test: complete BDB parser (handle internal/overflow pages, support all page sizes)

This aims to complete our test framework BDB parser to reflect
our read-only BDB parser in the wallet codebase. This could be
useful both for making review of #26606 easier and to also possibly
improve our functional tests for the BDB parser by comparing with
an alternative implementation.

Author: theStack

test/functional/test_framework/bdb.py

@@ -6,44 +6,55 @@
 Utilities for working directly with the wallet's BDB database file
 
 This is specific to the configuration of BDB used in this project:
-    - pagesize: 4096 bytes
     - Outer database contains single subdatabase named 'main'
     - btree
-    - btree leaf pages
+    - btree internal, leaf and overflow pages
 
-Each key-value pair is two entries in a btree leaf. The first is the key, the one that follows
+Each key-value pair is two entries in a btree leaf, which optionally refers to overflow pages
+if the data doesn't fit into a single page. The first entry is the key, the one that follows
 is the value. And so on. Note that the entry data is itself not in the correct order. Instead
 entry offsets are stored in the correct order and those offsets are needed to then retrieve
-the data itself.
+the data itself. Note that this implementation currently only supports reading databases that
+are in the same endianness as the host.
 
 Page format can be found in BDB source code dbinc/db_page.h
-This only implements the deserialization of btree metadata pages and normal btree pages. Overflow
-pages are not implemented but may be needed in the future if dealing with wallets with large
-transactions.
 
 `db_dump -da wallet.dat` is useful to see the data in a wallet.dat BDB file
 """
 
 import struct
 
 # Important constants
-PAGESIZE = 4096
+PAGE_HEADER_SIZE = 26
 OUTER_META_PAGE = 0
-INNER_META_PAGE = 2
 
 # Page type values
 BTREE_INTERNAL = 3
 BTREE_LEAF = 5
+OVERFLOW_DATA = 7
 BTREE_META = 9
 
+# Record type values
+RECORD_KEYDATA = 1
+RECORD_OVERFLOW_DATA = 3
+
 # Some magic numbers for sanity checking
 BTREE_MAGIC = 0x053162
 DB_VERSION = 9
-
-# Deserializes a leaf page into a dict.
-# Btree internal pages have the same header, for those, return None.
-# For the btree leaf pages, deserialize them and put all the data into a dict
-def dump_leaf_page(data):
+SUBDATABASE_NAME = b'main'
+
+# Deserializes an internal, leaf or overflow page into a dict.
+# In addition to the common page header fields, the result contains an 'entries'
+# array of dicts with the following fields, depending on the page type:
+#     internal page [BTREE_INTERNAL]:
+#         - 'page_num': referenced page number (used to find further pages to process)
+#     leaf page [BTREE_LEAF]:
+#         - 'record_type': record type, must be RECORD_KEYDATA or RECORD_OVERFLOW_DATA
+#         - 'data': binary data (key or value payload),  if record type is RECORD_KEYDATA
+#         - 'page_num': referenced overflow page number, if record type is RECORD_OVERFLOW_DATA
+#     overflow page [OVERFLOW_DATA]:
+#         - 'data': binary data (part of key or value payload)
+def dump_page(data):
     page_info = {}
     page_header = data[0:26]
     _, pgno, prev_pgno, next_pgno, entries, hf_offset, level, pg_type = struct.unpack('QIIIHHBB', page_header)
@@ -56,20 +67,35 @@ def dump_leaf_page(data):
     page_info['entry_offsets'] = struct.unpack('{}H'.format(entries), data[26:26 + entries * 2])
     page_info['entries'] = []
 
-    if pg_type == BTREE_INTERNAL:
-        # Skip internal pages. These are the internal nodes of the btree and don't contain anything relevant to us
-        return None
+    assert pg_type in (BTREE_INTERNAL, BTREE_LEAF, OVERFLOW_DATA)
 
-    assert pg_type == BTREE_LEAF, 'A non-btree leaf page has been encountered while dumping leaves'
+    if pg_type == OVERFLOW_DATA:
+        assert entries == 1
+        page_info['entries'].append({'data': data[26:26 + hf_offset]})
+        return page_info
 
     for i in range(0, entries):
+        entry = {}
         offset = page_info['entry_offsets'][i]
-        entry = {'offset': offset}
-        page_data_header = data[offset:offset + 3]
-        e_len, pg_type = struct.unpack('HB', page_data_header)
-        entry['len'] = e_len
-        entry['pg_type'] = pg_type
-        entry['data'] = data[offset + 3:offset + 3 + e_len]
+        record_header = data[offset:offset + 3]
+        offset += 3
+        e_len, record_type = struct.unpack('HB', record_header)
+
+        if pg_type == BTREE_INTERNAL:
+            assert record_type == RECORD_KEYDATA
+            internal_record_data = data[offset:offset + 9]
+            _, page_num, _ = struct.unpack('=BII', internal_record_data)
+            entry['page_num'] = page_num
+        elif pg_type == BTREE_LEAF:
+            assert record_type in (RECORD_KEYDATA, RECORD_OVERFLOW_DATA)
+            entry['record_type'] = record_type
+            if record_type == RECORD_KEYDATA:
+                entry['data'] = data[offset:offset + e_len]
+            elif record_type == RECORD_OVERFLOW_DATA:
+                overflow_record_data = data[offset:offset + 9]
+                _, page_num, _ = struct.unpack('=BII', overflow_record_data)
+                entry['page_num'] = page_num
+
         page_info['entries'].append(entry)
 
     return page_info
@@ -115,37 +141,70 @@ def dump_meta_page(page):
     return metadata
 
 # Given the dict from dump_leaf_page, get the key-value pairs and put them into a dict
-def extract_kv_pairs(page_data):
+def extract_kv_pairs(page_data, pages):
     out = {}
     last_key = None
     for i, entry in enumerate(page_data['entries']):
+        data = b''
+        if entry['record_type'] == RECORD_KEYDATA:
+            data = entry['data']
+        elif entry['record_type'] == RECORD_OVERFLOW_DATA:
+            next_page = entry['page_num']
+            while next_page != 0:
+                opage = pages[next_page]
+                opage_info = dump_page(opage)
+                data += opage_info['entries'][0]['data']
+                next_page = opage_info['next_pgno']
+
         # By virtue of these all being pairs, even number entries are keys, and odd are values
         if i % 2 == 0:
             out[entry['data']] = b''
-            last_key = entry['data']
+            last_key = data
         else:
-            out[last_key] = entry['data']
+            out[last_key] = data
     return out
 
 # Extract the key-value pairs of the BDB file given in filename
 def dump_bdb_kv(filename):
     # Read in the BDB file and start deserializing it
     pages = []
     with open(filename, 'rb') as f:
-        data = f.read(PAGESIZE)
-        while len(data) > 0:
-            pages.append(data)
-            data = f.read(PAGESIZE)
+        # Determine pagesize first
+        data = f.read(PAGE_HEADER_SIZE)
+        pagesize = struct.unpack('I', data[20:24])[0]
+        assert pagesize in (512, 1024, 2048, 4096, 8192, 16384, 32768, 65536)
 
-    # Sanity check the meta pages
-    dump_meta_page(pages[OUTER_META_PAGE])
-    dump_meta_page(pages[INNER_META_PAGE])
+        # Read rest of first page
+        data += f.read(pagesize - PAGE_HEADER_SIZE)
+        assert len(data) == pagesize
 
-    # Fetch the kv pairs from the leaf pages
+        # Read all remaining pages
+        while len(data) > 0:
+            pages.append(data)
+            data = f.read(pagesize)
+
+    # Sanity check the meta pages, read root page
+    outer_meta_info = dump_meta_page(pages[OUTER_META_PAGE])
+    root_page_info = dump_page(pages[outer_meta_info['root']])
+    assert root_page_info['pg_type'] == BTREE_LEAF
+    assert len(root_page_info['entries']) == 2
+    assert root_page_info['entries'][0]['data'] == SUBDATABASE_NAME
+    assert len(root_page_info['entries'][1]['data']) == 4
+    inner_meta_page = int.from_bytes(root_page_info['entries'][1]['data'], 'big')
+    inner_meta_info = dump_meta_page(pages[inner_meta_page])
+
+    # Fetch the kv pairs from the pages
     kv = {}
-    for i in range(3, len(pages)):
-        info = dump_leaf_page(pages[i])
-        if info is not None:
-            info_kv = extract_kv_pairs(info)
+    pages_to_process = [inner_meta_info['root']]
+    while len(pages_to_process) > 0:
+        curr_page_no = pages_to_process.pop()
+        assert curr_page_no <= outer_meta_info['last_pgno']
+        info = dump_page(pages[curr_page_no])
+        assert info['pg_type'] in (BTREE_INTERNAL, BTREE_LEAF)
+        if info['pg_type'] == BTREE_INTERNAL:
+            for entry in info['entries']:
+                pages_to_process.append(entry['page_num'])
+        elif info['pg_type'] == BTREE_LEAF:
+            info_kv = extract_kv_pairs(info, pages)
             kv = {**kv, **info_kv}
     return kv