Improve process output watcher's handling of multi-byte UTF8 characters

chromeos/process_proxy/process_output_watcher.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROMEOS_PROCESS_PROXY_PROCESS_OUTPUT_WATCHER_H_
 #define CHROMEOS_PROCESS_PROXY_PROCESS_OUTPUT_WATCHER_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "chromeos/chromeos_export.h"
 
-namespace {
-
-const int kReadBufferSize = 256;
-
-}  // namespace
-
 namespace chromeos {
 
 enum ProcessOutputType {
   PROCESS_OUTPUT_TYPE_OUT,
   PROCESS_OUTPUT_TYPE_ERR,
   PROCESS_OUTPUT_TYPE_EXIT
 };
 
 typedef base::Callback<void(ProcessOutputType, const std::string&)>
       ProcessOutputCallback;
 
+// Observes output on |out_fd| and invokes |callback| when some output is
+// detected. It assumes UTF8 output.
+// If output is detected in |stop_fd|, the watcher is stopped.
 // This class should live on its own thread because running class makes
 // underlying thread block. It deletes itself when watching is stopped.
 class CHROMEOS_EXPORT ProcessOutputWatcher {
  public:
   ProcessOutputWatcher(int out_fd, int stop_fd,
                        const ProcessOutputCallback& callback);
 
   // This will block current thread!!!!
   void Start();
 
  private:
   // The object will destroy itself when it stops watching process output.
   ~ProcessOutputWatcher();
 
   // Listens to output from supplied fds. It guarantees data written to one fd
   // will be reported in order that it has been written (this is not true across
   // fds, it would be nicer if it was).
   void WatchProcessOutput();
 
   // Verifies that fds that we got are properly set.
   void VerifyFileDescriptor(int fd);
 
   // Reads data from fd, and when it's done, invokes callback function.
   void ReadFromFd(ProcessOutputType type, int* fd);
 
+  // Checks if the read buffer has any trailing incomplete UTF8 characters and
+  // returns the read buffer size without them.
+  size_t OutputSizeWithoutIncompleteUTF8();
+
+  // Processes new |read_buffer_| state and notifies observer about new process
+  // output.
+  void ReportOutput(ProcessOutputType type, size_t new_bytes_count);
+
   // It will just delete this.
   void OnStop();
 
-  char read_buffer_[kReadBufferSize];
-  ssize_t read_buffer_size_;
+  char read_buffer_[256];
+  // Maximum read buffer content size.
+  size_t read_buffer_capacity_;
+  // Current read bufferi content size.
+  size_t read_buffer_size_;
 
   int out_fd_;
   int stop_fd_;
   int max_fd_;
 
   // Callback that will be invoked when some output is detected.
   ProcessOutputCallback on_read_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessOutputWatcher);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_PROCESS_PROXY_PROCESS_OUTPUT_WATCHER_H_