magic: try to auto-detect output_format by default (dzen2/i3bar/xmobar)

1 files changed, 142 insertions, 0 deletions

diff --git a/src/auto_detect_format.c b/src/auto_detect_format.c
new file mode 100644
index 0000000..b8dfdfc
--- /dev/null
+++ b/src/auto_detect_format.c
@@ -0,0 +1,142 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <dirent.h>
+
+#include "i3status.h"
+
+/*
+ * This function tries to automatically find out where i3status is being piped
+ * to and choses the appropriate output format.
+ *
+ * It is a little hackish but should work for most setups :).
+ *
+ * By iterating through /proc/<number>/stat and finding out the parent process
+ * id (just like pstree(1) or ps(1) work), we can get all children of our
+ * parent. When the output of i3status is being piped somewhere, the shell
+ * (parent process) spawns i3status and the destination process, so we will
+ * find our own process and the pipe target.
+ *
+ * We then check whether the pipe target’s name is known and chose the format.
+ *
+ */
+char *auto_detect_format() {
+    pid_t myppid = getppid();
+    pid_t mypid = getpid();
+
+    DIR *dir;
+    struct dirent *entry;
+    char path[255];
+    /* the relevant contents (for us) are:
+     * <pid> (<program name>) <status> <ppid>
+     * which should well fit into one page of 4096 bytes */
+    char buffer[4096];
+
+    char *format = NULL;
+
+    char *parentname = NULL;
+
+    if (!(dir = opendir("/proc")))
+        return NULL;
+
+    /* First pass: get the executable name of the parent.
+     * Upon error, we directly return NULL as we cannot continue without the
+     * name of our parent process. */
+    while ((entry = readdir(dir)) != NULL) {
+        pid_t pid = (pid_t)atoi(entry->d_name);
+        if (pid != myppid)
+            continue;
+
+        if (snprintf(path, sizeof(path), "/proc/%d/stat", pid) == -1 ||
+            !slurp(path, buffer, 4095))
+            goto out;
+
+        buffer[4095] = '\0';
+        char *leftbracket = strchr(buffer, '(');
+        char *rightbracket = strrchr(buffer, ')');
+        if (!leftbracket ||
+            !rightbracket ||
+            !(parentname = malloc((rightbracket - leftbracket))))
+            goto out;
+        *rightbracket = '\0';
+        strcpy(parentname, leftbracket + 1);
+    }
+
+    if (!parentname)
+        goto out;
+
+    rewinddir(dir);
+
+    while ((entry = readdir(dir)) != NULL) {
+        pid_t pid = (pid_t)atoi(entry->d_name);
+        if (pid == 0 || pid == mypid)
+            continue;
+
+        if (snprintf(path, sizeof(path), "/proc/%d/stat", pid) == -1)
+            continue;
+
+        char *name = NULL;
+        pid_t ppid;
+        int loopcnt = 0;
+        /* Now we need to find out the name of the process.
+         * To avoid the possible race condition of the process existing already
+         * but not executing the destination (shell after fork() and before
+         * exec()), we check if the name equals its parent.
+         *
+         * We try this for up to 0.5 seconds, then we give up.
+         */
+        do {
+            /* give the scheduler a chance between each iteration, don’t hog
+             * the CPU too much */
+            if (name)
+                usleep(50);
+
+            if (!slurp(path, buffer, 4095))
+                break;
+            buffer[4095] = '\0';
+            char *leftbracket = strchr(buffer, '(');
+            char *rightbracket = strrchr(buffer, ')');
+            if (!leftbracket ||
+                !rightbracket ||
+                sscanf(rightbracket + 2, "%*c %d", &ppid) != 1 ||
+                ppid != myppid)
+                break;
+            *rightbracket = '\0';
+            name = leftbracket + 1;
+        } while (strcmp(parentname, name) == 0 && loopcnt++ < 10000);
+
+        if (!name)
+            continue;
+
+        /* Check for known destination programs and set format */
+        char *newfmt = NULL;
+        if (strcasecmp(name, "i3bar") == 0)
+            newfmt = "none";
+        else if (strcasecmp(name, "dzen2") == 0)
+            newfmt = "dzen2";
+        else if (strcasecmp(name, "xmobar") == 0)
+            newfmt = "xmobar";
+
+        if (newfmt && format) {
+            fprintf(stderr, "i3status: cannot auto-configure, situation ambiguous (format \"%s\" *and* \"%s\" detected)\n", newfmt, format);
+            format = NULL;
+            break;
+        } else {
+            format = newfmt;
+        }
+    }
+
+out:
+    closedir(dir);
+
+    return format;
+}