upload-pack: Handle empty request

The client uses empty requests when:
- It is already up to date
- `git ls-remote`

Signed-off-by: Paul-Elliot <[email protected]>

fuzz/smart.ml

@@ -193,7 +193,9 @@ let () =
   let wants = List.map Digestif.SHA1.to_hex wants in
   let v = Smart.Want.v ~capabilities:[] wants in
   let str = to_string v in
-  let res = of_string str in
-  Crowbar.check_eq ~pp:Smart.Want.pp
-    ~eq:(Smart.Want.equal ~uid:String.equal ~reference:String.equal)
-    v res
+  match of_string str with
+  | Some res ->
+      Crowbar.check_eq ~pp:Smart.Want.pp
+        ~eq:(Smart.Want.equal ~uid:String.equal ~reference:String.equal)
+        v res
+  | None -> Crowbar.failf "Invalid empty fetch request (%S)" str

src/not-so-smart/protocol.ml

@@ -623,7 +623,9 @@ module Decoder = struct
         let v = peek_pkt decoder in
         if Sub.is_empty v then (
           junk_pkt decoder;
-          return (Want.v ~capabilities (first_want :: List.rev wants)) decoder
+          return
+            (Some (Want.v ~capabilities (first_want :: List.rev wants)))
+            decoder
           (* TODO else if start with shallow or depth request or filter request then *))
         else
           match Sub.cut ~sep:v_space v with
@@ -639,7 +641,8 @@ module Decoder = struct
 
     let decode_first_want decoder =
       let v = peek_pkt decoder in
-      if Sub.is_prefix v ~affix:v_want then (
+      if Sub.is_empty v then return None decoder
+      else if Sub.is_prefix v ~affix:v_want then (
         let v = v |> Sub.with_range ~first:(Sub.length v_want) in
         (* NOTE(dinosaure): we accept more than Git. The BNF syntax of
            [first-want] is:

src/not-so-smart/protocol.mli

@@ -205,7 +205,10 @@ module Decoder : sig
     ?sideband:bool -> decoder -> (string Status.t, [> error ]) state
 
   val decode_packet : trim:bool -> decoder -> (string, [> error ]) state
-  val decode_want : decoder -> ((string, string) Want.t, [> error ]) state
+
+  val decode_want :
+    decoder -> ((string, string) Want.t option, [> error ]) state
+
   val decode_have : decoder -> (string Have.t, [> error ]) state
 
   val decode_commands :

src/not-so-smart/smart.ml

@@ -45,7 +45,7 @@ module Witness = struct
     | Ack : string Negotiation.t recv
     | Flush : unit recv
     | Shallows : string Shallow.t list recv
-    | Want : (string, string) Want.t recv
+    | Want : (string, string) Want.t option recv
     | Have : string Have.t recv
 end
 

src/not-so-smart/smart.mli

@@ -250,7 +250,7 @@ val shallows : string Shallow.t list recv
 val status : bool -> string Status.t recv
 val packet : trim:bool -> string recv
 val send_advertised_refs : (string, string) Advertised_refs.t send
-val recv_want : (string, string) Want.t recv
+val recv_want : (string, string) Want.t option recv
 val recv_have : string Have.t recv
 val bind : ('a, 'err) t -> f:('a -> ('b, 'err) t) -> ('b, 'err) t
 val ( let* ) : ('a, 'err) t -> ('a -> ('b, 'err) t) -> ('b, 'err) t