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+librefetch(8) -- downloads or creates a liberated source tarball
+================================================================
+
+## SYNOPSIS
+
+`librefetch` [<OPTIONS>] <SOURCE-URL> [<OUTPUT-FILE>]<br>
+`librefetch` `-`[`g`|`S`|`M`|`h`]
+
+## DESCRIPTION
+
+`librefetch` is a program to streamline creation of custom source
+tarballs for `PKGBUILD(5)` files.
+
+If a URL mentioned in the <source> array in a `PKGBUILD` is in a
+location that Parabola uploads "custom" source tarballs to (or
+configured locations), and no file is at that URL, librefetch will
+automatically create it for you.
+
+This works because a post-install script for the package configures
+`librefetch` as the download agent for `https://` URLs in
+`makepkg.conf`; allowing it to jump in and create a file if need be.
+Because of this, it is almost never necessary to call `librefetch`
+manually.
+
+The post-install script also configures `librefetch` as the download
+agent for `libre://` URLs, for compatibility with `PKGBUILD` files
+that used a previous version of librefetch.
+
+There are 5 modes:
+
+ * `download`: Download the tarball from the configured mirror.
+ * `create`: Create the tarball from a `PKGBUILD`/`SRCBUILD`.
+ * `checksums`: Generate integrity checks for source files.
+ * `srcbuild`: Print the effective build script.
+ * `makepkg`: Generate and print the location of the effective makepkg
+   script.
+ * `help`: Print `librefetch` usage information.
+
+The normal mode of operation is `download` mode.  If `download` mode
+fails, it may choose to try `create` mode.
+
+## OPTIONS
+
+ * `-C`: Force `create` mode (don't download)
+ * `-D`: Force `download` mode (don't create)
+ * `-p` <file>: Use an alternate build script for `create` mode
+   (instead of `PKGBUILD`).  If an `SRCBUILD` file exists in the same
+   directory, it is used instead.
+ * `-g` | `--geninteg`: Use `checksums` mode: Generate integrity
+   checks for source files.
+ * `-S` | `--srcbuild`: Use `srcbuild` mode: print the effective build
+   script.
+ * `-M` | `--makepkg`: Use `makepkg` mode: generate and print the
+   location of the effective makepkg script.
+ * `-h` | `--help`: Use `help` mode: Show usage information.
+
+Other options, if they are documented in `makepkg -h`, are passed to
+the modified copy of makepkg created during `create` mode.
+
+## DOWNLOAD MODE
+
+If <SOURCE-URL> begins with the string `libre://`, it is replaced with
+the first value in <MIRRORS>, as configured in `librefetch.conf(5)`;
+this is for compatibility with `PKGBUILD` files that used a previous
+version of librefetch.
+
+It uses <DOWNLOADER>, as configured in `librefetch.conf` to attempt to
+download the source tarball from that URL.  If that fails, and
+following conditions are met, it proceeds to `create` mode:
+
+ * The `-D` flag has not been specified to inhibit `create` mode.
+ * The <SOURCE-URL> begins with one of the values in <MIRRORS>.
+
+The latter requirement allows librefetch to be used as a generic
+HTTP(S) download agent, that can automatically create files from
+whitelisted locations.
+
+## CREATE MODE
+
+The principle of `create` mode is that a special `PKGBUILD(5)` (called
+`SRCBUILD(5)`) installs source files to <$pkgdir>, and the resulting
+"package" is then used as a source tarball.  The `SRCBUILD` exists in
+the same directory as the `PKGBUILD`.  It can be created manually, or
+generated on-the-fly from the `PKGBUILD`.  Extra steps are taken to
+ensure that as long as the same directory contents go in, an identical
+tarball will come out--the checksum of the file should not change
+based on when it is built or who builds it.
+
+The `SRCBUILD` is either created, or sanitized if it already exists.
+If the output filename does not end with `.sig` or `.sig.part`, then
+the `SRCBUILD` is fed to a modified version of `makepkg(8)`.  If the
+output filename does end with `.sig` or `.sig.part`, then it uses GPG
+to create a signature.  If the file it is trying to sign does not
+exist yet, librefetch recurses on itself to create it.
+
+The reason `makepkg` must be modified is that we need the resulting
+tarball to be deterministic (as well as not containing package
+metadata).
+
+When this documentation speaks of a file being modified, it is a
+temporary copy of the file that is modified, your original file will
+remain intact.
+
+## SRCBUILD GENERATION
+
+As explained in the `CREATE MODE` section, in `create` mode, this
+program generates an `SRCBUILD` file.  For debugging purposes, this
+file can be printed instead of executed with `srcbuild` mode.
+
+### PRE-EXISTING SRCBUILD
+
+The use of `SRCBUILD` files pre-dates `librefetch`.  By convention,
+they set <PKGDEST> and <PKGEXT> in `package()` in order to modify the
+behavior of `makepkg`.  Because a modified version of `makepkg` is
+used, this interferes with the correct behavior.  To compensate for
+this, lines containing "`PKGDEST=`" or "`PKGEXT=`" are deleted from
+the `SRCBUILD`.
+
+The general idea is that `build()` makes any modifications to the
+source, then `package()` copies it from <$srcdir> to <$pkgdir>.
+
+### SRCBUILD FROM PKGBUILD
+
+Possibly more elegant than having a separate `SRCBUILD` file is having
+an `mksource()` function in the main `PKGBUILD`.  This results in less
+boilerplate and fewer files to edit.
+
+Note that this only happens if a file named `SRCBUILD` doesn't already
+exist; when migrating a package from a manually created `SRCBUILD` to
+this method, the `SRCBUILD` must be deleted (or renamed) for this to
+work.
+
+The dynamically created `SRCBUILD` is created by copying `PKGBUILD` to
+a temporary file, then re-setting variables and re-defining functions.
+Following is a table of the translations.
+
+    Variables
+      source       = mksource
+      noextract    = mknoextract
+      *sums        = mk*sums (md5, sha1, sha224, sha256, sha384, sha512)
+      depends      = <empty>
+      checkdepends = <empty>
+      makedepends  = mkdepends
+      *_$CARCH     = <unset>
+    Functions
+      prepare() { :; }
+      build()   { mksource; }
+      check()   { :; }
+      package() { cp -a "$srcdir"/*/ "$pkgdir/"; }
+
+The `mksource()` function does not need to be defined.  If it isn't
+defined, then no transformations will be made to the source between it
+being extracted to <$srcdir> and copied to <$pkgdir>.
+
+In summary:
+
+ * Set <mksource=()> and <mkmd5sums=()> to act as <source=()> and
+   <md5sums=()>, respectively.
+ * Declare a `mksource()` function to make modifications to the
+   source, if necessary.
+
+Other changes:
+
+ * <pkgname> is set to <pkgbase>, or the first element of the
+   <pkgname> array (the effect is that split packaging is turned
+   off).
+ * <options=()> is set have `makepkg` avoid making changes to
+   <$pkgdir>.  The exact change is:
+
+      options=(!strip docs libtool staticlibs emptydirs !zipman purge !upx)
+
+ * <PURGE_TARGETS=()> has VCS directories added to it:
+
+      PURGE_TARGETS=(.bzr/ .cvs/ .git/ .hg/ .svn/ .makepkg/)
+
+### MAKEPKG MODIFICATIONS
+
+The following modifications are made to makepkg:
+
+ * Allow us to manipulate the output file (<$pkg_file>)
+ * Do not include metadata in the output file (<${comp_files[@]}>)
+ * Force 'ustar' tar format, don't allow it to upgrade to 'pax' to
+   store extended file attributes.
+ * Don't symlink the resulting file into the current directory.
+ * <PURGE_TARGETS> interprets an item as a directory if it ends with a
+   slash ("/").
+ * Timestamps in <$pkgdir> are reset to the date specified in
+   <SOURCE_DATE_EPOCH>[1], or "1990-01-01 0:0:0 +0" if it's not set, so
+   that the resulting tarball will be the same, regardless of when it
+   was created.
+ * Sort the files included in the tarball; normally the order of files
+   in a tarball is essentially random (even if it tends to be the same
+   when re-created on the same machine).
+ * append `-libre` to <$srcdir>
+ * append `-libre` to <$pkgbasedir> (which becomes <$pkgdir>)
+ * Don't check if the package has already been built.
+
+For debugging purposes, this modified makepkg can be printed instead
+of executed with `makepkg` mode.  Before it is run in create mode,
+`PKGEXT`, `PKGDEST`, and `pkg_file` are set as environment variables.
+
+## CONFIGURATION
+
+See `librefetch.conf(5)` for details on configuring librefetch using
+the `librefetch.conf` file.
+
+## SEE ALSO
+
+librefetch.conf(5), makepkg(8), PKGBUILD(5), SRCBUILD(5)
+
+## NOTES
+
+ 1. <SOURCE_DATE_EPOCH> specification for build systems
+    https://reproducible-builds.org/specs/source-date-epoch/