add $STAGIT_BASEURL environment variable to make Atom links absolute

With feedback from adc, thanks!

stagit.1

@@ -1,4 +1,4 @@
-.Dd July 19, 2020
+.Dd March 4, 2021
 .Dt STAGIT 1
 .Os
 .Sh NAME
@@ -103,6 +103,14 @@ favicon image.
 .It style.css
 CSS stylesheet.
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width Ds
+.It Ev STAGIT_BASEURL
+Base URL to make links in atom.xml absolute.
+For example: STAGIT_BASE_URL="https://git.codemadness.org/stagit/".
+.El
+.Sh EXIT STATUS
+.Ex -std
 .Sh SEE ALSO
 .Xr stagit-index 1
 .Sh AUTHORS

stagit.c

@@ -58,6 +58,7 @@ struct referenceinfo {
 
 static git_repository *repo;
 
+static const char *baseurl = ""; /* base URL to make absolute RSS/Atom URI */
 static const char *relpath = "";
 static const char *repodir;
 
@@ -807,8 +808,8 @@ printcommitatom(FILE *fp, struct commitinfo *ci, const char *tag)
 		xmlencode(fp, ci->summary, strlen(ci->summary));
 		fputs("</title>\n", fp);
 	}
-	fprintf(fp, "<link rel=\"alternate\" type=\"text/html\" href=\"commit/%s.html\" />\n",
-	        ci->oid);
+	fprintf(fp, "<link rel=\"alternate\" type=\"text/html\" href=\"%scommit/%s.html\" />\n",
+	        baseurl, ci->oid);
 
 	if (ci->author) {
 		fputs("<author>\n<name>", fp);
@@ -1184,6 +1185,9 @@ main(int argc, char *argv[])
 	}
 #endif
 
+	if ((p = getenv("STAGIT_BASEURL")))
+		baseurl = p;
+
 	if (git_repository_open_ext(&repo, repodir,
 		GIT_REPOSITORY_OPEN_NO_SEARCH, NULL) < 0) {
 		fprintf(stderr, "%s: cannot open repository\n", argv[0]);