InlineModelResolver.uniqueName throws StringIndexOutOfBoundsException for titles starting with a separator (camelCaseFlattenNaming)

Start in modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/InlineModelResolver.java at uniqueName(String key), then trace its caller resolveModelName(title, key). Reproduce through OpenAPIV3Parser with flattening and camelCaseFlattenNaming enabled using a title beginning with a separator or an empty title; done means valid input no longer throws and produces a non-empty model name.

Summary

InlineModelResolver.uniqueName() crashes with an uncaught StringIndexOutOfBoundsException when camelCaseFlattenNaming is enabled and the input key (a schema title, or a derived fallback name) is empty or starts with one of the separator characters (-, _, |, whitespace). The first token produced by key.split(...) is then the empty string, and substring(0, 1) is called on it unconditionally.

Static-analysis finding against current master; not executed here.

Location

• File: modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/InlineModelResolver.java
• Function: uniqueName(String key), lines ~441-455; specifically:

for (int i = 0; i < key.split("[-|\\s|_]").length; i++) {
    uniqueKey = key.split("[-|\\s|_]")[i];
    uniqueKey = uniqueKey.substring(0, 1).toUpperCase() + uniqueKey.substring(1);   // <-- throws

• Reached from resolveModelName(title, key) (~line 418), which prefers uniqueName(title) whenever title != null.

Problem

Java's split() removes trailing empty strings but keeps leading ones. For any key whose first character is a separator - e.g. " foo", "-foo", "_foo" - or for the empty string "" (split result [""]), element 0 of the split array is "". The loop body then executes "".substring(0, 1), which throws StringIndexOutOfBoundsException: begin 1, end 0, length 0. There is no guard for empty tokens anywhere in the loop.

Because resolveModelName() passes the schema's free-form title straight into uniqueName(), any inline schema whose title begins with such a character (or is "") triggers this when flattening runs with camel-case naming enabled.

Trigger / Reproduction

Static analysis only; not run here. Trigger conditions per the code paths above:

ParseOptions options = new ParseOptions();
options.setResolve(true);
options.setFlatten(true);
options.setCamelCaseFlattenNaming(true);
new OpenAPIV3Parser().readContents(spec, null, options);

with an inline schema whose title starts with a separator or is empty, e.g.:

paths:
  /things:
    post:
      requestBody:
        content:
          application/json:
            schema:
              type: object
              title: " my model"      # or "-", "_x", ""
              properties:
                name: { type: string }

" my model".split("[-|\s|_]") yields ["", "my", "model"]; iteration 0 calls "".substring(0, 1) and throws.

Note that "" as title also crashes here, which overlaps with the empty-title report in #2118 - but #2118 describes the degenerate empty component name outcome (default options), not this exception path with camelCaseFlattenNaming=true.

Expected Behavior

A malformed/unusual title should degrade gracefully: skip empty tokens (or fall back to the provided fallback key / a synthesized name like inline_object) instead of throwing an unhandled runtime exception out of flatten().

Actual Behavior

StringIndexOutOfBoundsException propagates from InlineModelResolver.flatten(); parsing aborts even though the document itself is valid.

Impact

Library consumers using the documented flatten + camelCaseFlattenNaming combination get a hard failure on valid documents containing titles with leading separators/spaces (free-form strings users legitimately control, e.g. " LED status"). Since OpenAPIV3Parser catches and logs exceptions in some paths (catch (Exception e) around resolving), the failure can also surface merely as a silently un-flattened/partially processed API instead of clean output, depending on call site.

Suggested Direction

Inside the loop, skip empty tokens before calling substring (e.g. if (uniqueKey.isEmpty()) continue;), and after concatenation fall back to a non-empty default name if the sanitized result is blank. That fixes both the exception and the adjacent blank-name outcome from #2118 for the camel-case path.

Evidence

• InlineModelResolver.java lines 444-452: unconditional substring(0, 1) on each split token; no empty-token guard.
• Java String.split semantics retain leading empty strings (only trailing empties are removed).
• resolveModelName() line 422: title wins over the fallback key whenever non-null, so user-controlled titles flow directly into the vulnerable code.