From baaa19b92751598b6519a64eed2b1beb06b2e662 Mon Sep 17 00:00:00 2001
From: Igor Ribeiro de Assis <igor.assis@gmail.com>
Date: Wed, 18 Nov 2020 20:55:49 +0100
Subject: [PATCH] Do not read the whole file to compute SHA1 hash (fixes 15997)
 (#16006)

* Do not read the whole file to compute SHA1 hash (fixes 15997)

* Update lib/std/sha1.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

* Update lib/std/sha1.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

* Directly break from loop

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

 [backport:1.2] [backport:1.4]
---
 lib/std/sha1.nim | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/std/sha1.nim b/lib/std/sha1.nim
index 8f35a44ff6..9763b286e5 100644
--- a/lib/std/sha1.nim
+++ b/lib/std/sha1.nim
@@ -213,7 +213,22 @@ proc secureHashFile*(filename: string): SecureHash =
   ## **See also:**
   ## * `secureHash proc <#secureHash,openArray[char]>`_ for generating a ``SecureHash`` from a string
   ## * `parseSecureHash proc <#parseSecureHash,string>`_ for converting a string ``hash`` to ``SecureHash``
-  secureHash(readFile(filename))
+  const BufferLength = 8192
+
+  let f = open(filename)
+  var state = newSha1State()
+  var buffer = newString(BufferLength)
+  while true:
+    let length = readChars(f, buffer, 0, BufferLength)
+    if length == 0:
+      break
+    buffer.setLen(length)
+    state.update(buffer)
+    if length != BufferLength:
+      break
+  close(f)
+
+  SecureHash(state.finalize())
 
 proc `$`*(self: SecureHash): string =
   ## Returns the string representation of a ``SecureHash``.