loader: rework process model

Originally we had several loader processes so that the loader did not
need asynchronity for loading several buffers at once. Since then, the
scope of what loader does has been reduced significantly, and with
that loader has become mostly asynchronous.

This patch finishes the above work as follows:

* We only fork a single loader process for the browser. It is a waste of
  resources to do otherwise, and would have made future work on a
  download manager very difficult.

* loader becomes (almost) fully async. Now the only sync part is a)
  processing commands and b) waiting for clients to consume responses.
  b) is a bit more problematic than a), but should not cause problems
  unless some other horrible bug exists in a client. (TODO: make it
  fully async.)
  This gives us a noticable improvement in CSS loading speed, since all
  resources can now be queried at once (even before the previous ones
  are connected).

* Buffers now only get processes when the *connection* is finished. So
  headers, status code, etc. are handled by the client, and the buffer
  is forked when the loader starts streaming the response body.
  As a result, mailcap entries can simply dup2 the first UNIX domain
  socket connection as their stdin. This allows us to remove the ugly
  (and slow) `canredir' hack, which required us to send file handles on
  a tour accross the entire codebase.

* The "cache" has been reworked somewhat:
	- Since canredir is gone, buffer-level requests usually start
	  in a suspended state, and are explicitly resumed only after
	  the client could decide whether it wants to cache the response.
	- Instead of a flag on Request and the URL as the cache key,
	  we now use a global counter and the special `cache:' scheme.

* misc fixes: referer_from is now actually respected by buffers (not
  just the pager), load info display should work slightly better, etc.

1 files changed, 38 insertions, 62 deletions

diff --git a/src/utils/twtstr.nim b/src/utils/twtstr.nim
index 765ec24a..4d6b48ea 100644
--- a/src/utils/twtstr.nim
+++ b/src/utils/twtstr.nim
@@ -345,8 +345,8 @@ func japaneseNumber*(i: int): string =
     dec n
 
 # Implements https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#signed-integers
-func parseInt32*(s: string): Option[int32] =
-  var sign: int32 = 1
+func parseIntImpl[T: SomeSignedInt](s: string): Option[T] =
+  var sign: T = 1
   var i = 0
   if i < s.len and s[i] == '-':
     sign = -1
@@ -354,82 +354,58 @@ func parseInt32*(s: string): Option[int32] =
   elif i < s.len and s[i] == '+':
     inc i
   if i == s.len or s[i] notin AsciiDigit:
-    return none(int32)
-  var integer = int32(decValue(s[i]))
+    return none(T)
+  var integer = T(decValue(s[i]))
   inc i
   while i < s.len and isDigit(s[i]):
-    if unlikely(integer != 0 and high(int32) div 10 < integer):
-      return none(int32) # overflow
+    if unlikely(integer != 0 and high(T) div 10 < integer):
+      return none(T) # overflow
     integer *= 10
-    let c = int32(decValue(s[i]))
-    if unlikely(high(int32) - c < integer):
-      return none(int32) # overflow
+    let c = T(decValue(s[i]))
+    if unlikely(high(T) - c < integer):
+      return none(T) # overflow
     integer += c
     inc i
   return some(sign * integer)
 
-func parseInt64*(s: string): Opt[int64] =
-  var sign: int64 = 1
-  var i = 0
-  if i < s.len and s[i] == '-':
-    sign = -1
-    inc i
-  elif i < s.len and s[i] == '+':
-    inc i
-  if i == s.len or s[i] notin AsciiDigit:
-    return err()
-  var integer = int64(decValue(s[i]))
-  inc i
-  while i < s.len and isDigit(s[i]):
-    if unlikely(integer != 0 and high(int64) div 10 < integer):
-      return err() # overflow
-    integer *= 10
-    let c = int64(decValue(s[i]))
-    if unlikely(high(int64) - c < integer):
-      return err() # overflow
-    integer += c
-    inc i
-  return ok(sign * integer)
+func parseInt32*(s: string): Option[int32] =
+  return parseIntImpl[int32](s)
 
-func parseUInt8*(s: string): Option[uint8] =
-  var i = 0
-  if i < s.len and s[i] == '+':
-    inc i
-  if i == s.len or s[i] notin AsciiDigit:
-    return none(uint8)
-  var integer = uint8(decValue(s[i]))
-  inc i
-  while i < s.len and isDigit(s[i]):
-    if unlikely(integer != 0 and high(uint8) div 10 < integer):
-      return none(uint8) # overflow
-    integer *= 10
-    let c = uint8(decValue(s[i]))
-    if unlikely(high(uint8) - c < integer):
-      return none(uint8) # overflow
-    integer += uint8(c)
-    inc i
-  return some(integer)
+func parseInt64*(s: string): Option[int64] =
+  return parseIntImpl[int64](s)
 
-func parseUInt32*(s: string): Option[uint32] =
+func parseUIntImpl[T: SomeUnsignedInt](s: string; allowSign: static bool):
+    Option[T] =
   var i = 0
-  if i < s.len and s[i] == '+':
-    inc i
-  if i == s.len or s[i] notin AsciiDigit:
-    return none(uint32)
-  var integer = uint32(decValue(s[i]))
+  when allowSign:
+    if i < s.len and s[i] == '+':
+      inc i
+    if i == s.len or s[i] notin AsciiDigit:
+      return none(T)
+  var integer = T(decValue(s[i]))
   inc i
-  while i < s.len and isDigit(s[i]):
-    if unlikely(integer != 0 and high(uint32) div 10 < integer):
-      return none(uint32) # overflow
+  while i < s.len and s[i] in AsciiDigit:
+    if unlikely(integer != 0 and high(T) div 10 < integer):
+      return none(T) # overflow
     integer *= 10
-    let c = uint32(decValue(s[i]))
-    if unlikely(high(uint32) - c < integer):
-      return none(uint32) # overflow
-    integer += c
+    let c = T(decValue(s[i]))
+    if unlikely(high(T) - c < integer):
+      return none(T) # overflow
+    integer += T(c)
     inc i
   return some(integer)
 
+func parseUInt8*(s: string; allowSign: static bool): Option[uint8] =
+  return parseUIntImpl[uint8](s, allowSign)
+
+func parseUInt16*(s: string; allowSign: static bool): Option[uint16] =
+  return parseUIntImpl[uint16](s, allowSign)
+
+func parseUInt32*(s: string; allowSign: static bool): Option[uint32] =
+  return parseUIntImpl[uint32](s, allowSign)
+
 #TODO not sure where this algorithm is from...
+# (probably from CSS)
 func parseFloat64*(s: string): float64 =
   var sign = 1f64
   var t = 1