doc/proto: add a page for the ei-scanner

In case someone is actually planning to use that one
2025-12-26 13:20:06 +01:00 · 2023-03-10 14:25:34 +10:00 · 2023-03-10 14:25:34 +10:00 · 37f4351a67
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+---
+title: Code Generation
+draft: false
+archetype: "chapter"
+weight: 5
+---
+
+## ei-scanner
+
+In the libei repo, we use the
+[ei-scanner](https://gitlab.freedesktop.org/libinput/libei/-/blob/main/proto/ei-scanner)
+to generate bindings for C and Python (for tests) as well the [interface
+documentation]({{< relref "interfaces/" >}}) in this documentation.
+
+Note: these generated protocol bindings are **not** part of libei's API contract.
+
+The `ei-scanner` is written in Python but is intended to be useful to anyone that needs generated
+bindings. It parses the [`protocol.xml`](https://gitlab.freedesktop.org/libinput/libei/-/blob/main/proto/protocol.xml)
+file and passes its content as data to [Jinja](https://jinja.palletsprojects.com/).
+
+See [here](https://gitlab.freedesktop.org/libinput/libei/-/blob/main/src/ei-proto.c.tmpl)
+for the template that generates the C source for libei and libeis.
+
+
+{{% notice  style="primary" %}}
+If you plan to use the `ei-scanner` to generate language bindings, please get
+in contact with us through the [issue tracker](https://gitlab.freedesktop.org/libinput/libei/-/issues/).
+{{% /notice %}}
+
+### Usage
+```
+$ ei-scanner --help
+usage: ei-scanner [-h] [--component {ei,eis,brei}] [--output OUTPUT]
+                  [--jinja-extra-data JINJA_EXTRA_DATA]
+                  [--jinja-extra-data-file JINJA_EXTRA_DATA_FILE]
+                  protocol template
+
+ei-scanner is a tool to parse the EI protocol description XML and
+pass the data to a Jinja2 template. That template can then be
+used to generate protocol bindings for the desired language.
+
+typical usages:
+     ei-scanner --component=ei protocol.xml my-template.tpl
+     ei-scanner --component=eis --output=bindings.rs
+        protocol.xml bindings.rs.tpl
+
+Elements in the XML file are provided as variables with attributes
+generally matching the XML file. For example, each interface has
+requests, events and enums, and each of those has a name.
+
+ei-scanner additionally provides the following values to the Jinja2 templates:
+    - interface.incoming and interface.outgoing: maps to the
+       requests/events of the interface, depending on the component.
+    - argument.signature: a single-character signature type mapping
+      from the protocol XML type:
+        uint32 -> "u"
+        int32 -> "i"
+        float -> "f"
+        fd -> "h"
+        new_id -> "n"
+        object -> "o"
+        string -> "s"
+
+ei-scanner adds the following Jinja2 filters for convenience:
+    {{foo|c_type}} ... resolves to "struct foo *"
+    {{foo|as_c_arg}} ... resolves to "struct foo *foo"
+    {{foo_bar|camel}} ... resolves to "FooBar"
+
+positional arguments:
+  protocol              The protocol XML file
+  template              The Jinja2 compatible template file
+
+options:
+  -h, --help            show this help message and exit
+  --component {ei,eis,brei}
+  --output OUTPUT       Output file to write to
+  --jinja-extra-data JINJA_EXTRA_DATA
+                        Extra data (in JSON format) to pass through
+                        to the Jinja template as 'extra'
+  --jinja-extra-data-file JINJA_EXTRA_DATA_FILE
+                        Path to file with extra data to pass through
+                        to the Jinja template as 'extra'
+
+```