hooks: Fix the race condition that causes EPIPE

The hooks handler in the main daemon didn't wait for the hook client to
write fully, and sometimes prematurely closes the connection, causing
the hook client's splice to return EPIPE (or SIGPIPE if the signal
handler wasn't installed).

To remedy this, we call shutdown(sock, SHUT_WR) in the client, so that
attempts to read on the server side return EOF. Then we can simply use
io.Copy(&buf, conn) on the server side to fetch all of the data into a
buffer.

2 files changed, 17 insertions, 0 deletions

diff --git a/git_hooks_client/git_hooks_client.c b/git_hooks_client/git_hooks_client.c
index e00ab3a..6471aa8 100644
--- a/git_hooks_client/git_hooks_client.c
+++ b/git_hooks_client/git_hooks_client.c
@@ -163,6 +163,16 @@ int main(int argc, char *argv[]) {
 	}
 
 	/*
+	 * The sending part of the UNIX socket should be shut down, to let
+	 * io.Copy on the Go side return.
+	 */
+	if (shutdown(sock, SHUT_WR) == -1) {
+		perror("shutdown internal socket");
+		close(sock);
+		return EXIT_FAILURE;
+	}
+
+	/*
 	 * The first byte of the response from the UNIX domain socket is the
 	 * status code. We read it and record it as our return value.
 	 */
diff --git a/git_hooks_handle.go b/git_hooks_handle.go
index 91f1894..e9b163a 100644
--- a/git_hooks_handle.go
+++ b/git_hooks_handle.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"io"
 	"net"
 	"os"
 	"path/filepath"
@@ -72,6 +73,12 @@ func hooks_handle_connection(conn net.Conn) {
 		args = append(args, arg.String())
 	}
 
+	var stdin bytes.Buffer
+	_, err = io.Copy(&stdin, conn)
+	if err != nil {
+		fmt.Fprintln(conn, "Failed to read to the stdin buffer:", err.Error())
+	}
+
 	switch filepath.Base(args[0]) {
 	case "pre-receive":
 		if pack_to_hook.direct_access {