Re: [PATCH 05/11] config-batch: add NUL-terminated I/O format

From: Derrick Stolee <redacted>

When using automated tools, it is critical to allow for input/output formats
that include special characters such as spaces and newlines. While the
existing protocol for 'git config-batch' is human-readable and has some
capacity for some spaces in certain positions, it is not available for
spaces in the config key or newlines in the config values.

Add the '-z' option to signal the use of NUL-terminated strings. To
understand where commands end regardless of potential future formats, use
two NUL bytes in a row to terminate a command. To allow for empty string
values, each token is provided in a <length>:<value> format, making "0:"
the empty string value.

Update the existing 'help' and 'get' commands to match this format. Create
helper methods that make it easy to parse and print in both formats
simultaneously.

Signed-off-by: Derrick Stolee <redacted>
---
 Documentation/git-config-batch.adoc |  57 ++++++++-
 builtin/config-batch.c              | 188 +++++++++++++++++++++++++---
 t/t1312-config-batch.sh             |  69 ++++++++++
 3 files changed, 293 insertions(+), 21 deletions(-)

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index 1fff68a13c..3c9a3bb763 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc

@@ -21,6 +21,15 @@ multiple configuration values, the `git config-batch` command allows a
 single process to handle multiple requests using a machine-parseable
 interface across `stdin` and `stdout`.
 
+OPTIONS
+-------
+
+`-z`::
+	If specified, then use the NUL-terminated input and output

+	format instead of the space and newline format. This format is
+	useful when the strings involved may include spaces or newlines.
+	See PROTOCOL for more details.
+
 PROTOCOL
 --------
 By default, the protocol uses line feeds (`LF`) to signal the end of a

@@ -41,13 +50,13 @@ These are the commands that are currently understood:
 `help` version 1::
 	The `help` command lists the currently-available commands in
 	this version of Git. The output is multi-line, but the first
-	line provides the count of possible commands via `help count <N>`.
-	The next `<N>` lines are of the form `help <command> <version>`
+	line provides the count of possible commands via `help 1 count <N>`.
+	The next `<N>` lines are of the form `help 1 <command> <version>`
 	to state that this Git version supports that `<command>` at
 	version `<version>`. Note that the same command may have multiple
 	available versions.
 +
-Here is the currentl output of the help text at the latest version:
+Here is the current output of the help text at the latest version:

 +
 ------------
 help 1 count 2

@@ -102,6 +111,48 @@ get 1 missing <key> [<value-pattern>|<value>]
 where `<value-pattern>` or `<value>` is only supplied if provided in
 the command.
 
+NUL-Terminated Format
+~~~~~~~~~~~~~~~~~~~~~
+
+When `-z` is given, the protocol changes in some structural ways.
+
+First, each command is terminated with two NUL bytes, providing a clear
+boundary between commands regardless of future possibilities of new
+command formats.
+
+Second, any time that a space _would_ be used to partition tokens in a
+command, a NUL byte is used instead. Further, each token is prefixed
+with `<N>:` where `<N>` is a decimal representation of the length of
+the string between the `:` and the next NUL byte. Any disagreement in
+these lengths is treated as a parsing error. This use of a length does