Add rust buildcache to dockerfile

Dockerfile

@@ -1,7 +1,26 @@
 FROM rust:1.68-alpine3.17 AS bin-builder
 
-COPY backend .
+# Install dependencies
 RUN apk add --no-cache openssl-dev openssl-libs-static musl-dev
+
+# This will build all dependencies and store them in docker's cache.
+# This way, it won't be necessary to recompile everything everytime
+COPY backend/Cargo.toml .
+COPY backend/Cargo.lock .
+RUN echo '[[bin]]' >> Cargo.toml && \
+    echo 'name = "cache"' >> Cargo.toml && \
+    echo 'path = "cache.rs"' >> Cargo.toml && \
+    echo 'fn main() {eprintln!("Caching crates...")}' > cache.rs && \
+    export OPENSSL_STATIC=1 && \
+    export OPENSSL_LIB_DIR=/usr/lib && \
+    export OPENSSL_INCLUDE_DIR=/usr/include/openssl && \
+    cargo build --release 
+RUN rm cache.rs && \
+    rm Cargo.toml
+
+# Build wimple-wkd
+COPY backend/Cargo.toml .
+COPY backend/src src
 RUN export OPENSSL_STATIC=1 && \
     export OPENSSL_LIB_DIR=/usr/lib &&\ 
     export OPENSSL_INCLUDE_DIR=/usr/include/openssl && \
@@ -10,16 +29,21 @@ RUN export OPENSSL_STATIC=1 && \
 
 FROM node:19-alpine3.17 AS webpage-builder
 
+# Build website
 COPY website .
 RUN npm install -g pnpm && \
     pnpm install && \
     pnpm run build
 COPY assets assets
+
+# Move website in templates folder
 RUN mv dist assets/webpage
 
 
 FROM alpine:3.17
 
+# Put everything together
+# It uses user `wkd` for added security
 WORKDIR /wkd
 RUN adduser --no-create-home --disabled-password wkd && \
     chown -R wkd:wkd /wkd