Remove use of istream in RTC event log parser.

Bug: webrtc:11933,webrtc:8982
Change-Id: I8008eb704549e690d7c778f743a5b9cd0c52892c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208941
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Reviewed-by: Elad Alon <eladalon@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33603}

logging/rtc_event_log/encoder/blob_encoding.cc

@@ -58,49 +58,30 @@ std::vector<absl::string_view> DecodeBlobs(absl::string_view encoded_blobs,
     return std::vector<absl::string_view>();
   }
 
-  size_t read_idx = 0;
-
   // Read the lengths of all blobs.
   std::vector<uint64_t> lengths(num_of_blobs);
   for (size_t i = 0; i < num_of_blobs; ++i) {
-    if (read_idx >= encoded_blobs.length()) {
-      RTC_DCHECK_EQ(read_idx, encoded_blobs.length());
-      RTC_LOG(LS_WARNING) << "Corrupt input; excessive number of blobs.";
-      return std::vector<absl::string_view>();
-    }
-
-    const size_t read_bytes =
-        DecodeVarInt(encoded_blobs.substr(read_idx), &lengths[i]);
-    if (read_bytes == 0) {
+    bool success = false;
+    std::tie(success, encoded_blobs) = DecodeVarInt(encoded_blobs, &lengths[i]);
+    if (!success) {
       RTC_LOG(LS_WARNING) << "Corrupt input; varint decoding failed.";
       return std::vector<absl::string_view>();
     }
-
-    read_idx += read_bytes;
-
-    // Note: It might be that read_idx == encoded_blobs.length(), if this
-    // is the last iteration, and all of the blobs are the empty string.
-    RTC_DCHECK_LE(read_idx, encoded_blobs.length());
   }
 
   // Read the blobs themselves.
   std::vector<absl::string_view> blobs(num_of_blobs);
   for (size_t i = 0; i < num_of_blobs; ++i) {
-    if (read_idx + lengths[i] < read_idx) {  // Wrap-around detection.
-      RTC_LOG(LS_WARNING) << "Corrupt input; unreasonably large blob sequence.";
-      return std::vector<absl::string_view>();
-    }
-
-    if (read_idx + lengths[i] > encoded_blobs.length()) {
+    if (lengths[i] > encoded_blobs.length()) {
       RTC_LOG(LS_WARNING) << "Corrupt input; blob sizes exceed input size.";
       return std::vector<absl::string_view>();
     }
 
-    blobs[i] = encoded_blobs.substr(read_idx, lengths[i]);
-    read_idx += lengths[i];
+    blobs[i] = encoded_blobs.substr(0, lengths[i]);
+    encoded_blobs = encoded_blobs.substr(lengths[i]);
   }
 
-  if (read_idx != encoded_blobs.length()) {
+  if (!encoded_blobs.empty()) {
     RTC_LOG(LS_WARNING) << "Corrupt input; unrecognized trailer.";
     return std::vector<absl::string_view>();
   }

logging/rtc_event_log/encoder/var_int.cc

@@ -39,7 +39,8 @@ std::string EncodeVarInt(uint64_t input) {
 
 // There is some code duplication between the flavors of this function.
 // For performance's sake, it's best to just keep it.
-size_t DecodeVarInt(absl::string_view input, uint64_t* output) {
+std::pair<bool, absl::string_view> DecodeVarInt(absl::string_view input,
+                                                uint64_t* output) {
   RTC_DCHECK(output);
 
   uint64_t decoded = 0;
@@ -48,11 +49,11 @@ size_t DecodeVarInt(absl::string_view input, uint64_t* output) {
                 << static_cast<uint64_t>(7 * i));
     if (!(input[i] & 0x80)) {
       *output = decoded;
-      return i + 1;
+      return {true, input.substr(i + 1)};
     }
   }
 
-  return 0;
+  return {false, input};
 }
 
 // There is some code duplication between the flavors of this function.

logging/rtc_event_log/encoder/var_int.h

@@ -15,6 +15,7 @@
 #include <stdint.h>
 
 #include <string>
+#include <utility>
 
 #include "absl/strings/string_view.h"
 #include "rtc_base/bit_buffer.h"
@@ -26,20 +27,23 @@ extern const size_t kMaxVarIntLengthBytes;
 // Encode a given uint64_t as a varint. From least to most significant,
 // each batch of seven bits are put into the lower bits of a byte, and the last
 // remaining bit in that byte (the highest one) marks whether additional bytes
-// follow (which happens if and only if there are other bits in |input| which
+// follow (which happens if and only if there are other bits in `input` which
 // are non-zero).
 // Notes: If input == 0, one byte is used. If input is uint64_t::max, exactly
 // kMaxVarIntLengthBytes are used.
 std::string EncodeVarInt(uint64_t input);
 
 // Inverse of EncodeVarInt().
-// If decoding is successful, a non-zero number is returned, indicating the
-// number of bytes read from |input|, and the decoded varint is written
-// into |output|.
-// If not successful, 0 is returned, and |output| is not modified.
-size_t DecodeVarInt(absl::string_view input, uint64_t* output);
+// Returns true and the remaining (unread) slice of the input if decoding
+// succeeds. Returns false otherwise and `output` is not modified.
+std::pair<bool, absl::string_view> DecodeVarInt(absl::string_view input,
+                                                uint64_t* output);
 
 // Same as other version, but uses a rtc::BitBuffer for input.
+// If decoding is successful, a non-zero number is returned, indicating the
+// number of bytes read from `input`, and the decoded varint is written
+// into `output`.
+// If not successful, 0 is returned, and `output` is not modified.
 // Some bits may be consumed even if a varint fails to be read.
 size_t DecodeVarInt(rtc::BitBuffer* input, uint64_t* output);