Add net::GzipSourceStream

net/filter/gzip_source_stream.cc

Index: net/filter/gzip_source_stream.cc
diff --git a/net/filter/gzip_source_stream.cc b/net/filter/gzip_source_stream.cc
new file mode 100644
index 0000000000000000000000000000000000000000..31aaebd325328ef25577b93e9f11c44372001779
--- /dev/null
+++ b/net/filter/gzip_source_stream.cc
@@ -0,0 +1,224 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/filter/gzip_source_stream.h"
+
+#include "base/bind.h"
+#include "base/bit_cast.h"
+#include "base/logging.h"
+#include "net/base/io_buffer.h"
+#include "third_party/zlib/zlib.h"
+
+namespace net {
+
+namespace {
+
+const char kDeflate[] = "DEFLATE";
+const char kGzip[] = "GZIP";
+const char kGzipFallback[] = "GZIP_FALLBACK";
+
+}  // namespace
+
+GzipSourceStream::~GzipSourceStream() {
+  if (zlib_stream_)
+    inflateEnd(zlib_stream_.get());
+}
+
+std::unique_ptr<GzipSourceStream> GzipSourceStream::Create(
+    std::unique_ptr<SourceStream> upstream,
+    SourceStream::SourceType type) {
+  std::unique_ptr<GzipSourceStream> source(
+      new GzipSourceStream(std::move(upstream), type));
+
+  if (!source->Init())
+    return nullptr;
+  return source;
+}
+
+GzipSourceStream::GzipSourceStream(std::unique_ptr<SourceStream> upstream,
+                                   SourceStream::SourceType type)
+    : FilterSourceStream(type, std::move(upstream)),
+      zlib_header_added_(false),
+      gzip_footer_bytes_left_(0),
+      input_state_(STATE_START) {}
+
+bool GzipSourceStream::Init() {
+  zlib_stream_.reset(new z_stream);
+  if (!zlib_stream_)
+    return false;
+  memset(zlib_stream_.get(), 0, sizeof(z_stream));
+
+  int ret;
+  if (type() == TYPE_GZIP || type() == TYPE_GZIP_FALLBACK) {
+    ret = inflateInit2(zlib_stream_.get(), -MAX_WBITS);
+  } else {
+    ret = inflateInit(zlib_stream_.get());
+  }
+  DCHECK_NE(Z_VERSION_ERROR, ret);
+  return ret == Z_OK;
+}
+
+std::string GzipSourceStream::GetTypeAsString() const {
+  switch (type()) {
+    case TYPE_GZIP:
+      return kGzip;
+    case TYPE_GZIP_FALLBACK:
+      return kGzipFallback;
+    case TYPE_DEFLATE:
+      return kDeflate;
+    default:
+      NOTREACHED();
+      return "";
+  }
+}
+
+int GzipSourceStream::FilterData(IOBuffer* output_buffer,
+                                 int output_buffer_size,
+                                 IOBuffer* input_buffer,
+                                 int input_buffer_size,
+                                 int* consumed_bytes,
+                                 bool /*upstream_end_reached*/) {
+  if (input_buffer_size == 0)
+    return 0;
+  *consumed_bytes = 0;
+  int bytes_out = 0;
+  int bytes_used = 0;
+  while (true) {
+    InputState state = input_state_;
+    switch (state) {
+      case STATE_START:
+        if (type() == TYPE_DEFLATE) {
+          input_state_ = STATE_COMPRESSED_BODY;
+          break;
+        }
+        // If this stream is not really gzipped as detected by
+        // ShouldFallbackToPlain, pretend that the zlib stream has ended.
+        if (ShouldFallbackToPlain(input_buffer->data()[0])) {
+          input_state_ = STATE_UNCOMPRESSED_BODY;
+        } else {
+          input_state_ = STATE_GZIP_HEADER;
+        }
+        break;
+      case STATE_GZIP_HEADER: {
+        const size_t kGzipFooterBytes = 8;
+        const char* end = nullptr;
+        GZipHeader::Status status = gzip_header_.ReadMore(
+            input_buffer->data(), input_buffer_size, &end);
+        if (status == GZipHeader::INCOMPLETE_HEADER) {
+          *consumed_bytes += input_buffer_size;
+        } else if (status == GZipHeader::COMPLETE_HEADER) {
+          // If there is a valid header, there should also be a valid footer.
+          gzip_footer_bytes_left_ = kGzipFooterBytes;
+          *consumed_bytes += end - input_buffer->data();
+          input_state_ = STATE_COMPRESSED_BODY;
+        } else if (status == GZipHeader::INVALID_HEADER) {
+          return ERR_CONTENT_DECODING_FAILED;
+        }
+        break;
+      }
+      case STATE_COMPRESSED_BODY: {
+        DCHECK_LE(0, *consumed_bytes);
+        zlib_stream_.get()->next_in =
+            bit_cast<Bytef*>(input_buffer->data() + *consumed_bytes);
+        zlib_stream_.get()->avail_in = input_buffer_size - *consumed_bytes;

[Randy Smith (Not in Mondays), 2016/09/21 20:57:05]

Thought (i.e. not even a suggestion, just tossing it out in case you like the
idea): You could have a char* variable at the top of the function initialized to
input_buffer->data(), and then increment it and decrement input_buffer_size
through this function, so that this section of code would always have simple
variables to access the input buffer through. 

[xunjieli, 2016/09/22 17:20:49]

Done.

+        zlib_stream_.get()->next_out = bit_cast<Bytef*>(output_buffer->data());
+        zlib_stream_.get()->avail_out = output_buffer_size;
+
+        int ret = inflate(zlib_stream_.get(), Z_NO_FLUSH);
+
+        // Sometime misconfigured servers omit the zlib header, relying on
+        // clients to splice it back in.
+        if (ret < 0 && !zlib_header_added_) {
+          zlib_header_added_ = true;
+          if (!InsertZlibHeader())
+            return ERR_CONTENT_DECODING_FAILED;
+
+          zlib_stream_.get()->next_in = bit_cast<Bytef*>(input_buffer->data());
+          zlib_stream_.get()->avail_in = input_buffer_size;
+          zlib_stream_.get()->next_out =
+              bit_cast<Bytef*>(output_buffer->data());
+          zlib_stream_.get()->avail_out = output_buffer_size;
+
+          ret = inflate(zlib_stream_.get(), Z_NO_FLUSH);
+          // TODO(xunjieli): add a histogram to see how often this happens. The
+          // original bug for this behavior was ancient and maybe it doesn't
+          // happen in the wild any more?
+        }
+
+        bytes_used =
+            input_buffer_size - *consumed_bytes - zlib_stream_.get()->avail_in;
+        bytes_out = output_buffer_size - zlib_stream_.get()->avail_out;
+
+        *consumed_bytes += base::checked_cast<int>(bytes_used);
+
+        if (ret != Z_STREAM_END && ret != Z_OK)
+          return ERR_CONTENT_DECODING_FAILED;
+        DCHECK_LE(*consumed_bytes, input_buffer_size);
+        if (*consumed_bytes == input_buffer_size)
+          return bytes_out;

[Randy Smith (Not in Mondays), 2016/09/21 20:57:06]

I'm confused.  Above here there is code to (IIUC) handle the case where we loop
a couple of times in STATE_COMPRESSED_BODY; we modified *consumed_bytes and then
use it to figure out how far we've gotten in the input buffer.  But this implies
that the the zlib inflate function will accept all the incoming data in one call
unless it reaches the end of the compressed data.  What am I missing?

(I'm also confused because it's my assumption that the inflate function will
respect the limits on the output buffer, and my assumption is that if the output
buffer is limited enough it may choose not to read the entire input buffer.  But
maybe it commits to always reading the entire input buffer and doing internal
buffering if necessary?)

[xunjieli, 2016/09/22 17:20:49]

Done. Thanks for catching that! That's bug in my code. I have updated it and
added a test where we use a 1 byte output buffer which will catch this bug.

+        // Pass any futher data uncompressed.
+        input_state_ = STATE_UNCOMPRESSED_BODY;
+        break;
+      }
+      case STATE_UNCOMPRESSED_BODY:
+        return bytes_out + Passthrough(output_buffer->data() + bytes_out,
+                                       output_buffer_size - bytes_out,
+                                       input_buffer->data() + *consumed_bytes,
+                                       input_buffer_size - *consumed_bytes,
+                                       consumed_bytes);
+    }
+  }
+  NOTREACHED();
+  return ERR_UNEXPECTED;
+}
+
+size_t GzipSourceStream::Passthrough(char* output_buffer,
+                                     int output_buffer_size,
+                                     char* input_buffer,
+                                     int input_buffer_size,
+                                     int* consumed_bytes) {
+  size_t footer_bytes_skipped = NumGzipFooterBytesToSkip(input_buffer_size);

[Randy Smith (Not in Mondays), 2016/09/21 20:57:06]

Why not implement this with a separate state?  It would make this function
simpler--it could just be "passthrough" without the magic two layers deep inside
NumGzipFooterBytesToSkip() and it would be clear at the top level we're moving
through the footer.  

And it would also give us an easy, separate function in which to validate the
footer if we so choose (NumGzipFooterBytesToSkip() could be that currently, but
the name doesn't sound like a validation function and has no way to return an
error, so it's not ideal.)

[xunjieli, 2016/09/22 17:20:49]

Done.

+  size_t to_copy = input_buffer_size - footer_bytes_skipped;
+  if (to_copy > base::checked_cast<size_t>(output_buffer_size))
+    to_copy = output_buffer_size;
+  memcpy(output_buffer, input_buffer, to_copy);
+  *consumed_bytes += to_copy + footer_bytes_skipped;
+  return to_copy;
+}
+
+bool GzipSourceStream::InsertZlibHeader() {
+  char dummy_header[] = {0x78, 0x01};
+  char dummy_output[4];
+
+  inflateReset(zlib_stream_.get());
+  zlib_stream_.get()->next_in = bit_cast<Bytef*>(&dummy_header[0]);
+  zlib_stream_.get()->avail_in = sizeof(dummy_header);
+  zlib_stream_.get()->next_out = bit_cast<Bytef*>(&dummy_output[0]);
+  zlib_stream_.get()->avail_out = sizeof(dummy_output);
+
+  int ret = inflate(zlib_stream_.get(), Z_NO_FLUSH);
+  return ret == Z_OK;
+}
+
+// Dumb heuristic. Gzip files always start with a two-byte magic value per RFC
+// 1952 2.3.1, so if the first byte isn't the first byte of the gzip magic, and
+// this filter is checking whether it should fallback, then fallback.
+bool GzipSourceStream::ShouldFallbackToPlain(char first_byte) {
+  if (type() != TYPE_GZIP_FALLBACK)
+    return false;
+  static const char kGzipFirstByte = 0x1f;
+  return first_byte != kGzipFirstByte;
+}
+
+size_t GzipSourceStream::NumGzipFooterBytesToSkip(int input_buffer_size) {
+  if (gzip_footer_bytes_left_ == 0)
+    return 0;
+  size_t to_read = gzip_footer_bytes_left_;
+  if (to_read > base::checked_cast<size_t>(input_buffer_size))
+    to_read = input_buffer_size;
+  gzip_footer_bytes_left_ -= to_read;
+  return to_read;
+}
+
+}  // namespace net