Add support for environment variable expansion

This patch teaches cgit to expand environment variables in certain
cgitrc option values (cache_root, scan-path, include) plus when
finding the location of cgitrc itself.

One use case for this feature is virtual hosting - e.g. by setting
$CGIT_CONFIG='/etc/cgitrc/$HTTP_HOST' in httpd.conf, all virtual
hosts automatically gets their own cgitrc.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

3 files changed, 78 insertions, 5 deletions

diff --git a/cgit.c b/cgit.c
index 9305d0a..37154e3 100644
--- a/cgit.c
+++ b/cgit.c
@@ -145,13 +145,13 @@ void config_cb(const char *name, const char *value)
                 ctx.cfg.enable_tree_linenumbers = atoi(value);
         else if (!strcmp(name, "max-stats"))
                 ctx.cfg.max_stats = cgit_find_stats_period(value, NULL);
         else if (!strcmp(name, "cache-size"))
                 ctx.cfg.cache_size = atoi(value);
         else if (!strcmp(name, "cache-root"))
-                ctx.cfg.cache_root = xstrdup(value);
+                ctx.cfg.cache_root = xstrdup(expand_macros(value));
         else if (!strcmp(name, "cache-root-ttl"))
                 ctx.cfg.cache_root_ttl = atoi(value);
         else if (!strcmp(name, "cache-repo-ttl"))
                 ctx.cfg.cache_repo_ttl = atoi(value);
         else if (!strcmp(name, "cache-scanrc-ttl"))
                 ctx.cfg.cache_scanrc_ttl = atoi(value);
@@ -174,15 +174,15 @@ void config_cb(const char *name, const char *value)
         else if (!strcmp(name, "max-repo-count"))
                 ctx.cfg.max_repo_count = atoi(value);
         else if (!strcmp(name, "max-commit-count"))
                 ctx.cfg.max_commit_count = atoi(value);
         else if (!strcmp(name, "scan-path"))
                 if (!ctx.cfg.nocache && ctx.cfg.cache_size)
-                        process_cached_repolist(value);
+                        process_cached_repolist(expand_macros(value));
                 else
-                        scan_tree(value, repo_config);
+                        scan_tree(expand_macros(value), repo_config);
         else if (!strcmp(name, "source-filter"))
                 ctx.cfg.source_filter = new_filter(value, 1);
         else if (!strcmp(name, "summary-log"))
                 ctx.cfg.summary_log = atoi(value);
         else if (!strcmp(name, "summary-branches"))
                 ctx.cfg.summary_branches = atoi(value);
@@ -200,13 +200,13 @@ void config_cb(const char *name, const char *value)
                 ctx.cfg.clone_prefix = xstrdup(value);
         else if (!strcmp(name, "local-time"))
                 ctx.cfg.local_time = atoi(value);
         else if (!prefixcmp(name, "mimetype."))
                 add_mimetype(name + 9, value);
         else if (!strcmp(name, "include"))
-                parse_configfile(value, config_cb);
+                parse_configfile(expand_macros(value), config_cb);
 }
 
 static void querystring_cb(const char *name, const char *value)
 {
         if (!value)
                 value = "";
@@ -685,13 +685,13 @@ int main(int argc, const char **argv)
         prepare_context(&ctx);
         cgit_repolist.length = 0;
         cgit_repolist.count = 0;
         cgit_repolist.repos = NULL;
 
         cgit_parse_args(argc, argv);
-        parse_configfile(ctx.env.cgit_config, config_cb);
+        parse_configfile(expand_macros(ctx.env.cgit_config), config_cb);
         ctx.repo = NULL;
         http_parse_querystring(ctx.qry.raw, querystring_cb);
 
         /* If virtual-root isn't specified in cgitrc, lets pretend
          * that virtual-root equals SCRIPT_NAME.
          */
diff --git a/cgit.h b/cgit.h
index cd4af72..568e0c0 100644
--- a/cgit.h
+++ b/cgit.h
@@ -293,7 +293,9 @@ extern int cgit_parse_snapshots_mask(const char *str);
 
 extern int cgit_open_filter(struct cgit_filter *filter);
 extern int cgit_close_filter(struct cgit_filter *filter);
 
 extern int readfile(const char *path, char **buf, size_t *size);
 
+extern char *expand_macros(const char *txt);
+
 #endif /* CGIT_H */
diff --git a/shared.c b/shared.c
index 5f46793..76d26dd 100644
--- a/shared.c
+++ b/shared.c
@@ -420,6 +420,77 @@ int readfile(const char *path, char **buf, size_t *size)
         *size = read_in_full(fd, *buf, st.st_size);
         e = errno;
         (*buf)[*size] = '\0';
         close(fd);
         return (*size == st.st_size ? 0 : e);
 }
+
+int is_token_char(char c)
+{
+        return isalnum(c) || c == '_';
+}
+
+/* Replace name with getenv(name), return pointer to zero-terminating char
+ */
+char *expand_macro(char *name, int maxlength)
+{
+        char *value;
+        int len;
+
+        len = 0;
+        value = getenv(name);
+        if (value) {
+                len = strlen(value);
+                if (len > maxlength)
+                        len = maxlength;
+                strncpy(name, value, len);
+        }
+        return name + len;
+}
+
+#define EXPBUFSIZE (1024 * 8)
+
+/* Replace all tokens prefixed by '$' in the specified text with the
+ * value of the named environment variable.
+ * NB: the return value is a static buffer, i.e. it must be strdup'd
+ * by the caller.
+ */
+char *expand_macros(const char *txt)
+{
+        static char result[EXPBUFSIZE];
+        char *p, *start;
+        int len;
+
+        p = result;
+        start = NULL;
+        while (p < result + EXPBUFSIZE - 1 && txt && *txt) {
+                *p = *txt;
+                if (start) {
+                        if (!is_token_char(*txt)) {
+                                if (p - start > 0) {
+                                        *p = '\0';
+                                        len = result + EXPBUFSIZE - start - 1;
+                                        p = expand_macro(start, len) - 1;
+                                }
+                                start = NULL;
+                                txt--;
+                        }
+                        p++;
+                        txt++;
+                        continue;
+                }
+                if (*txt == '$') {
+                        start = p;
+                        txt++;
+                        continue;
+                }
+                p++;
+                txt++;
+        }
+        *p = '\0';
+        if (start && p - start > 0) {
+                len = result + EXPBUFSIZE - start - 1;
+                p = expand_macro(start, len);
+                *p = '\0';
+        }
+        return result;
+}