Add documentation and examples

.gitignore

@@ -19,3 +19,6 @@ target/
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
+
+*.snap
+squashfs-root

README.md

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+# Snappy Env
+
+This program can be used to add runtime environment variable support to snaps. 
+By adding this program to the command chain of snapped applications, it will add support for:
+- Converting snap options to environment variables based on a custom mapping
+- Taking path to env files as input, loaded before starting the applications
+
+The program is intended to be used by the Env Injector Snapcraft extension; the documentation for that is available [here](https://forum.snapcraft.io/t/the-env-injector-extension/41477).
+
+There are currently two implementations for the Snapcraft extension. The Rust implementation is considered more stable.
+
+To use snappy-env directly and without the Snapcraft extension; refer to [snap/snapcraft.yaml](snap/snapcraft.yaml) as an example.

snap/hooks/configure

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+#!/bin/bash
+
+# Do nothing
+# This is only to allow setting snap configuration options from outside

snap/local/bin/env.sh

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+#!/bin/bash
+
+env

snap/snapcraft.yaml

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+name: envtester
+base: core24
+version: 'demo'
+summary: Demonstration of snappy-env program
+description: A demo snap to test the usage of snappy-env
+
+grade: stable
+confinement: strict
+
+apps:
+  # App using bash implementation
+  app-bash:
+    environment:
+     env_alias: app-bash
+    command-chain:
+      - bin/env-exporter.sh
+    command: bin/env.sh
+
+  # App using Rust implementation
+  app-rust:
+    environment:
+     env_alias: app-rust
+    command-chain:
+      - bin/env-exporter
+    command: bin/env.sh
+
+  # App without using snappy-env, for benchmarking purposes
+  app:
+    command: bin/env.sh
+
+parts:
+  myapp:
+    plugin: dump
+    source: snap/local
+
+  env-exporter-bash:
+    plugin: dump
+    source: env-exporter.sh
+    source-type: file
+    organize:
+      env-exporter.sh: bin/env-exporter.sh
+
+  env-exporter-rust:
+    plugin: nil
+    source: .
+    build-snaps: 
+      - rustup
+    build-packages:
+      - upx-ucl # for binary compression
+    override-build: |
+      rustup default stable
+
+      TARGET=x86_64-unknown-linux-gnu
+
+      rustup target add $TARGET
+      cargo build --target $TARGET --release
+      mkdir -p $SNAPCRAFT_PART_INSTALL/bin
+
+      # compress the binary
+      upx --best --lzma target/$TARGET/release/env-exporter
+      cp target/$TARGET/release/env-exporter $SNAPCRAFT_PART_INSTALL/bin
+