1.12 compat (#1243)

Author: quinnj

src/Streams.jl

@@ -294,13 +294,21 @@ _alloc_request(buf::IOBuffer, recommended_size::UInt) = Base.alloc_request(buf,
         nb = min(length(buffer.data), buffer.maxsize) - ptr + 1
         return (Ptr{Cvoid}(pointer(buffer.data, ptr)), nb)
     end
-else
+elseif VERSION < v"1.12"
     function _alloc_request(buffer::Base.GenericIOBuffer, recommended_size::UInt)
         Base.ensureroom(buffer, Int(recommended_size))
         ptr = buffer.append ? buffer.size + 1 : buffer.ptr
         nb = min(length(buffer.data)-buffer.offset, buffer.maxsize) + buffer.offset - ptr + 1
         return (Ptr{Cvoid}(pointer(buffer.data, ptr)), nb)
     end
+else
+    function _alloc_request(buffer::Base.GenericIOBuffer, recommended_size::UInt)
+        Base.ensureroom(buffer, recommended_size)
+        ptr = buffer.append ? buffer.size + 1 : buffer.ptr
+        start_offset = ptr - 1
+        nb = max(0, min(length(buffer.data) - start_offset, buffer.maxsize - (start_offset - Base.get_offset(buffer))))
+        return (Ptr{Cvoid}(pointer(buffer.data, ptr)), nb)
+    end
 end
 
 function Base.readbytes!(http::Stream, buf::Base.GenericIOBuffer, n=bytesavailable(http))