Moves file detection to separate findNextImageAfter() function.

This also uses some additional buffers to make the code easier to follow (hopefully) and help protect against excessively long paths.

src/BlueSCSI_disk.cpp

@@ -540,6 +540,82 @@ static void scsiDiskLoadConfig(int target_idx, const char *section)
     }
 }
 
+// Finds filename with the lowest lexical order _after_ the given filename in
+// the given folder. If there is no file after the given one, or if there is
+// no current file, this will return the lowest filename encountered.
+static int findNextImageAfter(image_config_t &img,
+        const char* dirname, const char* filename,
+        char* buf, size_t buflen)
+{
+    FsFile dir;
+    if (dirname[0] == '\0')
+    {
+        log("Image directory name invalid for ID", (img.scsiId & 7));
+        return 0;
+    }
+    if (!dir.open(dirname))
+    {
+        log("Image directory '", dirname, "' couldn't be opened");
+    }
+    if (!dir.isDir())
+    {
+        log("Can't find images in '", dirname, "', not a directory");
+        dir.close();
+        return 0;
+    }
+
+    char first_name[MAX_FILE_PATH] = {'\0'};
+    char candidate_name[MAX_FILE_PATH] = {'\0'};
+    FsFile file;
+    while (file.openNext(&dir, O_RDONLY))
+    {
+        if (file.isDir()) continue;
+        if (!file.getName(buf, MAX_FILE_PATH))
+        {
+            log("Image directory '", dirname, "'had invalid file");
+            continue;
+        }
+        if (!scsiDiskFilenameValid(buf)) continue;
+
+        // keep track of the first item to allow wrapping
+        // without having to iterate again
+        if (first_name[0] == '\0' || strcmp(buf, first_name) < 0)
+        {
+            strncpy(first_name, buf, sizeof(first_name));
+        }
+
+        // discard if no selected name, or if candidate is before (or is) selected
+        if (filename[0] == '\0' || strcmp(buf, filename) <= 0) continue;
+
+        // if we got this far and the candidate is either 1) not set, or 2) is a
+        // lower item than what has been encountered thus far, it is the best choice
+        if (candidate_name[0] == '\0' || strcmp(buf, candidate_name) < 0)
+        {
+            strncpy(candidate_name, buf, sizeof(candidate_name));
+        }
+    }
+
+    if (candidate_name[0] != '\0')
+    {
+        img.image_index++;
+        strncpy(img.current_image, candidate_name, sizeof(img.current_image));
+        strncpy(buf, candidate_name, buflen);
+        return strlen(candidate_name);
+    }
+    else if (first_name[0] != '\0')
+    {
+        img.image_index = 0;
+        strncpy(img.current_image, first_name, sizeof(img.current_image));
+        strncpy(buf, first_name, buflen);
+        return strlen(first_name);
+    }
+    else
+    {
+        log("Image directory '", dirname, "' was empty");
+        return 0;
+    }
+}
+
 int scsiDiskGetNextImageName(image_config_t &img, char *buf, size_t buflen)
 {
     int target_idx = img.scsiId & 7;
@@ -556,97 +632,38 @@ int scsiDiskGetNextImageName(image_config_t &img, char *buf, size_t buflen)
     if (img.image_directory)
     {
         // image directory was found during startup
-        FsFile dir;
+        char dirname[MAX_FILE_PATH];
         char key[] = "ImgDir";
-        ini_gets(section, key, "", buf, buflen, CONFIGFILE);
-        if (buf[0] != '\0')
-        {
-            if (!dir.open(buf))
-            {
-                log("ImgDir '", buf, "' couldn't be opened.");
-            }
-            if (!dir.isDir())
-            {
-                log("ImgDir '", buf, "' is not a directory.");
-                dir.close();
-                return false;
-            }
-        }
-        else
+        int dirlen = ini_gets(section, key, "", dirname, sizeof(dirname), CONFIGFILE);
+        if (!dirlen)
         {
             // If image_directory set but ImageDir is not, could be used to
             // indicate an image directory configured via folder structure.
             // Not implemented, so treat this as equivalent to missing ImageDir
-            return false;
-        }
-
-        // Find the filename with the lowest lexical order _after_ the
-        // currently selected file. If there is none, or if there is no
-        // current file, use the lowest filename encountered.
-        char first_name[MAX_FILE_PATH] = {'\0'};
-        char candidate_name[MAX_FILE_PATH] = {'\0'};
-        FsFile file;
-        while (file.openNext(&dir, O_RDONLY))
-        {
-            if (file.isDir()) continue;
-            if (!file.getName(buf, MAX_FILE_PATH))
-            {
-                log("Image directory had invalid file for ID", target_idx);
-                continue;
-            }
-            if (!scsiDiskFilenameValid(buf)) continue;
-
-            // keep track of the first item to allow wrapping
-            // without having to iterate again
-            if (first_name[0] == '\0' || strcmp(buf, first_name) < 0)
-            {
-                strncpy(first_name, buf, sizeof(first_name));
-            }
-
-            // discard if no selected name, or if candidate is before (or is) selected
-            if (img.current_image[0] == '\0' || strcmp(buf, img.current_image) <= 0) continue;
-
-            // if we got this far and the candidate is either 1) not set, or 2) is a
-            // lower item than what has been encountered thus far, it is the best choice
-            if (candidate_name[0] == '\0' || strcmp(buf, candidate_name) < 0)
-            {
-                strncpy(candidate_name, buf, sizeof(candidate_name));
-            }
+            return 0;
         }
 
-        // create base path for the result
-        // *TODO* this needs handling for leading and trailing slashes
-        int dirlen = dir.getName(buf, buflen);
-        dir.close(); // done with this
-        if (dirlen > 0 && dirlen - 1 < buflen)
-        {
-            buf[dirlen] = '/';
-            dirlen++;
-        }
-        else
-        {
-            log("Image directory name invalid for ID", target_idx);
-        }
+        // find the next filename
+        char nextname[MAX_FILE_PATH];
+        int nextlen = findNextImageAfter(img, dirname, img.current_image, nextname, sizeof(nextname));
 
-        // append the filename
-        if (candidate_name[0] != '\0')
+        if (nextlen == 0)
         {
-            strncpy(img.current_image, candidate_name, sizeof(img.current_image));
-            strncpy(buf + dirlen, candidate_name, buflen - dirlen);
-            img.image_index++;
-            return dirlen + strlen(candidate_name);
+            log("Image directory was empty for ID", target_idx);
+            return 0;
         }
-        else if (first_name[0] != '\0')
+        else if (buflen < nextlen + dirlen + 1)
         {
-            strncpy(img.current_image, first_name, sizeof(img.current_image));
-            strncpy(buf + dirlen, first_name, buflen - dirlen);
-            img.image_index = 0;
-            return dirlen + strlen(first_name);
+            log("Directory '", dirname, "' and file '", nextname, "' exceed allowed length");
+            return 0;
         }
         else
         {
-            log("Image directory was empty for ID", target_idx);
-            return 0;
+            // construct a return value
+            strncpy(buf, dirname, buflen);
+            buf[dirlen] = '/';
+            strncpy(buf + dirlen + 1, nextname, buflen - dirlen - 1);
+            return dirlen + nextlen;
         }
     }
     else