Software Heritage Filesystem (SwhFS) — Tutorial

Installation

The Software Heritage virtual filesystem (SwhFS) is available from PyPI as swh.fuse. It can be installed from there using pip:

$ pip install swh.fuse

Setup and teardown

SwhFS is controlled by the swh fs command-line interface (CLI).

Like all filesystems, SwhFS must be “mounted” before use and “unmounted” afterwards. Users should first mount the archive as a whole and then browse archived objects looking up their SWHIDs below the archive/ entry-point. To mount the Software Heritage archive, use the swh fs mount command:

$ mkdir swhfs
$ swh fs mount swhfs/  # mount the archive

$ ls -1F swhfs/  # list entry points
archive/  # <- start browsing from here
meta/

By default SwhFS daemonizes into background and logs to syslog; it can be kept in foreground, logging to the console, by passing -f/--foreground to mount.

To unmount use swh fs umount PATH. Note that, since SwhFS is a user-space filesystem, mounting and unmounting it are not privileged operations, any user can do it.

The configuration file ~/.swh/config/global.yml is read if present. Its main use case is inserting a per-user authentication token for the SWH API, which might be needed in case of heavy use to bypass the default API rate limit. See the configuration documentation for details.

Lazy loading

Once mounted, the archive can be navigated as if it were locally available on-disk. Archived objects are referenced by Software Heritage identifiers (SWHIDs). They are loaded on-demand from the archive and populate lazily the archive/ directory below the SwhFS mount point.

SWHIDs for source code that is not locally available can be obtained in various ways: searching on the Software Heritage website; finding SWHID references in scientific papers, Wikidata, and software bills of materials using the SPDX standard; deriving SWHIDs from other version control system references (e.g., as SWHIDs version 1 are compatible with Git, a Git commit identifier like 9d76c0b163675505d1a901e5fe5249a2c55609bc can be turned into a SWHID by simply prefixing it with swh:1:rev: to obtain swh:1:rev:9d76c0b163675505d1a901e5fe5249a2c55609bc).

Source code files

Here is a SwhFS Hello World:

$ cd swhfs/

$ cat archive/swh:1:cnt:c839dea9e8e6f0528b468214348fee8669b305b2
#include <stdio.h>

int main(void) {
    printf("Hello, World!\n");
}

Given the SWHID of a source code file, we can directly access it via the filesystem.

Metadata about archived source code artifacts is also locally available. For each entry under archive/ there is a matching JSON file under meta/, corresponding to what the Software Heritage Web API will return. For example, here is what the Software Heritage archive knows about the above Hello World implementation:

$ jq meta/swh:1:cnt:c839dea9e8e6f0528b468214348fee8669b305b2.json
{
  "length": 67,
  "status": "visible",
  "checksums": {
    "sha256": "06dfb5d936f50b3cb80152aa053724e4a18417c35f745b66ab9571c25afd0f79",
    "sha1": "459ee8545e5ba6cb819ba41e6ea2f0011cedd728",
    "blake2s256": "87e6ab9c92681e9a022a8f4679dcd9d9b841fe4146edcbc15329fc66d8c82b4f",
    "sha1_git": "c839dea9e8e6f0528b468214348fee8669b305b2"
  },
  "data_url": "https://archive.softwareheritage.org/api/1/content/sha1_git:c839dea9e8e6f0528b468214348fee8669b305b2/raw/",
  "filetype_url": "https://archive.softwareheritage.org/api/1/content/sha1_git:c839dea9e8e6f0528b468214348fee8669b305b2/filetype/",
  "language_url": "https://archive.softwareheritage.org/api/1/content/sha1_git:c839dea9e8e6f0528b468214348fee8669b305b2/language/",
  "license_url": "https://archive.softwareheritage.org/api/1/content/sha1_git:c839dea9e8e6f0528b468214348fee8669b305b2/license/"
}

Source code trees

In addition to individual source code files, we can also browse entire source code directories. Here is the historical Apollo 11 source code, where we can find interesting comments about the antenna during landing:

$ cd archive/swh:1:dir:1fee702c7e6d14395bbf5ac3598e73bcbf97b030

$ ls | wc -l
127

$ grep -i antenna THE_LUNAR_LANDING.s | cut -f 5
# IS THE LR ANTENNA IN POSITION 1 YET
# BRANCH IF ANTENNA ALREADY IN POSITION 1

We can checkout the commit of a more modern code base, like jQuery, and count its JavaScript lines of code (SLOC):

$ cd archive/swh:1:rev:9d76c0b163675505d1a901e5fe5249a2c55609bc

$ ls -F
history/
meta.json@
parent@
parents/
root@

$ find root/src/ -type f -name '*.js' | xargs cat | wc -l
10136

History browsing

meta.json files of revision objects contain complete commit metadata, e.g.:

$ jq '.author.name, .date, .message' meta.json
"Michal Golebiowski-Owczarek"
"2020-03-02T23:02:42+01:00"
"Data:Event:Manipulation: Prevent collisions with Object.prototype ..."

Commit history can be browsed commit-by-commit digging into directories parent(s)/ directories or, more efficiently, using the history summaries located under history/:

$ ls -f history/by-page/000/ | wc -l
6469

$ ls -f history/by-page/000/ | head -n 5
swh:1:rev:358b769a00c3a09a8ec621b8dcb2d5e31b7da69a
swh:1:rev:4a7fc8544e2020c75047456d11979e4e3a517fdf
swh:1:rev:364476c3dc1231603ba61fc08068fa89fb095e1a
swh:1:rev:721744a9fab5b597febea64e466272eabfdb9463
swh:1:rev:4592595b478be979141ce35c693dbc6b65647173

The jQuery commit at hand is preceded by 6469 commits, which can be listed in git log order via the by-page view. The by-hash and by-date views list commits sharded by commit identifier and timestamp:

$ ls history/by-hash/00/ | head -n 5
swh:1:rev:00a9c2e5f4c855382435cec6b3908eb9bd5a53b7
swh:1:rev:005040379d8b64aacbe54941d878efa6e86df1cc
swh:1:rev:00cc67af23bf9cf2cdbaeaeee6ded76baf0292f0
swh:1:rev:00575d4d8c7421c5119f181009374ff2e7736127
swh:1:rev:0019a463bdcb81dc6ba3434505a45774ca27f363

$ ls -F history/by-date/
2006/
2007/
2008/
...
2018/
2019/
2020/

$ ls -f history/by-date/2020/03/16/
swh:1:ref:90fed4b453a5becdb7f173d9e3c1492390a1441f

$ jq .date history/by-date/2020/03/16/*/meta.json
"2020-03-16T21:49:29+01:00"

Note that to populate the by-date view metadata about all commits in the history are needed. To avoid blocking on that, metadata are retrieved asynchronously, populating the view incrementally. The hidden by-date/.status file provides a progress report and is removed upon completion.

Repository snapshots and branches

Snapshot objects keep track of where each branch and release (or “tag”) pointed at archival time. Here is an example using the Unix history repository, which uses historical Unix releases as branch names:

$ cd archive/swh:1:snp:2ca5d6eff8f04a671c0d5b13646cede522c64b7d

$ ls -f | wc -l
210

$ ls -f | grep Bell
refs%2Fheads%2FBell-32V-Snapshot-Development
refs%2Fheads%2FBell-Release
refs%2Ftags%2FBell-32V

$ cd refs%2Fheads%2FBell-Release
$ jq .message,.date meta.json
"Bell 32V release ..."
"1979-05-02T23:26:55-05:00"

$ grep core root/usr/src/games/fortune.c
        printf("Memory fault -- core dumped\n");

We can check that 3 of the 210 branches correspond to historical Bell Labs UNIX releases. And We can dig into the fortune implementation of UNIX/32V instantly, without having to clone a 1.6  GiB repository first.