Add preliminary encode/decode of varints

protobuf_serialization.nim

@@ -1,7 +1,113 @@
-# This is just an example to get you started. A typical library package
-# exports the main API in this file. Note that you cannot rename this file
-# but you can remove it if you wish.
+import faststreams
 
-proc add*(x, y: int): int =
-  ## Adds two files together.
-  return x + y
+const
+  MaxMessageSize* = 1'u shl 22
+
+type
+  ProtoBuffer* = ref object
+    fieldNum: int
+    outstream: OutputStreamVar
+
+  ProtoWireType* = enum
+    ## Protobuf's field types enum
+    Varint, Fixed64, Length, StartGroup, EndGroup, Fixed32
+
+  ProtoField* = object
+    ## Protobuf's message field representation object
+    index: int
+    case kind: ProtoWireType
+    of Varint:
+      vint*: uint64
+    of Fixed64:
+      vfloat64*: float64
+    of Length:
+      vbuffer*: OutputStreamVar
+    of Fixed32:
+      vfloat32*: float32
+    of StartGroup, EndGroup:
+      discard
+
+  SomeSVarint* = int | int64 | int32 | int16 | int8 | enum
+  SomeUVarint* = uint | uint64 | uint32 | uint16 | uint8 | byte | bool
+  SomeVarint* = SomeSVarint | SomeUVarint
+
+proc newProtoBuffer*(): ProtoBuffer =
+  ProtoBuffer(outstream: OutputStream.init(), fieldNum: 1)
+
+# Main interface
+proc encode*(): ProtoBuffer =
+  discard
+
+proc decode*[T](source: ProtoBuffer): T =
+  discard
+
+template wireType(firstByte: byte): ProtoWireType =
+  (firstByte and 0b111).ProtoWireType
+
+template fieldNumber(firstByte: byte): uint =
+  (firstByte shr 3) and 0b1111
+
+template protoHeader*(fieldNum: int, wire: ProtoWireType): byte =
+  ## Get protobuf's field header integer for ``index`` and ``wire``.
+  ((cast[uint](fieldNum) shl 3) or cast[uint](wire)).byte
+
+proc encodeVarint(stream: OutputStreamVar, fieldNum: int, value: SomeVarint) {.inline.} =
+  let header = protoHeader(fieldNum, Varint)
+  stream.append header
+
+  when value is enum:
+    var value = cast[type(ord(value))](value)
+  elif value is bool:
+    var value = cast[byte](value)
+  else:
+    var value = value
+
+  when type(value) is SomeSVarint:
+    if value < type(value)(0):
+      value = not(value shl type(value)(1))
+    else:
+      value = value shl type(value)(1)
+
+  while value > type(value)(0b0111_1111):
+    stream.append byte((value and 0b0111_1111) or 0b1000_0000)
+    value = value shr 7
+  stream.append byte(value and 0b1111_1111)
+
+proc encode(protobuf: ProtoBuffer, value: SomeVarint) {.inline.} =
+  protobuf.outstream.encodeVarint(protobuf.fieldNum, value)
+  inc protobuf.fieldNum
+
+proc decode[T: SomeVarint](bytes: var seq[byte], ty: typedesc[T], offset = 0): tuple[fieldNum: uint, value: T] {.inline.} =
+  # Only up to 128 bits supported by the spec
+  assert (bytes.len - 1) <= 16
+
+  let wireTy = wireType(bytes[offset])
+  if wireTy != Varint:
+    raise newException(Exception, "Not a varint!")
+
+  result.fieldNum = fieldNumber(bytes[offset])
+  result.value = cast[ty](0)
+  var shiftAmount = 0
+  var i = offset + 1
+  while true:
+    result.value += T(bytes[i] and 0b0111_1111) shl shiftAmount
+    shiftAmount += 7
+    if (bytes[i] shr 7) == 0:
+      break
+    i += 1
+
+  when ty is SomeSVarint:
+    if (result.value and T(1)) != T(0):
+      result.value = cast[T](not(result.value shr T(1)))
+    else:
+      result.value = cast[T](result.value shr T(1))
+
+proc main() =
+  let proto = newProtoBuffer()
+  proto.encode(-1500000)
+  var input: seq[byte] = proto.outstream.getOutput
+  echo input
+
+  echo decode(input, int64)
+
+main()

protobuf_serialization.nimble

@@ -11,4 +11,4 @@ skipDirs      = @["tests"]
 
 # Dependencies
 
-requires "nim >= 1.0.6"
+requires "nim >= 1.0.6", "faststreams"