERT(!boundary.isEmpty());
     ASSERT(contentID.isEmpty() || contentID[0] == '<');
@@ -169,16 +181,20 @@ void MHTMLArchive::generateMHTMLPart(
         stringBuilder.append("\r\n");
     }
 
-    const char* contentEncoding = 0;
-    if (encodingPolicy == UseBinaryEncoding)
-        contentEncoding = binary;
-    else if (MIMETypeRegistry::isSupportedJavaScriptMIMEType(resource.mimeType) || MIMETypeRegistry::isSupportedNonImageMIMEType(resource.mimeType))
-        contentEncoding = quotedPrintable;
-    else
-        contentEncoding = base64;
+    const char* contentEncodingText = 0;
+    Encoding encoding = Encoding::Base64;
+    if (encodingPolicy == UseBinaryEncoding) {
+        contentEncodingText = binary;
+        encoding = Encoding::Binary;
+    } else if (MIMETypeRegistry::isSupportedJavaScriptMIMEType(resource.mimeType) || MIMETypeRegistry::isSupportedNonImageMIMEType(resource.mimeType)) {
+        contentEncodingText = quotedPrintable;
+        encoding = Encoding::QuotedPrintable;
+    } else {
+        contentEncodingText = base64;
+    }
 
     stringBuilder.append("Content-Transfer-Encoding: ");
-    stringBuilder.append(contentEncoding);
+    stringBuilder.append(contentEncodingText);
     stringBuilder.append("\r\n");
 
     if (!resource.url.protocolIsAbout()) {
@@ -190,13 +206,24 @@ void MHTMLArchive::generateMHTMLPart(
     stringBuilder.append("\r\n");
 
     CString asciiString = stringBuilder.toString().utf8();
-    outputBuffer.append(asciiString.data(), asciiString.length());
 
-    if (!strcmp(contentEncoding, binary)) {
+    // Best guess for a reserved size. It should work well for binary and base64
+    // (see https://en.wikipedia.org/wiki/Base64#MIME); not so much for
+    // quoted-printable which is harder to estimate.
+    std::size_t expectedFinalSize = outputBuffer.size() + asciiString.length();
+    if (encoding == Encoding::Base64)
+        expectedFinalSize += static_cast<std::size_t>(resource.data->size() * 1.37);
+    else
+        expectedFinalSize += resource.data->size();
+    outputBuffer.reserve(expectedFinalSize);
+
+    outputBuffer.insert(outputBuffer.end(), asciiString.data(), asciiString.data() + asciiString.length());
+
+    if (encoding == Encoding::Binary) {
         const char* data;
         size_t position = 0;
         while (size_t length = resource.data->getSomeData(data, position)) {
-            outputBuffer.append(data, length);
+            outputBuffer.insert(outputBuffer.end(), data, data + length);
             position += length;
         }
     } else {
@@ -204,12 +231,13 @@ void MHTMLArchive::generateMHTMLPart(
         const char* data = resource.data->data();
         size_t dataLength = resource.data->size();
         Vector<char> encodedData;
-        if (!strcmp(contentEncoding, quotedPrintable)) {
+        if (encoding == Encoding::QuotedPrintable) {
             quotedPrintableEncode(data, dataLength, encodedData);
-            outputBuffer.append(encodedData.data(), encodedData.size());
-            outputBuffer.append("\r\n", 2u);
+            outputBuffer.insert(outputBuffer.end(), encodedData.data(), encodedData.data() + encodedData.size());
+            outputBuffer.push_back('\r');
+            outputBuffer.push_back('\n');
         } else {
-            ASSERT(!strcmp(contentEncoding, base64));
+            DCHECK(encoding == Encoding::Base64);

[carlosk, 2016/10/03 23:51:05]

I replaced ASSERT with DCHECK here as I understand this is the way forward.
Should I replace all other occurrences in this file?

             // We are not specifying insertLFs = true below as it would cut the lines with LFs and MHTML requires CRLFs.
             base64Encode(data, dataLength, encodedData);
             const size_t maximumLineLength = 76;
@@ -217,8 +245,9 @@ void MHTMLArchive::generateMHTMLPart(
             size_t encodedDataLength = encodedData.size();
             do {
                 size_t lineLength = std::min(encodedDataLength - index, maximumLineLength);
-                outputBuffer.append(encodedData.data() + index, lineLength);
-                outputBuffer.append("\r\n", 2u);
+                outputBuffer.insert(outputBuffer.end(), encodedData.data() + index, encodedData.data() + index + lineLength);
+                outputBuffer.push_back('\r');
+                outputBuffer.push_back('\n');
                 index += maximumLineLength;
             } while (index < encodedDataLength);
         }
@@ -227,11 +256,12 @@ void MHTMLArchive::generateMHTMLPart(
 
 void MHTMLArchive::generateMHTMLFooter(
     const String& boundary,
-    SharedBuffer& outputBuffer)
+    std::vector<char>& outputBuffer)
 {
     ASSERT(!boundary.isEmpty());
     CString asciiString = String("--" + boundary + "--\r\n").utf8();
-    outputBuffer.append(asciiString.data(), asciiString.length());
+    outputBuffer.reserve(outputBuffer.size() + asciiString.length());
+    outputBuffer.insert(outputBuffer.end(), asciiString.data(), asciiString.data() + asciiString.length());
 }
 
 void MHTMLArchive::setMainResource(ArchiveResource* mainResource)