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diff --git a/src/upb_stream.h b/src/upb_stream.h
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+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * This file defines four general-purpose streaming interfaces for protobuf
+ * data or bytes:
+ *
+ * - upb_src: pull interface for protobuf data.
+ * - upb_sink: push interface for protobuf data.
+ * - upb_bytesrc: pull interface for bytes.
+ * - upb_bytesink: push interface for bytes.
+ *
+ * These interfaces are used as general-purpose glue in upb.  For example, the
+ * decoder interface works by implementing a upb_src and calling a upb_bytesrc.
+ *
+ * Copyright (c) 2010 Joshua Haberman.  See LICENSE for details.
+ *
+ */
+
+#ifndef UPB_SRCSINK_H
+#define UPB_SRCSINK_H
+
+#include "upb_stream_vtbl.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Forward-declare.  We can't include upb_def.h; it would be circular.
+struct _upb_fielddef;
+
+// Note!  The "eof" flags work like feof() in C; they cannot report end-of-file
+// until a read has failed due to eof.  They cannot preemptively tell you that
+// the next call will fail due to eof.  Since these are the semantics that C
+// and UNIX provide, we're stuck with them if we want to support eg. stdio.
+
+/* upb_src ********************************************************************/
+
+// TODO: decide how to handle unknown fields.
+
+// Retrieves the fielddef for the next field in the stream.  Returns NULL on
+// error or end-of-stream.
+struct _upb_fielddef *upb_src_getdef(upb_src *src);
+
+// Retrieves and stores the next value in "val".  For string types "val" must
+// be a newly-recycled string.  Returns false on error.
+bool upb_src_getval(upb_src *src, upb_valueptr val);
+bool upb_src_getstr(upb_src *src, upb_string *val);
+
+// Like upb_src_getval() but skips the value.
+bool upb_src_skipval(upb_src *src);
+
+// Descends into a submessage.  May only be called after a def has been
+// returned that indicates a submessage.
+bool upb_src_startmsg(upb_src *src);
+
+// Stops reading a submessage.  May be called before the stream is EOF, in
+// which case the rest of the submessage is skipped.
+bool upb_src_endmsg(upb_src *src);
+
+// Returns the current error/eof status for the stream.
+INLINE upb_status *upb_src_status(upb_src *src) { return &src->status; }
+INLINE bool upb_src_eof(upb_src *src) { return src->eof; }
+
+// The following functions are equivalent to upb_src_getval(), but take
+// pointers to specific types.  In debug mode this may check that the type
+// is compatible with the type being read.  This check will *not* be performed
+// in non-debug mode, and if you get the type wrong the behavior is undefined.
+bool upb_src_getbool(upb_src *src, bool *val);
+bool upb_src_getint32(upb_src *src, int32_t *val);
+bool upb_src_getint64(upb_src *src, int64_t *val);
+bool upb_src_getuint32(upb_src *src, uint32_t *val);
+bool upb_src_getuint64(upb_src *src, uint64_t *val);
+bool upb_src_getfloat(upb_src *src, float *val);
+bool upb_src_getdouble(upb_src *src, double *val);
+
+/* upb_sink *******************************************************************/
+
+// Puts the given fielddef into the stream.
+bool upb_sink_putdef(upb_sink *sink, struct _upb_fielddef *def);
+
+// Puts the given value into the stream.
+bool upb_sink_putval(upb_sink *sink, upb_value val);
+
+// Starts a submessage.  (needed?  the def tells us we're starting a submsg.)
+bool upb_sink_startmsg(upb_sink *sink);
+
+// Ends a submessage.
+bool upb_sink_endmsg(upb_sink *sink);
+
+// Returns the current error status for the stream.
+upb_status *upb_sink_status(upb_sink *sink);
+
+/* upb_bytesrc ****************************************************************/
+
+// Returns the next string in the stream.  false is returned on error or eof.
+// The string must be at least "minlen" bytes long unless the stream is eof.
+bool upb_bytesrc_get(upb_bytesrc *src, upb_string *str, upb_strlen_t minlen);
+
+// Appends the next "len" bytes in the stream in-place to "str".  This should
+// be used when the caller needs to build a contiguous string of the existing
+// data in "str" with more data.
+bool upb_bytesrc_append(upb_bytesrc *src, upb_string *str, upb_strlen_t len);
+
+// Returns the current error status for the stream.
+INLINE upb_status *upb_bytesrc_status(upb_bytesrc *src) { return &src->status; }
+INLINE bool upb_bytesrc_eof(upb_bytesrc *src) { return src->eof; }
+
+/* upb_bytesink ***************************************************************/
+
+// Puts the given string.  Returns the number of bytes that were actually,
+// consumed, which may be fewer than were in the string, or <0 on error.
+int32_t upb_bytesink_put(upb_bytesink *sink, upb_string *str);
+
+// Returns the current error status for the stream.
+upb_status *upb_bytesink_status(upb_bytesink *sink);
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif