From fa644567834f3e1ca8fe7e24f6cc4638bc7c1005 Mon Sep 17 00:00:00 2001
From: Chris Dickinson <chris@dylibso.com>
Date: Mon, 8 Jan 2024 12:20:17 -0800
Subject: [PATCH] fix: support input_offset()

Add support for fetching the Extism address of the input block. Notably,
the input block _may_ be null, in which case the function returns `0n`.

Fixes https://github.com/extism/js-sdk/issues/47
---
 src/call-context.ts    |   5 +++++
 src/mod.test.ts        |  11 +++++++++++
 wasm/input_offset.wasm | Bin 0 -> 318 bytes
 3 files changed, 16 insertions(+)
 create mode 100644 wasm/input_offset.wasm

diff --git a/src/call-context.ts b/src/call-context.ts
index d8e0b54..d3be7e0 100644
--- a/src/call-context.ts
+++ b/src/call-context.ts
@@ -199,6 +199,11 @@ export class CallContext {
       block?.view.setBigUint64(Number(offset), n, true);
     },
 
+    input_offset: () => {
+      const blockIdx = this.#stack[this.#stack.length - 1][0];
+      return Block.indexToAddress(blockIdx || 0);
+    },
+
     input_length: () => {
       return BigInt(this.#input?.byteLength ?? 0);
     },
diff --git a/src/mod.test.ts b/src/mod.test.ts
index cdc26da..32665f6 100644
--- a/src/mod.test.ts
+++ b/src/mod.test.ts
@@ -505,6 +505,17 @@ if (typeof WebAssembly === 'undefined') {
     }
   });
 
+  test('plugin can call input_offset', async () => {
+    const plugin = await createPlugin('http://localhost:8124/wasm/input_offset.wasm');
+    try {
+      const input = 'hello world';
+      const hw = await plugin.call('input_offset_length', input);
+      assert.equal(hw?.getBigUint64(0, true), input.length);
+    } finally {
+      await plugin.close();
+    }
+  });
+
   test('plugin can fail gracefully', async () => {
     const plugin = await createPlugin('http://localhost:8124/wasm/fail.wasm');
     try {
diff --git a/wasm/input_offset.wasm b/wasm/input_offset.wasm
new file mode 100644
index 0000000000000000000000000000000000000000..163adce509d225ba6de9e1d80ba0563d0a256e66
GIT binary patch
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literal 0
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