add mitmproxy/nginx-debug inspection capabilities

- avoid some caching for non-blob urls

Dockerfile

@@ -1,10 +1,18 @@
 # We start from my nginx fork which includes the proxy-connect module from tEngine
 # Source is available at https://github.com/rpardini/nginx-proxy-connect-stable-alpine
-# Its equivalent to nginx:stable-alpine 1.14.0, with alpine 3.7
-FROM rpardini/nginx-proxy-connect-stable-alpine:latest
+FROM rpardini/nginx-proxy-connect-stable-alpine:nginx-1.14.0-alpine-3.8
 
 # Add openssl, bash and ca-certificates, then clean apk cache -- yeah complain all you want.
-RUN apk add --update openssl bash ca-certificates && rm -rf /var/cache/apk/*
+# Also added deps for mitmproxy.
+RUN apk add --update openssl bash ca-certificates su-exec git g++ libffi libffi-dev libstdc++ openssl openssl-dev python3 python3-dev
+RUN LDFLAGS=-L/lib pip3 install mitmproxy
+RUN apk del --purge git g++ libffi-dev openssl-dev python3-dev && rm -rf /var/cache/apk/* && rm -rf ~/.cache/pip
+
+# Required for mitmproxy
+ENV LANG=en_US.UTF-8
+
+# Check the installed mitmproxy version
+RUN mitmproxy --version
 
 # Create the cache directory and CA directory
 RUN mkdir -p /docker_mirror_cache /ca
@@ -27,6 +35,9 @@ RUN chmod +x /create_ca_cert.sh /entrypoint.sh
 # Clients should only use 3128, not anything else.
 EXPOSE 3128
 
+# In debug mode, 8081 exposes the mitmweb interface.
+EXPOSE 8081
+
 ## Default envs.
 # A space delimited list of registries we should proxy and cache; this is in addition to the central DockerHub.
 ENV REGISTRIES="k8s.gcr.io gcr.io quay.io"
@@ -34,6 +45,8 @@ ENV REGISTRIES="k8s.gcr.io gcr.io quay.io"
 ENV AUTH_REGISTRIES="some.authenticated.registry:oneuser:onepassword another.registry:user:password"
 # Should we verify upstream's certificates? Default to true.
 ENV VERIFY_SSL="true"
+# Enable debugging mode; this inserts mitmproxy/mitmweb between the CONNECT proxy and the caching layer
+ENV DEBUG="true"
 
 # Did you want a shell? Sorry. This only does one job; use exec /bin/bash if you wanna inspect stuff
 ENTRYPOINT ["/entrypoint.sh"]