MONGOCRYPT-905 Reduce allocations when parsing FLE2TagAndEncryptedMetadataBlocks (#1161)

Author: erwee

src/mc-fle2-find-range-payload-private-v2.h

@@ -85,8 +85,8 @@ BSON_STATIC_ASSERT2(alignof_mc_FLE2FindRangePayloadV2_t,
 
 /**
  * EdgeFindTokenSetV2 is the following BSON document:
- * d: <binary> // EDCDerivedFromDataTokenAndContentionFactor
- * s: <binary> // ESCDerivedFromDataTokenAndContentionFactor
+ * d: <binary> // EDCDerivedFromDataToken
+ * s: <binary> // ESCDerivedFromDataToken
  * l: <binary> // ServerDerivedFromDataToken
  *
  * Instances of mc_EdgeFindTokenSetV2_t are expected to be owned by

src/mc-fle2-payload-iev-v2.c

@@ -622,11 +622,12 @@ bool mc_FLE2IndexedEncryptedValueV2_parse(mc_FLE2IndexedEncryptedValueV2_t *iev,
     // Read each metadata element in buff
     for (uint32_t i = 0; i < iev->edge_count; i++) {
         _mongocrypt_buffer_t tmp_buf;
+        const uint8_t *mbuf = NULL;
 
-        CHECK_AND_RETURN(mc_reader_read_buffer(&reader, &tmp_buf, kMetadataLen, status));
-        CHECK_AND_RETURN(mc_FLE2TagAndEncryptedMetadataBlock_parse(&iev->metadata[i], &tmp_buf, status));
+        CHECK_AND_RETURN(mc_reader_read_bytes(&reader, &mbuf, kMetadataLen, status));
+        _mongocrypt_buffer_from_data(&tmp_buf, mbuf, kMetadataLen);
 
-        _mongocrypt_buffer_cleanup(&tmp_buf);
+        CHECK_AND_RETURN(mc_FLE2TagAndEncryptedMetadataBlock_parse(&iev->metadata[i], &tmp_buf, status));
     }
 
     return true;

src/mc-fle2-tag-and-encrypted-metadata-block-private.h

@@ -17,20 +17,21 @@
 #ifndef MC_FLE2_TAG_AND_ENCRYPTED_METADATA_BLOCK_H
 #define MC_FLE2_TAG_AND_ENCRYPTED_METADATA_BLOCK_H
 
-#include "mc-reader-private.h"
-#include "mc-writer-private.h"
-#include "mongocrypt-private.h"
+#include "mongocrypt-buffer-private.h"
 
-#define kMetadataLen 96U // encCount(32) + tag(32) + encZeros(32)
+#define kFieldLen 32U
+#define kMetadataLen 96U // encryptedCount(32) + tag(32) + encryptedZeros(32)
 
 typedef struct _mc_FLE2TagAndEncryptedMetadataBlock_t {
+    // The contiguous metadata block buffer.
+    _mongocrypt_buffer_t rawBlock;
+
+    // The following are unowned buffers that each points to a field in rawBlock.
     _mongocrypt_buffer_t encryptedCount;
     _mongocrypt_buffer_t tag;
     _mongocrypt_buffer_t encryptedZeros;
 } mc_FLE2TagAndEncryptedMetadataBlock_t;
 
-#define kFieldLen 32U
-
 void mc_FLE2TagAndEncryptedMetadataBlock_init(mc_FLE2TagAndEncryptedMetadataBlock_t *metadata);
 
 void mc_FLE2TagAndEncryptedMetadataBlock_cleanup(mc_FLE2TagAndEncryptedMetadataBlock_t *metadata);

src/mc-fle2-tag-and-encrypted-metadata-block.c

@@ -33,6 +33,7 @@ void mc_FLE2TagAndEncryptedMetadataBlock_init(mc_FLE2TagAndEncryptedMetadataBloc
 void mc_FLE2TagAndEncryptedMetadataBlock_cleanup(mc_FLE2TagAndEncryptedMetadataBlock_t *metadata) {
     BSON_ASSERT_PARAM(metadata);
 
+    _mongocrypt_buffer_cleanup(&metadata->rawBlock);
     _mongocrypt_buffer_cleanup(&metadata->encryptedCount);
     _mongocrypt_buffer_cleanup(&metadata->tag);
     _mongocrypt_buffer_cleanup(&metadata->encryptedZeros);
@@ -54,11 +55,16 @@ bool mc_FLE2TagAndEncryptedMetadataBlock_parse(mc_FLE2TagAndEncryptedMetadataBlo
 
     mc_FLE2TagAndEncryptedMetadataBlock_init(metadata);
 
-    CHECK_AND_RETURN(mc_reader_read_buffer(&reader, &metadata->encryptedCount, kFieldLen, status));
+    CHECK_AND_RETURN(mc_reader_read_buffer(&reader, &metadata->rawBlock, kMetadataLen, status));
 
-    CHECK_AND_RETURN(mc_reader_read_buffer(&reader, &metadata->tag, kFieldLen, status));
+    uint64_t offset = 0;
+    _mongocrypt_buffer_from_data(&metadata->encryptedCount, metadata->rawBlock.data + offset, kFieldLen);
 
-    CHECK_AND_RETURN(mc_reader_read_buffer(&reader, &metadata->encryptedZeros, kFieldLen, status));
+    offset += kFieldLen;
+    _mongocrypt_buffer_from_data(&metadata->tag, metadata->rawBlock.data + offset, kFieldLen);
+
+    offset += kFieldLen;
+    _mongocrypt_buffer_from_data(&metadata->encryptedZeros, metadata->rawBlock.data + offset, kFieldLen);
 
     return true;
 }
@@ -72,12 +78,7 @@ bool mc_FLE2TagAndEncryptedMetadataBlock_serialize(const mc_FLE2TagAndEncryptedM
     _mongocrypt_buffer_resize(buf, kMetadataLen);
     mc_writer_t writer;
     mc_writer_init_from_buffer(&writer, buf, __func__);
-
-    CHECK_AND_RETURN(mc_writer_write_buffer(&writer, &metadata->encryptedCount, kFieldLen, status));
-
-    CHECK_AND_RETURN(mc_writer_write_buffer(&writer, &metadata->tag, kFieldLen, status));
-
-    CHECK_AND_RETURN(mc_writer_write_buffer(&writer, &metadata->encryptedZeros, kFieldLen, status));
+    CHECK_AND_RETURN(mc_writer_write_buffer(&writer, &metadata->rawBlock, kMetadataLen, status));
 
     return true;
 }
@@ -92,6 +93,7 @@ bool mc_FLE2TagAndEncryptedMetadataBlock_serialize(const mc_FLE2TagAndEncryptedM
 
 bool mc_FLE2TagAndEncryptedMetadataBlock_validate(const mc_FLE2TagAndEncryptedMetadataBlock_t *metadata,
                                                   mongocrypt_status_t *status) {
+    CHECK(metadata->rawBlock.len == kMetadataLen, "Length of metadata block was unexpected");
     CHECK(metadata->encryptedCount.len == kFieldLen, "Length of encrypted count was unexpected");
     CHECK(metadata->tag.len == kFieldLen, "Length of tag was unexpected");
     CHECK(metadata->encryptedZeros.len == kFieldLen, "Length of encrypted zeros was unexpected");