Mojo content handler shebang support

mojo/common/data_pipe_utils.cc

Index: mojo/common/data_pipe_utils.cc
diff --git a/mojo/common/data_pipe_utils.cc b/mojo/common/data_pipe_utils.cc
index 428a5897b05074ebcae62029659adbace64314c7..b26b1946cf7ed53a8c77012152cd939d4e37f1a9 100644
--- a/mojo/common/data_pipe_utils.cc
+++ b/mojo/common/data_pipe_utils.cc
@@ -11,6 +11,7 @@
 #include "base/files/scoped_file.h"
 #include "base/message_loop/message_loop.h"
 #include "base/task_runner_util.h"
+#include "base/threading/platform_thread.h"
 
 namespace mojo {
 namespace common {
@@ -58,8 +59,137 @@ size_t CopyToFileHelper(FILE* fp, const void* buffer, uint32_t num_bytes) {
   return fwrite(buffer, 1, num_bytes, fp);
 }
 
+// Sleep for as long as max_sleep_micros if the deadline hasn't been reached
+// and the number of bytes read is still increasing. Returns true if sleep
+// was actually called.
+//
+// This class is a substitute for being able to wait until N bytes are available
+// from a data pipe. The MaybeSleep method is called when num_bytes_read are
+// available but more are needed by the Peek operation. If a second
+// Peek operation finds the same number of bytes after sleeping we assume
+// that there's no point in trying again.
+// TODO(hansmuller): this heuristic is weak. crbug.com/429377
+class PeekSleeper {
+ public:
+  explicit PeekSleeper(MojoTimeTicks deadline)
+      : deadline_(deadline),
+        last_number_bytes_read_(0),
+        max_sleep_micros_(1000 * 10) {
+  }
+
+  bool MaybeSleep(uint32 num_bytes_read) {
+    if (num_bytes_read > 0 && last_number_bytes_read_ >= num_bytes_read)
+      return false;
+    last_number_bytes_read_ = num_bytes_read;
+
+    MojoTimeTicks now(GetTimeTicksNow());
+    if (now > deadline_)
+      return false;
+
+    MojoTimeTicks sleep_time = (deadline_ == 0)
+        ? max_sleep_micros_
+        : std::min<int64>(deadline_ - now, max_sleep_micros_);
+    base::PlatformThread::Sleep(base::TimeDelta::FromMicroseconds(sleep_time));
+    return true;
+  }
+
+ private:
+  MojoTimeTicks deadline_; // 0 => MOJO_DEADLINE_INDEFINITE
+  uint32 last_number_bytes_read_;
+  const MojoTimeTicks max_sleep_micros_; // microseconds
+};
+
+enum PeekStatus { kSuccess, kFail, kKeepReading };
+typedef const base::Callback<PeekStatus(const void*, uint32_t, std::string*)>&
+    PeekFunc;
+
+// When data is available on source, call peek_func and then either return true
+// and value, continue waiting for enough data to satisfy peek_func, or fail
+// and return false. Fail if the timeout is exceeded.
+bool BlockingPeekHelper(DataPipeConsumerHandle source,
+                        std::string* value,
+                        MojoDeadline timeout,
+                        PeekFunc peek_func) {
+  DCHECK(value);
+  value->clear();
+
+  MojoTimeTicks deadline = (timeout == MOJO_DEADLINE_INDEFINITE) ? 0
+      : 1 + GetTimeTicksNow() + static_cast<MojoTimeTicks>(timeout);
+  PeekSleeper sleeper(deadline);
+  MojoResult result = MOJO_RESULT_OK;
+
+  while(result == MOJO_RESULT_OK) {
+    const void* buffer;
+    uint32_t num_bytes;
+    result =
+        BeginReadDataRaw(source, &buffer, &num_bytes, MOJO_READ_DATA_FLAG_NONE);
+
+    if (result == MOJO_RESULT_OK) {
+      PeekStatus status = peek_func.Run(buffer, num_bytes, value);
+      if (EndReadDataRaw(source, 0) != MOJO_RESULT_OK)
+        return false;
+      switch (status) {
+        case PeekStatus::kSuccess: return true;
+        case PeekStatus::kFail: return false;
+        case PeekStatus::kKeepReading: break;
+      }
+      if (!sleeper.MaybeSleep(num_bytes))
+        return false;
+    } else if (result == MOJO_RESULT_SHOULD_WAIT) {
+      MojoTimeTicks now(GetTimeTicksNow());
+      if (timeout == MOJO_DEADLINE_INDEFINITE || now < deadline)
+        result = Wait(source, MOJO_HANDLE_SIGNAL_READABLE, deadline - now);
+    }
+  }
+
+  return false;
+}
+
+PeekStatus PeekLine(size_t max_line_length,
+                    const void* buffer,
+                    uint32 buffer_num_bytes,
+                    std::string* line) {
+  const char* p = static_cast<const char*>(buffer);
+  size_t max_p_index = std::min<size_t>(buffer_num_bytes, max_line_length);
+  for (size_t i = 0; i < max_p_index; i++) {
+    if (p[i] == '\n') {
+      *line = std::string(p, i + 1); // Include the trailing newline.
+      return PeekStatus::kSuccess;
+    }
+  }
+  return (buffer_num_bytes >= max_line_length)
+      ? PeekStatus::kFail : PeekStatus::kKeepReading;
+}
+
+PeekStatus PeekNBytes(size_t bytes_length,
+                      const void* buffer,
+                      uint32 buffer_num_bytes,
+                      std::string* bytes) {
+  if (buffer_num_bytes >= bytes_length) {
+    const char* p = static_cast<const char*>(buffer);
+    *bytes = std::string(p, bytes_length);
+    return PeekStatus::kSuccess;
+  }
+  return PeekStatus::kKeepReading;
+}
+
 } // namespace
 
+bool BlockingPeekNBytes(DataPipeConsumerHandle source,
+                        std::string* bytes,
+                        size_t bytes_length,
+                        MojoDeadline timeout) {
+  PeekFunc peek_nbytes = base::Bind(PeekNBytes, bytes_length);
+  return BlockingPeekHelper(source, bytes, timeout, peek_nbytes);
+}
+
+bool BlockingPeekLine(DataPipeConsumerHandle source,
+                      std::string* line,
+                      size_t max_line_length,
+                      MojoDeadline timeout) {
+  PeekFunc peek_line = base::Bind(PeekLine, max_line_length);
+  return BlockingPeekHelper(source, line, timeout, peek_line);
+}
 
 // TODO(hansmuller): Add a max_size parameter.
 bool BlockingCopyToString(ScopedDataPipeConsumerHandle source,