Respect the XDG_CACHE_HOME environment variable

Fixes: #16

README.md

@@ -37,10 +37,11 @@ bb\_clientd:
 
 ```sh
 umount ~/bb_clientd; fusermount -u ~/bb_clientd
+export XDG_CACHE_HOME=${XDG_CACHE_HOME:-~/.cache}
 mkdir -p \
-    ~/.cache/bb_clientd/ac/persistent_state \
-    ~/.cache/bb_clientd/cas/persistent_state \
-    ~/.cache/bb_clientd/outputs \
+    ${XDG_CACHE_HOME}/bb_clientd/ac/persistent_state \
+    ${XDG_CACHE_HOME}/bb_clientd/cas/persistent_state \
+    ${XDG_CACHE_HOME}/bb_clientd/outputs \
     ~/bb_clientd
 OS=$(uname) bazel run //cmd/bb_clientd $(bazel info workspace)/configs/bb_clientd.jsonnet
 ```
@@ -118,7 +119,7 @@ bazel build --remote_executor mycluster-prod.example.com --remote_instance_name
 You can let it use bb\_clientd by running it like this instead:
 
 ```
-bazel build --remote_executor unix:${HOME}/.cache/bb_clientd/grpc --remote_instance_name mycluster-prod.example.com/hello [more options]
+bazel build --remote_executor unix:${XDG_CACHE_HOME:-~/.cache}/bb_clientd/grpc --remote_instance_name mycluster-prod.example.com/hello [more options]
 ```
 
 Notice how the hostname of the cluster has become a prefix of
@@ -130,9 +131,9 @@ traffic needs to be routed.
 You may wish to add `--remote_bytestream_uri_prefix` to the `bazel build`
 command with the URI of the _real_ remote executor. This will cause Bazel's
 build event stream to emit URIs with this prefix rather than
-`${HOME}/.cache/bb_clientd/grpc`. Some build event consumers offer features
-that require access to the remote cache; this is necssary for those features
-to access the canonical remote.
+`${XDG_CACHE_HOME:-~/.cache}/bb_clientd/grpc`. Some build event
+consumers offer features that require access to the remote cache; this
+is necssary for those features to access the canonical remote.
 
 ### ... as a system local cache
 
@@ -142,7 +143,7 @@ name acts as its own namespace. This means that if you want to cache the
 results of a build performed locally, you may run Bazel as follows:
 
 ```
-bazel build --remote_cache unix:${HOME}/.cache/bb_clientd/grpc --remote_instance_name local/some/project --remote_upload_local_results=true [more options]
+bazel build --remote_cache unix:${XDG_CACHE_HOME:-~/.cache}/bb_clientd/grpc --remote_instance_name local/some/project --remote_upload_local_results=true [more options]
 ```
 
 The advantage of this option over Bazel's own `--disk_cache` flag is
@@ -256,5 +257,5 @@ Bazel can be configured to use this feature by providing the following
 additional command line arguments:
 
 ```
---experimental_remote_output_service unix:${HOME}/.cache/bb_clientd/grpc --experimental_remote_output_service_output_path_prefix ${HOME}/bb_clientd/outputs
+--experimental_remote_output_service unix:${XDG_CACHE_HOME:-~/.cache}/bb_clientd/grpc --experimental_remote_output_service_output_path_prefix ${HOME}/bb_clientd/outputs
 ```

configs/bb_clientd.jsonnet

@@ -36,8 +36,7 @@ local blobstoreConfig(authorizationHeader, proxyURL) = {
 };
 
 local os = std.extVar('OS');
-local homeDirectory = std.extVar('HOME');
-local cacheDirectory = homeDirectory + '/.cache/bb_clientd';
+local cacheDirectory = std.extVar('XDG_CACHE_HOME') + '/bb_clientd';
 
 {
   // Options that users can override.
@@ -184,8 +183,9 @@ local cacheDirectory = homeDirectory + '/.cache/bb_clientd';
   // The FUSE or NFSv4 file system through which data stored in the
   // Content Addressable Storage can be loaded lazily. This file system
   // relies on credentials captured through gRPC.
-  mount: if $.useNFSv4 then {
-    mountPath: homeDirectory + '/bb_clientd',
+  mount: {
+    mountPath: std.extVar('HOME') + '/bb_clientd',
+  } + if $.useNFSv4 then {
     nfsv4: {
       enforcedLeaseTime: '120s',
       announcedLeaseTime: '60s',
@@ -195,7 +195,6 @@ local cacheDirectory = homeDirectory + '/.cache/bb_clientd';
       Linux: { linux: { mountOptions: ['vers=4.1'] } },
     }[os],
   } else {
-    mountPath: homeDirectory + '/bb_clientd',
     fuse: {
       directoryEntryValidity: '300s',
       inodeAttributeValidity: '300s',

configs/linux/launch_bb_clientd_linux.sh

@@ -6,18 +6,19 @@ set -eu
 fusermount -u ~/bb_clientd || true
 
 # Remove UNIX socket, so that builds will not attept to send gRPC traffic.
-rm -f ~/.cache/bb_clientd/grpc
+export XDG_CACHE_HOME=${XDG_CACHE_HOME:-~/.cache}
+rm -f ${XDG_CACHE_HOME}/bb_clientd/grpc
 
 if [ "$1" = "start" ]; then
   # Create directories that are used by bb_clientd.
   mkdir -p \
-      ~/.cache/bb_clientd/ac/persistent_state \
-      ~/.cache/bb_clientd/cas/persistent_state \
-      ~/.cache/bb_clientd/outputs \
+      ${XDG_CACHE_HOME}/bb_clientd/ac/persistent_state \
+      ${XDG_CACHE_HOME}/bb_clientd/cas/persistent_state \
+      ${XDG_CACHE_HOME}/bb_clientd/outputs \
       ~/bb_clientd
 
   # Discard logs of the previous invocation.
-  rm -f ~/.cache/bb_clientd/log
+  rm -f ${XDG_CACHE_HOME}/bb_clientd/log
 
   # Use either the user provided or system-wide configuration file, based
   # on whether the former is present.