kg: add new handler for rendering the topology graph

docker: add missing fonts for rasterized graphviz  output formats

add missing license header

kg: do not export handlers

use http package for status codes

keep checks for errors in a single line

simplify error message about failed invocation of dot

pass node hostname and subnet to graph handler

use SVG as default format for graph handler

register health handler with HandleFunc

add option for selecting layout to graph handler and using circo as new default

e2e: add tests for HTTP handlers

e2e: fix and simplify handler tests

add should comments to assertions

e2s: use assert_fail instead of assert _not

add missing mime-type header for graph handler

use switch/case statements for validating formats / layouts

e2e: fix handlers tests

Co-authored-by: leonnicolas <60091705+leonnicolas@users.noreply.github.com>

graph-handler: add missing font to Dockerfile

Dockerfile: remove unnecessary font

This commit leaves Noto as the only font package, as one font package is
sufficient for the container.

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

Dockerfile

@@ -11,7 +11,7 @@ ARG GOARCH
 ARG ALPINE_VERSION=v3.12
 LABEL maintainer="squat <lserven@gmail.com>"
 RUN echo -e "https://alpine.global.ssl.fastly.net/alpine/$ALPINE_VERSION/main\nhttps://alpine.global.ssl.fastly.net/alpine/$ALPINE_VERSION/community" > /etc/apk/repositories && \
-    apk add --no-cache ipset iptables ip6tables wireguard-tools
+    apk add --no-cache ipset iptables ip6tables wireguard-tools graphviz font-noto
 COPY --from=cni bridge host-local loopback portmap /opt/cni/bin/
 COPY bin/linux/$GOARCH/kg /opt/bin/
 ENTRYPOINT ["/opt/bin/kg"]