1 files changed, 25 insertions, 0 deletions
diff --git a/src/lib/istream-try.h b/src/lib/istream-try.h
new file mode 100644
index 0000000..6f0f8b7
--- /dev/null
+++ b/src/lib/istream-try.h
@@ -0,0 +1,25 @@
+#ifndef ISTREAM_TRY_H
+#define ISTREAM_TRY_H
+
+/* Read from the first input stream that doesn't fail with EINVAL. If any of
+   the streams fail with non-EINVAL, it's treated as a fatal failure and the
+   error is immediately returned. If a stream returns 0, more data is waited
+   for before continuing to the next stream. This allows the last stream to
+   be a fallback stream that always succeeds.
+
+   Once the stream is detected, all the other streams are unreferenced.
+   The streams should usually be children of the same parent tee-istream.
+
+   Detecting whether istream-tee buffer is full or not is a bit tricky.
+   There's no visible difference between non-blocking istream returning 0 and
+   istream-tee buffer being full. To work around this, we treat used buffer
+   sizes <= min_buffer_full_size as being non-blocking istreams, while
+   buffer sizes > min_buffer_full_size are assumed to be due to istream-tee
+   max buffer size being reached. Practically this means that
+   min_buffer_full_size must be smaller than the smallest of the istreams'
+   maximum buffer sizes, but large enough that all the istreams would have
+   returned EINVAL on invalid input by that position. */
+struct istream *istream_try_create(struct istream *const input[],
+				   size_t min_buffer_full_size);
+
+#endif