4 files changed, 44 insertions, 1 deletions
diff --git a/src/blogc/funcvars.c b/src/blogc/funcvars.c
index beb5f8a..25a22bf 100644
--- a/src/blogc/funcvars.c
+++ b/src/blogc/funcvars.c
@@ -38,6 +38,7 @@ static const struct func_map {
     {"BLOGC_SYSINFO_DATETIME", blogc_sysinfo_inject_datetime},
 #endif
 
+    {"BLOGC_SYSINFO_INSIDE_DOCKER", blogc_sysinfo_inject_inside_docker},
     {NULL, NULL},
 };
 
diff --git a/src/blogc/sysinfo.c b/src/blogc/sysinfo.c
index 61c8b1d..9d03b61 100644
--- a/src/blogc/sysinfo.c
+++ b/src/blogc/sysinfo.c
@@ -26,7 +26,11 @@
 #include <time.h>
 #endif /* HAVE_TIME_H */
 
+#include <stdbool.h>
 #include <stdlib.h>
+#include <string.h>
+#include "../common/error.h"
+#include "../common/file.h"
 #include "../common/utils.h"
 #include "sysinfo.h"
 
@@ -116,3 +120,38 @@ blogc_sysinfo_inject_datetime(bc_trie_t *global)
 
     bc_trie_insert(global, "BLOGC_SYSINFO_DATETIME", t);
 }
+
+
+// it is obviously impossible that the same process runs inside and outside
+// docker at the same time, then an unprotected global variable should be fine
+// here
+static bool inside_docker_evaluated = false;
+static bool inside_docker = false;
+
+bool
+blogc_sysinfo_get_inside_docker(void)
+{
+    if (inside_docker_evaluated)
+        return inside_docker;
+    inside_docker_evaluated = true;
+
+    size_t len;
+    bc_error_t *err = NULL;
+    char *contents = bc_file_get_contents("/proc/1/cgroup", false, &len, &err);
+    if (err != NULL) {
+        inside_docker = false;
+        return inside_docker;
+    }
+
+    bool inside_docker = NULL != strstr(contents, "/docker/");
+    free(contents);
+    return inside_docker;
+}
+
+
+void
+blogc_sysinfo_inject_inside_docker(bc_trie_t *global)
+{
+    if (blogc_sysinfo_get_inside_docker())
+        bc_trie_insert(global, "BLOGC_SYSINFO_INSIDE_DOCKER", bc_strdup("1"));
+}
diff --git a/src/blogc/sysinfo.h b/src/blogc/sysinfo.h
index 25f2177..783b656 100644
--- a/src/blogc/sysinfo.h
+++ b/src/blogc/sysinfo.h
@@ -31,6 +31,7 @@
 #define HAVE_SYSINFO_DATETIME 1
 #endif /* HAVE_TIME_H */
 
+#include <stdbool.h>
 #include "../common/utils.h"
 
 char* blogc_sysinfo_get_hostname(void);
@@ -39,5 +40,7 @@ char* blogc_sysinfo_get_username(void);
 void blogc_sysinfo_inject_username(bc_trie_t *global);
 char* blogc_sysinfo_get_datetime(void);
 void blogc_sysinfo_inject_datetime(bc_trie_t *global);
+bool blogc_sysinfo_get_inside_docker(void);
+void blogc_sysinfo_inject_inside_docker(bc_trie_t *global);
 
 #endif /* ___SYSINFO_H */
diff --git a/src/common/file.c b/src/common/file.c
index d64a0d8..1e55f64 100644
--- a/src/common/file.c
+++ b/src/common/file.c
@@ -20,7 +20,7 @@
 char*
 bc_file_get_contents(const char *path, bool utf8, size_t *len, bc_error_t **err)
 {
-    if (path == NULL || err == NULL || *err != NULL)
+    if (path == NULL || len == NULL || err == NULL || *err != NULL)
         return NULL;
 
     *len = 0;