diff --git a/src/Streams.jl b/src/Streams.jl
index d89d3265c..e0f05cfdd 100644
--- a/src/Streams.jl
+++ b/src/Streams.jl
@@ -1,6 +1,6 @@
 module Streams
 
-export Stream, closebody, isaborted, setstatus
+export Stream, closebody, isaborted, setstatus, readall!
 
 using Sockets, LoggingExtras
 using ..IOExtras, ..Messages, ..ConnectionPool, ..Conditions, ..Exceptions
@@ -252,15 +252,13 @@ function Base.read(http::Stream, ::Type{UInt8})
 end
 
 function http_unsafe_read(http::Stream, p::Ptr{UInt8}, n::UInt)::Int
-
     ntr = UInt(ntoread(http))
-    if ntr == 0
-        return 0
-    end
+    ntr == 0 && return 0
+    # If there is spare space in `p`
+    # read two extra bytes
+    # (`\r\n` at end ofchunk).
     unsafe_read(http.stream, p, min(n, ntr + (http.readchunked ? 2 : 0)))
-                                             # If there is spare space in `p`
-                                             # read two extra bytes
-    n = min(n, ntr)                          # (`\r\n` at end ofchunk).
+    n = min(n, ntr)
     update_ntoread(http, n)
     return n
 end
@@ -268,7 +266,7 @@ end
 function Base.readbytes!(http::Stream, buf::AbstractVector{UInt8},
                                        n=length(buf))
     @require n <= length(buf)
-    return http_unsafe_read(http, pointer(buf), UInt(n))
+    return GC.@preserve buf http_unsafe_read(http, pointer(buf), UInt(n))
 end
 
 function Base.unsafe_read(http::Stream, p::Ptr{UInt8}, n::UInt)
@@ -282,14 +280,20 @@ function Base.unsafe_read(http::Stream, p::Ptr{UInt8}, n::UInt)
     nothing
 end
 
-function Base.readbytes!(http::Stream, buf::IOBuffer, n=bytesavailable(http))
-    Base.ensureroom(buf, n)
-    unsafe_read(http, pointer(buf.data, buf.size + 1), n)
+@noinline bufcheck(buf, n) = ((buf.size + n) <= length(buf.data)) || throw(ArgumentError("Unable to grow response stream IOBuffer large enough for response body size"))
+
+function Base.readbytes!(http::Stream, buf::Base.GenericIOBuffer, n=bytesavailable(http))
+    Base.ensureroom(buf, buf.size + n)
+    # check if there's enough room in buf to write n bytes
+    bufcheck(buf, n)
+    data = buf.data
+    GC.@preserve data unsafe_read(http, pointer(data, buf.size + 1), n)
     buf.size += n
 end
 
-function Base.read(http::Stream)
-    buf = PipeBuffer()
+Base.read(http::Stream, buf::Base.GenericIOBuffer=PipeBuffer()) = take!(readall!(http, buf))
+
+function readall!(http::Stream, buf::Base.GenericIOBuffer=PipeBuffer())
     if ntoread(http) == unknown_length
         while !eof(http)
             readbytes!(http, buf)
@@ -299,7 +303,7 @@ function Base.read(http::Stream)
             readbytes!(http, buf, ntoread(http))
         end
     end
-    return take!(buf)
+    return buf
 end
 
 function Base.readuntil(http::Stream, f::Function)::ByteView
diff --git a/src/clientlayers/RetryRequest.jl b/src/clientlayers/RetryRequest.jl
index e0c23f869..8fa5850ef 100644
--- a/src/clientlayers/RetryRequest.jl
+++ b/src/clientlayers/RetryRequest.jl
@@ -22,7 +22,7 @@ e.g. `Sockets.DNSError`, `Base.EOFError` and `HTTP.StatusError`
 """
 function retrylayer(handler)
     return function(req::Request; retry::Bool=true, retries::Int=4,
-        retry_delays::ExponentialBackOff=ExponentialBackOff(n = retries), retry_check=FALSE,
+        retry_delays::ExponentialBackOff=ExponentialBackOff(n = retries, factor=3.0), retry_check=FALSE,
         retry_non_idempotent::Bool=false, kw...)
         if !retry || retries == 0
             # no retry
@@ -61,8 +61,8 @@ function retrylayer(handler)
                     @debugv 1 "🚷  No Retry: $(no_retry_reason(ex, req))"
                 end
                 return s, retry
-            end)
-
+            end
+        )
         return retry_request(req; kw...)
     end
 end
diff --git a/src/clientlayers/StreamRequest.jl b/src/clientlayers/StreamRequest.jl
index 2142157ee..5dcb283c2 100644
--- a/src/clientlayers/StreamRequest.jl
+++ b/src/clientlayers/StreamRequest.jl
@@ -128,10 +128,36 @@ function readbody(stream::Stream, res::Response, decompress::Union{Nothing, Bool
     end
 end
 
+# 2 most common types of IOBuffers
+const IOBuffers = Union{IOBuffer, Base.GenericIOBuffer{SubArray{UInt8, 1, Vector{UInt8}, Tuple{UnitRange{Int64}}, true}}}
+
 function readbody!(stream::Stream, res::Response, buf_or_stream)
     if !iserror(res)
         if isbytes(res.body)
-            res.body = read(buf_or_stream)
+            if length(res.body) > 0
+                # user-provided buffer to read response body into
+                # specify write=true to make the buffer writable
+                # but also specify maxsize, which means it won't be grown
+                # (we don't want to be changing the user's buffer for them)
+                body = IOBuffer(res.body; write=true, maxsize=length(res.body))
+                if buf_or_stream isa BufferStream
+                    # if it's a BufferStream, the response body was gzip encoded
+                    # so using the default write is fastest because it utilizes
+                    # readavailable under the hood, for which BufferStream is optimized
+                    write(body, buf_or_stream)
+                elseif buf_or_stream isa Stream
+                    # for HTTP.Stream, there's already an optimized read method
+                    # that just needs an IOBuffer to write into
+                    readall!(buf_or_stream, body)
+                else
+                    error("unreachable")
+                end
+            else
+                res.body = read(buf_or_stream)
+            end
+        elseif (res.body isa IOBuffers || res.body isa Base.GenericIOBuffer) && buf_or_stream isa Stream
+            # optimization for IOBuffer response_stream to avoid temporary allocations
+            readall!(buf_or_stream, res.body)
         else
             write(res.body, buf_or_stream)
         end
diff --git a/test/client.jl b/test/client.jl
index 6195025ec..f45cf3505 100644
--- a/test/client.jl
+++ b/test/client.jl
@@ -122,6 +122,34 @@ end
             x["headers"]["Host"] == y["headers"]["Host"] &&
             x["headers"]["User-Agent"] == y["headers"]["User-Agent"]
         end
+
+        # pass pre-allocated buffer
+        body = zeros(UInt8, 100)
+        r = HTTP.get("https://$httpbin/bytes/100"; response_stream=body, socket_type_tls=tls)
+        @test body === r.body
+
+        # wrapping pre-allocated buffer in IOBuffer will write to buffer directly
+        io = IOBuffer(body; write=true)
+        r = HTTP.get("https://$httpbin/bytes/100"; response_stream=io, socket_type_tls=tls)
+        @test body === r.body.data
+
+        # if provided buffer is too small, we won't grow it for user
+        body = zeros(UInt8, 10)
+        @test_throws HTTP.RequestError HTTP.get("https://$httpbin/bytes/100"; response_stream=body, socket_type_tls=tls, retry=false)
+
+        # also won't shrink it if buffer provided is larger than response body
+        body = zeros(UInt8, 10)
+        r = HTTP.get("https://$httpbin/bytes/5"; response_stream=body, socket_type_tls=tls)
+        @test body === r.body
+        @test length(body) == 10
+        @test HTTP.header(r, "Content-Length") == "5"
+
+        # but if you wrap it in a writable IOBuffer, we will grow it
+        io = IOBuffer(body; write=true)
+        r = HTTP.get("https://$httpbin/bytes/100"; response_stream=io, socket_type_tls=tls)
+        # same Array, though it was resized larger
+        @test body === r.body.data
+        @test length(body) == 100
     end
 
     @testset "Client Body Posting - Vector{UTF8}, String, IOStream, IOBuffer, BufferStream, Dict, NamedTuple" begin