fix:feature/sglang-provider (#302)

Co-authored-by: zhaochaojin <zhaochaojin@didiglobal.com>
Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

env.example

@@ -68,6 +68,10 @@ AI_MODEL=global.anthropic.claude-sonnet-4-5-20250929-v1:0
 # SILICONFLOW_API_KEY=sk-...
 # SILICONFLOW_BASE_URL=https://api.siliconflow.com/v1  # Optional: switch to https://api.siliconflow.cn/v1 if needed
 
+# SGLang Configuration (OpenAI-compatible)
+# SGLANG_API_KEY=your-sglang-api-key
+# SGLANG_BASE_URL=http://127.0.0.1:8000/v1  # Your SGLang endpoint
+
 # Vercel AI Gateway Configuration
 # Get your API key from: https://vercel.com/ai-gateway
 # Model format: "provider/model" e.g., "openai/gpt-4o", "anthropic/claude-sonnet-4-5"

lib/ai-providers.ts

@@ -19,6 +19,7 @@ export type ProviderName =
     | "openrouter"
     | "deepseek"
     | "siliconflow"
+    | "sglang"
     | "gateway"
 
 interface ModelConfig {
@@ -50,6 +51,7 @@ const ALLOWED_CLIENT_PROVIDERS: ProviderName[] = [
     "openrouter",
     "deepseek",
     "siliconflow",
+    "sglang",
     "gateway",
 ]
 
@@ -343,6 +345,7 @@ function buildProviderOptions(
         case "deepseek":
         case "openrouter":
         case "siliconflow":
+        case "sglang":
         case "gateway": {
             // These providers don't have reasoning configs in AI SDK yet
             // Gateway passes through to underlying providers which handle their own configs
@@ -367,6 +370,7 @@ const PROVIDER_ENV_VARS: Record<ProviderName, string | null> = {
     openrouter: "OPENROUTER_API_KEY",
     deepseek: "DEEPSEEK_API_KEY",
     siliconflow: "SILICONFLOW_API_KEY",
+    sglang: "SGLANG_API_KEY",
     gateway: "AI_GATEWAY_API_KEY",
 }
 
@@ -432,7 +436,7 @@ function validateProviderCredentials(provider: ProviderName): void {
  * Get the AI model based on environment variables
  *
  * Environment variables:
- * - AI_PROVIDER: The provider to use (bedrock, openai, anthropic, google, azure, ollama, openrouter, deepseek, siliconflow)
+ * - AI_PROVIDER: The provider to use (bedrock, openai, anthropic, google, azure, ollama, openrouter, deepseek, siliconflow, sglang, gateway)
  * - AI_MODEL: The model ID/name for the selected provider
  *
  * Provider-specific env vars:
@@ -448,6 +452,8 @@ function validateProviderCredentials(provider: ProviderName): void {
  * - DEEPSEEK_BASE_URL: DeepSeek endpoint (optional)
  * - SILICONFLOW_API_KEY: SiliconFlow API key
  * - SILICONFLOW_BASE_URL: SiliconFlow endpoint (optional, defaults to https://api.siliconflow.com/v1)
+ * - SGLANG_API_KEY: SGLang API key
+ * - SGLANG_BASE_URL: SGLang endpoint (optional)
  */
 export function getAIModel(overrides?: ClientOverrides): ModelConfig {
     // SECURITY: Prevent SSRF attacks (GHSA-9qf7-mprq-9qgm)
@@ -516,6 +522,7 @@ export function getAIModel(overrides?: ClientOverrides): ModelConfig {
                         `- OPENROUTER_API_KEY for OpenRouter\n` +
                         `- AZURE_API_KEY for Azure\n` +
                         `- SILICONFLOW_API_KEY for SiliconFlow\n` +
+                        `- SGLANG_API_KEY for SGLang\n` +
                         `Or set AI_PROVIDER=ollama for local Ollama.`,
                 )
             } else {
@@ -698,6 +705,112 @@ export function getAIModel(overrides?: ClientOverrides): ModelConfig {
             break
         }
 
+        case "sglang": {
+            const apiKey = overrides?.apiKey || process.env.SGLANG_API_KEY
+            const baseURL = overrides?.baseUrl || process.env.SGLANG_BASE_URL
+
+            const sglangProvider = createOpenAI({
+                apiKey,
+                baseURL,
+                // Add a custom fetch wrapper to intercept and fix the stream from sglang
+                fetch: async (url, options) => {
+                    const response = await fetch(url, options)
+                    if (!response.body) {
+                        return response
+                    }
+
+                    // Create a transform stream to fix the non-compliant sglang stream
+                    let buffer = ""
+                    const decoder = new TextDecoder()
+
+                    const transformStream = new TransformStream({
+                        transform(chunk, controller) {
+                            buffer += decoder.decode(chunk, { stream: true })
+                            // Process all complete messages in the buffer
+                            let messageEndPos
+                            while (
+                                (messageEndPos = buffer.indexOf("\n\n")) !== -1
+                            ) {
+                                const message = buffer.substring(
+                                    0,
+                                    messageEndPos,
+                                )
+                                buffer = buffer.substring(messageEndPos + 2) // Move past the '\n\n'
+
+                                if (message.startsWith("data: ")) {
+                                    const jsonStr = message.substring(6).trim()
+                                    if (jsonStr === "[DONE]") {
+                                        controller.enqueue(
+                                            new TextEncoder().encode(
+                                                message + "\n\n",
+                                            ),
+                                        )
+                                        continue
+                                    }
+                                    try {
+                                        const data = JSON.parse(jsonStr)
+                                        const delta = data.choices?.[0]?.delta
+
+                                        if (delta) {
+                                            // Fix 1: remove invalid empty role
+                                            if (delta.role === "") {
+                                                delete delta.role
+                                            }
+                                            // Fix 2: remove non-standard reasoning_content field
+                                            if ("reasoning_content" in delta) {
+                                                delete delta.reasoning_content
+                                            }
+                                        }
+
+                                        // Re-serialize and forward the corrected data with the correct SSE format
+                                        controller.enqueue(
+                                            new TextEncoder().encode(
+                                                `data: ${JSON.stringify(data)}\n\n`,
+                                            ),
+                                        )
+                                    } catch (e) {
+                                        // If parsing fails, forward the original message to avoid breaking the stream.
+                                        controller.enqueue(
+                                            new TextEncoder().encode(
+                                                message + "\n\n",
+                                            ),
+                                        )
+                                    }
+                                } else if (message.trim() !== "") {
+                                    // Pass through other message types (e.g., 'event: ...')
+                                    controller.enqueue(
+                                        new TextEncoder().encode(
+                                            message + "\n\n",
+                                        ),
+                                    )
+                                }
+                            }
+                        },
+                        flush(controller) {
+                            // If there's anything left in the buffer, forward it.
+                            if (buffer.trim()) {
+                                controller.enqueue(
+                                    new TextEncoder().encode(buffer),
+                                )
+                            }
+                        },
+                    })
+
+                    const transformedBody =
+                        response.body.pipeThrough(transformStream)
+
+                    // Return a new response with the transformed body
+                    return new Response(transformedBody, {
+                        status: response.status,
+                        statusText: response.statusText,
+                        headers: response.headers,
+                    })
+                },
+            })
+            model = sglangProvider.chat(modelId)
+            break
+        }
+
         case "gateway": {
             // Vercel AI Gateway - unified access to multiple AI providers
             // Model format: "provider/model" e.g., "openai/gpt-4o", "anthropic/claude-sonnet-4-5"
@@ -721,7 +834,7 @@ export function getAIModel(overrides?: ClientOverrides): ModelConfig {
 
         default:
             throw new Error(
-                `Unknown AI provider: ${provider}. Supported providers: bedrock, openai, anthropic, google, azure, ollama, openrouter, deepseek, siliconflow, gateway`,
+                `Unknown AI provider: ${provider}. Supported providers: bedrock, openai, anthropic, google, azure, ollama, openrouter, deepseek, siliconflow, sglang, gateway`,
             )
     }