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
@@ -148,7 +148,7 @@ void config_cb(const char *name, const char *value)
         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"))
@@ -177,9 +177,9 @@ void config_cb(const char *name, const char *value)
                 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"))
@@ -203,7 +203,7 @@ void config_cb(const char *name, const char *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)
@@ -688,7 +688,7 @@ int main(int argc, const char **argv)
         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);
 
diff --git a/cgit.h b/cgit.h
index cd4af72..568e0c0 100644
--- a/cgit.h
+++ b/cgit.h
@@ -296,4 +296,6 @@ 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
@@ -423,3 +423,74 @@ int readfile(const char *path, char **buf, size_t *size)
         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;
+}