fix: flip decrement/increment on comparison

- this prevents wrapping size_t below 0

src/msh.c

@@ -21,7 +21,6 @@
 #define DEFAULTTOKENSCAPACITY   64
 #define DEFAULTHISTORYCAPACITY  128
 
-const int LINESIZE = 512;
 
 int cd(int argc, char** argv) {
     if (argc != 1) {
@@ -143,7 +142,7 @@ int main(int argc, char** argv) {
     int retval = 0;
     char*   line = NULL;
     size_t  linecapacity = 0;
-    char    prompt[LINESIZE] = {};
+    char    prompt[DEFAULTLINECAPACITY] = {};
     size_t  linelen = 0;
     char*   tokenwork = NULL;
     size_t  tokenworkcapacity = 0;
@@ -161,7 +160,7 @@ int main(int argc, char** argv) {
     int laststatus = 0;
 
     int wstatus;
-    char pwd[LINESIZE] = {};
+    char pwd[DEFAULTLINECAPACITY] = {};
     char* pwd_disp;
 
     char* user;
@@ -280,7 +279,7 @@ int main(int argc, char** argv) {
 
     // Main loop
     while(1) {
-        char* result = getcwd(pwd, LINESIZE - 1);
+        char* result = getcwd(pwd, DEFAULTLINECAPACITY - 1);
         if (result == NULL) {
             retval = 1;
             goto cleanup;
@@ -293,7 +292,7 @@ int main(int argc, char** argv) {
 
         snprintf(
             prompt,
-            LINESIZE,
+            DEFAULTLINECAPACITY,
 
             ANSI_BG_BLUE ANSI_FG_BLACK
             "%s"                                  // status
@@ -358,6 +357,7 @@ int main(int argc, char** argv) {
                             }
 
                             oldline = line;
+                            line = NULL;
                         }
                     } else if (ansi == ANSI_CURSOR_DOWN && historyoffset > 0) {
                         historyoffset--;
@@ -384,6 +384,11 @@ int main(int argc, char** argv) {
                     if (load_from_hist == 1) {
                         char*  historyline = history[historyi - (historyoffset)];
                         size_t historylinelen = strlen(historyline);
+
+                        if (line != NULL) {
+                            free(line);
+                        }
+
                         line = malloc(historylinelen + 1);
                         if (line == NULL) {
                             retval = 1;
@@ -401,8 +406,9 @@ int main(int argc, char** argv) {
                     }
                 } else if (ansi == ANSI_DELETE_WORD) {
                     if (cursor > 0) {
+                        // 0123 56
                         size_t index = strnrcspn(line, cursor, " \t");
-                        memmove(line + index, line + cursor, LINESIZE - cursor);
+                        memmove(line + index, line + cursor, linecapacity - cursor);
                         linelen -= cursor - index;
                         cursor = index;
                     }
@@ -423,12 +429,12 @@ int main(int argc, char** argv) {
                 if (cursor == linelen) {
                     line[cursor] = 0;
                 } else {
-                    memmove(line + cursor, line + cursor + 1, LINESIZE - (cursor));
+                    memmove(line + cursor, line + cursor + 1, linecapacity - (cursor));
                 }
             } else {
                 // We are typing
                 if (cursor != linelen) {
-                    memmove(line + cursor + 1, line + cursor, LINESIZE - cursor - 1);
+                    memmove(line + cursor + 1, line + cursor, linecapacity - cursor - 1);
                 }
 
                 line[cursor] = readc;
@@ -457,16 +463,28 @@ int main(int argc, char** argv) {
             fflush(stdout);
         }
 
+        // oldline is only valid while reading
+        if (oldline != NULL) {
+            free(oldline);
+            oldline = NULL;
+        }
+
         putc('\n', stdout);
 
         tcsetattr(fileno(stdin), 0, &orig_term);
 
         line[linelen] = 0;
 
+        if (linelen == 0) {
+            free(line);
+            line = NULL;
+            continue;
+        }
+
         fprintf(historyfile, "%s\n", line);
         fflush(historyfile);
         
-        while (tokenworkcapacity < linelen - 1) {
+        while (tokenworkcapacity + 1 < linelen) {
             tokenworkcapacity *= 2;
             tokenwork = realloc(tokenwork, tokenworkcapacity);
         }