Add Dockerfile for cross compilation

.dockerignore

@@ -0,0 +1 @@
+target

Cargo.toml

@@ -88,5 +88,5 @@ section = "sound"
 priority = "optional"
 assets = [
     ["target/release/librespot", "usr/bin/", "755"],
-    ["assets/librespot.service", "lib/systemd/system/", "644"]
+    ["contrib/librespot.service", "lib/systemd/system/", "644"]
 ]

README.md

@@ -60,6 +60,28 @@ The following backends are currently available :
 - PortAudio 
 - PulseAudio
 
+## Cross-compiling
+A cross compilation environment is provided as a docker image.
+Build the image from the root of the project with the following command :
+
+```
+$ docker build -t librespot-cross -f contrib/Dockerfile .
+```
+
+The resulting image can be used to build librespot for linux x86_64, armhf and armel.
+The compiled binaries will be located in /tmp/librespot-build
+
+```
+docker run -v /tmp/librespot-build:/build librespot-cross
+```
+
+If only one architecture is desired, cargo can be invoked directly with the appropriate options :
+```shell
+docker run -v /tmp/librespot-build:/build librespot-cross cargo build --release --no-default-features --features "with-syntex alsa-backend"
+docker run -v /tmp/librespot-build:/build librespot-cross cargo build --release --target arm-unknown-linux-gnueabihf --no-default-features --features "with-syntex alsa-backend"
+docker run -v /tmp/librespot-build:/build librespot-cross cargo build --release --target arm-unknown-linux-gnueabi --no-default-features --features "with-syntex alsa-backend"
+```
+
 ## Development
 When developing *librespot*, it is preferable to use Rust nightly, and build it using the following :
 ```shell

contrib/Dockerfile

@@ -0,0 +1,38 @@
+# Cross compilation environment for librespot
+# Build the docker image from the root of the project with the following command :
+# $ docker build -t librespot-cross -f contrib/Dockerfile .
+#
+# The resulting image can be used to build librespot for linux x86_64, armhf and armel.
+# $ docker run -v /tmp/librespot-build:/build librespot-cross
+#
+# The compiled binaries will be located in /tmp/librespot-build
+#
+# If only one architecture is desired, cargo can be invoked directly with the appropriate options :
+# $ docker run -v /tmp/librespot-build:/build librespot-cross cargo build --release --no-default-features --features "with-syntex alsa-backend"
+# $ docker run -v /tmp/librespot-build:/build librespot-cross cargo build --release --target arm-unknown-linux-gnueabihf --no-default-features --features "with-syntex alsa-backend"
+# $ docker run -v /tmp/librespot-build:/build librespot-cross cargo build --release --target arm-unknown-linux-gnueabi --no-default-features --features "with-syntex alsa-backend"
+#
+
+FROM debian:stretch
+
+RUN dpkg --add-architecture armhf
+RUN dpkg --add-architecture armel
+RUN apt-get update
+
+RUN apt-get install -y curl build-essential crossbuild-essential-armhf crossbuild-essential-armel
+RUN apt-get install -y libasound2-dev libasound2-dev:armhf libasound2-dev:armel
+
+RUN curl https://sh.rustup.rs -sSf | sh -s -- -y
+ENV PATH="/root/.cargo/bin/:${PATH}"
+RUN rustup target add arm-unknown-linux-gnueabi
+RUN rustup target add arm-unknown-linux-gnueabihf
+
+RUN echo '[target.arm-unknown-linux-gnueabihf]\nlinker = "arm-linux-gnueabihf-gcc"' > ~/.cargo/config
+RUN echo '[target.arm-unknown-linux-gnueabi]\nlinker = "arm-linux-gnueabi-gcc"' > ~/.cargo/config
+
+RUN mkdir /build
+ENV CARGO_TARGET_DIR /build
+
+ADD . /src
+WORKDIR /src
+CMD ["/src/contrib/docker-build.sh"]

contrib/docker-build.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+set -eux
+
+cargo build --release --no-default-features --features "with-syntex alsa-backend"
+cargo build --release --target arm-unknown-linux-gnueabihf --no-default-features --features "with-syntex alsa-backend"
+cargo build --release --target arm-unknown-linux-gnueabi --no-default-features --features "with-syntex alsa-backend"