fix: handle incomplete JSON chunks

lib/ai/pattern-model.ts

@@ -11,6 +11,8 @@ import type {
   ToolStartEvent,
 } from '@/lib/ai/types';
 
+import { extractErrorMessageOrDefault } from '../utils';
+
 const textDecoder = new TextDecoder();
 
 const SUPPORTED_EVENT_TYPES = [
@@ -80,6 +82,8 @@ export class PatternModel implements LanguageModelV1 {
    * to AI SDK supported chunks
    */
   private getTransformStream() {
+    let incompleteJsonFragment = '';
+
     return new TransformStream<string, LanguageModelV1StreamPart>({
       transform: (chunk, controller) => {
         if (ArrayBuffer.isView(chunk)) {
@@ -90,9 +94,64 @@ export class PatternModel implements LanguageModelV1 {
               chunk.byteLength,
             );
             const parsedChunk = textDecoder.decode(chunkBuffer).trim();
-            const events = parsedChunk
-              .split('\n')
-              .map((eventObject) => JSON.parse(eventObject));
+
+            /**
+             * Due to an issue with nginx, we have to handle the case where a
+             * chunk is not a complete JSON object
+             */
+            const jsonLines = parsedChunk.split('\n');
+
+            const { events, incompleteJson } = jsonLines.reduce<{
+              events: PatternStreamingResponseEvent[];
+              incompleteJson: string;
+              isLastLine: boolean;
+            }>(
+              (acc, line, index) => {
+                if (!line.trim()) return acc;
+
+                const jsonToTry = acc.incompleteJson + line;
+                const isLastLine = index === jsonLines.length - 1;
+
+                try {
+                  const event = JSON.parse(jsonToTry);
+                  return {
+                    // biome-ignore lint:‌ premature optimization
+                    ...acc,
+                    events: [...acc.events, event],
+                    incompleteJson: '',
+                    isLastLine,
+                  };
+                } catch (e) {
+                  if (isLastLine) {
+                    return {
+                      // biome-ignore lint:‌ premature optimization
+                      ...acc,
+                      incompleteJson: jsonToTry,
+                      isLastLine,
+                    };
+                  }
+
+                  controller.enqueue({
+                    type: 'error',
+                    error: `Failed to parse JSON: ${jsonToTry}`,
+                  });
+
+                  return {
+                    // biome-ignore lint:‌ premature optimization
+                    ...acc,
+                    incompleteJson: '',
+                    isLastLine,
+                  };
+                }
+              },
+              {
+                events: [],
+                incompleteJson: incompleteJsonFragment,
+                isLastLine: false,
+              },
+            );
+
+            incompleteJsonFragment = incompleteJson;
 
             events.forEach((event: PatternStreamingResponseEvent) => {
               if (event.type === 'token') {
@@ -115,7 +174,8 @@ export class PatternModel implements LanguageModelV1 {
           } catch (error) {
             controller.enqueue({
               type: 'error',
-              error: 'Cannot parse chunk due to corrupted data or invalid JSON',
+              error:
+                `Cannot parse chunk due to corrupted data or invalid JSON: ${extractErrorMessageOrDefault(error)}`,
             });
           }
         } else {
@@ -126,6 +186,7 @@ export class PatternModel implements LanguageModelV1 {
         }
       },
       flush: (controller) => {
+        // Handle any remaining incomplete JSON if present
         controller.enqueue({
           type: 'finish',
           finishReason: 'stop',