j2:Add support for inline shell directiveimplement-runsh

This allows for render-time shell command input to the output document.

This also simplifies the j2_readvar function to make it handle input
line by line rather than as a pure stream, character by character, which
had incredibly complex logic and was very brittle. The new method is
more durable, though is a bit less efficient due to reprocessing the
string, though it no longer seeks back and forth.

Add j2_strstr function and better protect against buffer overflow

This also updates the librem 5 no wifi post to print the current date
and time at pageload.

5 files changed, 96 insertions, 34 deletions

diff --git a/src/common.c b/src/common.c
index 1891d78..db33bc0 100644
--- a/src/common.c
+++ b/src/common.c
@@ -75,3 +75,23 @@ int html_read_title(char* path, char* out) {
   return -1;
 }
 
+
+char* runsh(char* cmd) {
+  char buf[2048] = {'\0'};
+  char* out = malloc(1);
+  FILE* fd = NULL;
+  unsigned long len = 0;
+
+  fd = popen(cmd, "r");
+  while(fgets(buf, 2048, fd) != NULL) {
+    len += strlen(buf);
+    out = realloc(out, len + 1);
+    strcat(out, buf);
+  }
+  pclose(fd);
+
+  if(out[len - 1] == '\n')
+    out[len-1] = '\0';
+  return out;
+}
+
diff --git a/src/common.h b/src/common.h
index aca549d..03529dd 100644
--- a/src/common.h
+++ b/src/common.h
@@ -16,6 +16,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 #ifndef _common_h
@@ -29,4 +30,6 @@ int file_exists(char*);
 
 int html_read_title(char*, char*);
 
+char* runsh(char*);
+
 #endif
diff --git a/src/j2.c b/src/j2.c
index 05fe442..b636c77 100644
--- a/src/j2.c
+++ b/src/j2.c
@@ -18,30 +18,47 @@
 #include "j2.h"
 
 
-int j2_readvar(FILE* fd, char* buf) {
-  char c;
-  int i = 0;
-  fpos_t startpos;
+char* j2_strstr(char* line) {
+  char* start;
+  char* end;
 
-  fgetpos(fd, &startpos);
-  //long seekstart = SEEK_CUR;
+  start = strstr(line, "{{ ");
+  if(start == NULL)
+    return NULL;
+  //start += 3; // Advance past the '{{ '
 
-  if((c = fgetc(fd)) != '{') {
-    fsetpos(fd, &startpos);
-    return -1;
-  }
-  if(fgetc(fd) != ' ') {
-    fsetpos(fd, &startpos);
-    return -1;
-  }
+  // Check for the var close to ensure a complete definition is present
+  end = strstr(start, " }}");
 
-  while((c = fgetc(fd)) != ' ') {
-    buf[i] = c;
-    i++;
-  }
+  // Incorrectly formatted, early return null
+  if(end == NULL)
+    return NULL;
+
+  return start;
+}
+
+
+char* j2_readvar(char* line, char* buf, int maxlen) {
+  char* start = NULL;
+  char* end   = NULL;
 
-  buf[i] = '\0';
-  return 1;
+  start = j2_strstr(line);
+  if(start == NULL)
+    return NULL;
+  start += 3;
+
+  // Because of how j2_strstr works, this will always work if start is not null
+  end = strstr(start, " }}");
+
+  // Only copy up to maxlen to avoid buffer overflows
+  if(end - start > maxlen) {
+    strncpy(buf, start, maxlen);
+    buf[maxlen] = '\0';
+  } else {
+    strncpy(buf, start, end - start);
+    buf[end - start] = '\0';
+  }
+  return end + 3;
 }
 
 
@@ -50,23 +67,42 @@ int j2_readvar(FILE* fd, char* buf) {
  * matching environment variables.
  */
 int j2_cat(char* path) {
-  char buf[512] = {'\0'};
-  char c;
+  char line[J2_MAXLINE] = {'\0'};
+  char buf[J2_MAXBUF] = {'\0'};
   FILE* fd = fopen(path, "r");
+  char* value    = NULL;
+  char* varstart = NULL;
+  char* varend   = NULL;
 
-  while((c = fgetc(fd)) != EOF) {
-    if(c == '{') {
-      if(j2_readvar(fd, buf) == -1) {
-        printf("{%s", buf);
-        continue;
-      }
+  while(fgets(line, J2_MAXLINE, fd) != NULL) {
+    varstart = j2_strstr(line);
 
-      printf("%s", getenv(buf));
-      fgetc(fd);
-      fgetc(fd);
+    if(!varstart) {
+      printf(line);
       continue;
     }
-    printf("%c", c);
+    varend = j2_readvar(varstart, buf, J2_MAXBUF);
+
+    // Break the beginning of the string and the beginning of the variable
+    // (this overwrites the first { that opens the variable def)
+    *varstart = '\0';
+    // Because of the inserted null byte, this will print from byte 0 to there
+    printf("%s", line);
+
+    // Execute the variable directive and print the output
+    if(strncmp(buf, "shell ", 6) == 0) {
+      // Execute the provided shell command and print that
+      value = runsh(&buf[6]);
+      printf("%s", value);
+      free(value);
+    } else {
+      // Print the referenced environment variable
+      value = getenv(buf);
+      printf("%s", value);
+    }
+
+    // varend points to after the final }} of the variable def
+    printf("%s", varend);
   }
 
   fclose(fd);
diff --git a/src/j2.h b/src/j2.h
index 3e958d3..c08f9ec 100644
--- a/src/j2.h
+++ b/src/j2.h
@@ -18,9 +18,12 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include "common.h"
 
-int j2_readvar(FILE*, char*);
+#define J2_MAXLINE 4096
+#define J2_MAXBUF  1024
 
+char* j2_readvar(char*, char*, int);
 
 /**
  * Reads a jinja file and cats the output, interpolating variables, values from
diff --git a/src/main.c b/src/main.c
index 0e608f6..297ea96 100644
--- a/src/main.c
+++ b/src/main.c
@@ -83,7 +83,7 @@ int main(int argc, char* argv[], char* envp[]) {
   setenv("PAGE_TITLE", title, 1);
 
   j2_cat(header);
-  catfile(path);
+  j2_cat(path);
   j2_cat(footer);
   fflush(stdout);