[misc] Consolidate control file reader (e.g. for pairing credentials) into misc.c

- also remove requirement to enter device name in .remote file

src/misc.c

@@ -533,6 +533,57 @@ m_realpath(const char *pathname)
   return ret;
 }
 
+char **
+m_readfile(const char *path, int num_lines)
+{
+  char buf[256];
+  FILE *fp;
+  char **lines;
+  char *line;
+  int i;
+
+  // Alloc array of char pointers
+  lines = calloc(num_lines, sizeof(char *));
+  if (!lines)
+    return NULL;
+
+  fp = fopen(path, "rb");
+  if (!fp)
+    {
+      DPRINTF(E_LOG, L_MISC, "Could not open file '%s' for reading: %s\n", path, strerror(errno));
+      free(lines);
+      return NULL;
+    }
+
+  for (i = 0; i < num_lines; i++)
+    {
+      line = fgets(buf, sizeof(buf), fp);
+      if (!line)
+	{
+	  DPRINTF(E_LOG, L_MISC, "File '%s' has fewer lines than expected (found %d, expected %d)\n", path, i, num_lines);
+	  goto error;
+	}
+
+      lines[i] = trimwhitespace(line);
+      if (strlen(lines[i]) == 0)
+	{
+	  DPRINTF(E_LOG, L_MISC, "Line %d in '%s' is invalid\n", i+1, path);
+	  goto error;
+	}
+    }
+
+  fclose(fp);
+
+  return lines;
+
+ error:
+  for (i = 0; i < num_lines; i++)
+    free(lines[i]);
+
+  free(lines);
+  fclose(fp);
+  return NULL;
+}
 
 char *
 unicode_fixup_string(char *str, const char *fromcode)