Since commit 0c499ea60f the send-pack builtin uses the side-band-64k
capability if advertised by the server. Unfortunately this breaks
pushing over the dump git protocol with a windows git client.

The detailed reasons for this breakage are (by courtesy of Jeff
Preshing, quoted from
MinGW wraps Windows sockets in CRT file descriptors in order to mimic
the functionality of POSIX sockets. This causes msvcrt.dll to treat
sockets as Installable File System (IFS) handles, calling ReadFile,
WriteFile, DuplicateHandle and CloseHandle on them. This approach works
well in simple cases on recent versions of Windows, but does not support
all usage patterns.  In particular, using this approach, any attempt to
read & write concurrently on the same socket (from one or more
processes) will deadlock in a scenario where the read waits for a
response from the server which is only invoked after the write. This is
what send_pack currently attempts to do in the use_sideband codepath.

The new config option "sendpack.sideband" allows to override the
side-band-64k capability of the server.

Other transportation methods like ssh and http/https still benefit from
the sideband channel, therefore the default value of "sendpack.sideband"
is still true.

Alternative approaches considered but deemed too invasive:
- Rewrite read/write wrappers in mingw.c in order to distinguish between
  a file descriptor which has a socket behind and a file descriptor
  which has a file behind.
- Turning the capability side-band-64k off completely. This would remove a 
  feature for users of non-affected transport protocols.

Signed-off-by: Thomas Braun <>

This patch, with a slightly less polished commit message, is already part of
msysgit/git see b68e386. 

A lengthy discussion can be found here [1].

What do you think, is this also for you as upstream interesting?


 Documentation/config.txt |  6 ++++++
 send-pack.c              | 14 +++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 1932e9b..13ff657 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2435,3 +2435,9 @@ web.browser::
        Specify a web browser that may be used by some commands.
        Currently only linkgit:git-instaweb[1] and linkgit:git-help[1]
        may use it.
+  Allows to disable the side-band-64k capability for send-pack even
+  when it is advertised by the server. Makes it possible to work
+  around a limitation in the git for windows implementation together
+  with the dump git protocol. Defaults to true.
diff --git a/send-pack.c b/send-pack.c
index 6129b0f..aace1fc 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -12,6 +12,16 @@
 #include "version.h"
 #include "sha1-array.h"
+static int config_use_sideband = 1;
+static int send_pack_config(const char *var, const char *value, void *unused)
+       if (!strcmp("sendpack.sideband", var))
+               config_use_sideband = git_config_bool(var, value);
+       return 0;
 static int feed_object(const unsigned char *sha1, int fd, int negative)
        char buf[42];
@@ -209,6 +219,8 @@ int send_pack(struct send_pack_args *args,
        int ret;
        struct async demux;
+       git_config(send_pack_config, NULL);
        /* Does the other end support the reporting? */
        if (server_supports("report-status"))
                status_report = 1;
@@ -216,7 +228,7 @@ int send_pack(struct send_pack_args *args,
                allow_deleting_refs = 1;
        if (server_supports("ofs-delta"))
                args->use_ofs_delta = 1;
-       if (server_supports("side-band-64k"))
+       if (config_use_sideband && server_supports("side-band-64k"))
                use_sideband = 1;
        if (server_supports("quiet"))
                quiet_supported = 1;

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