go/system: adding two-phase data pipe methods

mojo/public/go/system/data_pipe.go

Index: mojo/public/go/system/data_pipe.go
diff --git a/mojo/public/go/system/data_pipe.go b/mojo/public/go/system/data_pipe.go
index 7de27d13eea0be2a6b2adb48b8df56c390b7b18f..b79a1e0395c965452f96dcbbeccb3196c39b0e81 100644
--- a/mojo/public/go/system/data_pipe.go
+++ b/mojo/public/go/system/data_pipe.go
@@ -16,6 +16,31 @@ type ConsumerHandle interface {
 	// ReadData reads data from the data pipe consumer handle with the
 	// given flags. On success, returns the data that was read.
 	ReadData(flags MojoReadDataFlags) (MojoResult, []byte)
+
+	// BeginReadData begins a two-phase read from the data pipe consumer.
+	// On success, returns a slice from which the caller can read up to its
+	// length bytes of data. If flags has |MOJO_READ_DATA_FLAG_ALL_OR_NONE|
+	// set, then the slice length will be at least as large as |numBytes|,
+	// which must also be a multiple of the element size (otherwise the
+	// caller must check the length of the slice).
+	//
+	// During a two-phase read, this handle is *not* readable. E.g., read
+	// from this handle will return |MOJO_RESULT_BUSY|.
+	//
+	// Once the caller has finished reading data from the slice, it should
+	// call |EndReadData()| to specify the amount read and to complete the
+	// two-phase read.
+	BeginReadData(numBytes int, flags MojoReadDataFlags) (MojoResult, []byte)
+
+	// EndReadData ends a two-phase read from the data pipe consumer that
+	// was begun by a call to |BeginReadData()| on the same handle.
+	// |numBytesRead| should indicate the amount of data actually read; it
+	// must be less than or equal to the length of the slice returned by
+	// |BeginReadData()| and must be a multiple of the element size.
+	//
+	// On failure, the two-phase read (if any) is ended (so the handle may
+	// become readable again) but no data is "removed" from the data pipe.
+	EndReadData(numBytesRead int) MojoResult
 }
 
 // ProducerHandle is a handle for the producer part of a data pipe.
@@ -26,6 +51,34 @@ type ProducerHandle interface {
 	// given flags. On success, returns the number of bytes that were
 	// actually written.
 	WriteData(data []byte, flags MojoWriteDataFlags) (MojoResult, int)
+
+	// BeginWriteData begins a two-phase write to the data pipe producer.
+	// On success, returns a slice to which the caller can write. If flags
+	// has |MOJO_READ_DATA_FLAG_ALL_OR_NONE| set, then the slice length will
+	// be at least as large as |numBytes|, which must also be a multiple of
+	// the element size (otherwise the caller must check the length of the
+	// slice).
+	//
+	// During a two-phase write, this handle is *not* writable. E.g., write
+	// to this handle will return |MOJO_RESULT_BUSY|.
+	//
+	// Once the caller has finished writing data to the buffer, it should
+	// call |EndWriteData()| to specify the amount written and to complete
+	// the two-phase write.
+	BeginWriteData(numBytes int, flags MojoWriteDataFlags) (MojoResult, []byte)
+
+	// EndWriteData ends a two-phase write to the data pipe producer that
+	// was begun by a call to |BeginWriteData()| on the same handle.
+	// |numBytesWritten| should indicate the amount of data actually
+	// written; it must be less than or equal to the length of the slice
+	// returned by |BeginWriteData()| and must be a multiple of the element
+	// size. The slice returned from |BeginWriteData()| must have been
+	// filled with exactly |numBytesWritten| bytes of data.
+	//
+	// On failure, the two-phase write (if any) is ended (so the handle may
+	// become writable again, if there's space available) but no data
+	// written to the slice is "put into" the data pipe.
+	EndWriteData(numBytesWritten int) MojoResult
 }
 
 type dataPipeConsumer struct {
@@ -49,6 +102,19 @@ func (h *dataPipeConsumer) ReadData(flags MojoReadDataFlags) (MojoResult, []byte
 	return MojoResult(result), data
 }
 
+func (h *dataPipeConsumer) BeginReadData(numBytes int, flags MojoReadDataFlags) (MojoResult, []byte) {
+	cParams := C.MallocTwoPhaseActionParams()
+	defer C.FreeTwoPhaseActionParams(cParams)
+	*cParams.num_bytes = C.uint32_t(numBytes)
+	result := C.MojoBeginReadData(h.mojoHandle.cValue(), cParams.buffer, cParams.num_bytes, flags.cValue())
+	buffer := unsafeByteSlice(unsafe.Pointer(*cParams.buffer), int(*cParams.num_bytes))
+	return MojoResult(result), buffer
+}
+
+func (h *dataPipeConsumer) EndReadData(numBytesRead int) MojoResult {
+	return MojoResult(C.MojoEndReadData(h.mojoHandle.cValue(), C.uint32_t(numBytesRead)))
+}
+
 type dataPipeProducer struct {
 	baseHandle
 }
@@ -62,3 +128,16 @@ func (h *dataPipeProducer) WriteData(data []byte, flags MojoWriteDataFlags) (Moj
 	result := C.MojoWriteData(h.mojoHandle.cValue(), cParams.elements, cParams.num_bytes, flags.cValue())
 	return MojoResult(result), int(*cParams.num_bytes)
 }
+
+func (h *dataPipeProducer) BeginWriteData(numBytes int, flags MojoWriteDataFlags) (MojoResult, []byte) {
+	cParams := C.MallocTwoPhaseActionParams()
+	defer C.FreeTwoPhaseActionParams(cParams)
+	*cParams.num_bytes = C.uint32_t(numBytes)
+	result := C.MojoBeginWriteData(h.mojoHandle.cValue(), cParams.buffer, cParams.num_bytes, flags.cValue())
+	buffer := unsafeByteSlice(unsafe.Pointer(*cParams.buffer), int(*cParams.num_bytes))
+	return MojoResult(result), buffer
+}
+
+func (h *dataPipeProducer) EndWriteData(numBytesWritten int) MojoResult {
+	return MojoResult(C.MojoEndWriteData(h.mojoHandle.cValue(), C.uint32_t(numBytesWritten)))
+}