Address PR review feedback

- Extract shared `inflateData` and `base64ToUint8Array` into
  `lib/utils/compression.ts` to eliminate duplication between
  miam.ts and Label_H1_OHMA.ts (makrsmark)
- Add explicit error when inflate produces no output instead of
  silently skipping CRC validation (Copilot)
- Fix base64url support: convert `-`/`_` to `+`/`/` before decoding
  instead of stripping them (chatgpt-codex-connector)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kevinelliott

lib/plugins/Label_H1_OHMA.ts

@@ -1,47 +1,10 @@
 import { DecoderPlugin } from '../DecoderPlugin';
 import { DecodeResult, Message, Options } from '../DecoderPluginInterface';
 import { ResultFormatter } from '../utils/result_formatter';
-
-import * as pako from 'pako';
+import { base64ToUint8Array, inflateData } from '../utils/compression';
 
 const textDecoder = new TextDecoder();
 
-function base64ToUint8Array(base64: string): Uint8Array {
-  // Match Buffer.from(str, 'base64') behavior: strip non-base64 chars, handle missing padding
-  const cleaned = base64.replace(/[^A-Za-z0-9+/]/g, '');
-  const padded = cleaned + '='.repeat((4 - (cleaned.length % 4)) % 4);
-  const binary = atob(padded);
-  const bytes = new Uint8Array(binary.length);
-  for (let i = 0; i < binary.length; i++) {
-    bytes[i] = binary.charCodeAt(i);
-  }
-  return bytes;
-}
-
-/**
- * Inflate compressed data with support for partial/truncated streams.
- */
-function inflateData(data: Uint8Array): Uint8Array | undefined {
-  const chunks: Uint8Array[] = [];
-  const inflator = new pako.Inflate({ windowBits: 15 });
-  inflator.onData = (chunk: Uint8Array) => {
-    chunks.push(chunk);
-  };
-  inflator.push(data, 2); // Z_SYNC_FLUSH
-
-  if (chunks.length === 0) return undefined;
-  if (chunks.length === 1) return chunks[0];
-
-  const totalLen = chunks.reduce((sum, c) => sum + c.length, 0);
-  const result = new Uint8Array(totalLen);
-  let offset = 0;
-  for (const chunk of chunks) {
-    result.set(chunk, offset);
-    offset += chunk.length;
-  }
-  return result;
-}
-
 export class Label_H1_OHMA extends DecoderPlugin {
   name = 'label-h1-ohma';
 
@@ -61,7 +24,7 @@ export class Label_H1_OHMA extends DecoderPlugin {
     const data = message.text.split('OHMA')[1]; // throw out '/RTNOCR.' - even though it means something
     try {
       const compressedBuffer = base64ToUint8Array(data);
-      const result = inflateData(compressedBuffer);
+      const result = inflateData(compressedBuffer, false);
       if (!result || result.length === 0) {
         throw new Error('Decompression produced no output');
       }

lib/utils/compression.ts

@@ -0,0 +1,56 @@
+import * as pako from 'pako';
+
+/**
+ * Inflate compressed data with support for partial/truncated streams.
+ * Uses Z_SYNC_FLUSH to extract as much data as possible, even from
+ * incomplete deflate streams. Captures output via onData callback.
+ *
+ * @param data - The compressed input bytes
+ * @param raw - If true, use raw deflate (no zlib header); if false, expect zlib header
+ * @returns The decompressed bytes, or undefined if no output was produced
+ */
+export function inflateData(
+  data: Uint8Array,
+  raw: boolean,
+): Uint8Array | undefined {
+  const chunks: Uint8Array[] = [];
+  const inflator = new pako.Inflate({ windowBits: raw ? -15 : 15 });
+  inflator.onData = (chunk: Uint8Array) => {
+    chunks.push(chunk);
+  };
+  inflator.push(data, 2); // Z_SYNC_FLUSH
+
+  if (chunks.length === 0) return undefined;
+  if (chunks.length === 1) return chunks[0];
+
+  const totalLen = chunks.reduce((sum, c) => sum + c.length, 0);
+  const result = new Uint8Array(totalLen);
+  let offset = 0;
+  for (const chunk of chunks) {
+    result.set(chunk, offset);
+    offset += chunk.length;
+  }
+  return result;
+}
+
+/**
+ * Decode a base64 or base64url string to Uint8Array.
+ * Handles missing padding and converts base64url chars (- and _) to
+ * standard base64 chars (+ and /), matching Buffer.from(str, 'base64') behavior.
+ *
+ * @param base64 - The base64 or base64url encoded string
+ * @returns The decoded bytes
+ */
+export function base64ToUint8Array(base64: string): Uint8Array {
+  const cleaned = base64
+    .replace(/-/g, '+')
+    .replace(/_/g, '/')
+    .replace(/[^A-Za-z0-9+/]/g, '');
+  const padded = cleaned + '='.repeat((4 - (cleaned.length % 4)) % 4);
+  const binary = atob(padded);
+  const bytes = new Uint8Array(binary.length);
+  for (let i = 0; i < binary.length; i++) {
+    bytes[i] = binary.charCodeAt(i);
+  }
+  return bytes;
+}

lib/utils/miam.ts

@@ -1,34 +1,9 @@
 import { ascii85Decode } from './ascii85';
-import * as pako from 'pako';
+import { inflateData } from './compression';
 
 const textDecoder = new TextDecoder();
 const textEncoder = new TextEncoder();
 
-/**
- * Inflate compressed data with support for partial/truncated streams.
- * Captures output chunks via onData to handle Z_SYNC_FLUSH correctly.
- */
-function inflateData(data: Uint8Array, raw: boolean): Uint8Array | undefined {
-  const chunks: Uint8Array[] = [];
-  const inflator = new pako.Inflate({ windowBits: raw ? -15 : 15 });
-  inflator.onData = (chunk: Uint8Array) => {
-    chunks.push(chunk);
-  };
-  inflator.push(data, 2); // Z_SYNC_FLUSH
-
-  if (chunks.length === 0) return undefined;
-  if (chunks.length === 1) return chunks[0];
-
-  const totalLen = chunks.reduce((sum, c) => sum + c.length, 0);
-  const result = new Uint8Array(totalLen);
-  let offset = 0;
-  for (const chunk of chunks) {
-    result.set(chunk, offset);
-    offset += chunk.length;
-  }
-  return result;
-}
-
 enum MIAMVersion {
   V1 = 1,
   V2 = 2,
@@ -480,7 +455,12 @@ export class MIAMCoreUtils {
         ) >= 0
       ) {
         try {
-          pduData = inflateData(body, true) || null;
+          const inflated = inflateData(body, true);
+          if (inflated === undefined) {
+            pduErrors.push('Inflation produced no output for body');
+          } else {
+            pduData = inflated;
+          }
         } catch (e) {
           pduErrors.push('Inflation failed for body: ' + e);
         }