From d902127595623d7ca490305d6d699b57f08e802d Mon Sep 17 00:00:00 2001
From: Eugene Kabanov <eugene.kabanov@status.im>
Date: Tue, 28 Jan 2020 17:29:42 +0200
Subject: [PATCH] Fix LibP2P varint implementation to follow latest
 specification. (#65)

* Fix LibP2P varint implementation to decode only minimal valus.
---
 libp2p/varint.nim    | 23 +++++++-------------
 tests/testvarint.nim | 51 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 15 deletions(-)

diff --git a/libp2p/varint.nim b/libp2p/varint.nim
index 69fd910..9b8b70c 100644
--- a/libp2p/varint.nim
+++ b/libp2p/varint.nim
@@ -21,6 +21,7 @@ type
     Success,
     Overflow,
     Incomplete,
+    Overlong,
     Overrun
 
   PB* = object
@@ -99,6 +100,13 @@ proc getUVarint*[T: PB|LP](vtype: typedesc[T],
     outlen = 0
     outval = cast[type(outval)](0)
 
+  when vtype is LP:
+    if result == VarintStatus.Success:
+      if outlen != vsizeof(outval):
+        outval = cast[type(outval)](0)
+        outlen = 0
+        result = VarintStatus.Overlong
+
 proc putUVarint*[T: PB|LP](vtype: typedesc[T],
                            pbytes: var openarray[byte],
                            outlen: var int,
@@ -242,18 +250,3 @@ proc encodeVarint*(vtype: typedesc[LP],
     result.setLen(outsize)
   else:
     raise newException(VarintError, "Error '" & $res & "'")
-
-proc decodeSVarint*(data: openarray[byte]): int {.inline.} =
-  ## Decode signed integer from array ``data`` and return it as result.
-  var outsize = 0
-  let res = getSVarint(data, outsize, result)
-  if res != VarintStatus.Success:
-    raise newException(VarintError, "Error '" & $res & "'")
-
-proc decodeUVarint*[T: PB|LP](vtype: typedesc[T],
-                              data: openarray[byte]): uint {.inline.} =
-  ## Decode unsigned integer from array ``data`` and return it as result.
-  var outsize = 0
-  let res = vtype.getUVarint(data, outsize, result)
-  if res != VarintStatus.Success:
-    raise newException(VarintError, "Error '" & $res & "'")
diff --git a/tests/testvarint.nim b/tests/testvarint.nim
index 63e6b91..15caa0a 100644
--- a/tests/testvarint.nim
+++ b/tests/testvarint.nim
@@ -216,3 +216,54 @@ suite "Variable integer test suite":
                     0x8000_0000_0000_0000'u64) == VarintStatus.Overflow
       LP.putUVarint(buffer, length,
                     0xFFFF_FFFF_FFFF_FFFF'u64) == VarintStatus.Overflow
+
+  test "[LibP2P] Overlong values test":
+    const OverlongValues = [
+      # Zero bytes at the end
+      @[0x81'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8,
+        0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8,
+        0x80'u8, 0x00'u8],
+      # Zero bytes at the middle and zero byte at the end
+      @[0x81'u8, 0x80'u8, 0x81'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x81'u8,
+        0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8,
+        0x81'u8, 0x00'u8],
+      # Zero bytes at the middle and zero bytes at the end
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x80'u8, 0x80'u8, 0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x80'u8, 0x80'u8,
+        0x00'u8],
+      @[0x81'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x80'u8, 0x81'u8, 0x80'u8,
+        0x80'u8, 0x00'u8],
+    ]
+    var length = 0
+    var value = 0'u64
+
+    for item in OverlongValues:
+      check:
+        LP.getUVarint(item, length, value) == VarintStatus.Overlong
+        length == 0
+        value == 0
+
+    # We still should be able to decode zero value
+    check:
+      LP.getUVarint(@[0x00'u8], length, value) == VarintStatus.Success
+      length == 1
+      value == 0
+
+    # But not overlonged zero value
+    check:
+      LP.getUVarint(@[0x80'u8, 0x00'u8], length, value) == VarintStatus.Overlong
+      length == 0
+      value == 0