python client: implement v3 directory serialization/deserialization

python/pmtiles/tile.py

@@ -1,9 +1,21 @@
 from collections import namedtuple
+from enum import Enum
+import io
+import gzip
 
-Entry = namedtuple("Entry", ["tile_id", "offset", "length", "run_length"])
 Header = namedtuple("Header", [])
 
 
+class Entry:
+    __slots__ = ("tile_id", "offset", "length", "run_length")
+
+    def __init__(self, tile_id, offset, length, run_length):
+        self.tile_id = tile_id
+        self.offset = offset
+        self.length = length
+        self.run_length = run_length
+
+
 def rotate(n, xy, rx, ry):
     if ry == 0:
         if rx == 1:
@@ -87,12 +99,89 @@ def find_tile(entries, tile_id):
             return entries[n]
 
 
-def deserialize_directory(bytes):
-    pass
+def read_varint(b_io):
+    shift = 0
+    result = 0
+    while True:
+        raw = b_io.read(1)
+        if raw == b"":
+            raise EOFError("unexpectedly reached end of varint stream")
+        i = ord(raw)
+        result |= (i & 0x7F) << shift
+        shift += 7
+        if not (i & 0x80):
+            break
+    return result
 
 
-def serialize_directory(bytes):
-    pass
+def write_varint(b_io, i):
+    while True:
+        towrite = i & 0x7F
+        i >>= 7
+        if i:
+            b_io.write(bytes([towrite | 0x80]))
+        else:
+            b_io.write(bytes([towrite]))
+            break
+
+
+class Compression(Enum):
+    UNKNOWN = 0
+    NONE = 1
+    GZIP = 2
+    BROTLI = 3
+    ZSTD = 4
+
+
+def deserialize_directory(buf):
+    b_io = io.BytesIO(gzip.decompress(buf))
+    entries = []
+    num_entries = read_varint(b_io)
+
+    last_id = 0
+    for i in range(num_entries):
+        tmp = read_varint(b_io)
+        entries.append(Entry(last_id + tmp, 0, 0, 0))
+        last_id += tmp
+
+    for i in range(num_entries):
+        entries[i].run_length = read_varint(b_io)
+
+    for i in range(num_entries):
+        entries[i].length = read_varint(b_io)
+
+    for i in range(num_entries):
+        tmp = read_varint(b_io)
+        if i > 0 and tmp == 0:
+            entries[i].offset = entries[i - 1].offset + entries[i - 1].length
+        else:
+            entries[i].offset = tmp - 1
+
+    return entries
+
+
+def serialize_directory(entries):
+    b_io = io.BytesIO()
+    write_varint(b_io, len(entries))
+
+    last_id = 0
+    for e in entries:
+        write_varint(b_io, e.tile_id - last_id)
+        last_id = e.tile_id
+
+    for e in entries:
+        write_varint(b_io, e.run_length)
+
+    for e in entries:
+        write_varint(b_io, e.length)
+
+    for i, e in enumerate(entries):
+        if i > 0 and e.offset == entries[i - 1].offset + entries[i - 1].length:
+            write_varint(b_io, 0)
+        else:
+            write_varint(b_io, e.offset + 1)
+
+    return gzip.compress(b_io.getvalue())
 
 
 def deserialize_header(bytes):