Add blob-encoding support for RTC event logs
A blob is a string of binary information, whose length may not
necessarily be determined by looking into the string, so that
concatenating all blobs without explicitly including their lengths
as part of their encoding is not a viable option.
Bug: webrtc:8111
Change-Id: I89fdca660e89a6a71eff3ecb7b86416312b81f23
Reviewed-on: https://webrtc-review.googlesource.com/c/104201
Commit-Queue: Elad Alon <eladalon@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Reviewed-by: Yves Gerey <yvesg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25278}diff --git a/logging/rtc_event_log/encoder/blob_encoding.h b/logging/rtc_event_log/encoder/blob_encoding.h
new file mode 100644
index 0000000..3087534
--- /dev/null
+++ b/logging/rtc_event_log/encoder/blob_encoding.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef LOGGING_RTC_EVENT_LOG_ENCODER_BLOB_ENCODING_H_
+#define LOGGING_RTC_EVENT_LOG_ENCODER_BLOB_ENCODING_H_
+
+#include <string>
+#include <vector>
+
+#include "absl/strings/string_view.h"
+
+namespace webrtc {
+
+extern const size_t kMaxVarIntLengthBytes;
+
+// Encode/decode a sequence of strings, whose length is not known to be
+// discernable from the blob itself (i.e. without being transmitted OOB),
+// in a way that would allow us to separate them again on the decoding side.
+// The number of blobs is assumed to be transmitted OOB. For example, if
+// multiple sequences of different blobs are sent, but all sequences contain
+// the same number of blobs, it is beneficial to not encode the number of blobs.
+//
+// EncodeBlobs() must be given a non-empty vector. The blobs themselves may
+// be equal to "", though.
+// EncodeBlobs() may not fail.
+// EncodeBlobs() never returns the empty string.
+//
+// Calling DecodeBlobs() on an empty string, or with |num_of_blobs| set to 0,
+// is an error.
+// DecodeBlobs() returns an empty vector if it fails, e.g. due to a mismatch
+// between |num_of_blobs| and |encoded_blobs|, which can happen if
+// |encoded_blobs| is corrupted.
+// When successful, DecodeBlobs() returns a vector of string_view objects,
+// which refer to the original input (|encoded_blobs|), and therefore may
+// not outlive it.
+//
+// Note that the returned std::string might have been reserved for significantly
+// more memory than it ends up using. If the caller to EncodeBlobs() intends
+// to store the result long-term, he should consider shrink_to_fit()-ing it.
+std::string EncodeBlobs(const std::vector<std::string>& blobs);
+std::vector<absl::string_view> DecodeBlobs(absl::string_view encoded_blobs,
+ size_t num_of_blobs);
+
+} // namespace webrtc
+
+#endif // LOGGING_RTC_EVENT_LOG_ENCODER_BLOB_ENCODING_H_