java-native-access/jna · error · IllegalArgumentException

Structure exceeds provided memory bounds

Error message

Structure exceeds provided memory bounds

What it means

Structure.useMemory(Pointer) wraps an IndexOutOfBoundsException from the underlying memory access and rethrows it as this IllegalArgumentException. It means the externally supplied Pointer is smaller than the Structure's calculated size, so reading/writing the struct would run past the end of that memory block.

Source

Thrown at src/com/sun/jna/Structure.java:376

                this.memory.write(0, buf, 0, buf.length);
            }
            else {
                if (size == CALCULATE_SIZE) {
                    size = calculateSize(false);
                }
                if (size != CALCULATE_SIZE) {
                    this.memory = m.share(offset, size);
                } else {
                    // Ensure our memory pointer is initialized, even if we can't
                    // yet figure out a proper size/layout
                    this.memory = m.share(offset);
                }
            }
            this.array = null;
            this.readCalled = false;
        }
        catch(IndexOutOfBoundsException e) {
            throw new IllegalArgumentException("Structure exceeds provided memory bounds", e);
        }
    }

    /** Ensure this memory has its size and layout calculated and its
        memory allocated. */
    protected void ensureAllocated() {
        ensureAllocated(false);
    }

    /** Ensure this memory has its size and layout calculated and its
        memory allocated.
        @param avoidFFIType used when computing FFI type information
        to avoid recursion
    */
    private void ensureAllocated(boolean avoidFFIType) {
        if (memory == null) {
            allocateMemory(avoidFFIType);
        }

View on GitHub (pinned to d036ad9781)

Solutions

1. Ensure the supplied Pointer backs at least structure.size() bytes: allocate with new Memory(structure.size()) before useMemory.
2. Call structure.size()/calculateSize(true) first and size the buffer from that value, especially after modifying struct fields.
3. If the memory comes from native code, verify the native allocation matches the current Java field layout (field order, type sizes, alignment).
4. Catch IllegalArgumentException only to produce a better diagnostic; the fix is always providing a large-enough buffer.

Example fix

// before
MyStruct s = new MyStruct();
s.useMemory(smallBuffer); // IllegalArgumentException if smallBuffer.size() < s.size()

// after
MyStruct s = new MyStruct();
Memory m = new Memory(s.size());
s.useMemory(m);

MyStruct s = new MyStruct();
int needed = s.size();
if (ptr instanceof Memory && ((Memory) ptr).size() < needed) {
    throw new IllegalArgumentException("buffer too small: " + ((Memory) ptr).size() + " < " + needed);
}

static boolean fits(Pointer p, Structure s) { return !(p instanceof Memory) || ((Memory) p).size() >= s.size(); }

try {
    structure.useMemory(ptr);
} catch (IllegalArgumentException e) {
    // backing block smaller than structure.size(); reallocate and retry
    structure.useMemory(new Memory(structure.size()));
}

When it happens

Trigger: Calling structure.useMemory(ptr) (directly or via the constructor Structure(Pointer)) where the pointed-to block is shorter than calculateSize(); also triggered through read/write/toArray paths that call useMemory, and from ensureAllocated when sharing external memory.

Common situations: Mapping a Structure onto memory allocated by native code (or another smaller JNA Memory/struct) whose size was computed for a different/older struct definition; adding fields to a Java Structure without updating the native-side buffer size; reusing one small struct's memory for a larger struct via toArray-style sharing.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• Function <name> declared Structure[] at parameter <index> bu
• Function <name> declared Structure[] at parameter <index> bu
• Structure array must have non-zero length
• Bounds exceeds available space : size=<size>, offset=<off+sz
• Need an initialized array

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/9a68bf7ac3c218ae. Report an issue: GitHub.