Reuse authenticated immutable RS subsets for playback reads

src/stream/stream_buffer.c

@@ -27,6 +27,8 @@ struct stream_cached_batch {
     uint16_t count;
     uint8_t flags;
     int rejected;
+    int verified;
+    uint8_t verified_parts[(RS_MAX_BLOCKS + 7) / 8];
 };
 
 struct stream_buffer {
@@ -419,8 +421,11 @@ int stream_buffer_decode(struct stream_buffer *b, uint64_t seq, uint8_t *output,
         return STREAM_ERR_ARGUMENT;
     }
     const uint8_t *blocks[RS_MAX_BLOCKS] = {0};
-    for (uint32_t slot = batch->first_slot; slot != STREAM_SLOT_NONE; slot = b->slots[slot].next)
-        blocks[b->slots[slot].subblock] = b->data + slot * b->block_bytes + STREAM_BLOCK_RS_OFF;
+    for (uint32_t slot = batch->first_slot; slot != STREAM_SLOT_NONE; slot = b->slots[slot].next) {
+        unsigned sub = b->slots[slot].subblock;
+        if (!batch->verified || (batch->verified_parts[sub / 8] & (1u << (sub % 8))))
+            blocks[sub] = b->data + slot * b->block_bytes + STREAM_BLOCK_RS_OFF;
+    }
     size_t decoded_size = (size_t)(b->descriptor.n - b->descriptor.r) * (batch->block_size - RS_HEADER_SIZE);
     if (rs_decode(b->rs, blocks, batch->block_size, b->decode_output, rs_input_capacity(b->rs)) != RS_OK) {
         DEBUG_ERROR(DEBUG_CATEGORY_STREAM, "buffer decode RS failed seq=%llu present=%u", (unsigned long long)seq, batch->count);
@@ -428,7 +433,8 @@ int stream_buffer_decode(struct stream_buffer *b, uint64_t seq, uint8_t *output,
     }
     struct stream_batch_info expected = {.seq = batch->seq, .data_length = batch->data_length,
         .timestamp_ms = batch->timestamp_ms, .block_size = batch->block_size, .flags = batch->flags};
-    int result = stream_batch_verify(&b->descriptor, b->public_key, &expected, b->decode_output, decoded_size);
+    int result = batch->verified ? STREAM_OK
+                 : stream_batch_verify(&b->descriptor, b->public_key, &expected, b->decode_output, decoded_size);
     if (result != STREAM_OK) {
         if (result != STREAM_ERR_SIGNATURE && result != STREAM_ERR_FORMAT) return result;
         batch->rejected = 1; b->stats.rejected_batches++;
@@ -448,6 +454,16 @@ int stream_buffer_decode(struct stream_buffer *b, uint64_t seq, uint8_t *output,
         }
         return STREAM_REJECTED;
     }
+    if (!batch->verified) {
+        unsigned selected = 0;
+        for (unsigned sub = 0; sub < b->descriptor.n && selected < (unsigned)(b->descriptor.n - b->descriptor.r); sub++) {
+            if (!blocks[sub]) continue;
+            batch->verified_parts[sub / 8] |= (uint8_t)(1u << (sub % 8)); selected++;
+        }
+        batch->verified = 1;
+        DEBUG_TRACE(DEBUG_CATEGORY_STREAM, "buffer authenticated immutable RS set source=%llx seq=%llu parts=%u",
+                    (unsigned long long)b->descriptor.source_node_id, (unsigned long long)seq, selected);
+    }
     memcpy(output, b->decode_output + STREAM_BATCH_HEADER, batch->data_length);
     *length = batch->data_length;
     DEBUG_TRACE(DEBUG_CATEGORY_STREAM, "buffer decoded seq=%llu present=%u length=%u", (unsigned long long)seq, batch->count, batch->data_length);

src/stream/stream_buffer.h

@@ -59,6 +59,8 @@ int stream_buffer_read(struct stream_buffer *buffer, uint64_t seq, uint8_t subbl
 int stream_buffer_range(struct stream_buffer *buffer, uint8_t subblock, uint64_t *first, uint64_t *last);
 
 /* Восстановить пачку и проверить одну подпись; достаточно capacity >= действительной длины.
+ * После успеха фиксируется использованный набор k неизменяемых частей: повторное чтение не проверяет подпись заново
+ * и не доверяет поздним частям, которые не участвовали в подтверждённом восстановлении.
  * STREAM_REJECTED означает неверную подпись/подписанные метаданные; такая пачка повторно не декодируется.
  * Выход не меняется при WAIT/GAP/EXPIRED/REJECTED/ошибке; отсутствующие части в кольцо не добавляются. */
 int stream_buffer_decode(struct stream_buffer *buffer, uint64_t seq, uint8_t *output, size_t capacity, size_t *length);