Subject: [PATCH v3 05/12] simple-ipc: design documentation for new IPC mechanism

From: "Jeff Hostetler via GitGitGadget" <[email-masked]>
Date: Sat, 13 Feb 2021 00:09:06 +0000

From: Jeff Hostetler <[email-masked]>

Brief design documentation for new IPC mechanism allowing
foreground Git client to talk with an existing daemon process
at a known location using a named pipe or unix domain socket.

Signed-off-by: Johannes Schindelin <[email-masked]>
Signed-off-by: Jeff Hostetler <[email-masked]>
---
 Documentation/technical/api-simple-ipc.txt | 34 ++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 Documentation/technical/api-simple-ipc.txt

diff --git a/Documentation/technical/api-simple-ipc.txt b/Documentation/technical/api-simple-ipc.txt
new file mode 100644
index 000000000000..670a5c163e39
--- /dev/null
+++ b/Documentation/technical/api-simple-ipc.txt
@@ -0,0 +1,34 @@
+simple-ipc API
+==============
+
+The simple-ipc API is used to send an IPC message and response between
+a (presumably) foreground Git client process to a background server or
+daemon process.  The server process must already be running.  Multiple
+client processes can simultaneously communicate with the server
+process.
+
+Communication occurs over a named pipe on Windows and a Unix domain
+socket on other platforms.  Clients and the server rendezvous at a
+previously agreed-to application-specific pathname (which is outside
+the scope of this design).
+
+This IPC mechanism differs from the existing `sub-process.c` model
+(Documentation/technical/long-running-process-protocol.txt) and used
+by applications like Git-LFS.  In the simple-ipc model the server is
+assumed to be a very long-running system service.  In contrast, in the
+LFS-style sub-process model the helper is started with the foreground
+process and exits when the foreground process terminates.
+
+How the simple-ipc server is started is also outside the scope of the
+IPC mechanism.  For example, the server might be started during
+maintenance operations.
+
+The IPC protocol consists of a single request message from the client and
+an optional request message from the server.  For simplicity, pkt-line
+routines are used to hide chunking and buffering concerns.  Each side
+terminates their message with a flush packet.
+(Documentation/technical/protocol-common.txt)
+
+The actual format of the client and server messages is application
+specific.  The IPC layer transmits and receives an opaque buffer without
+any concern for the content within.
-- 
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