Manually specify openai-compat format and parse it (#4463)

* Manually specify openai-compat format and parse it

* fixup! Manually specify openai-compat format and parse it

* Expect base64 in embedding test arguments

* fixup! Manually specify openai-compat format and parse it

Remove debug logs

* fixup! Manually specify openai-compat format and parse it

Improve comment

* fixup! Manually specify openai-compat format and parse it

* Add tests to exercise base64 decode of embeddings

* Add tests to verify openai base64 and brokenness behavior

* feat: improve typing

* refactor: switch from jest to vitest for mocking in tests

---------

Co-authored-by: Dixie Flatline <dflatline>
Co-authored-by: Daniel Riccio <[email protected]>

Author: dflatline

src/services/code-index/embedders/__tests__/openai-compatible.spec.ts

@@ -1,4 +1,4 @@
-import { vitest, describe, it, expect, beforeEach, afterEach } from "vitest"
+import { vitest, describe, it, expect, beforeEach, afterEach, vi } from "vitest"
 import type { MockedClass, MockedFunction } from "vitest"
 import { OpenAI } from "openai"
 import { OpenAICompatibleEmbedder } from "../openai-compatible"
@@ -110,6 +110,7 @@ describe("OpenAICompatibleEmbedder", () => {
 			expect(mockEmbeddingsCreate).toHaveBeenCalledWith({
 				input: testTexts,
 				model: testModelId,
+				encoding_format: "base64",
 			})
 			expect(result).toEqual({
 				embeddings: [[0.1, 0.2, 0.3]],
@@ -130,6 +131,7 @@ describe("OpenAICompatibleEmbedder", () => {
 			expect(mockEmbeddingsCreate).toHaveBeenCalledWith({
 				input: testTexts,
 				model: testModelId,
+				encoding_format: "base64",
 			})
 			expect(result).toEqual({
 				embeddings: [
@@ -154,6 +156,7 @@ describe("OpenAICompatibleEmbedder", () => {
 			expect(mockEmbeddingsCreate).toHaveBeenCalledWith({
 				input: testTexts,
 				model: customModel,
+				encoding_format: "base64",
 			})
 		})
 
@@ -173,6 +176,97 @@ describe("OpenAICompatibleEmbedder", () => {
 			})
 		})
 
+		/**
+		 * Test base64 conversion logic
+		 */
+		describe("base64 conversion", () => {
+			it("should convert base64 encoded embeddings to float arrays", async () => {
+				const testTexts = ["Hello world"]
+
+				// Create a Float32Array with test values that can be exactly represented in Float32
+				const testEmbedding = new Float32Array([0.25, 0.5, 0.75, 1.0])
+
+				// Convert to base64 string (simulating what OpenAI API returns)
+				const buffer = Buffer.from(testEmbedding.buffer)
+				const base64String = buffer.toString("base64")
+
+				const mockResponse = {
+					data: [{ embedding: base64String }], // Base64 string instead of array
+					usage: { prompt_tokens: 10, total_tokens: 15 },
+				}
+				mockEmbeddingsCreate.mockResolvedValue(mockResponse)
+
+				const result = await embedder.createEmbeddings(testTexts)
+
+				expect(mockEmbeddingsCreate).toHaveBeenCalledWith({
+					input: testTexts,
+					model: testModelId,
+					encoding_format: "base64",
+				})
+
+				// Verify the base64 string was converted back to the original float array
+				expect(result).toEqual({
+					embeddings: [[0.25, 0.5, 0.75, 1.0]],
+					usage: { promptTokens: 10, totalTokens: 15 },
+				})
+			})
+
+			it("should handle multiple base64 encoded embeddings", async () => {
+				const testTexts = ["Hello world", "Goodbye world"]
+
+				// Create test embeddings with values that can be exactly represented in Float32
+				const embedding1 = new Float32Array([0.25, 0.5, 0.75])
+				const embedding2 = new Float32Array([1.0, 1.25, 1.5])
+
+				// Convert to base64 strings
+				const base64String1 = Buffer.from(embedding1.buffer).toString("base64")
+				const base64String2 = Buffer.from(embedding2.buffer).toString("base64")
+
+				const mockResponse = {
+					data: [{ embedding: base64String1 }, { embedding: base64String2 }],
+					usage: { prompt_tokens: 20, total_tokens: 30 },
+				}
+				mockEmbeddingsCreate.mockResolvedValue(mockResponse)
+
+				const result = await embedder.createEmbeddings(testTexts)
+
+				expect(result).toEqual({
+					embeddings: [
+						[0.25, 0.5, 0.75],
+						[1.0, 1.25, 1.5],
+					],
+					usage: { promptTokens: 20, totalTokens: 30 },
+				})
+			})
+
+			it("should handle mixed base64 and array embeddings", async () => {
+				const testTexts = ["Hello world", "Goodbye world"]
+
+				// Create one base64 embedding and one regular array (edge case)
+				const embedding1 = new Float32Array([0.25, 0.5, 0.75])
+				const base64String1 = Buffer.from(embedding1.buffer).toString("base64")
+
+				const mockResponse = {
+					data: [
+						{ embedding: base64String1 }, // Base64 string
+						{ embedding: [1.0, 1.25, 1.5] }, // Regular array
+					],
+					usage: { prompt_tokens: 20, total_tokens: 30 },
+				}
+				mockEmbeddingsCreate.mockResolvedValue(mockResponse)
+
+				const result = await embedder.createEmbeddings(testTexts)
+
+				expect(result).toEqual({
+					embeddings: [
+						[0.25, 0.5, 0.75],
+						[1.0, 1.25, 1.5],
+					],
+					usage: { promptTokens: 20, totalTokens: 30 },
+				})
+			})
+		})
+
 		/**
 		 * Test batching logic when texts exceed token limits
 		 */
@@ -249,11 +343,15 @@ describe("OpenAICompatibleEmbedder", () => {
 				const testTexts = ["Hello world"]
 				const rateLimitError = { status: 429, message: "Rate limit exceeded" }
 
+				// Create base64 encoded embedding for successful response
+				const testEmbedding = new Float32Array([0.25, 0.5, 0.75])
+				const base64String = Buffer.from(testEmbedding.buffer).toString("base64")
+
 				mockEmbeddingsCreate
 					.mockRejectedValueOnce(rateLimitError)
 					.mockRejectedValueOnce(rateLimitError)
 					.mockResolvedValueOnce({
-						data: [{ embedding: [0.1, 0.2, 0.3] }],
+						data: [{ embedding: base64String }],
 						usage: { prompt_tokens: 10, total_tokens: 15 },
 					})
 
@@ -268,7 +366,7 @@ describe("OpenAICompatibleEmbedder", () => {
 				expect(mockEmbeddingsCreate).toHaveBeenCalledTimes(3)
 				expect(console.warn).toHaveBeenCalledWith(expect.stringContaining("Rate limit hit, retrying in"))
 				expect(result).toEqual({
-					embeddings: [[0.1, 0.2, 0.3]],
+					embeddings: [[0.25, 0.5, 0.75]],
 					usage: { promptTokens: 10, totalTokens: 15 },
 				})
 			})
@@ -360,5 +458,84 @@ describe("OpenAICompatibleEmbedder", () => {
 				await expect(embedder.createEmbeddings(testTexts)).rejects.toThrow()
 			})
 		})
+
+		/**
+		 * Test to confirm OpenAI package bug with base64 encoding
+		 * This test verifies that when we request encoding_format: "base64",
+		 * the OpenAI package returns unparsed base64 strings as expected.
+		 * This is the behavior we rely on in our workaround.
+		 */
+		describe("OpenAI package base64 behavior verification", () => {
+			it("should return unparsed base64 when encoding_format is base64", async () => {
+				const testTexts = ["Hello world"]
+
+				// Create a real OpenAI instance to test the actual package behavior
+				const realOpenAI = new ((await vi.importActual("openai")) as any).OpenAI({
+					baseURL: testBaseUrl,
+					apiKey: testApiKey,
+				})
+
+				// Create test embedding data as base64 using values that can be exactly represented in Float32
+				const testEmbedding = new Float32Array([0.25, 0.5, 0.75, 1.0])
+				const buffer = Buffer.from(testEmbedding.buffer)
+				const base64String = buffer.toString("base64")
+
+				// Mock the raw API response that would come from OpenAI
+				const mockApiResponse = {
+					data: [
+						{
+							object: "embedding",
+							embedding: base64String, // Raw base64 string from API
+							index: 0,
+						},
+					],
+					model: "text-embedding-3-small",
+					object: "list",
+					usage: {
+						prompt_tokens: 2,
+						total_tokens: 2,
+					},
+				}
+
+				// Mock the methodRequest method which is called by post()
+				const mockMethodRequest = vi.fn()
+				const mockAPIPromise = {
+					then: vi.fn().mockImplementation((callback) => {
+						return Promise.resolve(callback(mockApiResponse))
+					}),
+					catch: vi.fn(),
+					finally: vi.fn(),
+				}
+				mockMethodRequest.mockReturnValue(mockAPIPromise)
+
+				// Replace the methodRequest method on the client
+				;(realOpenAI as any).post = vi.fn().mockImplementation((path, opts) => {
+					return mockMethodRequest("post", path, opts)
+				})
+
+				// Call the embeddings.create method with base64 encoding
+				const response = await realOpenAI.embeddings.create({
+					input: testTexts,
+					model: "text-embedding-3-small",
+					encoding_format: "base64",
+				})
+
+				// Verify that the response contains the raw base64 string
+				// This confirms the OpenAI package doesn't parse base64 when explicitly requested
+				expect(response.data[0].embedding).toBe(base64String)
+				expect(typeof response.data[0].embedding).toBe("string")
+
+				// Verify we can manually convert it back to the original float array
+				const returnedBuffer = Buffer.from(response.data[0].embedding as string, "base64")
+				const returnedFloat32Array = new Float32Array(
+					returnedBuffer.buffer,
+					returnedBuffer.byteOffset,
+					returnedBuffer.byteLength / 4,
+				)
+				const returnedArray = Array.from(returnedFloat32Array)
+
+				expect(returnedArray).toEqual([0.25, 0.5, 0.75, 1.0])
+			})
+		})
 	})
 })

src/services/code-index/embedders/openai-compatible.ts

@@ -8,6 +8,19 @@ import {
 } from "../constants"
 import { getDefaultModelId } from "../../../shared/embeddingModels"
 
+interface EmbeddingItem {
+	embedding: string | number[]
+	[key: string]: any
+}
+
+interface OpenAIEmbeddingResponse {
+	data: EmbeddingItem[]
+	usage?: {
+		prompt_tokens?: number
+		total_tokens?: number
+	}
+}
+
 /**
  * OpenAI Compatible implementation of the embedder interface with batching and rate limiting.
  * This embedder allows using any OpenAI-compatible API endpoint by specifying a custom baseURL.
@@ -108,13 +121,38 @@ export class OpenAICompatibleEmbedder implements IEmbedder {
 	): Promise<{ embeddings: number[][]; usage: { promptTokens: number; totalTokens: number } }> {
 		for (let attempts = 0; attempts < MAX_RETRIES; attempts++) {
 			try {
-				const response = await this.embeddingsClient.embeddings.create({
+				const response = (await this.embeddingsClient.embeddings.create({
 					input: batchTexts,
 					model: model,
+					// OpenAI package (as of v4.78.1) has a parsing issue that truncates embedding dimensions to 256
+					// when processing numeric arrays, which breaks compatibility with models using larger dimensions.
+					// By requesting base64 encoding, we bypass the package's parser and handle decoding ourselves.
+					encoding_format: "base64",
+				})) as OpenAIEmbeddingResponse
+
+				// Convert base64 embeddings to float32 arrays
+				const processedEmbeddings = response.data.map((item: EmbeddingItem) => {
+					if (typeof item.embedding === "string") {
+						const buffer = Buffer.from(item.embedding, "base64")
+
+						// Create Float32Array view over the buffer
+						const float32Array = new Float32Array(buffer.buffer, buffer.byteOffset, buffer.byteLength / 4)
+
+						return {
+							...item,
+							embedding: Array.from(float32Array),
+						}
+					}
+					return item
 				})
 
+				// Replace the original data with processed embeddings
+				response.data = processedEmbeddings
+
+				const embeddings = response.data.map((item) => item.embedding as number[])
+
 				return {
-					embeddings: response.data.map((item) => item.embedding),
+					embeddings: embeddings,
 					usage: {
 						promptTokens: response.usage?.prompt_tokens || 0,
 						totalTokens: response.usage?.total_tokens || 0,